How domestic solar panels work

The short version

A home solar system is a chain of simple steps. Sunlight lands on the panels on your roof. The panels make direct current (DC) electricity. An inverter changes that into the alternating current (AC) that your sockets and appliances use.

Your home uses what it can, as it is made. If the panels make more than you need, the extra can go to the grid. If they make less, the grid still tops you up as normal.

This page walks through each part of that chain. It also explains why two similar systems can give very different results, for example because of shade. For the money side, see our guide to solar panel costs and savings.

What happens inside a solar panel

A panel is a set of solar cells. Most are made from layers of silicon, which is a semiconductor. When light hits a cell, the cell builds up an electrical charge. That charge flows as direct current.

The cells do not need direct sunshine. They still work on a cloudy day, although the stronger the light, the more power they make.

This is why output changes through the day and the year. A bright June noon gives the most. A dull December afternoon gives very little. Our post on solar panels in winter shows what to expect through the seasons.

The inverter and the rest of the system

The inverter is the part that makes the power usable. Panels produce DC, yet your home needs AC. The inverter does that job, and it also watches the system for faults. Some models can report faults online.

Energy Saving Trust says panels should last 25 years or more. The inverter is different, because it often needs replacing after about 12 years. Read solar inverters explained to compare the main types.

A full home system has five parts. These are the panels, the mounting frame, the inverter, the wiring to your consumer unit, and the meters. A battery is an optional sixth part. It stores energy but does not create any. Our guide to solar batteries and export covers when one makes sense.

What decides how much power you get

Four things matter most. These are the size of the array, the direction the panels face, the tilt, and any shade.

Size is measured in kilowatts peak (kWp). That is the most the system can make in ideal conditions. Energy Saving Trust says the average home system is around 4.5 kWp. That size covers about 20 to 30 square metres of roof and uses around 12 panels.

Direction comes next. A south-facing roof is best for total output. East or west panels tend to make around 15 to 20 per cent less than south, according to Energy Saving Trust. They can still work well, because they make more power in the morning or the evening.

Shade is the factor people forget. Energy Saving Trust notes that shade can matter more than direction. A shaded south roof can make less than a sunny east roof. Trees, chimneys and nearby buildings are the usual causes. However, some systems use optimisers or microinverters so one shaded panel does not drag down the rest.

Our guide to roof and property suitability goes through these checks in more detail. The post on how many solar panels you need shows how to size a system.

How installers estimate your yearly output

Installers do not guess. MCS, the UK quality scheme for small renewables, sets out a standard method in its MIS 3002 installation standard. The result is a yearly estimate in kilowatt hours (kWh), which you should receive before you sign.

The method is simple. The installer multiplies your system size in kWp by a regional figure that fits your postcode, roof tilt and direction. Then they multiply by a shade factor. MCS builds the regional figures from European Commission solar data, then reduces them by 20 per cent.

MCS also requires a warning with the estimate. The estimate is guidance for the first year only, so it is not a guarantee. Real output changes with the weather from year to year.

If an installer quotes a number far above their MCS estimate, ask why, because extra estimates must not be given more prominence. The standard figure should come first.

Using your power, selling the rest

Generation is not the same as savings. The value depends on when you use the electricity, and what you would have paid for it. It also depends on what you get for any export.

Power you use as it is made is called self-consumption. It is the most valuable part, because it replaces electricity you would buy. A home that is empty all day uses less, while a home with people in uses more.

Power you do not use goes to the grid. In Great Britain, the Smart Export Guarantee (SEG) lets you be paid for it. Suppliers must offer a tariff to eligible generators, set their own rates, and keep them above zero. Payment is based on your export meter readings. You can pick any SEG supplier, not just your current one. Energy Saving Trust says a typical rate is around 12p per unit, as of its 1 October 2026 update, and that you would normally pay more than twice that to buy a unit. Rates vary, so check each supplier.

The Smart Export Guarantee explained post covers how to compare offers. For the full picture of value, read are solar panels worth it.

Adding a battery

A battery stores spare solar power so you can use it later, often in the evening. That raises your self-consumption. It can also, in some cases, let you charge from the grid on a cheap overnight rate.

A battery does not make power. It also has its own costs, losses and warranty terms, so it will not suit every home. Our post on solar battery cost and sizing explains how to judge usable capacity and what size suits a home.

Connecting safely to the grid

Every system must be connected to the local network in a safe way. Your installer handles this, since they hold the right forms. For small home systems, the route is usually called G98. It is a fit-and-notify process. The installer tells your network operator within 28 days of commissioning.

To meet G98, the equipment must shut down in a power cut. It also needs a lockable isolation switch. Larger systems use a different route, called G99. That one needs approval before the work starts, while G98 needs only a notice afterwards. GOV.UK says solar and battery installations must also be notified to the network operator.

Solar panels on houses are usually permitted development in England. That means you often do not need planning permission, although exceptions exist. See our guide to planning your installation for the details.

What a good survey confirms

An online tool can give a rough idea, but only a survey can confirm the design. A good survey checks the usable roof area, the roof structure and covering, shade at different times of year, the safe spot for the inverter, cable routes and access.

MCS requires installers to check that the roof can carry the load. For unusual roofs, a structural engineer must be consulted. You should also get a written output estimate before you sign, because it is your main way to judge the quote.

If you want to compare installers, our guide to choosing a solar installer lists what to ask for. After installation, keep an eye on the system, since faults are easy to miss. The maintenance and lifespan guide explains what to check and how often.