I'm a regular listener of Dale Vince's "Zero Carbonista" podcast. I have a lot of time for Dale. He's done a huge amount to push the green agenda forward, and I was a customer of Ecotricity, his renewable energy supply company, for many years.
But he's wrong about heat pumps.
In a recent episode of Zero Carbonista (Season 5, Episode 2, "Last Fool Standing" released 15th September 2023), Dale says:
A typical house uses 3000 units of electricity every year and 12000 units of gas. And if you swap that gas out for heat pump produced heat, with an efficiency of 2-to-1 (that means you get twice as much out as you put back in) you’ve got to use 6000 units of electricity to make 12000 units equivalent of heat. And therefore, you’re using 9000 units of electricity in total and your electricity bill has trebled. In fact, your energy bill overall has gone up 50% because of the differential between the price of gas and electricity. That’s the net effect, 50% higher energy bill if you use a heat pump over a gas boiler.
Let's run the numbers.
I'm going to be using the Ofgem Energy Price Cap for a standard variable tariff, applicable October to December 2023. For electricity, this is £0.27 per kWh with a £0.53 daily standing charge, and for gas it's £0.07 per kWh with a £0.30 daily standing charge.
- 3000kWh of electricity * £0.27 = £861
- 365 * £0.53 standing charge = £193.45
- Total for electricity = £1054.45
- 12000kWh of gas * £0.07 = £840
- 365 * £0.30 standing charge = £109.50
- Total for gas = £949.50
- Total for electricity plus gas = £2003.95
Dale is using a heat pump efficiency figure of 200%.
A heat pump uses electricity to move heat from outside to inside (like a fridge in reverse) so can counter-intuitively reach efficiency figures of much higher than 100%.
An efficiency figure of 200% is in fact very low, which I'll go into below, but let's use this figure for now.
A gas boiler is at best around 90% efficient, so if we have used 12000kWh of gas we've only produced a maximum of 12000 * 0.9 = 10,800kWh of heat.
Also, once the gas supply and meter is removed from a property, the gas standing charge is no longer payable.
- 10800kWh of heat @ 200% efficiency = 5400kWh of electricity.
- Added to the 3000kWh we were using for other purposes, gives a total of 8400kWh.
- 8400kWh * £0.27 = £2268
- 365 * £0.53 standing charge = £193.45
- Total for electricity = £2461.45
- None
Once you take into account the boiler effiency and remove the gas standing charge, the total bill is in fact "only" £457.50 higher, which is (457.50 / 2003.95) = 23% higher, not the 50% that Dale claims.
As I mentioned earlier, an efficiency figure of 200% for a heat pump is considered absymal, and is a strong indicator of a poorly installed heating system.
A study published by Energy Systems Catapult in 2023 as part of the Electrification of Heat Demonstration Project brought together monitoring data from 742 heat pumps install into "a broad spectrum of housing types and ages". It found that the median efficiency across the course of a 12 month period was 280%. Let's rerun the numbers using this figure.
- 10800kWh of heat @ 280% efficiency = 3857kWh of electricity.
- Added to the 3000kWh we were using for other purposes, gives a total of 6857kWh.
- 6857kWh * £0.27 = £1851.39
- 365 * £0.53 standing charge = £193.45
- Total for electricity = £2044.84
- None
Using a heat pump efficiency of 280%, he bill is now fact only £40.89 higher, which is (40.89 / 2003.95) = 2% higher.
Heat Geek, a company providing heating theory training, collected data from 57 heat pumps installed by engineers who had been through their training programme, again in a wide variety of property types and ages. They found an average efficiency (including hot water) of 402%.
- 10800kWh of heat @ 402% efficiency = 2687kWh of electricity.
- Added to the 3000kWh we were using for other purposes, gives a total of 5687kWh.
- 5687kWh * £0.27 = £1535.49
- 365 * £0.53 standing charge = £193.45
- Total for electricity = £1728.94
- None
Using a heat pump efficiency of 402%, he bill is now £275.01 lower, which is (275.01 / 2003.95) = 14% lower!
The electrification of heat is not really about cost, it's about reducing CO₂ emissions to reduce global boiling.
If we use the UK grid emissions factors for 2023, we can calculate the following:
- 12000kWh of gas * 0.18293kg CO2e per kWh = 2195.16kg
- 3000kWh of electricity * 0.22499kg CO2e per kWh = 647.97kg
- Total 2870.13kg
- 8400kWh of electricity * 0.22499kg CO2e per kWh = 1889.92kg
- 6857kWh of electricity * 0.22499kg CO2e per kWh = 1542.76kg
- 5687kWh of electricity * 0.22499kg CO2e per kWh = 1279.52kg
Even a very poorly installed heat pump, at 200% efficient, reduces total carbon emissions from an average home's energy usage by 34%. A well installed heat pump, at 402% efficient, reduces carbon emissions by 55%.
And as the UK electricity grid gets greener over the coming years, this figure will continue to improve.
Given that the Boiler Upgrade Scheme grant in the UK has just been increased to £7500, and given that technological developments and economies of scale have reduced prices to the extent that heat pumps can now, in some circumstances, be completely free, I think the conclusion is quite clear.
Sorry Dale, heat pumps are the future.