Use of micro CHP plants to support the local operation of electric heat pumps

There is a common assumption that to decarbonise the heat market in the UK a large number of households will need to switch from fossil fuel heating to heating with low carbon electricity. Electric heat pumps are the most energy efficient way of using electricity for space heating so it would appear logical to promote their use. Domestic electricity demand is highly stochastic and distribution supply transformers are sized to take advantage of load aggregation. This results in the transformers having capabilities between 1.4 and 9.8 KW per house depending on the number of houses connected to a specific transformer. Heat pumps are typically rated 3 to 6 kW and operate at a steady load for appreciable lengths of time. Consequently they should not be considered as stochastic loads. If these are installed in a high proportion of houses that previously used gas heating there is a real possibility that the local supply transformer would be overloaded. One alternative to replacing the transformers is to provide local generation. An obvious candidate for this is local combined heat and power units (CHP) as these are likely to be required to run at the same times of the year as the heat pumps. This paper examines the running characteristics of the two heating systems and looks at the running restrictions that would be required to produce complementary operation. The reduction in CO2 emissions of the resulting network will be compared with those produced by a similar sized network of houses using condensing boilers.