How solar panels turn daylight into electricity

Solar photovoltaic (PV) panels are made from silicon cells that produce direct current (DC) electricity when daylight hits them. They do not need blazing sunshine; diffuse light on a cloudy day still generates power, just at a lower rate. An inverter, usually fitted in the loft or garage, converts that DC electricity into alternating current (AC) for your home. A generation meter records output, and your smart meter shows how much you use. There are no moving parts, so maintenance is minimal: rain usually keeps the glass clean, and most panels come with a 25- to 30-year performance warranty. Output varies through the day and year, but a well-sited system generates useful electricity in every month.

Is your roof suitable?

Most UK roofs can host solar panels, but a few practical checks matter. Orientation is the biggest factor. A south-facing roof gives the highest annual output; east- or west-facing roofs still work well, shifting generation to morning or afternoon. A north-facing roof is rarely worthwhile unless the pitch is shallow and the roof is unshaded. Pitch also matters: 30 to 50 degrees is ideal, and most UK pitched roofs fall neatly into that range. Flat roofs can work with tilted mounting frames, though you may need more space between rows to avoid shading.

• Shading: Chimneys, dormers, trees, and neighbouring buildings can cut output sharply. Even a small shadow across one panel can reduce the performance of a whole string, so note shading at different times of day and seasons.
• Roof condition: If your roof covering is old, cracked, or likely to need replacement within a few years, do that work first. Removing and refitting panels later adds cost and hassle.
• Structure and access: Panels and mounting add roughly 15–20 kg per square metre. Most roofs cope easily, but a surveyor should check the timbers if the roof is older or has been altered.
• Planning and permissions: Domestic solar is usually permitted development, but flats, listed buildings, and conservation areas may need consent. Check with your local planning authority before ordering.

Choosing the right system size

System size is measured in kilowatts-peak (kWp). A typical modern panel is around 400W, so ten panels make a 4 kWp system. Each panel needs roughly 1.7 metres by 1 metre, meaning a 4 kWp array takes about 17 square metres of roof space. Most UK homes install between 2 kWp and 4 kWp, depending on roof area and electricity use. A typical household uses around 2,700 kWh of electricity a year, though that varies widely with heating, hot water, and electric vehicle charging.

• Match supply to demand: A system that generates more than you can use will export the surplus. That is not a problem, but it is worth checking export payments and considering a battery or a solar diverter for hot water.
• Inverter choice: String inverters are simple and cost-effective. Hybrid inverters allow you to add a battery later. Micro-inverters or power optimisers can help on shaded or complex roofs.
• Future plans: If you expect to buy an electric car or a heat pump, a slightly larger array may make sense, provided your roof and budget allow it.
• Grid connection: Your installer will notify your distribution network operator. Smaller systems are usually straightforward; larger ones may need approval before connection.

What output can you expect in the UK?

In the UK, a well-sited solar PV system typically generates between 850 and 1,100 kWh per kWp per year. The higher end is more likely in southern England, on a south-facing roof with little shading; the lower end applies to northern Scotland, east/west orientations, or shadier sites. As a rough example, a 4 kWp south-facing system in the Midlands might produce around 3,600 kWh a year.

Seasonality is striking. A sunny June day can generate five or six times as much as a dull December day. In winter, you may only cover a small share of your usage; in summer, you may export most of what you generate while you are out at work. Without a battery, a typical household might use 30–50% of its solar electricity directly. With a battery, that can rise to 70–80%. Smart tariffs and timing heavy appliances for the middle of the day can improve self-consumption further.

Before you book an installation survey

A good survey is not just a quick look at the roof. It should include a shade analysis, a yield estimate, and a clear explanation of what will be fitted and where. Prepare by gathering a year of electricity bills or smart meter readings, noting any planned home improvements, and deciding whether you want a battery now or later.

• Get at least three quotes from certified installers. Certification means the work meets recognised standards and can make you eligible for export payments.
• Ask for a written yield estimate in kWh per year, not just a system size.
• Check warranties for panels, inverter, battery, and workmanship, and ask who handles claims.
• Discuss cable routes and inverter location so you know what disruption to expect.
• Confirm who manages grid notification and building regulations compliance.

Solar panels are a long-term investment, but they are also a straightforward one. With a suitable roof and a well-sized system, you can cut your bills, lower your carbon footprint, and enjoy decades of quiet generation. Take your time, ask plenty of questions, and let the survey give you the confidence to proceed.