"Zero capital cost solar" sounds like it shouldn't be possible. Someone builds a solar system on your roof, you pay nothing upfront, and you end up with a lower electricity bill. Where's the catch?
There isn't one - but there is a structure behind it worth actually understanding, because it explains why the deal works for everyone involved, not just you.
What "behind-the-meter" means
It simply means the solar - and often battery - system is installed on your side of the electricity meter, generating power that's used directly on site rather than being exported to the grid and sold elsewhere. The generation and the consumption happen in the same place, which is what makes the arrangement financially interesting in the first place.
What a PPA actually is
A Power Purchase Agreement is a contract to buy power at an agreed rate over an agreed term - commonly ten to twenty-five years for an on-site system. In a behind-the-meter PPA, a third party (an investor, sometimes called the asset owner) pays to design, install, own and maintain the solar and battery system. You don't buy the equipment. You buy the electricity it generates, at an agreed PPA rate - with the contract defining whether that rate stays fixed for the term or moves over time (indexed, stepped, or periodically reviewed, sometimes with caps or floors). That detail matters enormously over a twenty-year agreement, so it's worth knowing which structure you're actually signing.
Who's actually taking the risk
This is the part that gets missed. The investor carries the capital cost, the maintenance obligation and the long-term ownership of physical equipment on someone else's roof, and has a strong incentive to keep the system performing well. Exactly how specific risks - underperformance, availability, curtailment, roof access, or outages caused by the customer - get allocated between the two parties is set out in the contract itself, not assumed automatically. In exchange for taking on the capital and ownership side, the investor receives a predictable, long-term revenue stream from the PPA rate - plus, depending on the structure, income from exporting any surplus generation the site doesn't use.
That's the trade that makes "zero cost to you" genuinely sustainable rather than too good to be true: someone is being paid for taking on the risk. It's just not you.
Why the PPA rate is usually lower than your grid rate
The investor isn't trying to match or beat the wholesale market unit by unit - they're pricing a long-term contract against their own cost of capital and equipment cost, spread over the full term. That structure typically allows the PPA rate to sit meaningfully below a normal commercial import rate, which is where the saving comes from, every month, for the life of the contract.
What you're actually signing up to
A long-term commitment to buy the power that system generates - usually with defined terms around what happens if you move premises, if the system underperforms, or at the end of the contract term (some agreements include an option to take ownership of the system outright at that point). None of this is complicated once it's laid out, but it does mean reading the actual agreement, not just the headline saving.
Why it isn't right for everyone
A site needs enough suitable roof or land, a demand profile that can actually use the generation - this is where half-hourly data comes back in, see what your data is actually telling you - and a genuine willingness to enter a long-term agreement rather than staying fully flexible year to year. It's a real trade, not a free lunch. Just one that's honestly explained.
Wondering whether a behind-the-meter PPA would actually work for your site? Send us your consumption data and we'll tell you honestly, not just sell you the pitch. Get in touch.