How many solar panels do I need, and will they fit?

Start with your electricity use

Find your annual electricity use in kWh on a bill or in your supplier account. Use that as a starting point, then consider changes such as an electric car or heat pump. Matching annual generation to annual use does not mean the home will run entirely on solar: electricity has to be available at the time you need it.

Panel numbers, system size and generation

For a simple illustration, ten 450-watt panels have a total rated capacity of 4.5 kilowatts peak (kWp): 10 × 450 ÷ 1,000. That is a power rating, not 4,500 kWh of electricity guaranteed each year. Annual generation needs a separate estimate for the roof and its surroundings.

How many panels will fit on my roof?

Dividing total roof area by the size of a panel is only a rough first check. A rectangular panel cannot fill every awkward corner. Roof edges, windows, chimneys and gaps between panels also use space. A layout shows where the proposed panels actually go, making it easier to discuss a practical design.

More panels or better-positioned panels?

Ask to compare the proposed layouts and their generation estimates. If extra panels use a different roof face, ask what they add to the total and to the price. On a shared roof, check that every proposed panel stays within the area you can use.

Let VERA check your home

Start with your address and VERA assesses the available roof data. You do not need to measure the roof yourself. Add your details to unlock the assessment and get your free quote; an installer will still need to confirm the final arrangement.

• Try the solar panel calculator