Before you start

The whole thing takes about three minutes. You do not need an account, a password or an email address to get a number, and nothing reaches the installer until you decide, at the very end, that you want them to have it.

The six questions

1. Your property. Your address, and a satellite map where you point at the roof you have in mind.
2. Your roof. Its shape and rough size, which way it faces, and whether anything shades it.
3. Your energy use. How much electricity you get through, answered whichever way suits you.
4. Your system. How many panels, which panel, and whether to add a battery. This is where you get to play.
5. Your estimate. The four numbers, and a monthly payment plan if the installer offers one.
6. Register your interest. Your name and email, if you want the installer to pick it up from here.

Only step 6 involves giving anyone your details. Steps 1 to 5 are yours alone.

Worth digging out first

An electricity bill, if you have one to hand. Two things on it make the estimate meaningfully better:

• Your yearly usage. On a UK bill this is the confirmed annual usage figure, usually near the bottom of your annual statement, written in kWh (a kilowatt hour, the unit electricity is sold in). This is the single most useful number you can give, because everything about savings follows from how much you actually use.
• What you pay per unit. Look for a rate in p/kWh, pence per kilowatt hour. If you are on a two-rate tariff, an EV tariff or Economy 7, there will be a day rate and a cheaper night rate. Both are worth having, because they change the savings figure noticeably.

You might also want a rough idea of your roof: whether it slopes or is flat, which way the sunniest face points, and whether a tree or a neighbour’s house puts it in shade for part of the day. None of that needs measuring. Looking out of the window is enough.

“I don’t know” is a real answer

Several questions can be left alone, and one of them, the question about your electricity use, has I honestly don’t know as an option you are meant to use. It is not a failure state. The calculator falls back to a typical figure for a home your size, and it tells the installer that it did, so they know to check with you rather than trusting a number you never gave.

The same goes for which way your roof faces: Not sure stays genuinely unknown. It is never quietly turned into “south” behind your back.

A vague answer you can stand behind beats a confident one you invented.

You can go back

Every step after the first has a Back to… link at the bottom, and your answers are still there when you return. Changing an answer and coming forward again re-does the sums.

If the first button does nothing

There is a known problem with the very first click. Pressing Start your estimate sometimes appears to do nothing at all, or lands you on a sign-in page you did not ask for. Reload the page and press it again, and it behaves. It is a fault on our side, not something you have done.

Next: step 1, your property.