Enter the size of a solar PV system in kilowatts-peak (kWp) and the expected yearly yield per kWp, and this estimates how much electricity it generates and what that is worth. A typical south-facing UK roof yields around 900 to 1,000 kWh per kWp a year.
Kilowatts-peak (kWp) is the rated output of the panels in full sun; the yield is how many kWh each kWp actually produces over a year where you are, which depends on latitude, roof direction, pitch and shading. A south-facing roof in the south of England manages close to 1,000 kWh per kWp; east or west facing or further north is lower. To turn this generation into a payback period, use the solar panel payback calculator, and see is solar worth it for the wider picture.
Common questions
How much does a 4kW solar system generate?
A 4kWp system on a good UK roof generates roughly 3,600 to 4,000 kWh a year, enough to cover a large share of a typical home's electricity, though most of it lands in the summer months.
What is kWp?
Kilowatts-peak is the maximum output of a solar array under standard full-sun test conditions. Real output is usually lower, which is why the yearly yield per kWp matters more than the headline figure.