Many UK homes need around 8 to 10 solar panels. That gives a system of roughly 3.2 to 4 kilowatts peak (kWp) when each panel is 400 watts. However, the right number for you depends on how much power you use and how much suitable roof you have.

This guide shows you how to work it out in four steps. Because you will know the sums yourself, you can check your installer’s design with confidence. For the wider picture, start with our guide to how solar panels work.

Step 1: Find out how much power you use

Look at your last 12 months of electricity bills. Your supplier’s app or online account will show the yearly total in kilowatt hours (kWh). Although a smart meter makes this easier, a paper bill works too.

Ofgem gives a useful yardstick. From 1 July 2026, its price cap uses 2,500 kWh a year as the typical electricity use for a home. Your own figure may sit well above or below that. For example, a family at home all day will use more than a couple who work out.

Plan for change as well, because an electric car or a heat pump can add thousands of units a year. If you expect either soon, tell your installer now. Our later guide on solar panels and heat pumps covers that case.

Step 2: Turn kWh into kWp

Solar size is measured in kilowatts peak. This is the most a system makes in ideal light. However, what you really want to know is how many kWh it makes in a year.

The European Commission’s PVGIS tool gives a free estimate for any UK address. For a 4 kWp system facing south at 35 degrees near Birmingham, PVGIS estimates about 3,870 kWh a year. That is roughly 970 kWh for each kWp. The tool assumes 14% system losses, while its weather data runs from 2005 to 2023.

Where you live changes the answer. The same setup gives about 4,090 kWh near London. In Glasgow, it gives about 3,430 kWh. As a result, a Scottish home may need a few more panels than a southern one to match the same bills.

A quick sum

Divide your yearly use by the yield per kWp, then divide by the panel size. Here are two examples, using 970 kWh per kWp and 400 W panels.

  • 2,500 kWh a year: 2,500 divided by 970 is about 2.6 kWp, so you need 6 or 7 panels.
  • 4,000 kWh a year: 4,000 divided by 970 is about 4.1 kWp, therefore you need about 10 panels.

These sums match yearly totals. However, they do not show what you can use in the home. Most of the power arrives at midday in summer, so you will not use all of it as it comes.

Step 3: Check your roof

Your roof sets the upper limit. MCS says an unshaded roof facing east, south or west is a good start. A south roof makes the most power. East and west roofs still work well, while they also spread output across the day.

PVGIS shows the effect. At the same Birmingham address, a 4 kWp system on a 35 degree east roof makes about 3,100 kWh a year. A west roof makes about 3,030 kWh. That is around 20% less than south, so you may want one or two extra panels, although it varies. Our guide to east-west and flat roof solar explains when that pays off.

Shade and space

Shade cuts output fast, so look at trees, chimneys and nearby buildings. Check the roof space as well, since panel sizes vary between makers. Ask for the datasheet and a roof layout drawing. Our page on roof and property suitability lists what surveyors look for.

Step 4: Weigh up cost and benefit

More panels cost more. However, the price rises more slowly than the output, because fixed costs such as scaffolding and the inverter stay much the same. Home Energy Scotland gives a wide range of £1,500 to £10,000 for installation, and it puts the average Scottish array at around 4 kWp for about £6,500. Costs still depend on your roof, your region and your installer.

Tax matters too. For example, HMRC’s rules put a 0% VAT rate on installing solar panels in Great Britain and Northern Ireland until 31 March 2027. After that date, the rate is 5%. Check the current rule when you get your quote, since it may change.

Our solar panel costs and savings guide covers prices in more depth. For the bigger question of whether it pays back, read are solar panels worth it.

Will the panels cover my winter use?

No system will, because winter days are short and dim. PVGIS suggests the same Birmingham setup makes about 130 to 150 kWh in each of December and January. It makes about 470 kWh in June. Plan for your panels to cut bills over the year, since they cannot cover every month. Our guide to solar panels in winter has the monthly detail.

Panels, inverter and battery must match

The panels are only part of the system. For example, the inverter changes their direct current into the alternating current your home uses. It should suit your panel total, so read our guide to solar inverters explained.

A battery stores spare daytime power for the evening. Because it is a separate choice with its own cost, we cover it in our post on solar battery cost and sizing. Our hub on batteries and export gives the wider view.

Export limits and grid rules

Your network operator must know about your system. In Great Britain, for example, National Grid says a small system under 16 amps per phase can use the G98 route. You, or your installer, notify the operator within 28 days of commissioning. On a single-phase supply, that means an inverter of about 3.68 kW, since 16 amps at 230 volts gives that figure.

Larger systems need approval first, under a process called G99. Therefore, read DNO grid connection, G98 and G99 before you pick a size close to that line. Spare power you export can earn payments under the Smart Export Guarantee.

A short checklist

Take this list to your quotes.

  • Your yearly kWh figure, plus any planned electric car or heat pump.
  • Panel count, wattage and total kWp on each quote.
  • The expected yearly kWh, and the tool used to work it out.
  • Roof direction, pitch and any shade allowance.
  • The inverter size and the grid route, G98 or G99.

Sources

Common questions

How many solar panels does a 3-bedroom house need?

Many 3-bedroom homes suit around 8 to 10 panels of 400 watts each. That is a 3.2 to 4 kWp system. Your own bills and roof matter more than the number of bedrooms.

Can I fit more panels than I use?

Yes, if your roof has space. You can sell the extra power through a Smart Export Guarantee tariff. However, a unit you use yourself saves more than a unit you export.

Is there a limit on system size for a house?

Not on the panels themselves. The grid route depends on the total inverter output, including any battery. A single-phase home can use the simple G98 route if total generation is up to 16 amps per phase, about 3.68 kW.

Does my roof direction change the number of panels?

Yes. A south roof makes the most power per panel. East and west roofs make less, so you may want a few more panels to reach the same yearly total.

Should I buy fewer panels and add a battery?

Not necessarily. Panels and batteries solve different problems. Size the panels first, then check whether a battery suits how you use power.