What is Kilowatt (kW)?
A unit of power equal to 1,000 watts, used to measure the instantaneous output of solar panels.
Quick Answer
UK electricity bills often confuse kW and kWh. Your solar system size is measured in kWp (kilowatt peak). Your electricity usage and generation are measured in kWh (kilowatt hours). A typical UK home has a peak demand of 3–7 kW and uses about 3,700 kWh per year.
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
Kilowatt (kW) Explained
A kilowatt (kW) is a unit of power equal to 1,000 watts. In solar energy, kW measures the rate at which electricity is being generated or consumed at any given moment. A solar panel rated at 400W produces 0.4 kW under optimal conditions. Power (kW) differs from energy (kWh), power is the instantaneous rate, while energy is power multiplied by time. A 4kW system running for 1 hour produces 4 kWh of energy.
How Does Kilowatt (kW) Work in the UK?
UK electricity bills often confuse kW and kWh. Your solar system size is measured in kWp (kilowatt peak). Your electricity usage and generation are measured in kWh (kilowatt hours). A typical UK home has a peak demand of 3–7 kW and uses about 3,700 kWh per year.
Frequently Asked Questions
What is the difference between kW and kWh?
kW is power (rate of energy flow at any moment). kWh is energy (total power used over time). Think of kW as speed and kWh as distance, a 4kW system running for 2 hours generates 8 kWh.
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John Rooney is the founder of Solar Info and has been covering the UK solar energy market since 2023. He researches every battery and inverter brand against manufacturer datasheets, MCS and Ofgem data, and feedback from the MCS-certified installers in our directory before publishing.