The cell grid of a solar panel, close up

Solar panels

Solar panels, tailored for the roof they sit on.

A solar panel turns daylight into electricity, and the array is the panels on your roof, taken together. We weigh each panel against the roof it will sit on, and the quote should name exactly which one was chosen.

Get my estimate All the kit
On the example
14 × 445 W
Adding up to
6.2 kWp
Made in a year
About 5,400 kWh

What a panel does

Daylight in, direct current out.

Each panel is a sheet of cells. Daylight on them makes a direct current, which an inverter turns into the alternating current your home runs on.

A panel’s rating in watts is its output in full sun, under standard test conditions. On the example estimate, 14 panels at 445 W add up to an array of 6.2 kWp.

Full sun is the exception, not the rule. A year’s output depends on pitch, direction and shade, so the example estimate works from the roof itself: at 35° and facing S–SW, about 5,400 kWh a year.

The cell grid of solar panels in warm late light, close up

What we weigh

The panel that suits your roof, not the one with the biggest number on the box.

  • 01

    Output per square metre

    Panels with the same rating can differ in size. On a small or crowded roof, the one that makes more per square metre fits a bigger array into the space there is; on a large, clear roof it matters less.

  • 02

    Coping with part-shade

    Inside a panel, cells are wired in groups, and a shaded group can be bypassed instead of holding back the rest. Under a chimney, how finely a panel is divided matters more than a few extra watts on the label.

  • 03

    Laid out for the roof

    We draw the array onto the roof we read from above, clear of the ridge, hips, edges and a safe walkway, and around roof lights, vents and flues. Panels go upright or on their side, whichever fits more of them out of the shade.

A brick house with a hipped slate roof seen straight down from the air: its chimney stack, a TV aerial, a small dormer and the trees along the garden
Read from above · example roofN ↑

Read from above

We measure the roof before we price it.

Aerial imagery gives us most of what a survey used to start with. We read it before anyone books a visit, so the visit checks our numbers instead of opening a sales conversation.

What happens on survey day

Finish

All-black or framed.

All-black panels are black from frame to backing. Framed panels have a silver frame, often with a paler backing between the cells. Many ranges come in both.

All-black

Best where
The array faces the street and one dark, even shape suits the front of the house.
Watch for
The exact model on the quote, because the all-black version of a range is a separate product.

Framed

Best where
The array faces the garden, and the choice can rest on output and price alone.
Watch for
A quote that lists panels by wattage alone, because the model decides the finish, the size and the warranty.

Warranties

Two promises from the manufacturer, and they are not the same.

Every panel makes a little less each year as it ages. That slow loss is degradation, and the performance warranty is the manufacturer’s promise about it: how much of its rated output the panel will still make after a set number of years.

The product warranty covers faults in the panel itself, often for a different term. The quote should name both. We keep them together with the installer’s workmanship warranty, so you know who covers what.

On the quote

What the installer’s quote should specify.

We check every line of the quote before it reaches you. These are the ones that should never be missing.

Reading a solar quote, line by line Every word on a quote

  • The make and model of every panel
  • How many panels, and the rating of each
  • All-black or framed
  • Where each panel goes, face by face
  • The product and performance warranties, each with its term

Manufacturers we see on quotes

  • AIKO
  • LONGi
  • JA Solar

Named because they turn up on quotes. We sell none of them.

Solar panels · questions

Asked about panels.

01Is a higher-wattage panel always better?

Not on its own. A higher rating often comes on a bigger panel, so fewer may fit. What counts is what the whole array makes on your roof, in your shade, for the price.

02Will panels work on a shaded or east–west roof?

Often, yes, just less than on a clear south-facing roof. An east–west array makes more of its power in the morning and evening. If the numbers don’t work, your estimate will say so.

03Do I need planning permission for panels?

Usually not. Most home solar is permitted development, but listed buildings, conservation areas and flats can need permission, so check first.

04Do you favour a particular manufacturer?

No. We never fit a panel, so we never need to sell you one. The manufacturers on this page are ones we see on quotes; the right panel is whichever suits your roof and prices well.

Every question

Keep reading

The rest of the system.

A bungalow with a panelled roof across an evening field

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Our estimate is free. If you proceed to survey, our partner installer invoices you directly; we receive a referral fee from them, never from you, and it never affects which installer we introduce.

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