Facts last checked 17 September 2026
The short answer
Solar PV (photovoltaic) panels turn daylight into electricity using layers of silicon, and an inverter converts that power into the kind your sockets use. On EU JRC PVGIS modelling, a 4 kWp south-facing system in London generates about 4,100 kWh a year, less on an east or west roof or further north. The Energy Saving Trust puts a typical 4.5 kWp home system at around £7,600 installed, paying for itself in roughly 9 to 12 years with export payments. A battery is optional, and on solar alone it rarely pays for itself.
How does a solar panel actually make electricity?
Each panel is a grid of solar cells, usually made from silicon. When light hits a cell it gives electrons enough energy to move, and that movement is an electric current. The stronger the light, the more current you get, but the cells do not need direct sun. They keep producing on cloudy days, just less.
The panels produce direct current (DC). Your home runs on alternating current (AC), so the system needs a few more parts:
- Inverter: converts DC from the panels into AC for your home. The Energy Saving Trust expects it to need replacing after around 12 years, well before the panels.
- Mounting rails, cabling and isolator switches: fix the panels to the roof and let the system be switched off safely.
- Export metering: a smart meter that records half-hourly exports, which you need to be paid for spare electricity.
- Battery (optional): stores surplus daytime power for the evening.
Solar PV is not the same as solar thermal, which heats water directly through roof collectors. PV makes electricity, which you can use for anything: lights, the fridge, an EV, or a heat pump.
What does kWp mean, and what size system suits a normal house?
kWp stands for kilowatt peak: the output a system is rated to produce under standard laboratory test conditions. It describes the size of the system, not what it will produce on your roof on a given day. A system of ten panels rated at 400 watts each is 4 kWp.
The Energy Saving Trust says most home systems are around 4.5 kWp. The right size for you depends on the roof area that gets good light, how much electricity you use, and whether a heat pump or EV is on the way. Bigger is not automatically better: electricity you cannot use or store is usually exported at a lower rate than you pay to import it.
How much electricity will it generate where you live?
We ran the European Commission's PVGIS model (SARAH3 satellite data, 2005 to 2023) for a 4 kWp system with a 35° roof pitch and the model's default 14% system losses. These are long-run averages. PVGIS puts the year-to-year standard deviation for the London system at about 160 kWh, so a dull year and a bright one can differ noticeably.
| Location and roof direction | Annual generation | Versus London south-facing |
|---|---|---|
| London, south-facing | 4,089 kWh | 100% |
| London, east-facing | 3,280 kWh | 80% |
| London, west-facing | 3,166 kWh | 77% |
| Manchester, south-facing | 3,544 kWh | 87% |
| Edinburgh, south-facing | 3,614 kWh | 88% |
Output is heavily seasonal. The same London system averages about 144 kWh in December and 493 kWh in June. Our guide to whether solar panels work in winter has the full month-by-month figures.
What does solar PV cost, and how long until it pays for itself?
The Energy Saving Trust puts a typical 4.5 kWp installation at around £7,600. Difficult roof access pushes the price up; fitting panels while scaffolding is already up for roof work brings it down.
| Location | Home all day | Home half the day | Out all day |
|---|---|---|---|
| London | 9 years | 9 years | 9 years |
| Manchester | 10 years | 10 years | 11 years |
| Aberystwyth | 9 years | 9 years | 10 years |
| Stirling | 11 years | 11 years | 12 years |
Installation of solar panels and batteries in homes is zero-rated for VAT until 31 March 2027, after which HMRC says it returns to the 5% reduced rate. There is no national grant for private solar on most homes. As a guide, Smart Energie's typical range for eight panels with a 5 kWh battery on a three-bedroom house is £8,500 to £13,000, confirmed at survey. How we price explains what moves that figure.
Where does the electricity go: your home, a battery or the grid?
Your home uses solar power first, whenever the panels are producing. The share of generation you use yourself is called self-consumption. Anything left over goes into a battery if you have one, then out to the grid.
Self-consumption is usually lower than people expect. Using the MCS self-consumption tables that certified installers must follow, a household using 3,500 to 4,000 kWh a year and out for half the day uses about 23% of a 4,100 kWh system's output directly. The rest is exported.
Exports are paid through the Smart Export Guarantee (SEG). Under Ofgem's rules, suppliers set their own rates and contract terms, but the rate must always be above zero, and you can choose any SEG supplier, not only the one you buy from. You need an MCS-certified installation (or an accredited equivalent) and a meter that records half-hourly exports. Whether adding a battery is worth it is covered in solar with or without a battery.
Is your roof suitable, and do you need planning permission?
- Direction: south is best. East or west still works, at roughly 20% to 23% less output in the PVGIS runs above. A mostly north-facing roof is rarely worth it.
- Shade: chimneys, trees and neighbouring buildings cost more output than people expect, especially in winter when the sun is low.
- Condition: if the roof covering needs replacing within a few years, do that first. Taking panels off and refitting them later adds cost.
- Space: dormers, rooflights, vents and roof edges all limit how many panels fit on a slope.
In England, rooftop panels on a house are usually permitted development, which means no planning application. The rules were updated from 27 August 2026. On a pitched roof, panels must not stick out more than 0.2 metres from the roof slope or rise above the highest part of the roof, excluding the chimney. Listed buildings are excluded. In a conservation area or World Heritage Site, panels are not permitted on a wall, balcony or roof enclosure that fronts a highway. If you are unsure, ask your council before anything is ordered.
What does a good installation look like?
Use an MCS-certified installer. The MCS solar standard (MIS 3002) requires a written performance estimate using its standard method, a self-consumption estimate, and a statement about any shading on your roof. If the quote has no shading assessment, ask why.
Maintenance is light. The Energy Saving Trust says UK rain keeps panels clean if they are tilted at 15° or more, and panels should last 25 years or more. Budget for one inverter replacement along the way. Our solar, battery and EV service page shows what a survey covers, and the retrofit planner shows how solar fits with the rest of your home.
Common questions
Do solar panels work on cloudy days?
Yes. The cells respond to daylight, not direct sunshine, so they keep producing under cloud, just at a lower rate. In the UK the bigger factor is season: a London 4 kWp system averages about 4.7 kWh a day in December against 16.4 kWh a day in June on PVGIS figures.
How many panels do I need?
Divide the system size by the panel rating. A 4 kWp system is ten 400 W panels, or fewer if the panels are more powerful. What matters more is how much of the roof faces south, east or west without shade, and how much electricity you use.
Will solar panels power my home in a power cut?
Not usually. A standard grid-connected system shuts down when the grid goes off, for the safety of people working on the network. Some battery systems can supply selected circuits in a power cut, but only if they are designed and wired to do that, so ask before you buy.
Do I need to tell my energy supplier?
To be paid for exports you apply to a Smart Export Guarantee supplier of your choice, with your MCS certificate and a smart meter set up to record exports. It does not have to be the supplier you buy electricity from.