How many solar panels will I need?
The right number of panels depends on the space on your roof and how much electricity your home uses. An installer can turn those details into a layout and an estimate of what the panels could generate.
Start with your electricity bill
Look for your yearly electricity use in kWh. This is more useful than the amount you pay each month, because prices vary. Tell the installer when you use electricity too: during the day, in the evening or both.
Include any plans for an electric car, heat pump or more time working at home. These can change how much electricity you need.
Check the space on your roof
Panels come in different sizes. An installer should show you a roof layout with the exact panel dimensions, allowing space around roof edges, windows, chimneys and other obstacles.
Roof direction and shade matter. South-facing roofs often produce the most electricity over a year, while east- and west-facing panels can spread generation across the day. Ask how trees or nearby buildings affect your roof.
How does panel power affect the number?
The power rating of a panel is shown in watts, or W. For example, nine 450 W panels make a 4.05 kWp system. kWp describes the combined rated power of the panels under standard test conditions.
Your installer can check how many panels fit your roof and how much electricity that layout could produce.
Ask how much electricity the panels will make
Your quote should give an estimated yearly output in kWh. Ask for a monthly breakdown too: panels usually generate much more in summer than in winter.
Find out how the installer has allowed for roof direction and shade. Our solar output guide helps you understand the figures.
Think about a battery afterwards
First work out how much electricity the panels could produce and how much you could use during the day. Then consider whether a battery would help you keep spare electricity for later.
Ask for the same panel layout priced with and without a battery.
What to take to an installer
- Your annual electricity use from a recent bill.
- When people are usually at home.
- Any roof details or known shading.
- Plans for an electric car, heat pump or other extra electricity use.
Before agreeing to work, check whether permission is needed and look through your written quote.
Your checklist at a glance
How many solar panels do I need - UK sizing checklist
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