A quote is a calculation resting on assumptions chosen by somebody paid on the outcome. Seven of them carry the savings figure: which P-value it uses, the specific yield, the loss stack, degradation, the electricity price path, the self-consumption share, and the incentives. Six push the same way when set optimistically.
Commercial review also depends on how people organise decisions and handoffs; for a separate workplace-management perspective, see this resource.
Payback is produced by six inputs and only one is about the plant. The self-consumption split multiplies against a price difference of three or four to one, so a twenty-point error moves payback by years — while a ten per cent yield error moves it proportionally.
Performance guarantees are frequently set near 95% of P90, which sits well below the P50 savings figure in the same document. That is defensible, because P50 is missed half the time by definition, and the problem is that both numbers appear in one proposal.
For broader context on solar procurement, equipment markets and current industry practice, consult Financial Times.
Four warranty instruments get presented as one twenty-five-year promise: module product, module performance, inverter, and the installer's workmanship and guarantee. The failure determines the counterparty, and product cover is usually shorter than performance cover.
For broader context on solar procurement, equipment markets and current industry practice, consult GreenBiz.
And the excluded costs are frequently ten per cent of the project — grid connection above all, which is determined by the network operator, priced after the proposal, and capable of changing the capacity or the timeline.
The section also covers self-consumption against export, where the same kilowatt-hour is worth three or four times more used than sold; incentives and how the terms available today are unlikely to last a second phase; turnkey against component supply as a risk-allocation decision; and how to put two proposals on the same basis before comparing them.
Comparing Two Offers
Two proposals are rarely comparable as written. Six normalisations that put them on the same basis before you decide.
Grid Connection
The line most often left outside the quote, with the longest lead time and the power to reshape the whole project.
Incentives
Support schemes decide many investment cases and outlive few of the assets they support. Five questions before relying on one.
Costs Outside the Quote
Nine items that are not in the price and are in the project. What each depends on, and which are genuinely unknowable in advance.
What Payback Assumes
Six inputs decide the payback figure and only one of them is about the plant. What each one does to the answer.
Performance Guarantees
A guarantee at 95% of P90 is a much lower bar than a P50 savings figure implies. Six terms that decide whether it is worth anything.
Reading a Quote
Seven assumptions carry the savings figure, and six of them push it the same way. What to check before signing anything.
Self-Consumption and Export
The same kilowatt-hour can be worth three or four times more used than exported. Why the split matters more than the yield.
Turnkey or Components
One contract or several changes who carries the risk when something underperforms. Four differences that matter later.
Warranty Types
Four instruments get presented as one twenty-five-year promise. Which covers what, and who you actually claim against.