TL/DR The carbon emissions associated with electrical generation in the UK have fallen so much it is has become greener – but not necessarily cheaper – to cook and heat using electricity.
Electricity Generation
The carbon intensity of a source of electricity is a measure of how much carbon dioxide (measured in kg) was emitted to make one unit of electrical energy: an electrical kilowatt hour (kWe).
The chart below shows the carbon intensity of electricity generated by various techniques. The average carbon intensity depends on generating mix – and how that varies with time.
When I began talking about Climate Change back in 2004, Coal, Gas and Nuclear were the main generating sources for UK electricity. And the average carbon intensity – if I remember correctly – was around 0.50 kg CO2 per kWe.
The generating mix in 2019 is radically different. The carbon intensity varies daily and seasonally between about 0.1 kg CO2 per kWe (at times of low demand and high renewable generation) and 0.4 kg CO2 per kWe (at times of high demand and low renewable generation). The average value is less than 0.3 kg CO2 per kWe and falling.
Data from My Grid GB https://www.mygridgb.co.uk/historicaldata/
The chart below shows how the carbon intensity of electricity varied through the month of December 2018. The average value was 0.243 kg CO2 per kWe .and the maximum and minimum values were 0.390 kg CO2 per kWe and 0.094 kg CO2 per kWe respectively.
In my home
I can choose to heat by using electricity or gas.
- If I heat using electricity then I can convert electrical energy into heat with 100% efficiency, so for every kW of electrical power I use, I generate 1 kW of thermal power (kWth). And hence release roughly 0.3 kg of carbon dioxide.
- If I heat using gas then I can convert chemical energy in the gas into heat with high efficiency – but not generally 100%. So (looking at the chart at the start of the article) for every 1 kWth, I emit at least 0.47 kg of carbon dioxide.
Now the price per kWh (one kilowatt hour) that I am charged by EDF, the French government-backed company that supplies my electricity and gas is:
- 26.6 pence for 1 kWh of electrical/thermal energy during the day.
- Generally higher carbon intensity ~ 0.4 kg CO2 per kWe.
- 5.0 pence for 1 kWh of electrical/thermal energy during the night.
- Generally lower carbon intensity ~ 0.15 kg CO2 per kWe
- 4.2 pence for 1 kWh of thermal energy (via gas) at any time.
- Always at least ~ 0.46 kg CO2 per kW
So the reduction in the carbon intensity of the UK’s generating mix means that switching to electricity now makes ‘green sense’. i.e. If I generate 1 kW heat in my house using electricity then less carbon dioxide is emitted than if I just burned the gas directly
But in order to make financial sense I would need to make sure that I didn’t use any ‘daytime’ electricity.
Mmmm. Well at least I have a choice!
Resources
- https://carbonintensity.org.uk/ has all kinds of interesting analysis of carbon intensity by time and location within the UK.
- http://electricityinfo.org/fuel-mix-last-24-hours/ has all kinds of fascinating info and archived historical data.
- http://grid.iamkate.com/ for more live grid data
- https://www.mygridgb.co.uk/historicaldata/for lots of interesting analysis
Protons for Breakfast 
May 7, 2019 at 2:48 pm |
But how can your home be 100% efficient when you convert electrical energy to heat? Doesn’t the increase in usage in the home increase the energy lost in the grid transmission on its way to your house? You may convert 100% of what comes in to your home, but by using electricity and not gas you are using more electricity and therefore subjecting that increased use to the losses of the grid. Gas on the other hand, I presume, has very little loss in the grid.
Also, if you cook with electricity (I assume when you say heat my home you include cooking) there are inefficiencies in the way the hob is heated- the time it takes to warm up, the heat retained by induction pans, etc that may make gas better in the summer. In winter I assume any heat not used on the food is just welcome in your kitchen and house. But in the summer, if you have to open the window or use the extractor to eject waste heat, the speed and responsiveness of gas might make it competitive to electricity.
Also, have you ever found a way of stir frying using electric hobs? Or is chinese cooking going to have to be abandoned along with internal combustion engines and holiday air travel?
Like you, I’m preparing myself for a future of sacrifice, but I really want to know what I will have to lose…
May 9, 2019 at 1:21 am |
Even with 8% grid losses, using electricity to heat and cook causes the emission of less CO2 than using gas.
For cooking, induction hobs are almost 100% efficient in transferring energy to the cooking pot compared with less than 50% heat transfer when cooking with gas.
Gases also have transmission losses – the gas is pressurised by gigantic turbines similar to those on aeroplanes – but I would guess the loss would be closer to 1% of the delivered calorific value.
The point of the article is that with low – and reducing – carbon intensity, electricity is becoming the greener way to cook and heat.
May 9, 2019 at 7:10 am |
Thank you. I thought as much. You won’t be surprised that as usual, you’ve got me thinking. There is so much that we do that we are ‘carbon blind’ to. And indeed we are blind to how much each misuse of a thing contributes to global warming. This is so different to dieting when we (whatever the actual weirdness of the digestive process) we can find out pretty accurately how many calories we’re inputting, and therefore how much we are contributing to are girth with each meal. Is there a case for metrology here? Should we attempt to ascribe the effect to more of our actions in terms of the amount of global warming we are causing? After all, if we make CO2, we are contributing to warming. By how much? We should be able to work it out as fractions of a degree. How many femtodegrees have I warmed the globe by driving to work today? How many femtodegrees to I cause by cooking one meal on gas? Obviously the individual occurrence is pretty meaningless, but the difference between holidaying abroad by air travel or staying at home will be interesting in femtodegrees when compared to more mundane things that we do. How much carbon I produce is interesting, but how much I warm the earth by is more viscerally informative.
May 12, 2019 at 12:22 pm |
Hi Michael
I’ve been reading your most recent blog posting with great interest, as usual. In fact, with even more than usual, since Sue and I have embarked on our latest carbon reduction act of folly. We are negotiating to have our gas boiler replaced by an air source heat pump. We have been thinking about this for years but had decided that the relative carbon intensities of electricity and direct gas heating did not favour switching to electric heating, except via an ASHP. The argument went as follows:
1. The carbon intensity of natural gas used in a boiler is around 0.18 to 0.20 kg CO2/kWh
2. This is still a lot less than the UK average for electricity generation (~0.27 kgCO2/kWh), although this is falling.
3. But an ASHP with a coefficient of performance (even in winter) of greater than say 2 will now give a carbon saving over natural has heating.
4. So we have decided to switch.
I think your conclusion, that it is already better from a carbon point of view to use direct electric heating, is based on assuming a very high carbon intensity for gas used for direct heating. I think you may have used the figure for carbon intensity of gas used to generate electricity? If so that makes a difference to the conclusion? Or is my whole life based on a miscalculation (quite probably … ;-(
Thanks for all your great posts
John