How do solar panels work?

You flick on a kettle at noon and, if the sun is out, the electricity heating it may have come straight off your roof seconds earlier. No fuel burned, no meter ticking up. Understanding the path that power takes (from a sheet of silicon to your sockets) tells you most of what you need to judge whether a system suits your home.

From sunlight to a flow of electrons

A solar panel is a sheet of silicon cells under glass. Silicon is the same material chip makers use, and it has a useful habit: when light hits it, the energy knocks electrons loose. Manufacturers treat two layers of the silicon so that one side pulls those loose electrons and the other pushes them. That imbalance gives the electrons somewhere to go, and a flow of electrons is an electric current.

The current that comes off a cell is direct current, or DC. It is the same steady, one-direction flow you get from a battery. A single cell produces a small voltage, so makers wire dozens of them together behind one pane of glass to build a panel, then wire panels together to build your array.

The light itself does the work, not the heat. A bright, cold winter day can suit a panel well, because silicon loses a little efficiency as it warms. Cloud cuts output but does not stop it; you still get diffuse light through cover, which is why a panel keeps trickling power on a grey afternoon. At night it makes nothing and sits idle.

How solar panels turn DC into power your house can use

Your home runs on alternating current, or AC, which switches direction many times a second. Every appliance you own expects it. So the DC from the roof has to be converted, and that is the job of the inverter.

The inverter is the brain of the system. It takes the variable DC coming down from the panels and shapes it into clean AC at the right voltage and frequency for your grid. It also tracks the panels moment to moment and nudges them to their most productive operating point as the light shifts.

Two common designs exist:

Inverter type	How it works	Best suited to
String inverter	One box near your meter handles the whole array	Simple, unshaded roofs
Microinverters	A small unit fixed under each panel	Roofs with shade or multiple orientations

Microinverters cost more and suit roofs where one shaded panel would otherwise drag the rest down. For a deeper look at the trade-offs, see solar inverters explained.

Your house first, the grid takes the rest

Once the power is AC, it joins your home's wiring and feeds whatever is running. The system serves your house first, because that is the cheapest electricity you will ever use: you skip the bill for those units.

When the panels make more than you are using, the surplus does not vanish. It flows back through your meter to the grid, and your supplier pays you for it under a scheme such as the Smart Export Guarantee in the UK or a feed-in arrangement elsewhere. The catch is that the export rate is usually far below the price you pay to import, so self-consumption beats export. That gap is the main reason people add a battery, which stores your midday surplus for the evening instead of selling it cheap and buying it back dear. We dig into that trade in solar batteries: when it pays.

When the panels make less than you need (at dusk or under heavy cloud) you pull the shortfall from the grid as you always have. The handover is seamless and you never notice it.

The four things that decide how much your solar panels produce

Two identical systems on two roofs can produce very different amounts each year. Four factors drive the gap.

Location sets the ceiling. According to the European Commission's PVGIS database, a panel in southern Spain typically generates around 1,400–1,700 kWh per kWp per year; the same panel in northern Germany produces roughly 850–1,000 kWh. That is a difference of 50–80%, and it is why a national average tells you little and why we run your numbers on local climate data rather than a single country figure.

Orientation and tilt decide how squarely you catch that sunlight. In the northern hemisphere a south-facing roof at a moderate tilt captures the most. East or west roofs still work and spread output across morning and evening, which can suit your usage better even if the annual total is lower.

Shade punishes a system out of proportion. A chimney, a tree, or a neighbour's extension shadowing part of the array at the wrong hour pulls down more than its share, especially on a single string inverter. A quick look at what casts a shadow across your roof through the day is worth doing before anything else.

Season stretches the supply across the year. You will harvest several times more in June than in December, both from longer days and a higher sun. A winter sun sitting low in the sky strikes the panels at a shallow angle and delivers less energy per hour.

These four factors are exactly what a proper estimate has to model. To see how many panels your roof would take, read how to size a solar system; to weigh the money, see is solar worth it in 2026.

How long do solar panels last?

Modern panels are warrantied for 25–30 years. Output declines slowly over that time. The National Renewable Energy Laboratory's analysis of more than 54,000 systems found a median degradation rate of around 0.5% per year (NREL PV Lifetime Project). At that rate, a panel at year 25 still produces around 87–88% of its rated output. Premium n-type panels (TOPCon and HJT) show rates closer to 0.3–0.4% per year.

Frequently asked questions

Do solar panels work on cloudy days?

Yes. Panels generate electricity from diffuse light as well as direct sunlight. Output falls (typically to 10–25% of rated power under heavy overcast) but does not reach zero. Northern European countries with frequent cloud cover still see strong solar adoption because even reduced generation cuts meaningful amounts off an electricity bill.

Do solar panels need direct sunlight to work?

No. They need light, not direct sun. Diffuse daylight on an overcast day still drives the photovoltaic effect. Output is lower than on a clear day, but generation continues. Temperature also plays a role: panels are slightly more efficient in cold, bright conditions than in hot summer sun.

What is the lifespan of a solar panel?

Most manufacturers warranty panels for 25–30 years, guaranteeing at least 80–87% of rated output at the end of that period. Real-world studies suggest many panels continue producing well beyond 30 years at reduced output. The inverter (warranted for 10–12 years) will usually need replacing once over the system's life.

How much of my electricity will solar panels cover?

It depends on your roof size, location, and how much power you use during daylight hours. A typical UK household with a 4 kWp system might generate 3,400–4,000 kWh per year and self-consume around 40–50% of that directly (McKenna, Pless and Darby, Energy Policy, 2018). A battery can raise self-consumption substantially, often into the 60–90% range depending on its size and your usage. Use our calculator below for a figure based on your actual roof and location.

Do solar panels increase home value?

Evidence suggests yes. A 2024 study by researchers at Swansea University and the University of Birmingham, analysing around five million UK property listings via Zoopla, found a selling-price premium of 6.1–7.1% for homes with solar panels (Asproudis et al., Energy Economics, 2024). US studies have found premiums of around 4% (Zillow, 2019). The effect varies by market and property type. For more detail, see do solar panels increase home value.

Estimate only, not a quote. Figures use local climate data and average tariffs; your installer's quote will be exact.