Are large thermal stores and Combined Heat and Power District Heating (CHP) with District Heating (DH) pipes to deliver heat to buildings is more likely to be a better solution to de carbonising the building heating sector than relying on large-scale electricity storage of renewable or nuclear electricity (the “all electric solution”) delivered to buildings via cable?
One of the most intractable energy problems in Europe is how to deal with the heating load of buildings, (11 EJ/y), which is the largest user of primary energy and is presently met largely with gas. This heat load will not go away due to the expense of insulating the legacy buildings beyond quite modest levels and the new build rate of new low energy buildings is too low to have any significant impact over the needed timescale.( Note. German energy policy is actually trying to promote insulation of legacy buildings, partly to offset the higher carbon emission due to nuclear phase out. Also, quite some activity is going on to insulate existing buildings. Some controversy exists on whether this is doing harm to them. Currently, the Federal and State governments cannot agree on who should provide the budget)
Electricity from renewables or nuclear cannot easily be used to substitute for gas heating due to the difficulties and expense of upgrading the power distribution grid to cope with the increase in peak electrical demand due to the heating load which occurs during the cold snaps. (Note: The French grid was under extreme pressure this winter) ( The French problem is that, although they are net exporters of power they have not managed to meet the demand peak with domestic supply. This is due to the enormous proportion of electric heating and the temperature sensitivity of French power demand, some 2-3 GW per centigrade. The solution has always been to import during peak load but this has become difficult after the closure of 8 German nuclear plants. Also France is addressing this problem with plans to build a number of CCGTs. As those peak power plants would not be profitable in the current market framework, the French have decided to change their framework and to introduce capacity markets which will be implemented in during coming years. Another interesting idea is to install small devices at the electric heaters allowing the TSO to switch customers off for a short while. A number of French companies have started to market these things, not amusing EdF ). The performance of air source heat pumps which if used en-masse in cities, (ground source would cause excessive ground freezing at high densities) degrades dramatically when the air temperature drops below OoC. ( Installing ground source heat pumps in France would be a real progress as they mainly use direct heating as far as we know)
It is not possible to envisage how to store renewable energy as electricity for week long periods for a country entirely heated by electricuty (unless geography is kind to you as e.g. in Norway or Brazil) which will come largely from wind for use during very cold, week long low wind periods to meet these heating peaks. However ower station waste heat, up to 19 EJ/y exceeds the building heat load of 11 EJ/y heat. Such waste heat can already be economically delivered to buildings in DH schemes as it already is in e.g. Denmark, Finland and Poland (There exist also DH networks in Holland with a huge CHP share!, Sweden and in all former socialist countries of Eastern Europe, including Germany where important DH networks also exist in the industrial heartland of the Ruhr Valley). DH schemes already provide such multi-day storages, and month-long and economically viable inter-seasonal designs have been prepared to store the low carbon heat. The thermal storages will allow the DH to use the excess heat capacity of CHP when these plants are in operation on windless days, and they can forward surplus wind energy converted to heat via large heat pumps and electric boilers and also utilize solar water heating in large scale as well as any other cheap heat such as waste heat from steelworks etc.
The existing fossil CHP power plants can readily back up and shadow wind generation, with their use declining over time as more renewable energy enters the generation mix.
Efficient large High Voltage heat pumps which can have a COP (heat out divided by electricity in) of 3.6 (less than 2 for domestic heat pumps during cold snaps) can be used to convert the surplus wind energy to heat and store it in thermal stores. CHP stations have a COP of at least 6 (and this can be much higher with lower supply temperatures), which is far superior to the individual electric heat pumps of 2 – 3.
Likewise, district cooling and large chilled water storage is an important technology to reduce the capacity for cooling and to shift the electricity load from the day-peak to night hours.
All in all District Heating and cooling with thermal storage are important elements in the smart city energy infrastructure.
Thermal storage is orders of magnitude cheaper than electricity storage.
Given that low-temperature heat stores (up to 95 oC) have already been designed that can store large quantities of heat inter-seasonally, and that DH can incorporate many forms of low temperature heat such as solar, geothermal, and waste industrial, then DH networks fed with heat from surplus wind, backed up by fossil fuel plants for low wind periods, seem a viable way forward for society. Work by the JRC Petten ( Background report on District Heating and Cooling, Potentials, Barriers, Best Practice and Measures of Promotion) indicates that even as far south as Barcelona these CHP-DH networks are viable, as the waste heat can be used to provide summer cooling via absorption heat pumps. The same forthcoming JRC report indicates that a capital spend of €319 billion for DH and CHP costs gives an approximate savings of €51.4 billion / year in fuel costs. It is clear that current interest in electricity storage is deficient and based on not clearly examining the problem ie “for what use do we actually want to store electricity for” .