Glossary
kWh
Kilowatt-hour: a unit of energy equal to using 1 kW for one hour. It's what your electricity bill charges for.
A kilowatt-hour (kWh) measures energy: how much electricity is produced or used over time. A 1 kW appliance running for an hour uses 1 kWh. An 800 W kit running flat out for an hour would produce 0.8 kWh, though real output varies all day with the sun.
Don’t confuse kWh with kW or W, which measure power at a single moment. A kit’s “800 W” is its maximum output rate; its kWh per year is what matters for your bill.
Every kWh your kit produces that you use in your home is a kWh you don’t buy. Under the Ofgem price cap for October to December 2026, the GB average unit rate for electricity paid by Direct Debit is 26.32p per kWh, including 0% VAT (Ofgem). Rates differ by region. Our calculator values the electricity you use from your kit at your region’s unit rate. Exported kWh are valued at zero unless you tell it you have an export tariff.