Zero Carbon, Zero Reality? Part 2

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Electric Heat Pumps







As my last blog noted, the government’s Renewable Heat Incentive (RHI) is subsidising wood-burning devices which may be worse for the climate than the oil or gas boilers that they replace. The RHI is also disbursing taxpayers’ money on electric heat pumps. These are the subject of this post.

Has DECC considered the potential consequences if consumers react to its offer by installing heat pumps by the 100,000? There are worries over network stability. There are even doubts that spending this money will reduce CO2 emissions.

Some recent Dutch work [2] examined a scenario in which significant numbers of dwellings change from gas-fired boilers to electric heat pumps for their space and water heating. In the early stages, the impact would be to overload the local transformers which reduce the mains voltage to 230 V AC. That could make it more difficult to recover from winter power cuts [3].

As critics have already pointed out, really large-scale use of heat pumps – beyond the Dutch scenario – would mean that the national grid would have to be extensively replaced. The existing cables and transformers are too small to ‘heat electric’ although they are perfectly adequate for our lights, appliances, fans, pumps and electronic devices.

It is not only that the national grid’s cables are insufficient for a large increase in peak load. Since we closed our oldest, dirtiest coal-fired power stations, very little spare generating capacity has been available compared to the winter maximum demand [4]. Privately-owned diesel generators are being called on to keep the network stable. With growth in peak demand, even this contribution could be insufficient.

We had major, unpleasant and disruptive power cuts in the early 1970s. An industrial dispute between the government and miners led to coal shortages in which the government failed ‘to keep the lights on’.

Today’s governments are terrified of any repeat of this. If it happens, it is regarded as a humiliation. Ministerial resignations or sackings are inevitable.

I think the odds are still better than evens that the network operators can maintain supply between 2014 and 2020; i.e., the period particularly highlighted by OFGEM. But why raise the risk by subsidising electric heating – of which one form is heat pumps – and thereby raising winter peak demand at a time when margins are so tight? [6]

The fact that CO2 emissions do not necessarily fall if an electric heat pump displaces a condensing gas or oil boiler system makes the policy look doubly foolish [7]. It should have been better thought out. If consumers install so many subsidised heat pumps that the network in the late 2010s or early 2020s struggles to cope, this attempt at ‘zero carbon’ will have backfired as badly as the ‘dash for biomass’ cited in my last blog of 2 May 2014.





[1] By respectively 7 p and 19 p per kWh of heat, rounded to the nearest 1 p.

[2] and The tacit assumption is that resistance heaters are used when the heat pump cannot meet the full demand.

[3] Even if the network could meet the steady-state demand, the transient demand on reconnecting all the loads at once would exceed the capacity of the transformer.

[4] The nationalised Central Electricity Generating Board required a plant margin of 24% above the simultaneous maximum demand. Today’s plant margin is 5%.

[5] If anything, a disruption to electricity supply might have greater consequences now than it did then. ‘Life as we know it’ is more dependent on a continuous supply of electricity in 2014 than it was in 1974. 40 years ago, London Underground operated its own power stations. It could switch between those and the national grid for greater security of supply. Shop tills were not yet electric. The telephone system had battery backup. In fact, the landline system still does but mobile telephone masts do not. The internet was not yet in use.

[6] Replacing a gas boiler by a heat pump adds a peak demand of 4.5 kilowatts (kW) to the national grid, assuming an existing house with a peak heat demand of 8 kW, a heat pump with a peak coefficient of performance/COP of 2.0 and network losses of 12% between the power station and the dwelling. New blocks of flats with electric heating also increase the peak demand.

[7] The Energy Saving Trust found in 2010 that a typical heat pump had a COP of 2.2. This would give relative CO2 emissions of:

a) gas-fired condensing boiler 0.24 kg/kWh
b) condensing LPG boiler 0.27 kg/kWh
c) condensing oil boiler 0.30 kg/kWh
d) electric heat pump 0.53/2.2 = 0.24 kg/kWh.

The CO2 intensity of 0.53 kg/kWh for mains electricity is from the government’s Standard Assessment of Performance. The assumed CO2 intensity of natural gas is 0.22 kg/kWh. Assuming that, as published, 40% of electricity in recent years was generated from coal at 0.92 kg/kWh and 35% from gas at 0.50 kg/kWh, with 12% network losses to small buildings, the likely CO2 intensity is somewhat higher at around 0.60 kg/kWh.

A more focussed policy might address the needs of rural buildings which have no other means of heating than electricity, possibly because they lack space for fuel storage. Compared to electric resistance heating, even a heat pump of COP 2.2 would reduce CO2 emissions by 55%.