Installation · Guide
How many solar panels do I need?
The Energy Saving Trust says the average home system is about 4.5 kWp, typically around 12 panels covering 20 to 30 square metres of roof. That’s a useful starting point, not an answer.
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Your usage
Start with how much electricity you use.
The right number for your home depends on how much electricity you use, how much roof you have and which way it faces, where you live, and whether you have (or plan) a battery or an electric car. Here’s how to work it out.
Your annual use is on your electricity bill, annual statement or supplier’s app, in kilowatt hours (kWh). If you can’t find it, Ofgem’s typical figures, used from 1 July 2026, give a guide for a home on a standard single-rate meter:
- low use: 1,600 kWh a year;
- medium use: 2,500 kWh a year;
- high use: 3,800 kWh a year.
Homes on multi-rate meters, such as Economy 7, typically use more: 1,900, 3,400 and 6,100 kWh for low, medium and high.
A heat pump, electric heating or an electric car can push use well above these. If you already have panels, see adding more solar panels.
Panel output
How big is a panel, and what does it produce?
Each panel is rated in watts (W), and a system’s total is given in kilowatts peak (kWp). The Energy Saving Trust’s average of 4.5 kWp from 12 panels works out at about 375 W a panel. Newer panels can be rated higher: one current 54-cell panel’s datasheet lists 450 to 485 W, a size of 1,757 by 1,134 mm (about 2 square metres) and a weight of 20.6 kg.
What each kWp produces in a year depends on where you live, the roof’s pitch and direction, and shading. MCS publishes the figures installers use. For a south-facing roof at 35 degrees, they give roughly:
- 833 kWh per kWp around Glasgow;
- 865 kWh around Manchester;
- 903 kWh around Newcastle;
- 984 kWh around London;
- 1,130 kWh near Brighton.
Real output varies from year to year. Government figures for feed-in tariff solar systems show a median load factor of 9.2% in 2024/25, a year with unusually few sun hours. That works out at about 800 kWh for each kW.
Roof space
Roof space, direction and shading.
- Direction. The Energy Saving Trust says an unshaded south-facing roof is ideal. East or west roofs still work but tend to get 15 to 20% less, and it doesn’t recommend north-facing roofs. See best direction and angle for solar panels for our figures.
- Shading. Nearby buildings, trees and chimneys can shade the roof and cut output.
- Usable space. Not all of a roof can be covered. The MCS installation standard says panels shouldn’t go within 400 mm of any edge of a home’s roof unless extra measures are taken, and vents, roof windows and chimneys take space too.
- Two roofs. East and west roofs together can work well, spreading generation through the day.
Got a flat roof? See solar panels on a flat roof.
Worked example
A worked example.
Take a household using 2,500 kWh a year (Ofgem’s medium figure), with a south-facing roof at 35 degrees near Manchester.
- MCS gives about 865 kWh a year for each kWp there.
- 2,500 divided by 865 is about 2.9 kWp.
- With 450 W panels, that’s seven panels (3.15 kWp), producing roughly 2,700 kWh in a typical year.
Producing as much as you use over a year isn’t the same as using it. Panels produce most in the middle of the day and in summer. In MCS’s own worked example, a household using 3,500 kWh a year with a 3 kWp system uses about 29% of the solar output at home without a battery, and about 82% with a 9 kWh battery.
So the simple sum is only a first step.
Grid connection
The 3.68 kW point: when your network operator needs to approve it first.
Every system connects to the grid under rules from the Energy Networks Association:
- Up to 16 amps per phase (about 3.68 kW on a normal single-phase home supply), Engineering Recommendation (EREC) G98 applies, and the installer notifies your network operator.
- Above that, EREC G99 applies, and an application goes to your network operator before connection. Even on the fast-track route for smaller systems, the planned connection date must be at least 10 working days after the application.
- Batteries count. The limit is the combined AC output of everything generating. MCS gives the example of 3 kW of solar and a 3 kW battery on the same single-phase supply: together they exceed 16 amps, so G99 applies.
- It’s the inverter output that counts, not the panels’ kWp rating, so your installer designs the system around the limit. Some systems use an export limitation scheme (EREC G100).
MCS requires the installer to deal with the network operator, so we handle this for you. We fit systems on both single-phase and three-phase supplies.
Batteries and EVs
Batteries, electric cars and heat pumps change the answer.
- A battery stores surplus daytime electricity for when the panels aren’t generating, so more of a larger array gets used at home. See solar battery storage and how long do solar batteries last?
- An electric car adds a lot of demand. The Energy Saving Trust points out you can charge it during the day while the panels are generating, but MCS notes the car often isn’t at home or plugged in then.
- A heat pump uses most in winter, when panels produce least. Government figures show solar output from October to December 2024 was about a third of the spring quarter’s.
If you’re planning any of these, size the system for the future, not just today’s bill. Adding panels later can mean scaffolding and design work all over again.
Survey
Why a survey gives the real number.
A desk calculation gets you into the right range. A survey pins it down:
- Shading. MCS says an accurate estimate of shading will typically need a site visit.
- Roof strength. The Planning Portal says the roof’s ability to carry the load has to be checked, and some roofs need strengthening.
- Layout. Exactly how many panels fit around edges, vents and roof windows.
- Your supply. Whether it’s single- or three-phase, and where the inverter and any battery can go.
Every MCS installer works out your performance estimate the same way: system size × the MCS figure for your postcode zone, pitch and direction × a shading factor. We survey, design the system and give you that estimate with a clear written quote, across England, Wales and southern Scotland. See solar panel installations.
Sources: Ofgem, typical domestic consumption values (2026); Energy Saving Trust; MCS 032:2025; Energy Networks Association.
Questions
The things people ask before they ring.
Not answered here? Call 0800 156 0191, Monday to Friday, 9:00am–5:00pm.
How many solar panels do I need to power a house?
There’s no fixed number. As a guide, a medium-use home (2,500 kWh a year, Ofgem’s typical figure) needs about 6 or 7 panels of 450 W on a south-facing roof to generate that much over a year, depending on where you live, and more on an east- or west-facing roof. You’ll want more again if you add a battery or an electric car.
How much roof space do I need for solar panels?
A modern panel is about 2 square metres. The Energy Saving Trust says a 4.5 kWp system typically covers 20 to 30 square metres. Allow extra for the gap at the roof edges and around vents and roof windows.
How much electricity does a 4 kW solar system produce a year?
Using MCS figures for a south-facing roof at 35 degrees, about 3,300 kWh around Glasgow, 3,500 kWh around Manchester and 4,500 kWh near Brighton. East or west roofs produce less, and shading reduces it further.
Can I have more than 3.68 kW of solar panels?
Yes. If the combined AC output is more than 16 amps per phase (about 3.68 kW on a single-phase supply), EREC G99 applies and your installer applies to the network operator before the system is connected. Batteries count towards the total.
Ready when you are
Want the real number for your roof?
We’ll call you back to talk it through, and you get a clear written quote before any work starts. Mon–Fri 9:00am–5:00pm.