Glossary · Renewably

Power and energy

kW (kilowatt): How fast something uses or makes electricity at a given moment - its power. A kettle is about 3 kW, a fridge about 0.1 kW, a home car charger usually 7 kW.
kWh (kilowatt hour), or "unit": An amount of electricity: 1 kW for one hour. A 3 kW kettle running for 20 minutes uses 1 kWh. Bills and prices are per kWh, often called a unit.
Amps (A): The current a device draws. In UK homes power in kW is roughly amps × 230 ÷ 1000: a 13 A plug can supply about 3 kW, a car charger set to 32 A about 7.4 kW, and a "granny cable" at 10 A about 2.3 kW.
kWp (kilowatt peak): The size of a set of solar panels: what they'd make in full, strong sunshine. Over a year a south-facing 1 kWp makes roughly 1,000 kWh in southern England, less further north.

p/kWh: Pence per kWh - the price of each unit of electricity. Prices on this site include VAT.
Standing charge: A fixed daily amount on top of the unit price, paid however much or little you use.
Time-of-use tariff: A tariff whose price depends on when you use electricity. Some have fixed cheap and dear times each day; others, like Octopus Agile, set a new price for every half hour.
Half hour: Time-of-use prices change on the hour and half hour, so the charts and plans work in half hours.
Peak: The early evening, usually 4pm to 7pm, when demand and prices are highest.
Estimate: Suppliers publish the next day's prices in the afternoon. Before then, the site shows its own estimate, marked as such - a guide, not the price you'll pay.
Price cap: The most a standard variable tariff can charge per unit and per day, set by Ofgem every three months. The tariff comparison uses it as the baseline.
Export: Electricity your home sends to the grid - from solar panels, say - and the price a supplier pays you for it.
Region: Great Britain is split into 14 electricity regions, and prices differ between them, so the site asks for yours.

COP (coefficient of performance): How efficient a heat pump is: the heat it delivers for each unit of electricity it uses. A COP of 3 means 3 kWh of heat from 1 kWh of electricity. It's higher in mild weather and lower in cold.
p/kWh of heat: What each unit of heat from a heat pump costs: the electricity price divided by the COP. It's the fair way to compare times of day, because a heat pump is more efficient when it's milder.
Usable capacity: How much energy a car or home battery can actually store and give back, in kWh - usually a little less than its headline size.
Charging efficiency: The share of the electricity from the wall that ends up in the car's battery; some is lost as heat. 90% is typical.
Round-trip efficiency: The share of the electricity put into a home battery that you get back out of it - typically around 90%.
Miles per kWh: How far an electric car goes on one unit of electricity - typically 3 to 4 miles.

Carbon intensity: How much carbon dioxide is emitted to generate each unit of electricity from the grid, in grams per kWh (gCO₂/kWh). It's lowest when it's windy and sunny, and changes through the day and from region to region.