There are two different types of appliance when it comes to working out energy use – the appliances that use a fixed amount, and the appliances that vary their consumption. The first type is simple and the necessary info is the item’s declared power in Watts or Kilowatts, such as these typical items:
- iron (1.5kW)
- toaster (1.4kW)
- kettle (3kW)
- electric blanket (50W on medium setting)
The next number required is the cost per kWh (kilowatt hour) for electricity charged by your electricity provider, normally given on your electricity bill in pence per kWh. At the time of writing in Sept 2020 the UK government price cap has been set to come into force in October at the level of 34p/kWh (or £0.34), so let’s use that.
Cost in £ = item’s power in Kilowatts x hours in use x £0.34
So for your kettle which takes 4 mins to boil or 4/60 of an hour, the sum is:
3.0kW x 4/60 hours x £0.34 = £0.068 or 7p if you round it up
So if you want a hot water bottle to take to bed in winter, that’s what it costs, depending on how full the kettle was.
Then there is an electric blanket, which runs for 2 hours if it has a timer, assuming you are just using it to warm the bed until you fall asleep, after which your duvet or blankets insulate you enough that you don’t need it:
0.050kW x 2 hours x £0.34 = £0.034 or 3p approximately
Measuring big appliances
With big appliances, it’s more tricky to work out how much they will cost to run as they are generally built and programmed to run as efficiently as possible, using thermostats, humidistats or program cycles which make the power consumption vary. The figures here are based on data from the Which? magazine’s latest article, for the average UK appliance on electricity at the October price cap (34p/kWh):
- Washing machine – 38p per load
- Tumble dryer – 44p per load
- Dishwasher – 38p per load
- Fridge-freezer – 28p per day
If you have an energy monitor plug you can input your electricity price, plug the appliance into the monitor plug and then into the wall, and it will display how much electricity it using and what it is costing.
Alternatively, your energy supplier may have installed a smart meter, or you may have your own home energy monitor, which will give you energy usage and costs.
If you can run your appliances at night between midnight and 6AM, then sign up for an Economy 7 tariff, where the overnight electricity price is generally half of the daytime rate.
The Carbon Cost
The electricity we use at home produces small amounts of CO2 when it is generated for the national grid.
It will be less at night because the UK national grid is served most nights entirely by its wind and nuclear capacity, with no fossil fuels being burnt. See this real-time “energy mix” display if you are up late one night: https://grid.iamkate.com/
The average rate across the whole year is 0.23 kg of CO2 per kWh of electricity. So if your annual electricity bill is for 5,000 kWh, then you’ve emitted 1.10 tonnes of CO2. If you use gas for central heating, then you will emit much more than this. All together, it generally makes up about 5 to 10% of our personal carbon footprint of about 15 tonnes per year.
1 or 2 tonnes of CO2 is roughly the “sustainable” amount that everyone in the world should restrict themselves to if we want to keep our planet’s climate just how it is. Even better, we would do this and also support massive CO2 drawdown operations to get the climate back to how it was before the extreme weather started.