How many solar panels do I need? A simple guide for UK homes

The short answer

The Energy Saving Trust says the average home solar system is 4.5kWp, which is roughly 12 panels covering 20 to 30 square metres of roof. The right number for you depends on three things: how much roof you have, how much electricity you use, and your budget.

“kWp” means kilowatt peak. It is the most power the panels can make in perfect conditions, and it is how installers describe the size of a system.

How big is one panel?

Home solar panels today are usually rated between about 350W and 450W each. A typical panel measures around 1.7 metres by 1 metre and weighs 18 to 25kg. Newer panels are more powerful than older ones, so you need fewer of them for the same size of system.

Here is roughly how many 400W panels make up common system sizes:

• 3kWp: about 8 panels, around 14 square metres of panel
• 4kWp: about 10 panels, around 17 square metres
• 5kWp: about 13 panels, around 22 square metres
• 6kWp: about 15 panels, around 26 square metres

Your roof needs a little more space than this, because installers leave gaps at the edges and around chimneys, vents and roof windows.

How much electricity will they make?

Government figures put typical output at about 840kWh a year for each kWp of panels in 2023/24, and about 806kWh in 2024/25, the least sunny year since 2012/13. So a 4.5kWp system makes roughly 3,600 to 3,800kWh a year. Homes in the south of England tend to do better, and homes in the north and Scotland a little worse. A roof facing east or west makes around 15 to 20% less than one facing south.

How much electricity do you use?

Ofgem’s figure for a typical home is 2,500kWh of electricity a year (from July 2026, down from 2,700kWh). Homes on Economy 7 typically use more, about 3,400kWh. Your own figure is on your annual energy statement, or you can add up the last 12 months of bills.

If you plan to get an electric car or a heat pump, your use will go up a lot, so it is worth sizing for that now rather than adding panels later.

A simple way to size your system

Divide your yearly electricity use by about 840. That gives a rough system size in kWp that would make about as much electricity in a year as you use:

• 2,500kWh a year: about 3kWp (8 panels)
• 3,500kWh a year: about 4.2kWp (11 panels)
• 5,000kWh a year: about 6kWp (15 panels)

This is a starting point, not a rule. Many people fit a bit more than this if their roof allows, and any spare electricity can be sold through the Smart Export Guarantee. Without a battery, though, most homes only use about a quarter to a third of their solar electricity themselves, so a battery often makes more difference to your savings than more panels.

The 3.68kW connection rule

Every solar system has to be registered with your local electricity network operator (the DNO). For a typical home on a single-phase supply, systems with an inverter output of up to 3.68kW are covered by a simple process called G98: your installer tells the network within 28 days of switching the system on.

Bigger systems need permission from the network before they are installed, under a process called G99. Your installer must apply and get approval before the system is connected, which can add time. Your installer handles the paperwork either way. Ask them which route your system needs and how long it will take.

Note that the 3.68kW limit is about the inverter, not the panels. Many 4kWp to 5kWp systems use an inverter that stays within the limit, because panels rarely run at full power.

What an installer will check

• The size, shape and direction of each part of your roof
• Shade from trees, chimneys and nearby buildings
• Your electricity use, and any plans for an electric car or heat pump
• Whether a battery makes sense for you
• Your electricity supply and fuse board

An MCS-certified installer must give you a realistic estimate of how your system is likely to perform before you sign a contract. If a quote doesn’t include one, ask for it. Our checklist for comparing solar quotes covers what else to look for.

What to do next

Want a number for your own home? Try our solar savings calculator, or answer a few quick questions below and we’ll match you with an installer who covers your area. It’s free and there’s no obligation.