Aggregated load profiles of domestic buildings: the implications of an all-electric future
Stephen Watson, Loughborough
Summary
The UK has a binding commitment to reduce CO2 emissions by 2050 to 80% below the 1990 level, with an intermediate target of 34% by 2020. Because houses, flats and other dwellings are responsible for 26% of UK CO2 emissions, they are a prime target for emissions reduction strategies.
As well as energy efficiency improvements to buildings’ fabric, changes in the way homes are heated have been proposed. This includes the idea of all-electric households in which homes are heated by electrical devices (typically heat pumps with some back-up resistance heating) powered by decarbonised electricity. Currently over 90% of UK homes have gas-fired space heating. Simple analyses have shown that if all these homes were heated electrically, with no shift in the time of heat demand, the electricity supply system would have to be massively reinforced and dispatchable generation massively increased, neither of which is desirable.
Load-shifting is therefore seen as necessary, and could be achieved in a number of ways. For example, electrically heated hot water could be stored in super-insulated thermal stores within houses, and used to supply space heating as necessary. Alternatively, as part of a district heating system, hot water might be stored at a district level. Advantages include lower heat losses for the same level of insulation (due to smaller surface area to volume ratio) and avoiding the need for bulky heat stores in individual homes. Indeed, district heating, using a variety of heat sources, is another method of space heating which could be used to replace gas-fired heating in many UK houses. In Denmark, 60% of houses are heated using district heating. However, there are limits to the heat demand density at which district heating is viable. Therefore, even if the UK vigorously pursues a policy of district heating, there will still be a significant proportion of homes heated by other methods. For these homes electric heating may prove the best option.
In considering the need for thermal storage, it is often implicitly assumed that the space heating load profile in the imagined all-electric future will be the same as that of the gas-fired present. There are reasons to believe that this may not be so. Firstly, human behaviour co-evolves with technology. For example, electric heat pumps respond very differently from gas-fired boilers, potentially leading to different user behaviour. Secondly, there are parts of the world which have significant proportions of their space heating demand met by electricity, such as Norway, Canada, and, to a lesser extent, France. These countries are able to meet this demand, apparently without the use of thermal stores. Perhaps groups of electrically heated households behave in such a way that the load profile presented to the grid is relatively smooth?
There may be useful knowledge to be gained by comparing the UK to countries where electric space heating is more common and identifying transferable practices.
In talking about load profiles for space heating, it is worth distinguishing between variations within a day, and variations between one day and another. Both kinds of variation could have important implications. This project will examine existing data on space heating load profiles, both with electric and gas-fired heating. If necessary, additional primary data might be gathered from a newly recruited sample of homes.
Having determined how all-electric homes are heated and why they are heated in this way it should be possible to build models that predict the aggregated load profile of communities of homes. Alternative types of model might be explored, such as probabilistic models. Using such a model it would be possible to understand whether load shifting is needed, the degree of shift necessary and how this might be achieved. This should make it possible to take a view about the feasibility of an all-electric UK future for homes.