How solar panels work

1. Light hits the panel. The panel is made of small cells, often silicon.
2. The cells make electricity. This is called DC.
3. A box called an inverter turns DC into AC. Your home uses AC.
4. Your home uses the power first. Spare power goes to the grid.

What is a kWh?

A kWh (kilowatt hour) is a unit of energy. It is what your bill counts. A 1,000 watt heater left on for one hour uses 1kWh.

kWp is different. It is the most power a system can make in perfect sun. A typical home system is about 4.5kWp. People often say "a 4kW system". That is close to this.

Is my roof right?

• South-facing is best.
• East or west works too. You get about 15–20% less.
• North-facing is not advised.
• Shade from trees or chimneys cuts output.
• A 4.5kWp system needs about 20–30 square metres of roof.

Do I need permission?

Most homes do not need planning permission. Check with your council if you live in a listed building, conservation area or national park. Your installer tells your local network company (DNO) about the system.

What is MCS?

MCS is a scheme that certifies installers and products. Use an MCS-certified installer. You usually need MCS to get paid for spare power under the Smart Export Guarantee.

Figures are typical and approximate. Last reviewed October 2026.