Solar PPA Explained: Structures, Tariff, Term and Who Owns the Asset

A power purchase agreement is the answer to a question most organisations ask about solar within the first ten minutes: can we get the benefit without finding the capital. The short answer is yes, and the longer answer is that you are trading capital for a twenty year commitment whose value depends entirely on terms that rarely get read as carefully as the headline tariff.

The structure is simple enough to describe in a sentence. A developer funds, builds, owns and maintains a solar system on your site or on your behalf, and you buy the electricity it produces at an agreed price for an agreed period. You pay nothing up front. You also own nothing.

Everything interesting is in the detail of that arrangement, and this article works through it: the structures available, the terms that decide whether the deal is good, what the developer is actually underwriting, and the cases where buying the system outright is plainly better.

What a PPA Is, and What It Is Not

A PPA is a contract to buy electricity. It is not a lease, not a loan, and not a service contract, although it is regularly confused with all three.

Under a lease or a hire purchase agreement, you are paying for the equipment and you generally end up owning it. Payments are fixed and do not depend on how much the system produces. If the system underperforms, you still owe the payment.

Under a PPA, you are paying for kilowatt hours. If the system produces nothing, you pay nothing. That single difference is the reason PPAs exist, because it moves performance risk from you to the developer. It is also the reason PPA tariffs are higher than a pure financing cost would imply: the developer is charging you for carrying that risk.

Under a straight purchase, you fund the system, own it, and keep every kilowatt hour it makes for the rest of its life. The economics are usually the best of the three by a clear margin, provided you have the capital and the appetite to own an asset. Our guide to commercial solar financing sets out the funding routes between those poles.

The Structures

On-site, behind the meter. The system sits on your roof or your land, connects on your side of the meter, and the power flows straight into your operations. This is the common commercial and industrial arrangement, and it is the cleanest, because the electricity never touches the grid and the value is simply the retail tariff you avoid paying. Your saving is the difference between your grid tariff and the PPA tariff, which makes the deal easy to evaluate.

Off-site or sleeved. The system is built elsewhere, often at utility scale, and the power reaches you through the grid under an arrangement with a supplier. This unlocks projects far larger than your roof and sites with better irradiance, at the cost of complexity: network charges, supplier arrangements and regulatory conditions all sit between the generator and your meter. In the UK these arrangements operate inside the licensing and network framework that Ofgem sets out, and the sleeving costs are frequently underestimated in early comparisons.

Virtual or financial. No electrons reach you at all. The contract is a financial hedge referencing a generator's output against a market price. This is a treasury instrument rather than an energy project, and it belongs to organisations with the sophistication to manage it. It is mentioned here mainly so it is not confused with the first two.

For most commercial and industrial buyers, especially outside heavily traded markets, the on-site behind-the-meter structure is the only one worth serious evaluation.

The three PPA structures. For most commercial and industrial buyers only the first is worth serious evaluation. Source: MIMAH engineering and commercial analysis.

The Terms That Decide Whether It Is a Good Deal

The tariff and its escalator. The headline price per kilowatt hour is the number everyone compares. The escalator, the annual percentage by which it rises, is the number that decides the outcome. A tariff that starts below your grid price and escalates faster than your grid price will cross over, and the year it crosses is the year the deal stops working for you. Model the full term, not year one. If the escalator is fixed and your grid tariff is volatile, understand that you have taken a view on future electricity prices whether or not you meant to.

The term. Fifteen to twenty five years is typical, because that is the period the developer needs to recover the asset. It is a long time to commit a site. If there is any prospect of the building being sold, the lease ending, the process changing or the operation relocating, the term is a risk and needs an exit.

Minimum purchase obligations. Some agreements require you to buy the output whether or not you can use it. If your load drops, through efficiency work, a shift change, or a downturn, you may be buying power you no longer need. Read what happens to unconsumed generation, and who gets the value if it is exported.

Performance guarantees. The developer should guarantee a minimum annual output, with compensation if it is missed. Without one, the performance risk you thought you had transferred has quietly stayed with you. Check what the guarantee excludes: grid outages, curtailment, your own site shutdowns and force majeure are commonly carved out, and a guarantee with wide enough exclusions is decorative.

Curtailment and site availability. If your plant shuts for a fortnight and cannot take the power, what happens. If the roof needs work and the array must come off, who pays. These clauses are boring until the day they apply.

Termination and buyout. What it costs to end the agreement early, and on what schedule that figure falls over time. Early termination values are often set to recover the developer's remaining return, which can make exit expensive in the early years. This is the clause most likely to surprise a buyer later.

End of term. Three outcomes are usual: the system is removed, ownership transfers to you, or the agreement extends. Which one, at what price, and who decides, should be written down at signature rather than negotiated in year twenty when the leverage is entirely on one side.

Roof and site obligations. A twenty year PPA on a roof with ten years of life left is a problem waiting to happen. Establish who pays to remove and reinstall the array when the roof is replaced, and get the roof surveyed before signing rather than after.

The eight terms that decide whether a PPA is a good deal. The headline tariff is not one of them on its own. Source: MIMAH engineering and commercial analysis.

What the Developer Is Underwriting

Understanding the developer's position makes the negotiation easier, because it explains which terms they can move and which they cannot.

The developer is funding an asset against your promise to buy its output for two decades. Their lender is therefore underwriting three things: your credit, because the revenue is your payment; your site, because the asset is bolted to it; and your load, because a system sized to a demand that disappears does not repay.

That is why a PPA offer varies so much between buyers for identical engineering. A strong covenant on a freehold site with a stable industrial load gets a keen tariff. A weaker covenant on a short leasehold with a seasonal load gets a higher one, or gets declined. If your offer looks expensive, the cause is often one of those three rather than the developer's margin, and fixing the underlying issue moves the price more than haggling does.

It also explains why developers resist flexible terms. Every option you gain is a risk their lender has to price.

When a PPA Beats Buying, and When It Does Not

A PPA is the better route when capital genuinely is not available or is committed to higher-returning uses in the core business, when the organisation does not want to own and maintain generating plant, when performance risk transfer is worth paying for, or when the accounting or tax treatment favours it in your jurisdiction.

Buying is better, usually by a wide margin, when capital is available and the cost of that capital is below what the PPA implies. The developer's return is embedded in your tariff for twenty years, and over the asset's life that is a large number. If you can fund the system, you keep it.

The comparison that matters is not PPA tariff against grid tariff. It is PPA over the full term against ownership over the full term, both modelled to the same horizon, including the operations and maintenance you would carry as an owner and the residual value you would hold at the end. That comparison is frequently not the one presented, because the developer has no reason to present it.

If you do buy, the maintenance obligation becomes yours, and it is worth understanding what that entails before choosing: our solar O&M contract guide covers what a competent maintenance arrangement includes.

Where PPAs Go Wrong

The escalator crossover. A tariff that rises faster than the grid price it was meant to beat. Model it to year twenty before signing.

A system sized to the wrong load. Oversizing suits a developer paid per kilowatt hour and does not suit you, particularly with a minimum purchase obligation attached. Get the sizing independently reviewed. For industrial sites, our guide to solar for factories covers how load profile drives sizing.

Weak or heavily excluded performance guarantees, which return the risk you were paying to transfer.

Maintenance drift. The developer owns the asset, so maintenance is their obligation, but their incentive is only to keep output above the guarantee floor. A system running at 92 percent of potential meets a 90 percent guarantee comfortably while quietly costing you the difference.

A developer who will not be there. A twenty year contract with a company that may not last five is a different product from the one described. Balance sheet, project pipeline, ownership and what happens if the contract is assigned all matter. The due diligence is much the same as for any long-term contractor, and our guide to choosing a solar EPC contractor applies directly.

Five ways a PPA goes wrong, all of them visible before signature. Source: MIMAH engineering and commercial analysis.

Emerging Markets Change the Calculation

In markets with unreliable grids and hard currency constraints, PPAs carry risks that mature-market templates do not price.

Currency. A tariff in dollars against revenue in local currency is a mismatch that has broken many otherwise sound projects. Who carries devaluation risk is a first-order term, not a detail.

Offtaker credit. Where the buyer is a utility or a public body, the value of the contract is the value of that promise, and payment histories are a matter of record rather than opinion. IRENA's published work on renewable procurement covers how these structures have performed across African markets.

Grid reliability. A PPA priced against grid electricity you are not reliably receiving is being compared to the wrong baseline. The right comparison is often against diesel, which changes the arithmetic substantially and usually in solar's favour.

Enforceability. A contract is worth what it can be enforced for. Governing law, dispute resolution and the practical route to remedy deserve attention early rather than late.

Getting the Comparison Right

Three things make a PPA evaluation honest. Model the full term rather than the first year. Compare against ownership rather than against the status quo alone. And have the technical assumptions underneath the tariff, the yield model, the degradation rate and the sizing, reviewed by somebody who is not being paid by the outcome.

MIMAH's renewable energy team reviews PPA offers on the engineering that sits underneath them: whether the system is sized to your actual load, whether the yield model is credible for your site, and whether the guarantees mean what they appear to. If you have an offer on the table and want it checked before you sign, get in touch.