Energy Cost
What does your kettle, fridge or gaming PC really cost per year? List your appliances with their power and how long they run, and see the energy, the cost and the CO₂ — and which one is the biggest energy hog.
Power vs. Energy
Power (watts) is how fast an appliance uses energy; energy (kilowatt-hours) is how much it uses in total. You pay for energy: a 2000 W kettle running for 3 minutes uses 0.1 kWh, the same as a 10 W router running for 10 hours.
That is why the surprises are usually small devices that are always on — routers, standby lights, an old fridge — and big devices that run for hours, like heaters and electric cars. Short bursts of high power, like a kettle or a hair dryer, often cost less than you’d think.
Cost per Year
by applianceTypical Power Use
| Appliance | Power | Typical use |
|---|
Worked Techniques
Divide the power by 1000 to get kilowatts, multiply by the hours of use, then by the price per kWh.
Every watt that is on all year costs about 2.60 at 0.30 per kWh. Ten devices on standby at 2 W each add up to 50 a year.
Add up the power of everything on one circuit and divide by the mains voltage. A kettle and a heater together on a 16 A circuit come close to the limit.
Sources & Verification
- A. R. Hambley, Electrical Engineering: Principles and Applications, 7th ed., Pearson, 2018 — Sec. 1.3 (Power and Energy).