Power and energy
Energy cost
- where
- energy cost (£)
- power (W)
- duration (h)
- tariff, unit price (£/kWh, excluding standing charge)
Explain this equation
Works out the running cost of a load from its power, how long it runs and the unit price. Useful for answering a customer’s “what will it cost to run?”.
P is the load’s real power, entered in watts and converted to kW. t(h) is the running time in hours. The tariff is the unit price in £ per kWh, excluding any standing charge.
Power times hours gives kWh used; each kWh costs the unit price. The 1000 in the working simply turns watts into kilowatts.
Sense check: 1 kW for 2 hours at £0.25/kWh costs £0.50. A 3 kW heater for 4 hours at 25p is about £3.
Watch out: enter the tariff in pounds, so 25p is 0.25. Standing charges, VAT changes and time-of-use rates are not included.
First find real energy consumption in kWh, then multiply by the supplied unit price. A tariff in pence must be divided by 100 for pounds.
Standing charges, taxes or time-varying rates must be added separately when applicable.
Enter your values to see the result.
Common mistake
Mixing pence and pounds.
Limits
Use the actual tariff and account separately for standing charges and other fees.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.