For homeowners

If you are thinking about solar panels, the usual first step is a phone call, a home visit, and a fortnight of waiting for a number. This is the shortcut. You answer six short questions about your home, and you get a figure straight away: how big a system your roof would take, what it would cost to install, what it would save you a year, and how long it would take to pay for itself.

Whose calculator is this?

The calculator belongs to one solar installer. It is not a comparison site, and it is not run by a price-comparison company. You will have arrived at it from an installer’s own website, or from a link they sent you, and it carries their name, their colours and their prices.

That matters more than it sounds. The costs and savings you see are the ones that installer actually works to, rather than a national average, which is why the same house can get different numbers from two different companies.

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1. The installer's name sits at the top of every screen. In these guides that is Meridian Solar, a company we invented for the pictures. On the real thing you will see the name of the firm you are dealing with, in their own colours.
2. One button to start. Nothing is sent to anyone until the last of the six steps, so you can look around first.
3. About three minutes, and no account. You do not sign up, choose a password or verify anything to get your estimate.
4. The prices come from that installer's own cost sheet, not from an industry average.

Every screenshot in this section was taken from a demonstration company called Meridian Solar. Your installer's version will look the same underneath, in their own branding.

What it does not do

Nobody rings you because you opened the calculator. Your details are only sent when you fill them in yourself at the last step, and even then an estimate is not an order. There is nothing to cancel, and nothing is booked.

Where to go next

• Getting an estimate walks through the six questions one at a time, with a picture of each. Start here if you are about to use the calculator, or are stuck partway through it.
• Understanding your estimate explains the four numbers you end up with, where they come from, and what they are honestly worth.
• Your account covers the optional account: what it gives you, how signing in works, and how to read a proper written quotation when one arrives.

There is also a glossary for the words the solar trade uses without explaining, and a page on what happens to your details.