The Somerford Energy Wiki

Energy, Explained.

A plain-English reference for anyone who has unexpectedly found themselves needing to understand an energy bill, a solar proposal, a grid connection or a market acronym. Search or browse below.

The world of energy and sustainability is full of tricky acronyms and concepts. We don't claim this is gospel, but if you need to get your head round something, this is a good place to start.

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95th Percentile Demand: The demand level exceeded only 5% of the time across a dataset - a way of describing a site's near-peak demand while deliberately excluding rare, extreme spikes that a simple maximum-demand figure would be skewed by.

A

AC Charging: EV charging using alternating current, with the vehicle’s onboard charger converting AC to DC for the battery. It is common for workplace and destination charging.
Active Power: The power in an AC system that does actual useful work, measured in kW - as distinct from reactive power (kVAr), which does no useful work but still uses network capacity.
Activity Data: The real, measured data (kWh consumed, litres of fuel burned, tonnes of material used) that an emissions factor is applied to in order to calculate a carbon footprint - the accuracy of a whole carbon report rests on how good this underlying data actually is.
Additionality: The extent to which an action genuinely causes additional renewable generation or carbon reduction that would not otherwise have happened. It is a key distinction when assessing green-energy claims.
Aggregation Fee: A fee charged by an aggregator for combining a generator's or flexible asset's output with others to access a market it couldn't reach alone - one of several charges worth netting off a headline PPA or flex rate before judging what a deal is really worth.
Aggregator: A company that combines the flexibility of multiple smaller sites or assets into a large enough package to participate in flexibility, balancing or capacity markets that individual small sites couldn't access on their own - usually taking a share of the resulting revenue.
Agreed Supply Capacity (ASC): The maximum electrical capacity, measured in kVA, that a site has agreed with its distribution network operator to take from the network. For larger sites it can affect network charges, and exceeding it can lead to additional costs.
Agrivoltaics: Solar generation designed to share land with active agricultural use underneath or between the panels, rather than displacing it - grazing, some arable crops and horticulture are the most common combinations in the UK.
Alarm (Monitoring): An automated notification triggered when a monitored asset's performance or status falls outside expected parameters - the practical trigger that turns remote monitoring data into an actual maintenance response, rather than data nobody's watching.
Allowed Revenue: The total revenue a network company (a DNO, National Grid) is permitted to recover from customers under its regulatory price control - the ceiling that, alongside the shape of individual tariffs, ultimately determines what shows up as network charges on a bill.
Amortisation: The gradual reduction of a loan balance (or the gradual expensing of an intangible asset) over time through scheduled payments or charges - the debt-side equivalent of depreciation on a physical asset.
AMR - Automatic Meter Reading: A meter that automatically sends consumption data to the supplier or data collector. AMR is common in business energy and avoids relying on manual meter readings.
Anaerobic Digestion (AD): A process that breaks down organic material (food waste, agricultural residues, sewage) in the absence of oxygen to produce biogas, which can be used directly for heat and power or upgraded to biomethane for the gas grid.
Ancillary Services: Services used by the system operator to maintain the secure operation of the electricity system, including frequency response, reserve and other balancing services.
ANM - Active Network Management: A system used by network operators to actively control generation or demand in constrained areas. A generator on an ANM connection may be curtailed when network limits are reached.
Annual Investment Allowance: A UK tax relief allowing eligible businesses to deduct the full cost of qualifying capital expenditure (including much solar and battery equipment) from taxable profits in the year it's incurred, rather than depreciating it slowly over many years - a genuinely material factor in project economics for corporation-tax-paying entities, though not relevant to non-taxpaying bodies like most sports clubs and charities.
Annual Quantity (AQ): The estimated amount of gas a site will use in a year, normally expressed in kWh. It is used in settlement, forecasting and sometimes pricing.
Anomaly Detection: Automatically identifying unusual or unexpected patterns in energy data - a sudden spike, a meter that's stopped updating, consumption that doesn't match the normal shape - useful for catching equipment faults or billing errors early rather than months later.
Anti-Islanding: The specific function within loss-of-mains protection that stops an onsite generator or battery from continuing to power a 'island' of local circuit after the wider grid connection has been lost. A standard, mandatory feature of grid-tied solar and battery inverters.
API (Energy Data): A programmatic connection allowing energy data (consumption, generation, market prices) to be pulled directly into another system automatically, rather than downloaded and re-entered by hand - increasingly how modern monitoring and dispatch platforms actually get their data.
Apparent Power: The total electrical power flowing in an AC system, measured in kVA. It combines useful real power with reactive power and is why a site drawing 100 kW may require more than 100 kVA of network capacity.
Arc Flash: A dangerous release of energy from an electrical fault, capable of causing severe burns even without direct contact. Arc-flash risk assessments and the correct PPE are a standard part of working safely around HV/LV switchgear.
Asset Register: A formal record of a site's generation and storage equipment - serial numbers, install dates, warranty terms, ownership - genuinely useful when a system changes hands, gets refinanced, or needs a warranty claim years after the original installer has moved on.
Augmentation: Adding extra battery capacity partway through a project's life specifically to offset degradation and keep the system's usable capacity at (or near) its original level - a design choice some larger battery projects plan for from the outset.
Automatic Transfer Switch (ATS): A switch that automatically transfers a site's electrical load from the normal grid supply to a backup source (typically a generator) when an outage is detected, then transfers back once the grid supply is restored.
Autonomy (Battery/Generator): How long a backup power system (battery, generator, UPS) can keep a site's critical loads running on its own, without external fuel resupply or grid restoration - a genuinely important number to define clearly at the design stage, since 'we have backup power' means very different things at 20 minutes versus 3 days.
Availability Charge: A network charge associated with the electrical capacity reserved for a site. It is particularly relevant to larger half-hourly supplies with an agreed supply capacity.
Availability Guarantee: A contractual commitment that a solar (or battery) system will be operational for at least a specified proportion of the time, with compensation if it falls short - a different, narrower promise than a generation guarantee, worth checking which (if either) a proposal actually includes.
Availability Payment: Payment made simply for being ready and able to respond to a flexibility or capacity signal if called upon, whether or not it's actually called - distinct from a utilisation payment, which is only paid when the asset actually responds.
Availability-Based Contract: An EaaS-style contract where payment is tied to the equipment simply being available and ready to perform, rather than tied to actual usage or output - shifts a meaningful amount of performance risk onto the provider rather than the customer.

B

Backwardation: A market condition where forward (future) prices are lower than the current spot price - can signal an expectation that today's tight conditions will ease. The opposite of contango.
Balance of Plant (BoP): Everything in a solar, battery or generation project other than the headline generating/storage equipment itself - cabling, structures, civils, switchgear, controls - often a larger and more variable share of total project cost than people initially expect.
Balancing: The continuous process of keeping electricity supply and demand matched. NESO is responsible for balancing Great Britain’s electricity system in real time.
Balancing and Settlement Code (BSC): The industry code, administered by Elexon, that sets out the detailed rules for how Great Britain's electricity market is balanced and settled - the rulebook behind most of the settlement terminology on this page.
Balancing Mechanism (BM): The market NESO uses to increase or reduce generation and demand close to real time to keep the electricity system balanced.
Bankability: How readily a project can secure debt or investment finance, based on the strength and predictability of its contracted revenues, technical risk and counterparty credit quality - a project can be commercially attractive and still not be bankable if its risk profile is too uncertain for a lender's comfort.
Bankable: Describes a project whose contracted revenues, technical risk and counterparty strength are solid enough that a lender is actually willing to finance it - a project can look great on paper and still not be bankable if the underlying risk allocation is too uncertain.
Base Year: The reference year a business measures its emissions reduction progress against - choosing (and occasionally recalculating) a sensible base year is a genuinely consequential decision, not just an administrative formality, since it directly shapes how much 'progress' a business can later claim.
Baseline (Analytics): A reference level of consumption or performance an actual result is measured against - used throughout energy analytics, from flexibility payments to M&V to weather normalisation, and only as trustworthy as the method used to build it.
Baseline Methodology: The agreed method for calculating what a flexible asset's demand or generation would have been without it responding to a flexibility signal - needed to fairly measure (and pay for) the actual difference it made. A genuinely tricky, and commercially important, technical problem.
Baseload: The relatively steady underlying level of electricity demand, or a wholesale electricity product covering every hour in a period. A site with a high baseload can often be attractive for onsite generation.
Baseload Analysis: Examining a site's lowest, most consistent level of demand (typically overnight or during shutdown periods) to identify equipment left running unnecessarily - very often one of the most cost-effective places to start an efficiency review, since baseload waste runs 24/7 whether anyone's watching or not.
Baseload PPA: A PPA structure where the buyer takes a flat, constant volume of power throughout the contract period, regardless of the generator's actual output pattern - simpler to price and manage than a shaped or pay-as-produced structure, but requires someone to absorb the difference between the flat volume and real generation.
Basis Risk: The risk that a hedge doesn't move exactly in line with the underlying exposure it's meant to protect against - relevant, for example, when a contract is priced against a national reference price that doesn't perfectly track a site's own local costs.
Battery as a Service: A commercial model where a third party funds, owns and operates a battery on a customer's site, with the customer paying for the benefit (savings, resilience, a revenue share) rather than the asset itself - the battery-specific version of the same EaaS logic.
Battery Cycle: A measure of battery use broadly equivalent to charging and discharging its full usable capacity once. Partial charge-discharge events can add together to form an equivalent full cycle.
Battery Degradation: The gradual loss of battery capacity or performance through age, cycling, temperature and operating conditions. It is central to long-term battery economics and warranties.
Battery Energy Storage System (BESS): A rechargeable battery system used to store electricity for later use. Commercial batteries can support solar self-consumption, peak shaving, resilience, flexibility services and energy trading.
Battery Management System (BMS): The electronic system that monitors and controls a battery's individual cells - balancing charge levels, protecting against unsafe conditions and reporting state of charge and health data to the wider site controller.
Battery Rack: The internal structure within a battery container or cabinet that holds individual battery modules in place, providing physical support, airflow and often the wiring pathway between modules and the wider system.
Behind-the-Meter (BTM): Energy generation or storage located on the customer’s side of the electricity meter. Electricity used behind the meter can reduce the amount bought from the grid.
Behind-the-Meter PPA: A Power Purchase Agreement where a third party funds and owns generation, usually solar, at the customer’s site and sells the electricity generated directly to the customer under a long-term agreement.
Bid-Offer Pair: The price at which a market participant offers to increase generation/reduce demand (offer) or reduce generation/increase demand (bid) within the Balancing Mechanism - the raw material NESO uses to keep the system balanced in real time.
Bidirectional Charging: EV charging capable of flowing power both ways - into the vehicle to charge it, and back out to the grid, building or home (V2G/V2H/V2B) - as opposed to conventional one-way charging. Relies on both a compatible vehicle and a compatible charger, which still meaningfully limits real-world availability.
Bifacial Solar Panel: A solar panel that can generate electricity from light reaching both its front and rear surfaces. The benefit depends heavily on mounting, spacing and how much light is reflected onto the rear of the panel.
Biodiversity Net Gain (BNG): A planning requirement for many developments in England to leave biodiversity measurably better than before the project, not just no worse - increasingly relevant to ground-mount solar and battery developments on greenfield land.
Bioenergy: Energy derived from organic material. Biomass (wood, agricultural residues) can be burned directly for heat and power. Anaerobic digestion breaks down food waste, agricultural residues or sewage to produce biogas, which can be used directly or upgraded to biomethane for the gas grid - the process leaves behind digestate, commonly used as an agricultural fertiliser. Mass balance accounting allows sustainable and conventional fuel to be physically mixed in shared infrastructure like the gas grid while still correctly tracking and attributing the sustainable share. Sustainable Aviation Fuel (SAF), made from similar renewable or waste feedstocks, is one of the few currently viable decarbonisation routes for aviation.
Black Start: The process of restoring an electricity system to operation after a total shutdown, without relying on the wider grid to bootstrap it back up - a genuinely difficult technical problem at national system level, and a specific service some flexible assets are contracted to help provide.
Blend and Extend: A renegotiation where a business blends its current (often high) fixed rate with current market pricing across a new, extended contract term, smoothing out the cost of an expensive existing deal rather than waiting it out or breaking it outright.
Block-and-Index: A flexible procurement structure combining fixed 'blocks' of pre-purchased volume with the remainder left exposed to (indexed against) the live wholesale market - a middle ground between fully fixed and fully flexible buying.
BM Unit: A defined unit (Balancing Mechanism Unit) representing a specific generator, demand source or portfolio for the purposes of participating in the Balancing Mechanism and being settled against it.
Boiler Upgrade Scheme (BUS): A government scheme supporting eligible heat-pump and biomass-boiler installations in England and Wales. It is mainly aimed at buildings replacing fossil-fuel heating.
Breakeven Spread: The minimum price difference between charging and discharging a battery needed to cover the real cost of doing so (efficiency losses, degradation, cycling cost) - the true bar an arbitrage opportunity has to clear before it's actually worth taking, not just the raw price difference.
BS 7671 - IET Wiring Regulations: The core UK standard governing the design, installation and testing of electrical wiring - referred to as 'the Regs' by most electricians, and the base-level standard most electrical work (including solar and battery installations) is required to comply with.
BSUoS - Balancing Services Use of System: A charge used to recover the cost of balancing Great Britain’s electricity system. It ultimately forms part of the wider cost of supplying electricity.
Budget Estimate: An early, non-binding indication from a DNO of the likely cost and feasibility of a proposed connection, used to sanity-check a project before committing to the time and (sometimes) cost of a formal connection application.
Buffer Tank: A thermal store holding hot (or cold) water to smooth out the mismatch between when heat is generated and when it's actually needed, letting a heat pump or boiler run more steadily rather than constantly cycling on and off to match instantaneous demand.
Building Management System (BMS): The centralised control system that manages a building's heating, cooling, ventilation, lighting and other services - often already installed for comfort and operational reasons, but under-used as an energy management tool without dedicated attention.
Bundled Certificate: A renewable certificate sold together with (bundled into) the physical electricity from the same generator, as opposed to an unbundled certificate traded separately from any specific physical power - bundled arrangements generally carry a stronger direct link between the certificate and a real, causally connected renewable project.
Busbar: A rigid metal bar or strip that carries electrical current within switchgear or a distribution board, generally able to carry more current than an equivalent cable. Busbar capacity is often the real ceiling on how much new load or generation a switchroom can accept.
Business Continuity: A business's broader plan for continuing critical operations through a disruption of any kind, of which power resilience is usually just one component alongside IT, staffing, supply chain and other dependencies.

C

C-rate: A way of describing how quickly a battery can charge or discharge relative to its energy capacity. A 1C 100 kWh battery could theoretically charge or discharge at 100 kW.
Calendar Ageing: The gradual capacity loss a battery experiences simply from the passage of time and storage conditions (temperature, average state of charge), separate from - and in addition to - the wear caused by actual cycling.
Calorific Value: A measure of the energy content of gas, used to convert the volume actually metered (cubic metres) into the kWh a bill is based on. Gas quality varies slightly, which is part of why a gas meter reading and a gas bill's kWh figure aren't a direct 1:1 conversion.
Cannibalisation: The effect where growing amounts of the same generation technology (typically solar or wind) push down the price during the hours they generate most, eroding the value each additional unit of that technology can capture in the market.
Capacity Charge: A charge linked to the amount of electrical network capacity reserved for a site. It is particularly relevant to larger supplies and should not be confused with the amount of electricity actually consumed.
Capacity Factor: The ratio of the energy an asset actually generates over a period to what it would generate running at full rated output the whole time. Solar in the UK typically runs at a 10-12% capacity factor; onshore wind more like 25-35%.
Capacity Factor - Wind: The share of a wind turbine's theoretical maximum output it actually achieves over a year, averaging roughly 25-35% for UK onshore wind and higher for offshore - a key number in any wind project's revenue modelling.
Capacity Market (CM): A mechanism designed to make sure enough electricity capacity is available when the system needs it. Generators, batteries and some demand-side resources can receive payments for committing capacity.
CAPEX - Capital Expenditure: The upfront investment required to buy, build or materially improve an asset, such as a solar array, battery or new electrical connection.
Capture Price: The average price a generator (particularly wind or solar) actually achieves for the electricity it sells, as opposed to the average wholesale price over the same period - these two numbers diverge because intermittent generators tend to produce more when everyone else is too, pushing prices down exactly when they're selling ('cannibalisation').
Carbon Capture and Storage (CCS): Technology that captures CO2 from an industrial process or power station before it reaches the atmosphere, then transports and permanently stores it, usually deep underground - a major plank of UK industrial decarbonisation policy, though currently deployed at only a handful of sites.
Carbon Intensity: The amount of greenhouse gas emissions associated with producing a unit of energy, commonly expressed as grams of CO2 equivalent per kWh.
Carbon Neutral: A claim that remaining greenhouse gas emissions have been balanced by removals or offsets. It is not the same thing as eliminating emissions, and the quality of the underlying approach matters.
Carbon Offset: A credit intended to compensate for emissions by funding or representing emissions reductions or removals elsewhere. Offset quality varies significantly and should not substitute for feasible direct reductions.
Carport Solar: Solar panels mounted on a canopy structure over a car park, generating electricity while also providing weather cover for vehicles - a common way to add meaningful solar capacity to a site whose roof space is limited or unsuitable.
CCA - Climate Change Agreement: A voluntary agreement that can give eligible energy-intensive businesses a discount on the Climate Change Levy in return for meeting energy-efficiency or carbon-reduction targets.
CCL - Climate Change Levy: A tax charged on electricity, gas and certain fuels supplied to many UK businesses and public-sector organisations. Some users and energy sources qualify for exemptions or reduced rates.
CfD - Contract for Difference: The UK’s main support mechanism for new large-scale low-carbon electricity generation. It provides generators with a degree of revenue certainty around an agreed strike price.
Change of Measurement Class: The formal process for moving a meter between settlement categories - most relevantly here, the process a site goes through when it moves from non-half-hourly to half-hourly settlement, which MHHS is making the default path for far more sites.
Change of Tenancy (COT): The formal process for updating who's responsible for a supply when a business moves into or out of a property. Handled badly (or not at all) it's a common cause of a new occupier ending up on an expensive deemed rate.
Change-in-Law Risk: The risk that a change in government policy, regulation or taxation during a long-term PPA materially affects one party's costs or revenues - a standard risk allocation point negotiated into most long-tenor PPA contracts.
Chargepoint Management System (CPMS): The software platform that operates, monitors and manages a network of EV chargers remotely - handling things like access control, payment, load management and fault reporting across a site or fleet.
Chargepoint Operator (CPO): The company that owns and operates a network of EV chargers, as distinct from the e-mobility service provider (eMSP) that might give drivers access to that network under their own app or card - similar in concept to the supplier/network split in the wider electricity market.
Check Meter: A secondary meter installed alongside the main fiscal (billing) meter, used to independently verify readings or to give a site its own real-time visibility without relying solely on the supplier's data.
CHP - Combined Heat and Power: A system that produces electricity and useful heat from the same fuel. CHP can be efficient where there is a consistent need for both, although its carbon case changes as grid electricity decarbonises.
Circuit Breaker: A protective electrical device that automatically interrupts a circuit when it detects excessive current or a fault.
Clipping: When a solar array could produce more DC power than its inverter is able to convert, so some potential generation is temporarily lost. A modest amount of clipping can be an intentional part of good solar design.
Code Modification: A formal proposal to change one of the industry codes (the BSC, the Grid Code, the DCUSA and others), going through a defined governance process before it can be adopted - the mechanism by which the detailed rules of the energy industry actually change over time.
Combined-Cycle Gas Turbine (CCGT): A gas power station design that captures waste heat from a gas turbine to raise steam and drive a second turbine, achieving significantly higher efficiency than a simple gas turbine alone - the workhorse of GB's gas generation fleet.
Commodity Cost: The cost of the electricity or gas itself in the wholesale market. It is only one part of the final business energy bill.
Common Distribution Charging Methodology (CDCM): The methodology used to set DUoS charges for most smaller and medium-sized electricity users - the rulebook behind the network-charging figures on a typical business electricity bill.
Community Battery: A larger, shared battery serving multiple households or a local area collectively, rather than a single site - allows the benefits of storage to reach properties (renters, those without suitable roofs) that couldn't practically host their own.
Community Energy: Local generation, supply or flexibility projects owned or led by a community group rather than a commercial developer or utility - varies widely in scale and structure, from a single shared solar array to more ambitious local energy schemes.
Competent Person: A person with the training, knowledge and experience to safely carry out a specific electrical task - a formal concept underpinning most UK electrical safety regulation, not just a general reassurance.
Compliance Testing: Formal testing carried out (often by an accredited third party) to confirm a newly connected generator or battery actually meets the technical requirements set out in its connection agreement, before it's allowed to operate at full capacity.
Concentrated Solar Power (CSP): A generation technology that uses mirrors to concentrate sunlight and generate heat (rather than converting light directly to electricity like conventional solar PV), which can then drive a turbine or be stored as thermal energy - not currently common in the UK's climate, but significant in sunnier regions.
Connection Agreement: The legal and technical agreement governing how a site is connected to an electricity or gas network, including relevant capacity and operating conditions.
Connection Offer: The formal proposal from a network operator setting out the works, costs, capacity and conditions associated with a new or modified connection.
Connection Reform: Changes to the electricity connections process intended to move viable projects through the queue more effectively rather than relying primarily on the date they originally applied.
Consolidated Billing: A single combined invoice covering multiple sites or meters within a business's portfolio, rather than separate bills per site. A genuine administrative time-saver for multi-site businesses, worth asking a supplier or broker about directly.
Constraint: A physical limitation on the electricity network that prevents power from flowing exactly as the market would otherwise choose. Managing constraints can create significant system costs.
Constraint Costs: Costs incurred when the system operator has to change generation or demand because parts of the network cannot carry the power flows that would otherwise occur.
Consumption Variance: The gap between a site's expected/forecast consumption and what it actually used - a routine line item in bill validation, and often the first thing worth interrogating when a bill looks wrong.
Containerised BESS: A battery system built into a standard shipping-container-style enclosure, pre-integrated with its power conversion, cooling and safety systems - the most common form factor for commercial and industrial battery installations, since it arrives largely pre-built rather than constructed on site.
Contango: A market condition where forward (future) prices are higher than the current spot price - often reflects storage, financing costs or an expectation that conditions will tighten. The opposite of backwardation.
Contestable Works: Connection works that a customer can competitively tender to an independent connection provider (ICP) rather than being obliged to use the DNO - things like cable-laying and civils. Non-contestable works (like the actual network connection point) stay with the DNO.
Contract End Date: The date an energy supply contract finishes. Businesses should normally review procurement well before this date rather than waiting until the final few weeks.
COP - Coefficient of Performance: A measure of heat-pump efficiency at a particular operating condition. A COP of 3 means roughly three units of heat are delivered for each unit of electricity used.
Corporate PPA: A long-term agreement under which a business buys electricity associated with a renewable generator. Structures vary significantly and can be physical, sleeved or financial.
Cost of Conserved Energy: The cost of an energy-efficiency measure expressed per unit of energy saved, allowing it to be compared directly against the cost of buying that same unit of energy - a useful way of judging whether an efficiency project is genuinely cheaper than not bothering.
Coterminous Contract: A contract deliberately timed to end on the same date as a business's other energy contracts, most often used to line up multiple sites so they can be tendered together as one portfolio rather than in a scattered, site-by-site sequence.
Counterfactual: What would have happened anyway, in the absence of a particular action or investment - the essential comparison point behind concepts like additionality, savings claims and carbon-reduction claims, and a genuinely useful question to ask of almost any 'X saved us £Y' statement.
Credit Cover: Collateral or guarantees a market participant must post to cover the financial risk they represent to the wider settlement system - relevant background to why smaller flexible-procurement or trading setups sometimes need financial backing behind them.
Critical Path: The sequence of dependent tasks in a project programme that determines the shortest possible completion time - delay to anything on the critical path delays the whole project; delay to something off it often doesn't, which is why not every slipped task is equally urgent.
Critical Raw Materials: Materials (lithium, cobalt, nickel, rare earth elements and others) considered economically important and at meaningful risk of supply disruption - relevant background to genuine, non-trivial supply-chain and pricing risk behind the batteries and solar equipment being installed today.
Critical Spare: A replacement part kept on hand (or contractually guaranteed to be available quickly) for a component whose failure would otherwise cause a long, costly outage - inverters and certain battery modules are common examples worth asking about explicitly.
Crossed Meter: A metering error where a meter has effectively been wired or registered to the wrong supply point, so it's recording someone else's (or the wrong) consumption. Rare, but a genuine explanation worth ruling out when a bill looks inexplicably wrong.
Current: The rate of flow of electricity through a circuit, measured in amps. Cable and fuse sizing is driven primarily by the current a circuit needs to carry.
Curtailment: Deliberately reducing the output of a generator or the operation of an asset, usually because of network constraints, export limits, market conditions or system requirements.
CUSC - Connection and Use of System Code: The industry code governing the terms on which parties connect to, and use, the electricity transmission system - the transmission-level equivalent of the DCUSA at distribution level.
Cut-In Speed / Cut-Out Speed: The wind speeds at which a turbine starts generating (cut-in) and automatically stops for safety in very high winds (cut-out) - a turbine sits idle both below and above these thresholds.
Cutover: The point at which a site or process actually switches from an old settlement or metering arrangement to a new one - in MHHS, the moment a site genuinely moves from its old settlement basis to half-hourly.
Cycle Budget: A deliberate limit on how many cycles per year a battery is allowed to complete, set to protect warranty terms and manage long-term degradation - a real constraint on how aggressively a battery can chase revenue in any given year.
Cycle Warranty: A battery warranty expressed in terms of a maximum number of charge/discharge cycles (or total energy throughput) rather than purely a number of years - relevant because a battery cycled hard for arbitrage or flexibility revenue can reach its warranty limit well before the calendar term ends.
Cadent Gas: A gas distribution network operator serving large parts of the Midlands, North West, East of England and North London.
Citizens Advice: Provides independent consumer advice, including support with energy-supplier problems and complaints. For many consumer disputes it is a more appropriate first contact than Ofgem.
Carbon Trust: An independent organisation providing advice, certification and standards on carbon reduction and energy efficiency, and a widely cited authority distinguishing genuine science-based decarbonisation from looser sustainability claims.
Climate Change Committee (CCC): The UK's independent statutory body advising government on emissions targets and reporting annually on progress toward them - a genuinely useful, non-partisan reference point for where UK climate policy is actually heading.

D

D0010: The data flow that carries a meter's actual consumption reading between meter operators, suppliers and other industry parties - the flow behind 'is my real read in the system yet'.
D0030: The data flow used to register or update a meter's core technical details on the industry systems - the digital record of what's actually installed at a site.
D0086: The industry data flow that actually changes which supplier is registered as active on a meter - the real technical event behind a supplier switch.
DA - Data Aggregator: An electricity-market role responsible for aggregating metering data for settlement. The role is changing as the market moves through Market-wide Half-Hourly Settlement.
Data Logger: A device that records readings (energy, temperature, other sensor data) at regular intervals for later analysis - the physical or embedded hardware sitting behind a lot of the half-hourly and sub-metered data used in energy analysis.
Data Transfer Catalogue (DTC): The industry-standard specification for exactly what data flows between suppliers, meter operators and other market parties, and in what format - the 'rulebook' underneath every D-number data flow.
Day-Ahead Market: A wholesale electricity market in which power is bought and sold for delivery the following day.
DC - Data Collector: An electricity-market role responsible for collecting and validating metering data used in settlement. Metering arrangements are changing under Market-wide Half-Hourly Settlement.
DC Rapid Charging: EV charging where the charger supplies direct current to the vehicle battery, allowing much higher charging rates than typical AC charging.
DC/AC Ratio: The ratio between the rated DC capacity of a solar array and the AC capacity of its inverter. Solar arrays are often deliberately larger on the DC side than the inverter rating.
DCUSA - Distribution Connection and Use of System Agreement: The industry agreement governing the terms on which parties connect to, and use, the electricity distribution network - the distribution-level equivalent of the CUSC at transmission level.
De Minimis Supply: A qualifying low-volume gas or electricity supply that can be eligible for a reduced rate of VAT (5% rather than 20%). Worth checking on very small sites rather than assuming standard-rate VAT applies by default.
De-Rated Margin: A measure of spare electricity generation capacity that accounts for the fact that not all capacity is reliably available when needed (a wind farm on a still day, for instance) - the more realistic, discounted version of simply adding up nameplate capacity figures.
Debt Service Coverage Ratio (DSCR): A measure of how comfortably a project's cash flow covers its debt repayments, used by lenders to assess how much debt a project can safely support - a low DSCR signals a project with little headroom if performance disappoints even slightly.
Deemed Contract: An energy supply arrangement that can arise automatically when a business occupies premises and uses energy without having agreed a formal supply contract. Deemed rates are often expensive.
Defects Period: A defined period after practical completion during which the contractor remains responsible for fixing any defects that emerge, before final retention payments are released.
Deflagration Panel: A pressure-relief panel built into a battery enclosure, designed to vent gas safely in the event of a fault rather than let pressure build up dangerously - a standard passive safety feature on modern containerised battery systems.
Degradation: The gradual reduction in the performance or usable capacity of equipment over time. Both solar panels and batteries degrade, although in different ways.
Degradation Cost: The notional cost of the battery wear caused by a specific cycle or trading decision, used internally by an optimiser to judge whether a given trade is actually worth doing once the wear-and-tear on the asset is priced in, not just the immediate revenue.
Degree Days: A measure of how cold or warm a period was relative to a reference temperature, used to weather-normalise energy consumption so like-for-like comparisons can be made between a mild year and a cold one.
Delta T: The temperature difference between a system's flow and return (in heating) or supply and return (in cooling) - a bigger delta T generally means a more efficient system, since less flow rate is needed to move the same amount of heat.
Demand Flexibility Service (DFS): A NESO scheme paying households and businesses to reduce electricity use during specific announced windows, usually winter evenings, when the system is under particular strain - one of the most visible and widely-discussed flexibility schemes in the current market.
Demand Response: Changing electricity demand in response to prices, network needs or system signals. This can include temporarily reducing load, shifting it to another time or using stored energy.
Demand Side Response (DSR): A commercial form of demand response where electricity users or distributed assets change consumption or generation to support the electricity system and may be paid for doing so.
Depot Charging: EV charging infrastructure installed at a fleet's home base rather than on public roads or at destinations - typically the backbone of a commercial fleet electrification plan, since it's where vehicles spend predictable overnight time.
Depth of Discharge (DoD): The proportion of a battery’s usable energy capacity that has been discharged. Battery warranties and operating strategies often place limits on depth of discharge.
Digital Twin: A live, data-fed digital model of a physical asset or site, kept continuously updated to mirror its real-world behaviour - increasingly used for things like predictive maintenance and dispatch optimisation on larger energy assets.
Direct Debit Discount: A reduced rate some suppliers offer for paying by direct debit rather than on receipt of invoice - a genuinely easy saving to check for, though it needs weighing against a business's own cashflow and payment-terms preferences.
Discount Rate: The rate used to convert future cash flows into today’s value. Higher discount rates reduce the present value placed on savings or income received far into the future.
Distributed Energy Resources (DER): A collective term for smaller-scale generation, storage and flexible demand located close to where electricity is used, rather than large centralised power stations - rooftop solar, batteries, EVs and flexible industrial loads are all examples.
Distribution Code: The technical rulebook governing how parties connect to and operate on the electricity distribution network - the distribution-level equivalent of the Grid Code, which covers transmission.
District Heating: A system distributing heat from a central energy centre to multiple buildings through insulated pipework, rather than each building generating its own heat - common on large developments, campuses and some town centres.
Diversity Factor: The ratio between the sum of individual equipment's maximum demands and the site's actual simultaneous maximum demand - in practice, not everything runs flat-out at once. Used when sizing electrical infrastructure so it isn't built for a peak that never actually occurs.
DNO - Distribution Network Operator: The company responsible for the regional electricity distribution network that carries power to most homes and businesses. The DNO deals with matters such as new connections, capacity changes and many generation connection applications.
Domestic Flexibility Aggregation: Combining the flexibility of many individual home batteries, EVs and smart appliances into a large enough pool to participate meaningfully in flexibility and balancing markets - the domestic-scale version of the aggregator/VPP concept used commercially, relevant as more of this technology reaches genuine market scale.
Double Materiality: A reporting principle requiring a business to disclose both how sustainability issues affect its own financial performance, and how its own activities affect the environment and society - a broader lens than traditional financial materiality alone.
DSEAR: Regulations (Dangerous Substances and Explosive Atmospheres Regulations) covering the risks from dangerous substances and explosive atmospheres in the workplace - relevant background to why some battery installations require specific hazardous-area assessment and design measures.
DSO - Distribution System Operator: The increasingly active system-management role performed at distribution level, including managing flexibility, network constraints and distributed generation as the electricity system becomes more decentralised.
Dual Incomer: A site electrical design fed from two independent grid connections (often from different substations), so a fault affecting one doesn't necessarily take the whole site down - a higher level of grid-side resilience than the vast majority of commercial sites actually have.
DUoS - Distribution Use of System: Charges associated with using the local electricity distribution network. The way they are recovered varies by customer type and can include time-banded, capacity and fixed elements.
DUoS Time Bands: Time periods used in some distribution charges. Historically often described using red, amber and green periods, although charging structures and terminology continue to evolve.
Dynamic Containment: One of NESO's fast frequency response services, designed to automatically and very quickly correct a large, sudden frequency deviation - one of several named frequency-response products a battery or flexible asset might be enrolled to provide.
Dynamic Load Management: A system that automatically shares available electrical capacity across multiple EV chargers in real time, based on what's actually being drawn at each moment, rather than each charger being allocated a fixed, worst-case share - often what makes a multi-charger site viable without expensive grid reinforcement.
Dynamic Network Management: Newer approaches to squeezing more usable capacity out of the existing electricity network without waiting for costly physical reinforcement. A dynamic operating envelope varies how much a site can import or export through the day based on real-time network conditions, rather than a single fixed limit. A non-wire alternative uses flexibility, storage or demand response to solve a local network constraint instead of building new physical infrastructure. Both are increasingly explicit parts of DNOs' own network planning toolkits.
Dynamic Tariff: An electricity tariff where prices can change frequently, sometimes every half hour, in response to wholesale or system conditions.
DESNZ - Department for Energy Security and Net Zero: The UK government department responsible for energy security, net zero policy and major areas of energy and climate policy.

E

Economy 7: A long-standing two-rate tariff structure offering roughly seven hours of cheaper overnight electricity in exchange for a higher daytime rate, historically aimed at storage heating - still relevant vocabulary when reading an older meter or tariff, though largely superseded commercially by half-hourly and dynamic tariffs.
Electricity Meter: The device that measures electrical energy imported from or exported to a site. Larger sites may have more complex metering arrangements than a typical domestic property.
Electricity Supplier: The licensed company that sells electricity to the end customer and issues the energy bill. The supplier is different from the DNO, which owns and operates the local network.
Electrification: Replacing technologies that directly use fossil fuels with electrical alternatives, such as replacing a gas boiler with a heat pump or diesel vehicles with EVs.
Electrode Boiler: A boiler that generates steam or hot water by passing electric current directly through the water itself, rather than through a conventional heating element or gas flame - can respond very quickly to electricity price or demand signals, making it relevant to some flexibility strategies.
Embedded Benefit: A cost saving that generation connected at distribution level (rather than transmission level) can create by reducing the amount of power that needs to flow through, and be charged for using, the higher-voltage transmission network. Part of the commercial logic behind onsite and local generation, beyond the direct energy saving.
Embedded Commission: Broker or intermediary commission built directly into the unit rate a business is quoted, rather than shown separately - the reason two quotes with an identical headline rate structure can carry very different amounts of margin, invisibly.
Embedded Generation: Electricity generation connected within a distribution network rather than directly to the high-voltage transmission system.
Emissions Intensity: Emissions expressed relative to some other measure of activity (revenue, floor area, units produced) rather than as an absolute total - useful for comparing efficiency across time or between sites of different sizes, though it can mask an absolute increase if the business has also grown.
Employer's Requirements: The client's own specification for what a project must deliver, used as the basis for tender and design - the document a contractor is ultimately building against, worth getting right before procurement starts rather than discovering gaps mid-project.
Energy Arbitrage: Charging a battery when electricity is relatively cheap and discharging it when electricity is more valuable or expensive. The achievable return depends on price spreads, efficiency, cycling and market access.
Energy as a Service (EaaS): A commercial model where a business pays for an energy outcome (heat, cooling, power, charging) as an ongoing service, rather than owning and operating the underlying equipment itself - the umbrella concept behind zero-capex solar, funded batteries and similar 'somebody else owns and runs it' structures.
Energy Attribute Certificate: A certificate representing the renewable or environmental attributes associated with a quantity of electricity. In Great Britain the main renewable electricity certificate is the REGO.
Energy Audit: A structured review of how energy is used at a site, usually to identify waste, operational improvements and potential investment opportunities.
Energy Broker: A person or business that helps customers obtain energy supply contracts, often receiving a fee or commission. Broker services and commercial models vary widely, so customers should understand how the broker is paid.
Energy Efficiency: Using less energy to deliver the same or a better outcome. Examples include improved controls, insulation, efficient motors, LED lighting and better operating practices.
Energy Management System (EnMS): A structured approach to measuring, managing and improving an organisation’s energy performance. ISO 50001 is the best-known formal energy-management standard.
Energy Performance Contract (EPC): A commercial arrangement where energy-efficiency improvements are delivered with some form of performance or savings commitment. The exact allocation of risk varies by contract.
Energy Price Cap: An Ofgem limit on the unit rates and standing charges suppliers can charge households on certain default tariffs. It does not cap the total bill and generally does not set prices for normal business energy contracts.
Energy Sharing: Arrangements that allow electricity generated in one place to be commercially allocated or sold to users elsewhere. The practical structure depends on metering, settlement, network and supplier arrangements.
Energy Storage: Technology that stores energy for later use. Batteries are the most familiar electrical example, but pumped hydro, thermal storage, compressed air and other technologies can also store energy.
Energy Tariff Types: The main structures a business energy contract can take: fixed (rates locked for the term), variable (rates can move, often tracking an index), flexible (volume bought in stages across the market rather than at one moment), dynamic (rates that can change every half hour in response to wholesale or system conditions), and time-of-use (different fixed rates by time band, without the minute-by-minute movement of a true dynamic tariff).
Energy Trading: Buying and selling electricity, gas or related products in wholesale or flexibility markets. Commercial users increasingly encounter trading concepts through flexible procurement and batteries.
EPC - Energy Performance Certificate: A certificate rating a building's energy efficiency on an A-G scale, required when a property is built, sold or let. A completely different thing from the other two common EPC meanings in this space (Engineering, Procurement and Construction; Energy Performance Contract) - worth checking which one anyone actually means when they say 'EPC'.
EPC - Engineering, Procurement and Construction: In renewable-energy projects, an EPC contractor takes responsibility for designing, procuring and constructing the system. Do not confuse this with an Energy Performance Certificate or Energy Performance Contract.
Equivalent Full Cycle: A standardised way of counting battery use that adds together multiple partial charge/discharge events until they total one full cycle's worth of throughput - allows a battery doing lots of small daily cycles to be compared fairly against one doing fewer, deeper cycles.
Erroneous Transfer: A supplier switch that happens by mistake - the wrong site, an unauthorised request, a data error - which can usually be unwound and reversed under industry rules if caught and reported promptly, rather than being treated as a done deal.
ESOS - Energy Savings Opportunity Scheme: A mandatory UK scheme requiring large businesses to carry out energy audits every four years, identifying (though not requiring action on) cost-effective energy-saving opportunities - worth checking whether a business is in scope, since the qualifying thresholds catch more businesses than people expect.
Estimated Annual Consumption (EAC): A supplier's estimate of a site's annual consumption, used to set billing and forecasts before enough real meter data exists (or where a site is on non-half-hourly settlement). A stale or wrong EAC is a common, fixable cause of consistently odd-looking bills.
Estimated Read: A meter reading calculated from historic usage patterns rather than an actual physical or remote read. Bills based on estimated reads are a common source of billing disputes once the true consumption comes through and needs reconciling.
EV - Electric Vehicle: A vehicle powered wholly or partly by electricity stored in a battery.
EVSE - Electric Vehicle Supply Equipment: The equipment used to supply electricity safely to an electric vehicle - commonly referred to as an EV charger.
Export: Electricity generated at a site and sent out onto the public network rather than being consumed on site.
Export Capacity: The maximum amount of electrical power a site is permitted to export to the network under its connection arrangements.
Export Limitation Scheme (ELS): A control system that restricts how much electricity a site exports to the network, allowing generation or storage capacity to be installed while respecting an agreed export limit.
Export MPAN: The MPAN identifying an electricity export point. It is normally required where exported electricity is to be properly metered and sold.
Extra High Voltage Distribution Charging Methodology (EDCM): The methodology used to set DUoS charges for the largest electricity users connected at extra-high voltage, distinct from the CDCM used for most smaller and medium-sized sites.
Electricity North West (ENWL): The electricity distribution network operator for the North West of England.
Elexon: The organisation that administers the Balancing and Settlement Code arrangements for Great Britain’s electricity market and plays a central role in electricity settlement.
Energy Ombudsman: An independent dispute-resolution service for unresolved complaints between consumers or eligible small businesses and participating energy companies, after the required complaints process has been followed.
Energy Networks Association (ENA): The industry body representing Great Britain and Ireland's gas and electricity network operators, and the publisher of the G98/G99/G100 engineering recommendations governing generation connections.
Energy UK: The trade association representing the UK energy industry, including major suppliers and generators, and a common source of industry-wide statements and data on energy policy issues.

F

Factory Acceptance Test (FAT): Testing carried out on equipment at the manufacturer's own factory before it's shipped to site, checking it performs correctly before the cost and difficulty of fixing a fault rises once it's installed and commissioned in the field.
Fault Code: A specific error identifier reported by equipment (an inverter, a battery system) when something goes wrong, used by O&M teams to diagnose the issue remotely before deciding whether a site visit is actually needed.
Fault Ride-Through: A requirement for larger generators and batteries to stay connected and keep operating through a brief network fault or voltage dip, rather than tripping offline - helps prevent a local fault cascading into a wider system problem.
Fault Tolerance: A system's ability to keep operating correctly even when one of its components fails, by design rather than by luck - the underlying engineering principle behind concepts like N+1 redundancy.
Feasibility Study: A more detailed, usually paid-for study a DNO carries out to establish exactly what a specific connection would require, ahead of a formal connection offer. A step up in both cost and reliability from a budget estimate.
Feed-in Tariff (FiT): A legacy UK support scheme that paid eligible small-scale renewable generators for generation and, in some cases, export. It closed to new applicants in 2019 but existing accredited installations can continue to receive payments.
Final Physical Notification (FPN): A market participant's final declared intention for how much they'll generate or consume in a given settlement period, submitted ahead of gate closure - one of the reference points the system uses to identify and price imbalances.
Firm Capacity: Capacity that can be reliably relied upon to be available when needed, as opposed to intermittent or weather-dependent capacity - a key distinction whenever someone talks about a project's capacity 'replacing' a certain amount of conventional generation.
Firm Connection: A network connection with rights to use the agreed capacity subject to the normal network rules, rather than being routinely curtailed under a flexible or non-firm arrangement.
Firm Gas: A gas supply arrangement without the interruption risk of an interruptible contract - the standard, more expensive, option most businesses actually hold.
Fixed Energy Contract: A supply contract where specified energy-price components are fixed for an agreed period. ‘Fixed’ does not always mean every element of the final bill is fixed, so the contract structure matters.
Flexibility Services: Services where generators, batteries or electricity users are paid to alter their behaviour to help manage the electricity system or local network.
Flexibility Stack: The full set of flexibility services and revenue streams a single asset could in principle participate in - the broader concept behind revenue stacking, describing the menu rather than any one asset's actual chosen combination.
Flexible Connection: A connection that allows the network operator to restrict import or export under defined circumstances, often enabling a project to connect sooner or more cheaply than with fully firm capacity.
Flexible Connection Agreement: A connection contract where the DNO retains the right to constrain (curtail) a generator or battery's import/export at certain times, in exchange for a faster or cheaper connection than a fully firm one would allow.
Flexible Energy Contract: A procurement arrangement where some or all wholesale energy is bought in stages rather than fixing the whole volume at one moment. It can reduce timing risk but requires governance and active management.
Floating Offshore Wind: Offshore wind turbines mounted on floating platforms rather than fixed foundations, allowing deployment in deeper water than fixed-bottom turbines can reach - an emerging technology particularly relevant to parts of the UK's deeper offshore waters.
Floating Solar: Solar panels mounted on a floating structure on a body of water (a reservoir, a lagoon) rather than on land or a roof - can suit sites with limited land but available water surface, with its own specific mounting, cabling and maintenance considerations.
Floor Price: A minimum price built into some PPA and merchant revenue structures, protecting the seller from very low market prices in exchange for usually giving up some upside if prices rise a lot - a form of partial hedge rather than a fully fixed price.
Floor Revenue: A minimum guaranteed level of income built into some battery optimisation or tolling contracts, protecting the owner from a genuinely bad trading year in exchange for typically giving up some of the upside in a good one.
Flow Temperature: The temperature at which heated water leaves a heat source and enters a building's heating system - a lower flow temperature (as heat pumps typically use compared with gas boilers) usually means better efficiency, but can require larger radiators or underfloor heating to deliver the same comfort.
Forward Curve: The set of current market prices for energy delivered at various points in the future (next month, next quarter, next winter, etc.), used as the reference for pricing fixed and flexible contracts and for deciding when to buy.
Forward Market: A market for buying or selling energy for delivery in future months, quarters or seasons. It is central to how suppliers and flexible procurement customers manage future price risk.
Free Cooling: Using naturally cool outside air (or water) to provide cooling instead of running mechanical refrigeration, whenever outside conditions allow - a genuinely significant, low-cost efficiency opportunity on sites with year-round cooling loads (server rooms, some industrial processes).
Frequency: The rate at which alternating current cycles, nominally 50 Hz in Great Britain. System frequency moves when electricity supply and demand are not perfectly balanced.
Frequency Response: A service that rapidly changes generation, storage or demand to help keep system frequency close to 50 Hz.
Front-End Engineering Design (FEED): A detailed design stage carried out after feasibility but before final investment decision and construction, refining a project's technical scope, cost and schedule to a level accurate enough to commit real capital against.
Fuel Mix Disclosure: A supplier's published breakdown of the generation sources (gas, nuclear, renewables, etc.) backing the electricity it supplies, which suppliers are required to disclose - a useful, comparable reference point when assessing how genuinely 'green' a given tariff actually is.
Fugitive Emissions: Unintentional releases of greenhouse gases from equipment, most commonly refrigerant leaks from cooling and refrigeration systems - an easy-to-overlook emissions source since it isn't tied to a fuel bill the way combustion emissions are.

G

G100: The engineering recommendation covering customer export limitation schemes. It is commonly relevant where a DNO permits generation or batteries provided export is actively limited.
G98: The engineering recommendation covering the connection of small-scale generation to distribution networks, generally for smaller installations that meet defined limits.
G99: The engineering recommendation governing the connection of larger generation and storage equipment to distribution networks. Many commercial solar and battery projects require a G99 application and approval.
Gas Day: The 24-hour period used for gas market and balancing purposes, running from 06:00 to 06:00 rather than midnight to midnight - a genuinely easy thing to get wrong when comparing gas and electricity data side by side.
Gas Meter: The device that measures the volume of gas passing into a site. Billing converts the measured volume into energy, normally kWh, using factors including calorific value.
Gas Storage: Facilities that store gas (often in depleted gas fields or salt caverns) during periods of lower demand, for withdrawal when demand is higher - relevant to gas security of supply and, indirectly, to how much price volatility the market experiences through the year.
Gas Supplier: The licensed company that sells gas to the end customer and issues the bill. It is separate from the gas transporter that owns the network.
Gas Transporter (GT): A company licensed to transport gas through a pipeline network. Most sites are connected to the main distribution networks, while some are served by independent gas transporters.
Gate Closure: The point, one hour before a given settlement period, after which no further changes can be made to physical or contractual electricity positions for that period - the market's own hard deadline for 'final answer'.
Generation Guarantee: A contractual commitment from an installer or O&M provider that a solar system will generate at least a specified amount of energy, with compensation payable if it falls short - worth checking exists (and reading the exclusions) rather than assuming a headline yield figure is contractually binding.
Generation Meter: A meter used to record the electricity generated by an onsite system. It is distinct from the import/export meter at the grid connection.
Geothermal Energy: Using heat from within the earth to generate electricity or provide heat directly. Conventional geothermal relies on naturally occurring hot water or steam and is mostly limited to specific geological locations. Enhanced Geothermal Systems (EGS) engineer artificial underground reservoirs to extract heat from hot rock in locations that lack that natural resource, potentially unlocking geothermal power well beyond the small number of naturally suitable UK sites.
Glint and Glare: A planning consideration assessing whether reflected sunlight from solar panels (or other reflective surfaces) could dazzle nearby road users, pilots or neighbouring properties - a standard technical study for larger ground-mount solar projects near roads or airports.
Green Tariff: An energy tariff marketed as renewable or environmentally preferable. The underlying renewable claim may rely on certificates, direct contracting or other arrangements, so not all green tariffs have the same additionality.
Greenwashing: Making environmental claims that are misleading, exaggerated or insufficiently supported by evidence.
Grid: A general term for the interconnected electricity networks that move power from generators to consumers. In Britain this includes both transmission and distribution networks.
Grid Code: The technical rulebook governing how generators, demand and network operators connect to and operate on Great Britain's electricity transmission system - one of several industry codes (alongside the Distribution Code, BSC, CUSC and others) sitting behind day-to-day market and technical arrangements.
Grid Connection: The physical and contractual arrangement allowing a site, generator or storage asset to import electricity from or export electricity to the public network.
Grid Connection Queue: The pipeline of projects seeking connection to the electricity network. Queue reform is intended to prioritise projects that are ready and strategically needed rather than simply first-come, first-served.
Grid Emissions Factor: The published figure representing the average carbon intensity of grid electricity, used to convert a business's kWh consumption into a carbon emissions figure for reporting purposes. Updated periodically as the generation mix changes, so an old factor can meaningfully overstate current emissions.
Grid Services Types: The broad families of paid service a flexible asset can offer the electricity system: frequency response (very fast, seconds-to-minutes, keeping system frequency stable), reserve services like STOR (slower, minutes-scale backup capacity), capacity market payments (being available during system stress, paid well ahead of time), wholesale/balancing mechanism trading (buying and selling directly against live prices), and local DNO flexibility (relieving a specific constrained part of the network rather than the whole system).
Grid Supply Point (GSP): The point where the high-voltage transmission network connects into a regional distribution network. Each GSP feeds a defined geographic area and sits behind some of the locational signals in network charging.
Grid-Forming Inverter: An inverter capable of independently setting its own voltage and frequency reference, rather than just following the grid's existing signal - increasingly important as more of the electricity system comes from inverter-based generation and storage rather than large spinning turbines.
Guarantees of Origin (GoO): The general European term for the certificate scheme proving electricity came from a renewable source - REGO is Great Britain's specific implementation of the same underlying concept.

H

Half-Hourly (HH) Data: Electricity consumption or export data recorded in 30-minute settlement periods. For businesses it is one of the most useful datasets for procurement, solar, battery and capacity analysis.
Half-Hourly Meter: A meter whose consumption data is collected for each half-hour settlement period. Historically associated with larger business supplies, half-hourly settlement is now expanding much more widely.
Hazardous Area Classification: A formal assessment identifying zones where an explosive or flammable atmosphere could occur, and classifying them so the correct equipment and precautions are used - relevant to some battery installations and any site handling flammable gas or fuel.
Heat as a Service: A commercial model where a business pays for delivered heat (a guaranteed temperature, a defined output) rather than owning and running the boiler or heat pump that produces it - the heating-specific version of the same zero-capex logic behind funded solar.
Heat Interface Unit (HIU): The equipment installed at each building or dwelling connected to a district heat network, transferring heat from the network into the local heating and hot water system without the two water circuits mixing directly.
Heat Network: A system that distributes heat from a central source to multiple buildings or customers through insulated pipes.
Heat Pump: A device that uses electricity to move heat from the air, ground or water into a building or process. It can deliver several units of heat for each unit of electricity consumed.
Heat Recovery: Capturing waste heat that would otherwise be lost (from flue gases, compressors, refrigeration, process exhaust) and reusing it elsewhere on site - frequently one of the cheapest genuine efficiency opportunities on an industrial site, because the heat has already been paid for once.
Hedging: Taking positions or contracts designed to reduce exposure to future energy-price movements. Fixing an electricity contract is itself a form of price-risk management.
High Voltage (HV): A voltage level above low voltage. Many larger commercial and industrial sites connect at HV, which can affect metering, network charges, equipment and connection arrangements.
Home Energy Management System (HEMS): A domestic control system that automatically coordinates a home's solar, battery, EV charging and smart appliances to minimise cost or maximise self-consumption - the domestic-scale cousin of the site controllers and EMS platforms used in commercial battery and solar systems.
Hourly Matching: Matching a business's actual electricity consumption against renewable generation on an hour-by-hour (or half-hour) basis, rather than the much looser annual matching that most current renewable claims (including most REGO-backed 'green' tariffs) actually rely on - a stricter, emerging standard sometimes referred to as '24/7 carbon-free energy'.
Hurdle Rate: The minimum acceptable return a project must clear before an investor or business will proceed with it - often set with reference to WACC plus a risk premium, and varies by how risky and how strategically important a given project is judged to be.
Hydrogen Colours (Green, Blue, Grey...): Hydrogen itself is colourless - the colour terms describe how it was produced, not the gas itself. Green hydrogen comes from water split by renewable electricity (electrolysis). Blue hydrogen comes from natural gas, with the resulting CO2 captured and stored rather than released. Grey hydrogen - the most common today - comes from natural gas with no capture at all. Pink (nuclear-powered electrolysis) and turquoise (methane pyrolysis) are less common variants.

I

Imbalance: The difference between the electricity a market participant contracted to buy or sell and the amount actually consumed or generated. The settlement system prices these differences.
Import: Electricity drawn from the public network into a site.
Import Capacity: The amount of electrical capacity a site is permitted or equipped to draw from the network. For larger sites this is often expressed in kVA.
Independent Connection Provider (ICP): A company, other than the regional DNO, accredited to design and build electricity connection infrastructure. Using an ICP for contestable works can sometimes be faster or cheaper than waiting in a DNO's own queue.
Independent Distribution Network Operator (IDNO): A licensed company that owns and operates local electricity distribution networks connected to a regional DNO network. New developments are often served by IDNO networks.
Independent Gas Transporter (IGT): A licensed company operating a gas network connected to the main gas distribution system. Some commercial and residential developments are supplied through IGT networks.
Industrial Heat Pump: A heat pump designed and sized for industrial process temperatures and loads, rather than the smaller domestic or commercial-space-heating scale most people picture - an emerging but genuinely significant route to decarbonising industrial heat where process temperatures allow it.
Inrush Current: A brief surge of current, often several times normal running current, that occurs when motors, transformers or some inverters first switch on. Relevant when sizing protection and when several large loads (e.g. EV chargers) could start simultaneously.
Insetting: Funding emissions-reduction activity within a business's own value chain (rather than buying an unrelated external offset) as a way of addressing its footprint - increasingly preferred over classic offsetting since the reduction is directly connected to the business's own operations.
Interconnectors: HVDC interconnectors are high-voltage direct current cables, usually undersea, connecting GB's electricity system to its European neighbours (IFA, IFA2, BritNed, Nemo Link, North Sea Link, Viking Link and others) - power flows either way depending on price and need. Market coupling links the day-ahead markets either side of an interconnector so power automatically flows toward the higher-priced market up to the cable's capacity limit; congestion rent is the revenue this price difference generates, usually captured by the interconnector owner.
Internal Carbon Price: A notional cost per tonne of CO2 a business applies internally to its own decision-making (capital approvals, project appraisal) even though it isn't actually charged that amount externally - a way of making climate impact a real, comparable line item in investment decisions rather than an afterthought.
Interruptible Gas: A gas supply arrangement where the transporter or supplier can, in defined circumstances (typically a system emergency), require a customer to reduce or stop consumption - usually offered at a lower price in exchange for accepting that risk.
Inverter: Equipment that converts DC electricity from solar panels or batteries into AC electricity suitable for use on the site or export to the grid.
Investable: Describes a project or business model with a clear enough revenue case and risk profile that outside capital would genuinely consider funding it - similar in spirit to bankable, but used more broadly across equity as well as debt-funded structures.
Investment-Grade Audit: A detailed energy audit rigorous enough to be relied on for an actual investment decision, going well beyond a quick walk-round survey - includes real measurement, verified savings estimates and enough detail for a lender or investor to trust the numbers.
IP Rating (Battery Enclosure): A standard rating (Ingress Protection) describing how well a battery enclosure resists dust and water - relevant to whether a system is genuinely suited to an outdoor, exposed location rather than needing a sheltered position.
IPMVP: The International Performance Measurement and Verification Protocol - the standard framework most measurement and verification (M&V) work follows when independently confirming how much an efficiency project actually saved.
IRR - Internal Rate of Return: A financial measure representing the discount rate at which a project’s net present value is zero. It is widely used to compare investments with different cash-flow profiles.
Irradiance: The amount of solar power falling on a surface at a particular moment, normally measured in watts per square metre. It is one of the main drivers of solar PV output.
Islanding: Operating part of an electrical system independently from the public grid. Standard grid-connected solar normally shuts down during a power cut unless the system has been specifically designed for islanded or backup operation.
ISO 50001: The internationally recognised standard for a formal energy management system, covering how an organisation measures, manages and continually improves its energy performance. Increasingly specified as a requirement in supplier and procurement tenders, not just a voluntary badge.
IV Curve Testing: A diagnostic test that measures a solar string's current and voltage across its full operating range, used to identify underperforming panels, wiring faults or degradation that a simple output reading wouldn't reveal on its own.

K

KPI Dashboard: A live summary view of a site or portfolio's key energy metrics (consumption, cost, carbon, generation), designed to be checked regularly rather than dug out of a spreadsheet only when something goes wrong.
kVA - kilovolt-ampere: A measure of apparent electrical power. It is commonly used for transformers, generators and a site’s agreed supply capacity.
kVAh - kilovolt-ampere-hour: A measure of apparent energy (as opposed to kWh, which measures real energy) - occasionally seen on bills for sites with reactive power charges, since it reflects the total electrical capacity used rather than only the useful portion of it.
kVAr - kilovolt-ampere reactive: A measure of reactive power in an AC electrical system. High reactive demand can indicate poor power factor and may affect network costs or capacity.
kW - kilowatt: A measure of power - how quickly electricity is being consumed or generated at a particular moment. It should not be confused with kWh, which measures energy over time.
kWh - kilowatt-hour: A measure of energy. Using 10 kW continuously for one hour consumes 10 kWh.
kWp - kilowatt-peak: The rated peak DC capacity of a solar PV system under standard test conditions. Actual output varies with weather, temperature, orientation and system design.

L

Landlord Consent: Formal permission from a building's owner (where different from the occupier) for a solar installation to go ahead - easy to overlook on a leased site, and can become a genuine blocker late in a project if not sorted early.
LCOE - Levelised Cost of Energy: An estimate of the average lifetime cost of producing each unit of energy from a project, taking account of capital cost, operating cost and generation.
LDZ - Local Distribution Zone: A geographical area used within the gas distribution system for operational, settlement and charging purposes.
LED Lighting: Lighting based on light-emitting diodes. LEDs generally use substantially less electricity than older lighting technologies and can also work well with occupancy and daylight controls.
Levelised Cost of Storage (LCOS): The battery-storage equivalent of LCOE - the average lifetime cost per unit of energy a storage system delivers, accounting for capex, opex, degradation and cycling, used to compare different storage technologies and sizes on a level footing.
Levy Exemption Certificate (LEC): A certificate historically used as evidence of an exemption from the Climate Change Levy on renewable electricity - a legacy term still occasionally seen on older contracts and bills, from before the exemption was withdrawn for most supplies.
Licence Exemption: A carve-out allowing certain electricity supply or generation activities to take place without holding a full supply or generation licence, subject to conditions - relevant background to how some private-wire and behind-the-meter arrangements are legally structured.
Lifetime Saving: The estimated cumulative financial saving produced by a project over its assumed operating life. It is only as reliable as the assumptions behind future prices, performance and maintenance.
Linepack: The gas physically stored within the transmission pipeline network itself at any given time, which acts as a short-term buffer helping balance supply and demand within a gas day.
Liquid Cooling (BESS): A battery thermal management approach that circulates coolant directly around the cells, generally allowing tighter temperature control and higher power density than air cooling - increasingly the default on larger commercial and utility-scale battery systems.
Liquidated Damages: A pre-agreed, contractually specified sum payable by a contractor if a project misses an agreed milestone (commonly completion date or performance level), rather than the parties having to prove actual loss after the fact.
Lithium Iron Phosphate (LFP): A lithium-ion battery chemistry known for strong safety characteristics and long cycle life, at the cost of slightly lower energy density than some alternatives - now the dominant choice for most stationary commercial and industrial battery storage.
LOA - Letter of Authority: A document authorising an energy adviser or broker to obtain information or deal with suppliers and other parties on a customer’s behalf. Its exact scope should be read carefully.
Load: The electrical demand created by equipment or a site at a particular moment.
Load Balancing: Managing multiple electrical loads so that total demand stays within an available connection or equipment limit. It is commonly used with EV charging.
Load Duration Curve: A chart ranking every recorded demand value across a period from highest to lowest, rather than plotting them in time order - reveals how much of the time a site is actually near its peak (useful for sizing capacity, solar and batteries) far more clearly than a normal time-series chart does.
Load Factor: A measure of how consistently a site uses its peak demand. A high load factor means demand is relatively steady; a low load factor means short peaks sit above much lower average consumption.
Load Shifting: Moving electricity consumption from one time period to another, often to avoid expensive periods, use more renewable generation or support the network.
Local Area Energy Planning (LAEP): A structured approach to planning a local area's future energy infrastructure (generation, networks, heat, transport) in a coordinated way, rather than each element being planned separately - an increasingly common tool for local authorities and network planners.
Location-Based Emissions: A method of calculating Scope 2 (purchased electricity) emissions using the average carbon intensity of the wider grid where a site is located, regardless of what specific electricity product or tariff the business actually buys.
Location-Based Scope 2: A method of calculating Scope 2 emissions using the average emissions intensity of the electricity grid in the location where energy is consumed.
Lockout/Tagout (LOTO): A safety procedure for physically locking and labelling isolated electrical equipment so it cannot be accidentally re-energised while someone is working on it.
Long Duration Energy Storage (LDES): Energy storage designed to discharge for substantially longer periods than conventional short-duration batteries. Technologies can include pumped hydro, compressed air, thermal storage and other systems.
Long-Duration Storage Technologies: An umbrella term for storage technologies built to discharge over many hours or days, rather than the 1-4 hour range of most commercial batteries. Emerging approaches include liquid-air energy storage (cooling air to a liquid using surplus electricity, then expanding it through a turbine later), thermal 'sand battery' storage (heating a cheap material to very high temperatures for later industrial or district heat use), and multi-day storage aimed at covering extended low-wind, low-sun periods a normal battery isn't sized for.
Long-Lead Item: Equipment (a large transformer, specific battery cells, certain switchgear) with a manufacturing or delivery lead time long enough that it needs to be ordered early in a project's programme, well before other work starts, to avoid it becoming the thing everything else waits on.
Loss Adjustment Factor: A factor applied to a site's metered consumption to account for the electricity lost in getting it from the generator to that specific point on the network, varying by voltage level and location - part of why final billed consumption can differ slightly from raw metered kWh.
Loss of Load Expectation (LOLE): A statistical measure, used in security-of-supply planning, of how many hours per year the system is expected to fail to meet demand under current and forecast generation and demand conditions - one of the key numbers behind decisions like the Capacity Market's target volumes.
Loss-of-Mains Protection: Protection built into a generator or battery inverter that automatically disconnects it from the network if it detects the grid has gone down, preventing it from accidentally continuing to energise a de-energised section of network (a safety hazard for engineers working on it).
Low Voltage (LV): The voltage level at which most smaller commercial premises and homes connect to the electricity distribution network.

M

Main Incomer: The point where a site's electricity supply first enters the building, typically the main switch or circuit breaker at the top of the distribution system. Everything downstream is sized and protected relative to this.
Managed Asset: An energy asset (solar, battery, EV chargers) that a third party owns and operates on a customer's site under a service contract, with the customer simply consuming the resulting benefit - the practical arrangement behind most EaaS and zero-capex propositions.
Managed Utility Service: A broader outsourced arrangement where a third party manages some or all of a business's utility procurement, billing validation and reporting as an ongoing service, rather than the business handling it in-house.
Marginal Abatement Cost Curve (MACC): A chart ranking a business's available emissions-reduction options by their cost per tonne of CO2 saved, from cheapest (sometimes cost-negative) to most expensive - a genuinely useful practical tool for deciding what to do first with a limited decarbonisation budget.
Market-Based Emissions: A method of calculating Scope 2 emissions using the specific contractual instruments a business has purchased (certificates, PPAs, supplier green tariffs), which can produce a very different (often lower) figure than the location-based method for the same physical electricity use.
Market-Based Scope 2: A method of calculating Scope 2 emissions using contractual instruments such as supplier products, certificates or PPAs where the accounting rules permit.
Market-wide Half-Hourly Settlement (MHHS): A major reform of Great Britain’s electricity market that moves far more customers to settlement using actual half-hourly consumption data, changing metering, data and supplier processes.
Material Modification: A change to an existing connection (increasing export capacity, adding a battery to an existing solar array, etc.) significant enough that it needs its own application and DNO approval, rather than being treated as business as usual.
Maximum Demand: The highest level of electrical demand recorded over a defined period. It is an important consideration when assessing capacity, solar, batteries and network requirements.
Maximum Export Capacity (MEC): The maximum export capability agreed for a generator or site connection. The exact contractual terminology and treatment depend on the network connection.
Maximum Import Capacity (MIC): A term used in some connection contexts for the maximum import capability agreed or available at a site. Terminology varies by network and agreement, so it should be read alongside the site’s formal connection documents.
Mean Time to Repair (MTTR): The average time it takes to fix a failed piece of equipment and restore normal operation - a key input, alongside failure frequency, into how much backup capacity and autonomy a resilient system actually needs.
Measurement and Verification (M&V): A structured methodology (commonly following the IPMVP protocol) for independently confirming how much energy an efficiency project actually saved, comparing real post-project performance against an adjusted baseline - important wherever a project's savings claim needs to be genuinely defensible, not just estimated.
MEES - Minimum Energy Efficiency Standards: Regulations requiring rented commercial (and domestic) properties to meet a minimum EPC rating before they can legally be let, with the minimum standard due to tighten over time. A property below the threshold generally can't be marketed or re-let until it's improved or a valid exemption is registered.
Merchant (Risk): Exposed to open market prices rather than protected by a fixed contract - a 'merchant' battery, generator or revenue stream carries more upside and more downside than a contracted equivalent, and the word is often used as shorthand for exactly that trade-off.
Merchant Battery: A battery operating without a long-term fixed-price offtake or tolling agreement, instead capturing whatever value it can from the wholesale market, flexibility services and arbitrage as conditions change - carries more revenue risk than a contracted battery, in exchange for full upside if prices or flex rates rise.
Merchant Solar: A solar project with no long-term fixed-price offtake agreement in place, instead selling its output at whatever the market price happens to be at the time - carries more revenue risk than a PPA-backed project, in exchange for full upside if prices rise.
Meter Asset Provider (MAP): The party that owns the physical meter, as distinct from the Meter Operator (MOP) who installs and maintains it, and the supplier who reads and bills from it - three genuinely separate roles behind what looks like one box on the wall.
Meter Multiplier: A factor applied to a meter's raw register reading to convert it into the actual energy consumed, used where a meter operates via a current transformer (CT) rather than reading the full current directly. Getting this wrong (or a supplier applying the wrong one) is a genuine, if uncommon, cause of badly incorrect bills.
Meter Operator (MOP): The party responsible for installing and maintaining certain business electricity metering equipment. Metering roles are evolving under MHHS.
Meter Point Administration Number (MPAN): The unique identifier for an electricity supply point. It identifies the connection rather than the physical meter, so changing meter or supplier does not normally change the MPAN.
Meter Point Reference Number (MPRN): The unique identifier for a gas supply point. It identifies the connection rather than the gas meter itself.
Metering Charges: Charges associated with installing, operating, maintaining, reading or administering metering equipment and data services.
Method Statement: A document setting out exactly how a piece of work will be carried out safely, step by step - paired with a risk assessment as standard practice before higher-risk electrical or construction work begins.
Microbusiness: A defined small-business category (based on staff numbers and energy consumption) that qualifies for certain additional consumer protections in energy contracts, similar in spirit to (though distinct from) domestic consumer protections.
Microgrid: A local energy system combining loads and potentially generation, storage and controls that can be managed as a coordinated system and may, if designed appropriately, operate independently from the wider grid.
Milestone Payment: A staged payment structure within a connection agreement, tied to defined project progress points, rather than the full connection cost being due upfront. Common on larger generation and battery connections.
Module-Level Monitoring: Monitoring that reports performance data for each individual solar panel, rather than only at string or inverter level - makes it much easier to spot a single underperforming or faulty panel that would otherwise be hidden within an averaged string-level reading.
MPPT - Maximum Power Point Tracking: The function within a solar inverter that continuously adjusts to draw the maximum possible power from the panels as sunlight, temperature and shading conditions change through the day.
MWh - megawatt-hour: A measure of energy equal to 1,000 kWh. Business energy consumption and generation are often expressed in MWh.
MCS - Microgeneration Certification Scheme: A standards and certification organisation covering small-scale renewable-energy technologies and installers. MCS certification is relevant to many domestic and small-scale renewable installations.

N

N-1 Security: A network design and operating principle where the system must be able to keep running safely even if any single piece of equipment (a transformer, a circuit) fails. Part of why some network reinforcement is required well before a site is anywhere near its own capacity limit.
N+1 Redundancy: A resilience design principle where a system has one more unit of capacity (a generator, a UPS module) than the minimum needed to meet demand, so a single failure doesn't cause an outage - a common minimum standard for genuinely critical sites.
NBP - National Balancing Point: The notional pricing point for wholesale gas trading in Great Britain - not a physical place, but the reference hub used to price gas contracts, the gas market's equivalent of Brent for oil.
Negative Electricity Prices: Wholesale periods when electricity prices fall below zero, usually because available generation is high relative to demand and system flexibility is limited.
Net Load: A site's electricity demand after subtracting any onsite generation - the actual amount still being drawn from (or exported to) the grid, as distinct from the site's total underlying (gross) demand.
Net Metering: A billing arrangement in some countries where exported generation offsets imported electricity on a net basis. It is not the standard commercial electricity arrangement in Great Britain, where import and export are generally treated separately.
Net Zero: A state where greenhouse gas emissions have been reduced as far as practicable and remaining emissions are balanced by durable removals. It is broader and generally more demanding than simply buying renewable electricity certificates.
Network Headroom: The spare capacity available on a section of network before reinforcement is needed. Low headroom near a site is one of the most common reasons a solar, battery or EV project gets an expensive or delayed connection offer.
Network Reinforcement: Work required to strengthen or upgrade the electricity network so it can accommodate additional import, generation or export capacity.
Nodal Pricing: An electricity pricing approach where the wholesale price varies at each individual network node based on local supply, demand and constraints, rather than one national price - a more granular version of zonal pricing, used in some other electricity markets and discussed as an option for Great Britain.
Non-Commodity Costs: The parts of an energy bill other than the wholesale electricity or gas itself, including network, policy, balancing, metering and supplier-related costs.
Non-Half-Hourly (NHH): The historic settlement approach for many smaller electricity customers, where consumption profiles rather than actual half-hourly data were used for settlement. MHHS is replacing much of this framework.
Non-Technical Losses: Energy that goes unaccounted for in a network not through physical (technical) losses like cable heating, but through theft, metering error or billing inaccuracy - distinct from, and usually much smaller than, technical losses in a well-run GB network.
NPV - Net Present Value: A financial measure that converts future cash flows into today’s money using a discount rate. A positive NPV indicates that a project is expected to create value under the assumptions used.
National Gas: The company responsible for Britain’s national gas transmission network, moving high-pressure gas around the country.
National Grid Electricity Distribution (NGED): A regional electricity distribution network operator covering the East Midlands, West Midlands, South West England and South Wales.
National Grid Electricity Transmission (NGET): The owner and operator of the high-voltage electricity transmission network in England and Wales. It is different from NESO, which operates the overall GB electricity system.
NESO - National Energy System Operator: The independent public corporation responsible for planning and operating Great Britain’s energy system, including real-time electricity balancing and strategic system planning. NESO took over the electricity system operator role previously associated with National Grid ESO.
Northern Gas Networks: The gas distribution network operator serving much of northern England, including the North East, northern Cumbria and much of Yorkshire.
Northern Powergrid (NPG): The electricity distribution network operator serving the North East, Yorkshire and northern Lincolnshire.

O

OCPP - Open Charge Point Protocol: An open industry-standard communication protocol allowing EV chargers and chargepoint management systems from different manufacturers to work together, rather than being locked into one vendor's proprietary system.
Off-Grid: Operating without reliance on the public electricity network. True off-grid operation is unusual for established commercial sites because sufficient generation, storage and backup capacity can be expensive.
Offtaker: The party buying a generator's output under a PPA - could be a business consuming it directly, a supplier, or a specialist offtaker sitting between the generator and the eventual end user.
Onboarding (MHHS): The process of formally bringing a meter or site into the new half-hourly settlement arrangements under MHHS, including the data flows and system changes needed to support it.
Onsite Generation: Electricity generated at the same site where it can be consumed, such as rooftop solar, CHP or other local generation.
OpenADR: An open technical standard for automatically sending demand-response signals between grid operators or aggregators and the sites/assets responding to them, allowing different manufacturers' equipment to participate without bespoke integration for each one.
OPEX - Operating Expenditure: The ongoing cost of operating and maintaining an asset or service, as distinct from the upfront capital cost.
Opportunity Cost (Battery): The value a battery gives up by being used for one purpose (say, solar self-consumption) instead of another (say, wholesale arbitrage) at the same moment - the real reason a battery can't simply do everything at once, however many revenue streams it's nominally stacking.
Optimisation Agreement: A contract appointing a specialist trading/optimisation firm to actively manage a battery's charge and discharge decisions across markets, in exchange for a fee or share of the resulting revenue - most owners don't run this themselves.
Option Agreement: A legal agreement giving a developer the right, but not the obligation, to lease or buy a piece of land for a project within a defined period and on pre-agreed terms - a common way developers secure land rights before committing to the full cost of planning and design.
Optionality: The commercial or contractual value of keeping future choices open, rather than locking into a single fixed path now - often cited (sometimes loosely) as a reason to prefer a flexible contract or a more adaptable technical design over a fully committed one, even when it costs slightly more upfront.
Organisational Boundary: The rules a business uses to decide which parts of its wider corporate structure (subsidiaries, joint ventures, leased sites) are actually included in its emissions reporting - a genuinely consequential methodological choice, not just an administrative one.
Orientation: The compass direction and angle at which solar panels face. South-facing is not automatically the only sensible commercial option - east-west layouts can sometimes better match a site’s demand or fit more capacity.
Out-of-Contract Rate: A supplier rate that may apply when a fixed business energy contract ends without a new agreement being in place. These rates can be materially higher than competitively procured contract rates.
Outcome-Based Contract: A contract structured around paying for a defined result (a certain temperature maintained, a certain saving achieved) rather than for the specific equipment or hours of work delivered - places the technical risk of actually achieving that outcome on the provider.
Outcome-Based Contract (Energy): A contract paying a provider based on an agreed result (a temperature maintained, a saving delivered) rather than for specific equipment or labour hours - places real performance risk on the provider rather than the customer.
Overstay Fee: A charge applied when a vehicle remains connected to a charger after charging has finished, intended to free up the bay for the next user - a genuine consideration for busy sites, less relevant for single-charger setups.
Ofgem - Office of Gas and Electricity Markets: Great Britain’s independent energy regulator. Ofgem regulates energy networks and markets, protects consumers and administers a number of environmental and social schemes. It does not normally set individual business energy contract prices.

P

P441: An electricity-industry change associated with settlement arrangements for certain non-domestic customers and the wider transition toward half-hourly settlement. Its practical effect depends on the metering and customer category involved.
P442: An electricity-industry modification connected with the move toward half-hourly settlement and changes to how certain metering and settlement arrangements operate.
P483: An electricity-industry modification relevant to aspects of non-domestic energy market arrangements. Where it affects a specific contract or metering setup, the detailed implementation rules should be checked rather than relying on the acronym alone.
P50: A project estimate with a 50% probability of being exceeded. In renewable generation it is often used as a central expected generation case.
P90: A more conservative project estimate with a 90% probability of being exceeded. It is often used by lenders and investors when testing downside generation risk.
P90 Energy Yield: A conservative estimate of a solar system's annual generation that has a 90% probability of actually being exceeded - commonly used by lenders and investors to stress-test a project's downside case, as opposed to the more commonly quoted P50 'central' estimate.
PAS 2060: A British Standard specification for demonstrating carbon neutrality, setting out a structured process of measuring, reducing and offsetting emissions with independent verification - a more rigorous benchmark than simply claiming carbon neutral status unsupported.
Pass-Through Charge: A cost in an energy contract that is passed through to the customer rather than fixed into the supplier’s unit rate. Network and policy costs are common examples.
Pay-as-Produced PPA: A PPA structure where the buyer pays for whatever volume the generator actually produces each half hour, rather than for a fixed, pre-agreed shape - shifts volume/shape risk toward the buyer, in exchange for a typically lower agreed price than a shaped or firm PPA.
Pay-per-kWh (Service Model): A service contract structure where the customer pays only for the energy actually delivered or saved, rather than a fixed subscription or the equipment itself - shifts performance risk onto the provider, since they only get paid if the system actually works.
Payback Period: The time taken for cumulative savings or income from a project to recover its initial cost. Simple payback is easy to understand but ignores the time value of money and benefits after payback.
Peak Demand: The highest electrical demand reached by a site during a period. Short peaks can have disproportionate importance for connection capacity and some charges.
Peak Shaving: Using batteries, generation or operational controls to reduce a site’s highest periods of grid demand.
Peak Sun Hours: A way of expressing a location's total daily solar irradiance as if it all arrived at the maximum standard-test-condition intensity for a set number of hours - a shorthand used in solar yield estimation, not a literal description of daylight length.
Peakload: A wholesale electricity product covering defined higher-demand hours, or more generally electricity demand during the busier parts of the day.
Performance Bond: A financial guarantee, usually from a bank or insurer, that compensates a client if a contractor fails to deliver a project as agreed - protection against the contractor itself going under or defaulting mid-project, not the same as a performance or generation guarantee on the equipment.
Performance Ratio (PR): The ratio between a solar system's actual measured energy output and the theoretical output it should achieve given the irradiance it received, expressed as a percentage - a good single number for judging whether a system is genuinely performing as designed, independent of how sunny the year happened to be.
Permanence: How durably a carbon removal or reduction claim actually lasts - a tree planted today can burn down or be felled decades later, unlike (for example) a geologically stored tonne of CO2. A key quality question when assessing any offset or removal claim.
Permit to Work: A formal, documented system authorising specific work on specific equipment under specific safety conditions, used for higher-risk electrical work like HV switching - a control, not just paperwork, designed to make sure the right isolations are genuinely in place before anyone starts.
Permitted Development: Certain categories of building work (including some solar installations, up to defined size and location limits) that can proceed without a full planning application - worth checking the specific thresholds rather than assuming a project automatically qualifies.
Perovskite Solar Cell: An emerging solar cell material that's cheaper to manufacture and can be layered with conventional silicon cells (as a 'tandem' cell) to push efficiency beyond what silicon alone can achieve - one of the most closely watched next-generation solar technologies, though long-term durability is still being proven at scale.
Phase Imbalance: An uneven spread of load across a three-phase supply's three phases. Left unmanaged it can cause overheating, tripped protection and reduced effective capacity - worth checking before adding EV chargers or single-phase loads to a three-phase board.
Potential Induced Degradation (PID): A form of solar panel performance loss caused by a voltage-driven interaction between the panel and its mounting/earthing system, distinct from normal age-related degradation - a design and installation quality issue rather than an inevitable feature of solar.
Power Conversion System (PCS): The equipment (essentially a specialised bidirectional inverter) that converts a battery's stored DC energy into AC for use or export, and converts incoming AC to DC to charge it - the battery-storage equivalent of a solar inverter.
Power Cut / Outage: An interruption to electricity supply. In Great Britain, 105 is the national number for reporting or getting information about power cuts.
Power Factor: The relationship between useful real power and total apparent power in an AC system. A poor power factor means more network capacity is required to deliver the same useful kW.
Power Factor Correction (PFC): Equipment, usually capacitor banks, installed to reduce a site's reactive power draw and improve its power factor - shrinking the gap between apparent power (what the network has to supply) and real power (what's actually used).
Power Optimiser: A device fitted to individual solar panels (or small groups) that maximises each one's output independently before it reaches the inverter, reducing the impact of partial shading or panel mismatch compared with a plain string inverter setup.
Power Purchase Agreement (PPA): A contract under which one party buys electricity from a generator, often over a long period. PPAs can range from onsite solar agreements to large corporate renewable-energy contracts.
Power Quality: A general term for how closely a site's actual voltage, frequency and waveform match the clean, stable supply that equipment is designed for. Poor power quality - sags, harmonics, imbalance - can shorten equipment life even without ever causing a full outage.
Practical Completion: The point at which a construction project is judged complete enough for its intended use, even if minor defects remain outstanding to be fixed during a subsequent defects period - the trigger for handover and, often, the start of warranty periods.
Predictive Maintenance: Using ongoing condition data (vibration, temperature, performance trends) to anticipate and fix equipment problems before they cause a failure, rather than waiting for a scheduled service interval or an actual breakdown.
Primary Data: Emissions data measured or collected directly from an actual activity (a real meter reading, an actual invoice), as opposed to secondary data drawn from industry averages or estimates - primary data is generally considered more accurate and increasingly expected for material emissions sources.
Primary Substation: A substation that steps electricity down from the higher distribution voltages (e.g. 33kV) to the levels used by most commercial and domestic connections (11kV/400V). The substation a site is fed from can materially affect how much new capacity is available.
Private Network: An electricity network owned or operated privately within a site, estate, campus or development rather than forming part of the public distribution network.
Private Wire: A privately owned electrical connection carrying power directly between generation and a user rather than relying entirely on the public distribution network.
Process Heat: Heat used directly in an industrial or manufacturing process (drying, curing, sterilising, etc.), as distinct from space heating for occupant comfort - often a much larger and harder-to-decarbonise share of a site's total energy use than most people initially assume.
Profile Class: A historic classification used to group non-half-hourly electricity customers with similar consumption patterns for settlement. MHHS is changing the importance of the old profile-class framework.
Prompt Market: The market for energy delivered very soon (within days), as opposed to the forward market for delivery months or years ahead. Prompt prices tend to be more volatile since there's less time for supply and demand to adjust.
Prosumer: A site or household that both produces (generates) and consumes electricity, rather than being purely a consumer - most sites with solar or a battery are, in this sense, already prosumers even if the term itself isn't widely used commercially.
Pumped Hydro Storage: A large-scale storage technology that pumps water uphill when electricity is available and releases it through turbines when electricity is needed.

R

Ramp Rate: The maximum rate at which a generator or battery is allowed to increase or decrease its output, sometimes specified in a connection agreement to protect network stability from sudden large swings in power.
Rapid Shutdown: A safety requirement (and the equipment that delivers it) allowing a solar array's DC voltage to be quickly reduced to a safe level, important for firefighters and engineers needing to work on or near a building during an emergency.
Reactive Power: Electrical power that moves back and forth in AC systems without doing useful work but is needed by certain equipment. Excessive reactive power can reduce available capacity and create charges.
Reconciliation: The process of correcting a bill once actual consumption data (rather than an estimate) becomes available, adjusting for the difference between what was charged and what was really used.
Recovery Time (Resilience): How long it takes a site to return to normal operation after an outage or disruption, as distinct from how long its backup power lasted during the event itself - both matter, but they're genuinely different numbers worth asking about separately.
REGO - Renewable Energy Guarantee of Origin: A certificate issued for renewable electricity generation in Great Britain. Suppliers use REGOs as evidence when making renewable electricity claims, but a REGO is not the same thing as directly funding new renewable generation.
Regulatory Asset Value (RAV): The value of a network company's assets as recognised by the regulator for the purpose of setting allowed returns - a technical concept, but the underlying reason network charges include a return on the physical infrastructure, not just its running costs.
Related MPAN: A second MPAN linked to the same physical site or connection as another - for example, a separate export MPAN sitting alongside a site's normal import MPAN. Worth knowing about since it's easy to overlook a related MPAN when reviewing 'all' of a site's supplies.
REMA - Review of Electricity Market Arrangements: A significant UK government review of how the electricity market is fundamentally structured and priced, including whether GB should move toward zonal or locational pricing rather than a single national price - a live policy question with real implications for where generation and flexible demand end up being most valuable.
Remaining Roof Life: How many years a roof is expected to last before needing replacement, assessed before installing solar - a genuinely important and sometimes-skipped check, since removing and refitting a solar array to replace an underlying roof partway through its life is expensive and disruptive.
REMIT / Market Abuse: REMIT (the Regulation on Energy Market Integrity and Transparency) is the EU/UK framework prohibiting insider trading and market manipulation in wholesale energy markets - relevant background to why some energy market information is subject to strict handling and disclosure rules.
Renewable Electricity: Electricity generated from sources that are naturally replenished, such as wind, solar, hydro and certain forms of biomass.
Renewables Obligation (RO): A long-running UK support scheme requiring electricity suppliers to present renewable certificates or make alternative payments. It is closed to most new generation but continues to affect existing accredited projects and electricity costs.
Renewal Notice Period: The window, specified in a contract, during which a business must give notice if it doesn't want the contract to automatically roll over or renew. Missing this window is one of the most common - and most avoidable - reasons a business ends up back on an expensive rate without meaning to.
Renomination (Gas): Revising an earlier declared gas volume nomination during the course of a gas day as actual demand becomes clearer, rather than being locked into the original forecast.
Repowering: Replacing an ageing generation or storage asset's core equipment (panels, inverters, battery cells) with newer, more efficient versions at the end of its useful life or warranty period, rather than decommissioning the whole site - can meaningfully extend a project's economic life.
Residual Mix: The average generation mix left over once all the certificates (REGOs) claimed by other suppliers and businesses have been subtracted out - typically dirtier than the grid average, since it's what's left after the genuinely renewable-certified electricity has been claimed elsewhere. Relevant to anyone not actively holding renewable certificates of their own.
Resilience: The ability of a site to continue operating through power interruptions or other energy-system problems. Solar or batteries do not automatically provide resilience unless the electrical system is designed to operate safely during an outage.
Resistance: A material's opposition to the flow of electrical current, measured in ohms. Resistance in cables and connections is what turns some electricity into heat, one source of system losses.
Response Time: How quickly an asset must be able to change its output or demand once instructed, for the purposes of a given flexibility or ancillary service - different services have very different response-time requirements, from seconds to minutes, and an asset's suitability for each depends heavily on this.
Response Time (SLA): The maximum time an O&M provider commits to acknowledging and responding to a reported fault, as distinct from the time to actually fix it (resolution time) - both figures matter, and a contract only specifying one is worth querying.
Retail Energy Code (REC): The industry code governing retail market arrangements between suppliers and other parties for both gas and electricity, consolidating several older codes as part of the industry's wider simplification of market governance.
Retention: A percentage of a contractor's payment deliberately withheld until after practical completion (and sometimes until the end of the defects period), giving the client leverage to ensure snagging and defects actually get fixed.
Revenue Stacking: Combining several different income streams from a single battery asset - solar self-consumption, peak shaving, wholesale arbitrage, flexibility/grid services - rather than relying on just one.
Reverse Power Flow: Electricity flowing backwards through a section of network - from what was designed as the demand side toward the source - typically caused by local generation (like solar) exceeding local demand. Networks built decades before rooftop solar sometimes weren't designed with this in mind, which is part of why some connections need reinforcement.
RIIO: Ofgem's price control framework ('Revenue = Incentives + Innovation + Outputs') that sets how much revenue network companies (DNOs, National Grid) are allowed to recover from customers, and what performance they have to deliver in return - the regulatory machinery ultimately behind every network charge on a bill.
Roaming (EV Charging): The ability for a driver to access and pay for charging on a network they're not directly signed up with, via agreements between different chargepoint operators and e-mobility service providers - the EV-charging equivalent of using a card on another bank's cash machine.
ROC - Renewables Obligation Certificate: A certificate issued to eligible renewable generators under the Renewables Obligation. ROCs can provide a significant part of the revenue for older renewable projects.
ROI - Return on Investment: A simple measure comparing the return from an investment with the amount invested. It is useful as a headline measure but can oversimplify long-lived energy projects.
Rollover / Evergreen Contract: A contract that automatically renews into a new term - often at a significantly higher rate - unless the customer actively gives notice within a specific window before the end date. One of the most common, avoidable causes of a business overpaying for energy, since the renewal often happens quietly with no obvious trigger to prompt a review.
Roof Lease: An agreement granting a third party the right to install and operate solar on a building's roof for an agreed term, in exchange for rent, a share of savings, or simply the benefit of the electricity produced - the legal foundation underneath most zero-capex rooftop solar deals.
Roof Loading: An assessment of how much additional weight a roof can safely support, carried out before installing solar - a structural, not just an electrical, question, and one of the first things a credible installer should check rather than assume.
Round-Trip Efficiency: The percentage of electricity recovered after charging and then discharging a storage system. A battery with 90% round-trip efficiency returns about 90 kWh for every 100 kWh put through a full charge-discharge cycle.
Route to Market: The commercial arrangement and party through which a battery (or generator) actually sells its output or services into the market - could be a supplier, an aggregator, a specialist optimiser or a direct market participant. A battery's technical spec means little without a genuine, credible route to market behind it.
Row Spacing / Inter-Row Shading: The gap left between rows of ground-mounted or flat-roof solar panels to stop one row shading the row behind it, especially in winter when the sun sits lower in the sky. A key trade-off in solar design: tighter spacing fits more capacity onto a given roof or field, but at some cost to winter output.
RECC - Renewable Energy Consumer Code: A consumer code for businesses selling or leasing small-scale renewable and low-carbon energy systems to domestic consumers.

S

Science-Based Target (SBT): An emissions-reduction target independently assessed against the level of decarbonisation climate science says is needed to limit global warming, typically validated through the Science Based Targets initiative (SBTi) - a step up in rigour from a business simply setting its own target.
SCOP - Seasonal Coefficient of Performance: A measure of heat-pump efficiency over a season rather than at one operating point. It is usually more useful than a single COP when estimating annual energy use.
Scope 1 Emissions: Direct greenhouse gas emissions from sources an organisation owns or controls, such as gas burned in its boilers or fuel used in company vehicles.
Scope 2 Emissions: Indirect greenhouse gas emissions associated with purchased electricity, steam, heat or cooling.
Scope 3 Emissions: Other indirect emissions across an organisation’s value chain, such as purchased goods, business travel, transport, waste and the use of sold products.
Second-Life Battery: A battery, most often from an electric vehicle, repurposed for stationary storage once its capacity has degraded too far for automotive use but is still perfectly usable for less demanding stationary applications.
SECR - Streamlined Energy and Carbon Reporting: A UK mandatory reporting framework requiring qualifying large companies to disclose their energy use and carbon emissions in their annual report - worth checking whether a business meets the qualifying thresholds, since (like ESOS) they catch more businesses than expected.
Sector Coupling: Linking previously separate energy sectors - electricity, heat, transport - so they can be optimised together rather than independently, for example using surplus renewable electricity to power heat pumps or EV charging rather than letting it go to waste.
Security Deposit: An upfront payment or guarantee a supplier can require from a business with limited credit history or higher perceived risk, before agreeing a contract - worth understanding early in a procurement process rather than discovering it late.
SEG - Smart Export Guarantee: A framework requiring certain electricity suppliers to offer tariffs for eligible small-scale low-carbon electricity exported to the grid. Export prices are set by suppliers rather than by a single national SEG rate.
Self-Consumption: The proportion of onsite generation used directly at the site rather than exported. Batteries can increase solar self-consumption by storing surplus generation for later use.
Sensitivity Analysis: Testing how a project’s results change when key assumptions change, such as electricity prices, generation, battery cost or export value.
Separation Distance: The minimum gap required between a battery installation and other buildings, boundaries or equipment, set for fire-safety reasons - a real site-planning constraint that can affect where a battery can actually go, not just an electrical question.
Service-Level Agreement (SLA): A contractual commitment defining exactly what standard of maintenance response an O&M provider is obliged to deliver - response times, resolution times, minimum availability - and often what happens (financially) if they don't.
Settlement: The process used by the electricity market to determine how much energy participants actually supplied or consumed and financially reconcile differences from contracted positions.
Settlement Period: A 30-minute window (there are 48 in a day) used as the basic unit for measuring, pricing and reconciling electricity supply and demand in Great Britain - the reason half-hourly data comes in 48-column daily blocks.
Shading: Anything that blocks sunlight from reaching solar panels, such as trees, buildings or rooftop equipment. Even partial shading can materially affect output depending on system design.
Shape: The pattern of electricity demand or generation over time. Two sites can use the same annual kWh but have very different shapes and therefore very different procurement, solar or battery economics.
Shape Risk: The commercial risk arising because a customer’s actual half-hourly consumption pattern differs from the standard or forecast profile used when pricing energy.
Shaped PPA: A PPA structure where the contracted volume follows an agreed profile closer to the generator's actual expected output pattern, rather than a flat baseload shape - reduces (but doesn't eliminate) the shape risk left over from a mismatch between contract and reality.
Shipper (Gas): The party responsible for arranging the transportation of gas through the network on behalf of a supplier, including balancing the gas they've contracted to deliver against what's actually flowing - a role most business customers never deal with directly, but one that sits behind every gas supply contract.
Short Term Operating Reserve (STOR): A balancing service where generators, batteries or flexible demand agree to be available to increase output or reduce demand at short notice when NESO needs extra reserve to keep the system balanced.
Shoulder Period: A time band sitting between peak and off-peak, used in some tariff and market structures - neither the cheapest nor the most expensive part of the day, but often glossed over in headline pricing.
Significant Code Review (SCR): A formal Ofgem-led process for making substantial changes to industry codes and market arrangements, used where a change is too significant to go through the normal, narrower code modification process.
Simple Payback: The initial project cost divided by annual savings or income. It is easy to understand but ignores financing, degradation, changing prices and value created after the payback point.
Single Line Diagram Review: A resilience-focused check of a site's own electrical single-line diagram, specifically looking for single points of failure, missing redundancy or unclear failover arrangements - a genuinely useful, often-skipped exercise before assuming a site's backup power actually works as intended.
Single Point of Failure: Any one component whose failure alone would take down an entire system, with no redundant backup to cover for it - identifying and deliberately removing these is the core discipline behind genuine resilience design, as distinct from just adding more equipment.
Single-Axis Tracker: A ground-mount solar structure that rotates panels to follow the sun's east-west path through the day, increasing energy yield versus a fixed-tilt array at the cost of extra mechanical complexity and maintenance - a design choice weighed on larger ground-mount projects, not usually relevant to rooftop.
Single-Line Diagram (SLD): A simplified schematic showing how a site's electrical system is connected - main incomer, switchgear, distribution boards, generation and key loads - using a single line to represent each circuit. Usually the first document an installer or DNO will ask for.
Single-Phase Supply: An electricity supply using one AC phase. It is common in homes and small premises but generally supports less power than a three-phase commercial supply.
Site Acceptance Test (SAT): Testing carried out once equipment is actually installed on site, confirming it performs correctly in its real, final location and configuration - complements, rather than replaces, factory acceptance testing done earlier.
Site Survey: A physical inspection of a site ahead of installation, checking roof condition, electrical infrastructure, access and any constraints a desktop assessment can't pick up - the point where a lot of paper assumptions get tested against reality, and worth insisting on before, not after, a contract is signed.
Sleeved PPA: A PPA structure where a licensed electricity supplier sits between a generator and the corporate buyer, handling physical supply, settlement and balancing while passing through the agreed renewable power arrangement.
Small Modular Reactor (SMR): A smaller, factory-buildable nuclear reactor design, intended to be cheaper and faster to deploy than a traditional large nuclear power station - currently at an earlier stage of commercial deployment in the UK than large-scale nuclear or renewables.
Smart Charging: Controlling when and how quickly EVs charge in response to available capacity, electricity prices, renewable generation or driver requirements.
Smart Export Guarantee: See SEG - Smart Export Guarantee.
Smart Meter: A meter capable of recording detailed energy use and communicating readings remotely. In business energy, the exact metering and settlement arrangement matters more than the label alone.
Snagging: The process of identifying and listing minor defects or unfinished items at the end of a construction project, to be fixed during the defects period rather than holding up practical completion for small issues.
Sodium-Ion Battery: A battery chemistry using sodium instead of lithium, generally cheaper and less reliant on constrained critical minerals, at the cost of somewhat lower energy density - an emerging alternative worth watching for stationary storage where space is less of a constraint than cost.
Solar Coverage: The proportion of a site’s total electricity demand supplied by solar generation over a period. It is different from self-consumption.
Solar Degradation: The gradual reduction in solar-panel output over time. Modern panels typically carry long performance warranties, but project models should still allow for degradation.
Solar Diverter: A device that automatically redirects surplus solar generation (that would otherwise be exported) into a hot-water immersion heater instead - a simple, low-cost way to capture extra value from solar generation without a battery, on both domestic and some smaller commercial sites.
Solar Farm: A large, typically ground-mounted solar installation built primarily to export electricity to the grid or under a PPA, rather than to serve a single site's own consumption - distinct in scale and commercial structure from most commercial rooftop or car-park solar.
Solar Fraction: The proportion of a site's total energy demand met by solar generation over a period - closely related to, but a slightly different cut of the numbers than, self-consumption or solar coverage. Different suppliers sometimes use these terms loosely, so it's worth checking exactly which one a headline figure refers to.
Solar PV - Photovoltaics: Technology that converts sunlight directly into electricity using semiconductor cells. Commercial solar PV can be installed on roofs, car parks or ground-mounted arrays.
Sole-Use Asset: Network infrastructure built and paid for as part of a connection that only serves the connecting customer, as distinct from shared reinforcement that benefits the wider network and other users too - relevant to who ultimately bears the reinforcement cost.
Solid-State Battery: A battery design that replaces the liquid electrolyte in a conventional lithium-ion cell with a solid material, promising better safety and energy density - still mostly in development for large-scale stationary storage, more advanced for smaller applications.
Spark Spread: The theoretical margin between the wholesale electricity price and the cost of the gas needed to generate it in a gas-fired power station - a rough proxy for how profitable (and therefore how likely to run) gas generation is at any given time, which matters because gas plant still often sets the marginal electricity price in GB.
Specific Yield: The amount of electricity a solar system generates per unit of installed capacity, usually expressed as kWh per kWp per year. It is useful for comparing expected performance between sites.
Spend-Based Emissions: A method for estimating Scope 3 emissions by applying an average emissions factor to how much money was spent in a given category, used where more precise activity data isn't available - a starting point, generally recognised as less accurate than activity-based methods.
Standards of Conduct: Ofgem-set rules governing how suppliers must treat domestic and microbusiness customers - covering things like clear information, fair treatment and complaints handling - relevant background to what recourse a smaller business customer actually has if something goes wrong.
Standing Charge: A fixed daily or periodic charge associated with keeping an energy supply available, regardless of how much energy is consumed.
State of Charge (SoC): The amount of energy currently stored in a battery, usually expressed as a percentage of its usable capacity.
State of Health (SoH): A measure of a battery's current capacity and performance relative to when it was new, expressed as a percentage - the practical, ongoing measure of how much degradation has actually occurred, tracked over the life of the asset.
Step-In Rights: Rights, usually held by a project's lenders, allowing them to take over (step into) a PPA or connection agreement if the original project company defaults - a standard piece of lender protection on financed projects, relevant background if a business is contracting with a project that has project finance behind it.
Stranded Asset: An asset that loses much or all of its economic value earlier than expected, typically because of a policy, market or technology shift - a real risk worth naming explicitly in any long-lived energy investment case, rather than assuming today's commercial logic holds unchanged for 25 years.
Stress Event: A real (or drilled) period where the electricity system is under genuine strain, used to test whether flexible assets enrolled in a service can actually deliver when it matters, not just on paper.
String Inverter: An inverter that converts DC electricity from a whole 'string' (series) of panels into AC together, as opposed to a microinverter which converts each panel individually. The more common choice for larger commercial rooftop and ground-mount arrays.
Submeter: A meter installed behind the main utility meter to measure a particular building, tenant, process or item of equipment.
Subscription Energy: A fixed regular payment covering an agreed energy service, structured more like a subscription than a traditional metered bill or financed asset - blurs the line between a supply contract and a service contract, and worth reading carefully to see which it actually is.
Supplier Margin: The amount included by an energy supplier to cover operating costs, risk and profit. It is one component of the difference between wholesale energy prices and the final customer price.
Switchgear: The combined equipment (switches, breakers, fuses) used to control, protect and isolate parts of an electrical system. Ageing switchgear is a common constraint when a site wants to add solar, batteries or EV charging.
Synthetic Inertia: Inertia-like frequency support provided artificially by fast-responding inverter-based equipment (batteries, some wind turbines), designed to substitute for the natural inertia that's being lost as fewer large spinning generators remain on the system.
System Inertia: The natural resistance to sudden frequency change provided by the physical spinning mass of large generators (traditionally gas, coal and nuclear turbines) - as more of the system's generation comes from inverter-based solar, wind and batteries (which don't have this physical spinning mass by default), maintaining enough system inertia becomes a genuine, actively-managed engineering challenge.
System Losses: Energy lost as electricity is transformed, transported, converted or stored. Solar inverters, cables, transformers and batteries all introduce some losses.
System Price: The single price used to value electricity imbalances in each settlement period - effectively what it costs (or is worth) to be short or long against your contracted position at that half hour. The real, unforgiving cost of getting your energy forecast wrong.
System Strength: A measure of how robust a section of the electricity network is to disturbances, closely related to inertia and short-circuit level - a 'weak grid' area can make it harder to connect and safely operate certain types of generation or large flexible loads.
Scottish and Southern Electricity Networks Distribution (SSEN Distribution): The electricity distribution network operator serving central southern England and the north of Scotland.
SGN: A gas distribution network operator serving Scotland and southern England.
SP Energy Networks (SPEN): The electricity network business operating distribution networks in parts of Scotland, Merseyside, Cheshire, North Wales and North Shropshire, as well as transmission in central and southern Scotland.
Solar Energy UK: The trade association for the UK solar and energy storage industry, publishing market data and standards and representing the sector in policy discussions.

T

Take-or-Pay: A contract term requiring a buyer to pay for a minimum agreed volume of energy whether or not they actually use it - a real risk to check for on any contract with volume commitments, particularly where demand might fall (e.g. through an efficiency project or a change in operations).
Targeted Charging Review (TCR): An Ofgem-led reform of how the 'residual' element of network charges is recovered, moving much of it away from being based purely on when electricity is used and toward fixed and capacity-based charges instead - part of why network-charging structures have been shifting in recent years.
Technical Availability: The proportion of time an asset is technically capable of operating, excluding periods lost to planned maintenance, faults or external constraints - the standard measure used to judge whether an O&M contractor is genuinely keeping equipment running as promised.
Temperature Coefficient: A measure of how much a solar panel's output drops for every degree its temperature rises above the standard 25°C test condition. Counterintuitively, panels are often slightly less efficient on a very hot, still summer day than a cold, bright spring one.
Tenor: The length of a contract's term - a 15-year tenor PPA and a 3-year tenor PPA carry very different risk and financing implications even at an identical headline price.
Terminal Value: The estimated value of a project or asset at the end of the period explicitly modelled in a financial appraisal, capturing everything beyond that point in a single figure rather than projecting cash flows indefinitely.
Thermal Runaway: An uncontrolled, self-accelerating rise in a battery cell's temperature that can lead to fire - the core safety risk battery design, cooling, fire suppression and separation distances are all built to prevent and contain.
Thermal Storage: Storing energy as heat or cold for later use, such as hot-water tanks, phase-change materials or chilled-water systems.
Thermography (Solar): Using infrared imaging to spot hot spots on solar panels or electrical connections that indicate a fault, before it causes a bigger failure or a fire risk - a standard part of a proper solar O&M inspection.
Third Party Intermediary (TPI) Regulation: The regulatory standards of conduct that energy brokers and other intermediaries are expected to meet when dealing with business customers - relevant background when assessing how a broker is expected to behave, and what recourse exists if they don't.
Three-Phase Supply: An AC electricity supply using three alternating phases. It is standard for many commercial and industrial sites and supports larger loads more efficiently than single-phase supply.
Time-of-Use Meter: A meter capable of recording (and a tariff capable of charging) different rates at different times of day, as opposed to a single flat rate regardless of when electricity is used.
TNUoS - Transmission Network Use of System: Charges associated with the cost of Britain’s high-voltage electricity transmission network. Charging arrangements differ between generators and demand users and are periodically reformed.
Tokamak: The doughnut-shaped magnetic chamber used in most nuclear fusion reactor designs to contain superheated plasma long enough for fusion reactions to occur.
Tolling Agreement: A commercial arrangement where a third party (a 'toller') pays a fee to use a battery's capacity for their own trading and optimisation strategy, taking on the market risk in exchange for a share of the upside - an alternative to a site or investor running the battery's dispatch strategy themselves.
Total Cost of Ownership (EV): A full comparison of the real cost of running an EV against a conventional vehicle, including purchase price, charging/fuel cost, maintenance, tax and residual value - the honest basis for a fleet electrification decision, rather than comparing upfront price alone.
Total Harmonic Distortion (THD): A measure of how far a site's voltage or current waveform deviates from a clean sine wave, often caused by variable-speed drives, LED drivers, chargers and inverters. High THD can cause equipment problems and is sometimes checked before connecting a large inverter-based system.
TPI - Third Party Intermediary: A broad term covering energy brokers, consultants and other intermediaries acting between customers and suppliers. Commercial models vary, so customers should understand services, authority and remuneration.
Tranche: A defined slice of a business's total forecast energy volume, purchased at one point in time as part of a staged (flexible) procurement strategy, rather than buying 100% of the volume in one go.
Transformer: Electrical equipment that changes voltage levels. Transformers are fundamental to moving electricity efficiently between transmission, distribution and site voltages.
Transition Risk: The financial risk a business faces from the shift to a low-carbon economy itself - changing regulation, shifting customer expectations, a stranded high-carbon asset - as distinct from physical climate risk (the risk from a changing climate's direct physical effects).
Transmission Demand Residual (TDR): The fixed, capacity-based part of a demand customer's TNUoS charge introduced as part of the TCR reforms, recovered regardless of when electricity is actually used - as distinct from the older forward-looking, time-banded element.
Transmission Network: The high-voltage electricity network used to move large amounts of power over long distances. In Great Britain it is distinct from the lower-voltage regional distribution networks.
Triad: The historic three half-hour periods of highest national electricity demand used in calculating certain TNUoS charges for some users. Demand charging arrangements are changing, so Triad should not be treated as a timeless feature of every business bill.
Triad Avoidance: The (now largely historic) practice of deliberately reducing demand during the three winter half-hours expected to set the annual Triad, to reduce a site's TNUoS charge. Reform means this specific strategy matters much less than it used to, but the underlying idea - some periods cost far more to be drawing power in than others - hasn't gone away.
Turn-Down / Turn-Up: The two directions demand flexibility can move in - turning demand down (using less) or turning it up (using more, often to absorb surplus renewable generation) - both are valuable to the system, though turn-down is the one most commercial flexibility offers default to.
Type A Generating Module: A regulatory classification (under the Grid Code) for the smallest category of generating equipment connecting to the network, generally covering typical rooftop-scale solar and small batteries. Determines which technical and compliance requirements actually apply.

U

UKCA Marking: The UK's own product conformity marking, broadly replacing CE marking for goods placed on the Great Britain market - relevant when checking that imported electrical, solar or battery equipment is legitimately certified for UK use.
Unit Rate: The price charged for each unit of energy consumed, normally shown in pence per kWh. It should be considered alongside standing charges and other contract or network costs.
UPS - Uninterruptible Power Supply: A system that provides near-instant backup power to critical equipment when the normal electricity supply fails. A UPS and a larger site battery can serve different purposes even when both use batteries.
Usable Capacity: The portion of a battery's total (nameplate) capacity that's actually available for charging and discharging in normal operation, after accounting for the buffer reserved to protect battery health - almost always meaningfully smaller than the headline kWh figure quoted.
UK Power Networks (UKPN): The electricity distribution network operator for London, the South East and the East of England.

V

V2G - Vehicle-to-Grid: Technology allowing an electric vehicle to export electricity back to the grid or participate in energy services, subject to compatible vehicles, chargers and commercial arrangements.
V2H - Vehicle-to-Home: Using an electric vehicle battery to supply electricity to a home or building. Commercial availability depends on vehicle, charger and connection compatibility.
Vanadium Redox Flow Battery: A battery technology that stores energy in liquid electrolyte tanks rather than solid cells, allowing power and energy capacity to be sized independently of each other - well suited to long-duration storage, though currently at a higher cost per kWh than lithium-ion for shorter durations.
Variable Speed Drive (VSD): Equipment that controls a motor's speed to match what's actually needed at any moment, rather than running it flat-out and throttling the output mechanically - one of the more reliably cost-effective efficiency upgrades on pumps, fans and compressors.
Virtual Power Plant (VPP): A collection of smaller, often geographically spread distributed assets (batteries, flexible demand, sometimes generation) coordinated together and offered into markets as if they were a single, larger power plant.
Virtual PPA (VPPA): A financial renewable-energy agreement where the buyer and generator settle a contract price against market prices without the electricity necessarily being physically delivered to the buyer’s site.
Voltage: The electrical 'pressure' that pushes current around a circuit, measured in volts. Most UK commercial supplies are either low voltage (230/400V) or high voltage (11kV and above).
Voltage Sag: A brief drop in voltage, often caused by a fault or a large piece of equipment starting up nearby. Sensitive electronics and some inverters can trip offline during a sag even without a full outage.
Volume Risk: The risk that actual energy consumption differs from forecast or contracted volumes, potentially affecting supplier costs or customer charges.
Volume Tolerance: The permitted variation between forecast or contracted energy volumes and actual consumption before additional charges or contractual consequences may apply.

W

Warranty Reserve: Money set aside (by an owner, or built into a contract by a provider) to cover the cost of warranty claims and repairs over an asset's life, rather than assuming nothing will ever go wrong - a sign of a realistic, not overly optimistic, O&M plan.
Wayleave: A legal right allowing a cable, line or piece of infrastructure to cross land owned by someone else, without that party owning the land itself - relevant wherever a private wire or export cable needs to cross a boundary the generator doesn't own.
Weather Normalisation: Adjusting energy consumption data to remove the effect of unusually hot, cold, sunny or windy weather, so that underlying trends (genuine efficiency improvement, growth, decline) can be seen clearly rather than obscured by year-to-year weather variation.
WEEE - Waste Electrical and Electronic Equipment: The regulatory framework governing how electronic equipment (including solar panels, inverters and batteries) must be collected, treated and recycled at end of life, rather than sent to general waste.
Weighted Average Cost of Capital (WACC): A blended figure representing the average cost of a project's financing across both its debt and equity, weighted by how much of each is used - a common benchmark 'hurdle' return a project needs to clear to be considered worth financing.
White-Label Supplier: An energy supplier operating under a partner or broker's own branding rather than its own name, while the underlying licensed supply is provided by the parent company - worth knowing when checking exactly who's actually contracted to supply a site.
Whole-Life Cost: The total cost of an asset across its entire life - purchase, installation, operation, maintenance and eventual disposal or decommissioning - rather than just the upfront capital cost. The right basis for comparing two options with very different running costs, even if their sticker prices look similar.
Whole-System Planning: Planning electricity, gas, heat and transport infrastructure together rather than each in isolation, on the basis that decisions in one (like widespread heat pump adoption) have direct knock-on effects on the others (like electricity network capacity).
Wholesale Electricity Price: The market price of electricity before the additional network, policy, balancing, metering, supplier and other costs required to deliver it to an end customer.
Wholesale Gas Price: The market price of gas before network, supplier, policy and other costs are added to the final customer bill.
Wholesale Market: The markets in which electricity and gas are traded before being sold on to end users. Business contract prices reflect wholesale markets but also include many other costs and supplier margins.
Witness Testing: Compliance or commissioning testing carried out with the DNO (or their representative) physically present to observe and sign off the results, rather than relying on the installer's own test report alone.
Wales & West Utilities: The gas distribution network operator serving Wales and the South West of England.

X

Xoserve: The organisation that provides central data and transactional services for the GB gas industry, playing a similar behind-the-scenes role for gas that Elexon plays for electricity settlement.

Y

Yield: The amount of energy generated by an asset over a period. For solar it is commonly expressed in kWh or MWh per year.

Z

Zero-Capex Energy: A general term for any arrangement - funded solar, a funded battery, an EaaS heating contract - where a business gets an energy benefit without paying the upfront capital cost itself, in exchange for an ongoing service payment or PPA.
Zonal Pricing: An electricity market design where wholesale prices vary by geographic zone based on local supply, demand and network constraints, rather than a single national price applying everywhere - one of the options under active consideration through REMA, with genuine implications for where future generation and flexible assets are best located.

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