Power & Energy Calculator
Calculate how much energy an appliance uses, what it costs to run, and how much CO₂ it produces. Useful for comparing appliances and understanding your electricity bill.
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Electrical Energy Guide
What should I know about Understanding kWh?
A kilowatt-hour (kWh) is the standard unit of electrical energy on your bill. One kWh = 1,000 watts running for 1 hour (or 100 watts for 10 hours, etc.). Energy = Power (kW) × Time (hours). A 2kW kettle used for 5 minutes uses 0.17 kWh. At 24.5p/kWh, that is 4p per boil. UK electricity price as of October 2024 is approximately 24.5p/kWh (Ofgem price cap). Annual household electricity usage averages 2,700–4,100 kWh depending on household size.
What do I need to know about Most Expensive Appliances?
Annual running costs at 24.5p/kWh and typical usage: electric storage heater (1kW × 8h = £714/year), immersion heater (3kW × 2h/day = £536), tumble dryer (2.5kW × 2h × 3 days/week = £191), electric oven (2kW × 1h/day = £179), dishwasher (1.2kW × 1h/day = £107), washing machine (1kW × 1h/day = £89), fridge-freezer (300W constant = £64), TV (80W × 4h/day = £28), LED lights (10W × 5h/day per bulb = £4.50). Replacing a 3-hour-per-day incandescent bulb (60W) with LED (8W) saves approximately £12/year per bulb, which adds up meaningfully across a whole house of multiple light fittings.
What do I need to know about CO₂ and Carbon Intensity?
The UK electricity grid's carbon intensity averages approximately 225g CO₂/kWh (2024), down from over 500g in 2000 as coal is replaced by renewables. At 225g/kWh, a 2kW tumble dryer used for 2 hours emits approximately 900g CO₂ per use. Annual household electricity use of 3,500 kWh produces approximately 790kg CO₂. Carbon intensity varies significantly by time of day — typically lower when wind generation is high (often at night or in stormy weather). Apps like Electricity Maps or the National Grid's own carbon intensity tracker let you check the current grid mix in real time, so energy-hungry tasks can be timed for lower-carbon periods if it matters to you.
What's the key thing to understand about Energy Efficiency Ratings?
UK appliance energy labels use an A–G scale (A+++ to G for older products). An A-rated fridge uses approximately 30% less energy than a D-rated equivalent. The EU/UK energy label shows estimated annual kWh consumption — divide by 365 for daily consumption and multiply by your unit rate. Heat pump tumble dryers (A-rated) typically use 1.5–2kWh per cycle vs 5kWh for a vented dryer — a significant running cost difference for heavy users. Induction hobs are approximately 85% efficient at transferring energy into the pan, compared to around 70% for gas, since gas loses more heat to the surrounding air rather than the cookware itself.