PRICE, CARBON AND SAFETY

Pick your
moment.

The best time to switch on depends on three things.

A plain white front-loading washing machine in a bright utility room, with a wicker laundry basket on the floor and daylight from a window — AI-generated image, not a photograph of a real person or place.

Know your tariff
Follow the wind
Never unattended
Three checks before you press start

What your tariff charges by the hour, how clean Britain's electricity is at that moment, and whether you will be at home and awake while the machine runs.

Updated 17 October 2026

THE SHORT ANSWER

It depends on
three clocks.

One for your bill, one for the grid,
and one for your own day.

PRICE

Only some tariffs vary

On a single-rate tariff a unit costs the same all day. Night-time is only cheaper on Economy 7 or a time of use tariff.

Check your tariff

CARBON

Cleanest when windy or sunny

Britain's electricity changes by the hour with demand, wind and sun. NESO's free carbon intensity forecast shows the greener times.

See the numbers

SAFETY

When you're home and awake

Fire services advise not running washing machines, dryers or dishwashers overnight or while you are out.

Plan a load

A QUICK TARIFF CHECK

Does the clock
change your bill?

Pick the kind of electricity tariff you are on. The bar shows how much the time of day can change what a load of washing costs you.

Based on Which?'s guide to time of use tariffs and NESO's carbon intensity guidance. Check your own supplier's hours and prices.

Tariff check

Choose your tariffSingle-rate tariffEconomy 7Smart time of useDynamic or agile

Single-rate tariffSame price all day

The charge is the same whatever the time, so running a machine at night saves nothing. Staffordshire Fire and Rescue says this is the case for most households.

Economy 7Seven cheaper night hours

Seven hours of cheaper electricity overnight, usually between midnight and 7am but it varies by supplier. Which? says you need to use at least 30% of your electricity at night for it to pay.

Smart time of useAvoid the peak

At least two rates: dearer at peak times when demand is highest, such as weekday evenings, and cheaper off peak, such as overnight. Peak rates can be higher than typical prices.

Dynamic or agileChanges through the day

Prices follow the market. NESO says that when there is too much renewable power and not enough demand, a provider may even pay you to use electricity.

Sources: Which?, Time of use tariffs explained (April 2026); NESO, What is carbon intensity?; Staffordshire Fire and Rescue Service (2022).

TWO NUMBERS WORTH KNOWING

Cleaner on average,
much cleaner at best.

How clean Britain's electricity was across 2024,
and how clean it got at its best half-hour.

125 g/kWh

Carbon intensity, grams of CO2 per kWh

NESO says 2024 was Britain's lowest carbon intensity year on record, averaging 125 g CO2/kWh, with zero carbon sources making 51% of electricity.

2024 AVERAGE · NESO

19 g/kWh

Lowest carbon intensity of 2024

The minimum carbon intensity record was 19 g CO2/kWh on 15 April 2024. Wind was the largest single source of electricity that year, at 30%.

RECORD LOW · NESO

Demand swings too: NESO recorded 2024's highest demand, 45,096 MW, at 5:30pm on 15 January, and the lowest, 15,074 MW, at 3:30am on 22 August.

Hands stacking plates into an open dishwasher in a warmly lit home kitchen in the evening — AI-generated image, not a photograph of a real person or place.

FOUR STEPS FOR A WELL-TIMED WASH

Cheaper, cleaner,
and safe.

None of this needs new kit. It is about knowing what your tariff charges, glancing at the grid, and staying with the machine while it runs.

Find out your tariff
Check your bill or supplier account. If you are on a single rate, the time of day does not change the price.
Look at the carbon forecast
NESO's Carbon Intensity app and website forecast how green the grid will be, region by region, more than 96 hours ahead.
Run it while you're home and awake
Fire services advise against running big appliances overnight or while you are out, so pick a greener or cheaper slot in your waking hours.
Keep the basics safe
Check appliances are not subject to a recall and cables are undamaged, and have a working smoke alarm on every floor.

WHY THE GRID CHANGES

Wind and sun
don't keep office hours.

NESO says carbon intensity varies by hour, day and season with demand and with how much low carbon power, such as wind, solar, hydro and nuclear, is running. Renewable electricity cannot yet be stored on a national scale, so it is best used when it is made.

The mix is cleaner than it was: coal came off Britain's system for the last time on 30 September 2024, after 142 years, and made up just 0.6% of generation that year.

Wind turbines turning on a green hillside under a bright, breezy sky with fast-moving clouds — AI-generated image, not a photograph of a real person or place.

Questions

Questions people ask

Is electricity cheaper at night?

Only on tariffs with different rates, such as Economy 7 or smart time of use tariffs. On a single-rate tariff the price per unit is the same all day, which Staffordshire Fire and Rescue says is the case for most households.

Is it safe to run the washing machine overnight?

Fire services advise against it. Staffordshire and Lancashire fire services say not to run washing machines, tumble dryers or dishwashers overnight or while you are out, because a fire at night gives sleeping people less time to escape.

When is Britain's electricity greenest?

It changes from hour to hour with demand and with how much wind, solar and other low carbon power is running. NESO's free Carbon Intensity app and website show forecasts for your region.

What is carbon intensity?

It is the grams of carbon dioxide produced to make one kilowatt hour of electricity. NESO says Britain averaged 125 g CO2/kWh in 2024, its lowest year on record, with a low of 19 g on 15 April.

Is Economy 7 worth it?

Which? says Economy 7 suits electrically heated homes, such as those with storage heaters, and that you need to use at least 30% of your electricity in the cheaper night hours for it to pay.

Pick your
moment.