Do solar panels work on cloudy days?

Yes, though at reduced output — panels generate from daylight, not direct sunlight specifically. A heavily overcast day might produce 10–25% of a clear day's output, not zero.

How long do solar panels last?

Most manufacturers warranty performance for 25 years, typically guaranteeing output stays above roughly 80–87% of the original rating by year 25. Physical lifespan often exceeds this.

Do solar panels work at night?

No — without sunlight there's no photovoltaic effect. Nighttime electricity use is covered by the grid, or by a battery charged during the day.

What's the difference between a panel's rated wattage and actual output?

Rated wattage is measured under standardised lab conditions. Real-world output depends on your specific location, orientation, shading, and weather — measured properly as kWh/kWp/year, not the panel's peak rating alone.

How Do Solar Panels Actually Work? A UK Homeowner's Explainer

Last reviewed 24 September 2026. Figures and schemes change — verify with an MCS-certified installer before you commit.

Solar panels generate electricity through the photovoltaic effect: sunlight striking a semiconductor material (almost always silicon) knocks electrons loose, creating a flow of direct current (DC) electricity. No moving parts, no burning fuel — just light hitting the right material. That's the whole principle. Everything else is about capturing, converting, and using that electricity efficiently.

The components, in order

Solar cells: individual silicon wafers, each generating a small DC voltage. Most panels sold today use 108–144 half-cut cells wired together (older designs used 60–72 full-size cells).
The panel (module): cells assembled behind glass, in a weatherproof frame. Most UK residential panels are rated around 400–460W under standard test conditions.
The inverter: converts the panel's DC output into AC electricity — the form your home's wiring and the UK grid actually use. Many electronics convert power back to DC internally, but only after it has come through your AC wiring, so this step is essential, not optional.
The meter: tracks how much electricity you generate, use directly, and export to the grid — this is what your export payments are based on.

Why panels are rated in watts, but that's not what you actually get

A panel's wattage rating (e.g. 440W) describes its output under Standard Test Conditions — a specific lab irradiance and temperature. Real-world UK output is lower and varies constantly with weather, time of day, and season. This is why generation is measured in kWh per kWp per year (kilowatt-hours generated per kilowatt-peak of installed capacity) rather than the panel's rated wattage alone — a more honest measure of what you'll actually get over a year. For a south-facing roof, the 15 UK counties we've measured range from about 740 kWh/kWp (Highland, around Inverness) to about 1,180 kWh/kWp (Cornwall), and orientation and shading move a given roof up or down from there.

What actually affects real output

Orientation and tilt: south-facing at roughly 30–40° tilt is the UK benchmark; other orientations reduce output (see our guide to roof orientation for the figures).
Shading: even partial shading on one panel can disproportionately reduce a whole string's output, depending on the inverter setup — this is a bigger effect than most people expect.
Temperature: counterintuitively, panels lose some efficiency as they get hotter, not colder — a cold, bright day can outperform a hot, hazy one per unit of sunlight received.
Panel degradation: modern panels lose roughly 0.3–0.6% of their output capacity per year — a real, gradual decline, not a cliff, but worth factoring into any 20+ year payback calculation.

Where the electricity goes

Once converted to AC, generated electricity is used in this order by a typical grid-tied system:

Your home's live demand — whatever you're using right now gets first claim, since this avoids both export and import costs
A battery, if you have one — charges from surplus, for use later
Export to the grid — whatever's left over. In Great Britain, the Smart Export Guarantee means larger suppliers must offer a per-kWh payment for it; Northern Ireland has no equivalent scheme, so any payment there is at your supplier's discretion

Which of these is actually the best destination for your specific surplus isn't fixed — it depends on your tariff rates. See our full method for that decision.