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Electricity consumption is measured in kilowatt-hours (kWh). One kWh = using 1,000 watts for 1 hour, or 100 watts for 10 hours, or any combination equalling 1,000 watt-hours. Your electricity bill charges you per kWh consumed. A typical UK home uses about 3,500 kWh/year; a US home averages about 10,500 kWh/year.
Approximate hourly costs at £0.28/kWh (UK 2024 average): Electric shower (9kW): 2.5p/min. Kettle (3kW): 0.84p per boil. Washing machine (2kW): 56p per cycle. LED bulb (9W): 0.025p/hr. Laptop (65W): 1.8p/hr. TV 55" LED (80W): 2.2p/hr. Fridge-freezer (150W): 42p/day. Rates vary significantly by country.
Watts (W) measure power — the rate of energy use at any instant. Kilowatt-hours (kWh) measure energy — the total amount consumed over time. A 100W bulb uses 100 watts of power; running it for 10 hours consumes 1 kWh of energy. Watts × hours ÷ 1,000 = kWh. This distinction is essential for understanding electricity bills.
The highest-impact actions: switch to LED lighting (75% less energy than incandescent), improve insulation, use smart thermostats, run large appliances (dishwasher, washing machine) off-peak when possible, replace old appliances with A+++ rated ones, fix draughts, consider solar panels, and be mindful of standby power (the average UK home wastes £80/year on standby).
Smart meters automatically send accurate electricity readings to your supplier, eliminating estimated bills and enabling time-of-use tariffs. They provide a real-time in-home display showing current energy use in kWh and £/p, helping you identify expensive habits. Smart meters are being rolled out across the UK and EU as part of energy efficiency programs.
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA) in an AC circuit, ranging from 0 to 1. A PF of 1.0 means all electrical power is used productively. Motors, transformers and electronic power supplies have PFs less than 1. Industrial customers pay penalties for low PF; power factor correction capacitors can improve it.
Solar panels generate DC electricity from sunlight, converted to AC by an inverter. Generation typically reduces daytime grid consumption. In the UK, the Smart Export Guarantee pays for surplus exported to the grid. A typical 3.5 kWp system generates 3,000–4,000 kWh/year in the UK, potentially saving £400–600/year depending on self-consumption and export rates.
In most countries, billing electricity is done per unit, where 1 unit = 1 kilowatt-hour (kWh). UK electricity rates in 2024 average approximately 24–29p per unit. To find your cost: multiply daily kWh consumption by your unit rate. Your meter displays cumulative units used; the difference between two readings gives consumption for that period.
