By Paul Homewood

We have been looking at the potential impact of electric cars on grid capacity, but this is likely to be swamped pretty quickly if the roll out of air heat pumps is carried out as planned,

The government’s plan is to be installing 600,000 a year by 2028, some of which will be in new build homes.

According to the Tradesmen Costs website, heat pumps would range from 6 KW for a terraced house to 9 KW for a typical detached.  If we take 8 KW as the norm, 25 million homes would potentially need 200 GW of grid capacity, purely for heating alone.

This assumes that they will all be working simultaneously, a not unreasonable assumption, given the need to heat houses in the early morning.

This quite clearly is a non runner, which is why the Committee on Climate Change has been pressing for hydrogen hybrid boilers, which can provide most of the heat on cold winter mornings.

However, we don’t have a hydrogen network, and are unlikely to for many years to come. The official plan is to set up a pilot scheme by 2030, but it will take many more years to extend it nationwide.

600,000 heat pump installations a year would mean an extra 5 GW of capacity would need to be added each year, so even by the mid 2030s, we would need an extra 35 GW.

I can honestly see a scenario where we are still allowed to use our gas boilers until hydrogen is rolled out, despite having a heat pump installed. (While at the same time being implored by National Grid to turn our heat pumps off!)


I have also been taking a fresh look at costings. When extra insulation is added, average costs are likely to be well in excess of £10,000:

And despite the misleading advertising often put out, running costs for an ASHP are much higher than a gas boiler.

A typical house uses about 11,000 KWh for heating and 4,000 KWh for hot water. Current gas prices are 2.5p/KWh, so the annual bill would be £375.

A heat pump working at COP 3.0 (ie efficiency of 300%) would consume 3666 KWh of electricity for heating alone. But heat pumps are inefficient when it comes to hot water. There is a particular issue with legionella, which thrives at water temperatures below 60C – a typical heat pump reaches about 50C.

The simple option is to install a separate electric water heater, which would increase the installation costs. In total then, you would need 7666 KWh of electricity for heating and hot water, which at a current price of 14.5p would cost £1112 a year, making you £737 worse off.

There are more complex solutions to supplying hot water, such as incorporating an auxiliary hot water in the heat pump system to raise the temperature to 60C. But it is not evident that running costs would be much less.

Better get your winter woollies out!


November 21, 2020 at 06:45AM