How Many Solar Panels Do I Need for My Home?

A typical home using 2,500 kWh a year needs roughly 6 or 7 panels of 400 W. Your area changes the exact number. Divide your yearly use by your area’s output per kilowatt, then divide by one panel’s rating. The sums below show each step.

Start with how much power you use

Your electricity bill or smart meter gives your yearly use in kWh. If you do not have it to hand, use a typical figure, although your real bills are better. Ofgem’s medium home value is 2,500 kWh a year from 1 July 2026.

Your own number can differ a lot, because homes vary. A home with an electric car, a heat pump or home working may use more. A flat with gas heating may use less. Use your real bills where you can.

Work out the system size in kWp

We size solar systems in kilowatts peak (kWp), which is the rated power of the panels in test conditions. However, each kWp makes a different amount of power depending on where you live.

PVGIS, the EU’s solar modelling tool, gives the output of a south-facing system at 35 degrees. Our table of solar output in 24 UK cities lists every town. Here are three examples from it.

• Aberdeen: 892 kWh per kWp a year
• Norwich: 1,030 kWh per kWp a year
• Plymouth: 1,121 kWh per kWp a year

Divide your yearly use by that figure. For example, for 2,500 kWh, you need about 2.8 kWp in Aberdeen, 2.4 kWp in Norwich and 2.2 kWp in Plymouth. Those sums come from our own arithmetic on the PVGIS numbers.

Turn kWp into panels

Next, divide by the rating of one panel. Panel ratings vary by model, so we take a 400 W panel, which is 0.4 kWp. We use it only to show the method, since your installer may quote a different rating.

• Aberdeen: 2.8 kWp is about 7 panels.
• Norwich: 2.4 kWp is about 6 panels.
• Plymouth: 2.2 kWp is about 6 panels.

Your installer will use the real rating of the panel they quote. A higher rating means fewer panels for the same system. However, the total kWp is what counts, not the number of panels.

Why bigger can be better

Matching your yearly use is only a starting point. Solar makes most power when you are out, so you will not use all of it at home. Much of your yearly total will go to the grid instead.

For this reason, many people choose a system larger than the sums above. A 10-panel system at 400 W is 4 kWp. In Aberdeen that makes about 3,568 kWh a year, and in Plymouth about 4,484 kWh, from the PVGIS figures. You pay more upfront, yet you produce more in the dull months too.

Surplus power earns a payment under the Smart Export Guarantee, but the rate varies by supplier, so do not count on it. Larger systems also bring grid rules into play. Our G98 and G99 guide explains the 16 A limit.

Fewer panels, bigger panels

Higher-rated panels mean fewer units on the roof, which changes the layout more than the total. Ask for a roof diagram showing where each panel goes, so you can see how the sums fit your house.

New homes follow different rules. The government’s Future Homes Standard response sets a solar requirement equal to 40% of a dwelling’s ground floor area. If a roof cannot make 720 kWh a year, no panels are needed. None of this applies to an existing house.

Roof space and shape

The roof sets the upper limit. Panels need clear space, away from shade, chimneys and the roof edge, because shade cuts output. East and west roofs make less than south, so they may need more panels for the same output.

The structure matters too, since panels add weight. The MCS standard (MIS 3002) says a suitably competent person must check that the roof can carry the system. Your installer should do this and keep the evidence.

Planning rules can also limit where panels go, so read whether solar panels need planning permission before you settle on a layout.

What it may cost

Cost depends on size, roof and extras. DESNZ publishes MCS data. For 2025/26, the median for installs up to 4 kW was around £1,780 per kW of declared net capacity. That figure covers Great Britain, includes VAT where it applies, and excludes batteries.

Which? gives about £7,600 for a 4.5 kWp system, citing Energy Saving Trust estimates.

Installation is zero-rated for VAT until 31 March 2027, but the rate rises after that. Our post on VAT on solar panels explains the change.

How to check a quote

Look for these points when you compare quotes, because they show how careful each installer is.

1. The system size in kWp and the number and rating of panels.
2. The expected yearly output in kWh, and the method behind it.
3. The roof direction and any shade allowance.
4. Whether the installer is MCS-certified.

Our guide to MCS-certified solar installers shows how to verify this, since it also affects export payments. For the full process, see our page on solar panel installation.

Next steps

Write down your yearly use, your roof direction and any shade. Then ask two or three installers to size a system for you. If their figures differ much from the PVGIS numbers, ask why. A sound answer should name the shading, roof angle or loss assumption behind the gap.

For local detail, read how solar panels perform in Aberdeen. You can also look at solar installers serving Plymouth or solar panels in Norwich. When you are ready, you can request quotes through our form. We store your enquiry in a central dashboard, and nobody is contacted automatically.