What the estimate is not

An instant estimate is a useful thing. It tells you, in three minutes, whether solar is roughly worth pursuing on your house, and roughly what scale of money is involved. It is worth being equally clear about what it is not, so that nobody finds out the awkward way.

The figures here are illustrative.Screenshots come from a demo installer with example pricing, so every cost, saving, payback period and instalment is made up. Your own numbers come from the pricing your installer has entered.

It is not a quotation

A quotation is a formal, itemised document from the installer, with a total, a breakdown, a validity date and their name on it. It is what you would sign against.

An estimate is a calculation from answers you typed in, some of which you may have guessed. Nobody has priced your specific job.

If the installer sends you a quotation later, it appears in your account and arrives by email, and it will not necessarily match the estimate. It supersedes it. See reading and accepting a quote.

It has not been surveyed

Nobody has seen your roof except from above, and the pictures may be years old.

A survey is where the estimate meets reality: the state of the roof covering, the rafters underneath, where the inverter can live, how the cable runs to the consumer unit, whether the scaffolding can even be put up, and how much of that roof face is genuinely usable once the vents, the chimney and the edges are taken out.

Any of those can change the panel count, and with it every one of your four numbers.

It is not an offer of credit

The instalment plan, if you saw one, is an illustration. Nobody has run a credit check, assessed affordability, or agreed to lend you anything. The estimate says so in the representative example, and it is worth repeating: you may be offered a different rate, or not be offered credit at all.

It is built on the installer’s assumptions

Every figure behind your estimate comes from a sheet that installer filled in: what a system generates in their region, what they charge per kWp, what scaffolding costs, how much of your own solar they assume you will use, and what the export payment is worth.

Those assumptions are theirs, not an industry standard and not ours. It is a reasonable question to ask them what they used, and a good installer will tell you.

It is only as good as your answers

The calculator is honest about its inputs, but it cannot check them. If you guessed at your electricity use, the savings figure is a guess with a pound sign on it. If you picked the wrong roof size band, the system size follows it.

This cuts both ways, which is the useful part: if the numbers look unpromising, it is worth checking whether one shaky answer is responsible before you give up on the idea.

What it genuinely is good for

Comparing options against each other. The assumptions may be arguable, but they are the same assumptions across every configuration you try, so the difference between eight panels and ten, or between a battery and no battery, is meaningful even where the absolute figures move later.

What is actually promised

One thing. The installer said they would get in touch within a stated number of hours. Everything else, the survey, the quotation, the finance, the work itself, happens later and separately, and each is its own decision.

Next: do you need an account?