How do solar panels work?
From daylight on the roof to the sockets in your home: what each part of a solar PV system does, how much a UK roof produces and what happens to the electricity you don't use.
Solar panels turn daylight into electricity. The cells in each panel produce direct current (DC) when light hits them; an inverter converts that into the alternating current (AC) your home uses at 230 V; and the power flows through your consumer unit to whatever is switched on. Anything your home isn't using at that moment is exported to the grid, and your smart meter records it separately, so you can be paid for it if you're on an export tariff. There are no moving parts and nothing burns.
The rest of this guide explains each step, what the items on a UK quote actually do, how much electricity a panel makes here, and what happens to the power you don't use, which is where most explanations go wrong.
From daylight to your sockets in four steps
- The cell absorbs light and produces DC electricity. It needs light, not heat, which is why panels still work on a cold, bright winter day.
- The panel (or module) connects many cells behind toughened glass, with a frame and a junction box. It's the part you see on the roof.
- The inverter converts DC into AC, constantly adjusts to get the most power out of the panels, and runs the safety protection that UK grid rules require.
- Your consumer unit (fuse board) sends the electricity to your circuits. Whatever isn't used goes out to the grid through your meter.
The order matters: your home always uses solar power first, and only the surplus is exported. There's no switch deciding this; your appliances' demand does it automatically, second by second.
What each item on a UK quote does
A UK solar quote usually lists more than panels and an inverter. Here's what the common items are for:
| Item on the quote | What it does |
|---|---|
| Panels (modules) | Convert light into DC electricity. The quote should give the exact model and its rated power in watts |
| Inverter | Converts DC to AC. A string inverter serves groups of panels; a hybrid inverter also manages a battery; microinverters sit behind each panel |
| Optimisers | Small units behind individual panels that reduce the impact of shade on the rest of a string |
| Mounting kit | Rails, hooks or in-roof trays that fix the panels to the roof |
| DC and AC isolators | Switches that let an electrician safely disconnect parts of the system |
| Generation meter or monitoring | Records how much the panels produce, separately from what you import or export |
| Battery (optional) | Stores surplus for later instead of exporting it |
| Scaffolding and bird mesh | Access for the installers, and mesh to stop pigeons nesting under the panels |
String inverters, microinverters and optimisers each suit different roofs. Our guide to microinverters vs string inverters explains when each one makes sense.
How much light becomes electricity
A panel's efficiency tells you how much of the light hitting it becomes electricity. On four current datasheets we checked (JinkoSolar Tiger Neo 54HL4R-B, Trina Solar Vertex S+ NEG9R.28, LONGi Hi-MO X6 Scientist and AIKO Neostar 2P), the highest-rated version of each ranges from 22.02% to 24.3%.
Most of the rest becomes heat. That's physics, not a defect, and it has a practical consequence: a hot cell produces less. Each datasheet states how much less with the temperature coefficient of power, which is between −0.26% and −0.29% per °C on those four models. In the UK this matters less than in southern Europe, but it's still one of the fair ways to compare two panels. Higher efficiency is most useful when roof space is tight; it doesn't automatically give the best return.
How much a panel produces in the UK
Efficiency helps you compare panels. What matters for your bills is how many kilowatt-hours (kWh) the system produces in a year. A system's size is given in kilowatts peak (kWp), its rated power under standard test conditions; a 4 kWp system does not produce 4 kWh every hour.
Using PVGIS, the European Commission's free solar estimator (version 5.3, SARAH3 data, panels facing south at 35°, 14% system losses), 1 kWp produces about 1,019 kWh a year in London, 886 kWh in Manchester, 903 kWh in Edinburgh and 1,121 kWh in Plymouth in an average year; actual output varies from year to year.
The difference between the sunniest and cloudiest of those cities is real: about a fifth. An east- or west-facing roof loses about as much (PVGIS: roughly 20–23% less than south in London), heavy shade can lose more, and how much of the output you use at home matters more still for what it's worth. Your installer should give you an MCS performance estimate for your own roof, which is the figure to compare quotes on.
What happens to the electricity you don't use
Electricity you don't use at the moment it's generated is exported to the grid. What you get for it depends on where you live and which tariff you choose:
- In Great Britain, the Smart Export Guarantee (SEG) requires larger electricity suppliers (those with at least 150,000 domestic customers) to offer you an export tariff. Each supplier sets its own rate; the only rule is that it must be above zero. You need a smart meter that records export, and an MCS-certified installation (or equivalent) for systems up to 50 kW.
- In Northern Ireland, the SEG doesn't apply. Export payments come from individual suppliers' own microgeneration tariffs.
- The Feed-in Tariff closed to new applicants on 1 April 2019. Homes already on it keep their payments.
Export usually pays less than you pay for import. For example, the Ofgem price cap unit rate for October to December 2026 is 26.32p/kWh (direct debit, GB average, no VAT), while E.ON Next's Flex Export tariff, which is open to customers of any supplier, pays 6p/kWh (variable, as of 23 September 2026). Some suppliers pay more, but usually only if you also buy your electricity from them. That gap is why using your solar power at home, or storing it in a solar battery, is worth more per kWh than exporting it, though a battery has its own cost to weigh up. Our SEG guide compares the tariffs and their conditions.
What a solar system doesn't need
- It doesn't need a battery. The system works without one. A battery lets you use more of your own electricity later instead of exporting it.
- It doesn't need heat. It needs light; heat slightly reduces output.
- It doesn't need direct sun all day. Output drops a lot under heavy cloud, but it doesn't stop.
- It doesn't need a perfectly south-facing roof. East- and west-facing roofs produce less, but by a predictable amount that your installer should calculate before you buy.
UK grid rules require every grid-connected inverter to have loss-of-mains protection: when the grid goes down, the inverter stops exporting so it can't feed power into lines that engineers may be working on. An ordinary system therefore produces nothing in a power cut, even in full sun. Backup needs a battery system and inverter designed and installed to supply your home when it's cut off from the grid; a battery alone doesn't guarantee it.
Connecting to the grid
Your installer, not you, deals with your local distribution network operator (DNO). If the combined output of all your inverters is no more than 16 A per phase, which is 3.68 kW on a single-phase supply, the system falls under the standard called G98: the installer fits it and then notifies the DNO within 28 days. Above that, including when a battery's own inverter takes the total over the limit, the installer has to apply under G99 and get approval before connecting. That's why you may see a 3.68 kW inverter on a quote for a larger set of panels.
To see what a system would produce on your roof and what it could be worth, try our calculator. For the full picture of costs and savings, read are solar panels worth it?
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Frequently asked questions
How do solar panels work, in one sentence?
The cells turn daylight into DC electricity, the inverter converts it to 230 V AC, your home uses it first and any surplus is exported to the grid, where your smart meter records it.
Do solar panels work in winter and on cloudy days?
Yes. Panels work on light, not heat. In winter they produce less because days are shorter and the sun is lower: in London, PVGIS estimates about 123 kWh per kWp in June but about 36 kWh per kWp in December. Under heavy cloud, output drops sharply but doesn't stop.
Do solar panels work at night?
No. Without light the cells produce nothing. At night your home runs on grid electricity, or on a battery if you have one.
Do I need a battery for solar panels to work?
No. A system works normally without one. A battery lets you use more of your own solar power in the evening instead of exporting it for a lower rate.
Will I be paid for the electricity I export?
In Great Britain, yes, if the system is MCS-certified (or has an equivalent certificate), you have a meter that records export (usually a smart meter) and you sign up to a Smart Export Guarantee tariff. Rates are set by each supplier and change, so compare them before choosing. In Northern Ireland, export payments come from suppliers' own tariffs instead.
How long do solar panels keep working?
They don't stop on a set date. Panels slowly lose output over time, and manufacturers guarantee a minimum output, often for 25 or 30 years. Our guide on how long solar panels last explains the warranties.