How Do Solar Panels Work? Simple Explanation

You don't need to understand quantum physics to get how solar panels work. The short version: sunlight hits silicon, electrons move, your kettle boils. Everything else is detail.

But if you're spending £5,000 to £8,000 on a solar system, it's worth understanding what's actually happening on your roof. See our guide on how many solar panels to install for more detail. Not because you need to become an engineer, but because it helps you make better decisions about system size, panel placement, and whether the quotes you're getting make sense.

The 30-Second Version

Solar panels are made of photovoltaic (PV) cells. Each cell is a thin wafer of silicon, the same material in computer chips. When sunlight hits the cell, it knocks electrons loose from the silicon atoms. Those electrons flow through a circuit, creating direct current (DC) electricity. An inverter in your house converts that DC into alternating current (AC), which is what your sockets, lights and appliances run on.

That's it. No combustion, no steam, no turbines, no moving parts. Sunlight in, electricity out.

A typical residential panel contains 60 or 72 of these cells wired together. A 4 kW system on a UK roof uses 10 to 12 panels, depending on the wattage of each panel. Modern panels produce between 350 W and 450 W each, according to MCS product data.

PV Cells: How They Actually Generate Electricity

Each PV cell has two layers of silicon, treated differently. The top layer is "doped" with phosphorus, giving it extra electrons (negative charge). The bottom layer is doped with boron, creating gaps where electrons are missing (positive charge). Where these two layers meet, you get an electric field.

When a photon of light hits the cell with enough energy, it knocks an electron free from the silicon. The electric field at the junction pushes that electron towards the top layer, and it flows through an external circuit to get back to the bottom layer. That flow of electrons is electricity.

The whole process is called the photovoltaic effect, discovered in 1839 by French physicist Edmond Becquerel. It took another 115 years before Bell Labs built the first practical silicon solar cell in 1954. The cells on your roof work on exactly the same principle, just vastly more efficient.

Modern monocrystalline panels convert 20% to 22% of the sunlight hitting them into electricity, according to the Energy Saving Trust. That might sound low, but it's more than enough to power a home. The sun delivers roughly 1,000 watts per square metre to the UK on a clear day. Even at 20% efficiency, a few square metres of panels generate serious power.

What Happens on Cloudy Days

This is the question everyone asks, and the answer surprises most people.

Solar panels don't need direct sunlight. They need light. On a cloudy day in the UK, your panels still produce electricity, just less of it. A heavily overcast day might deliver 10% to 25% of the output you'd get on a clear sunny day. Light cloud cover? You might still get 50% to 70%.

The UK receives between 750 and 1,500 hours of sunshine per year depending on location, according to Met Office data. The south coast gets the most, Scotland and Northern Ireland the least. But even in Glasgow, a 4 kW system generates around 3,000 kWh per year. In Cornwall, the same system produces closer to 4,200 kWh.

Here's what matters more than cloud cover: temperature. Solar panels actually work slightly better in cooler conditions. A panel at 25°C produces its rated output. At 45°C (a hot summer roof), output drops by about 10%. British weather, with its mild temperatures and long summer days, is genuinely well-suited to solar. Germany, which gets less sunshine than most of the UK, is the largest solar market in Europe.

Inverters: Turning DC to AC

Your panels produce direct current (DC). Your home runs on alternating current (AC). The inverter bridges that gap, and it's arguably the most important component in your system after the panels themselves.

Three types are common in UK homes:

String inverter: all panels wire into a single box, usually mounted in your garage or loft. Cheapest option. Works well when all panels face the same direction and have similar shading. If one panel underperforms (shade, dirt, a pigeon sitting on it), it can drag down the whole string.

Microinverters: a small inverter attached to each individual panel. More expensive (add £500 to £1,000 to system cost) but each panel operates independently. Best for roofs with multiple orientations or partial shading. Enphase is the dominant brand in the UK market.

Hybrid inverter: a string inverter with a built-in battery connection. Costs £200 to £400 more than a standard string inverter. If you think you might add a solar battery in the future, this saves you replacing the inverter later.

Inverters typically last 10 to 15 years, shorter than the panels themselves. Budget £800 to £1,500 for a replacement during the system's lifetime. Some manufacturers now offer 25-year inverter warranties, which is worth asking about.

How Much Electricity Do Solar Panels Actually Produce?

Real numbers for UK homes, based on Energy Saving Trust data and MCS performance estimates.

The average UK household uses about 3,500 kWh of electricity per year, per Ofgem data. A 4 kW south-facing system generates roughly that amount. But you won't use all of it directly, because generation peaks during the day when you might be out. Without a battery, expect to self-consume 30% to 50% and export the rest under the Smart Export Guarantee.

Do Solar Panels Work in the UK?

We hear this one constantly. "But we don't get enough sun in Britain." It's the most common objection, and it's wrong.

The UK gets enough solar irradiance to make panels a solid investment across the entire country. Not just the south coast. Scotland, Wales, Northern Ireland, all of it.

Here's the data. The UK receives between 900 and 1,200 kWh of solar irradiance per square metre per year, according to the European Commission's PVGIS tool. Germany receives 950 to 1,150 kWh. Germany has over 80 GW of installed solar capacity and is the fourth-largest solar market in the world. If solar works in Berlin, it works in Birmingham.

The reason solar works in the UK isn't about blazing sunshine. It's about long summer days. In June, the UK gets 16 to 17 hours of daylight. Even with cloud cover, that's a lot of photons hitting your panels. The annual generation figures in the table above reflect real UK conditions, clouds and all.

What does affect performance is roof orientation and shading. South-facing is ideal, but east and west-facing roofs still produce 80% to 85% of the output. North-facing is the only orientation where the maths struggle. And shading from trees or neighbouring buildings matters more than cloud cover, because shade blocks light from specific panels rather than reducing it evenly.

For what a system costs in 2026, see our guide on solar panel costs. To check whether the investment makes sense for your specific home, read are solar panels worth it. And for available financial support, our solar grants guide covers every scheme currently running.

Want to check what your home qualifies for? Open the eligibility checker. Takes two minutes.