February 08 2021:
Dr Richard Hall, Energy Transitions.
Solar Heat Working Group Chair.
Decarbonising the power grid was merely a prelude to the UK’s major net zero energy challenge; decarbonising the national gas grid. In the UK, residential and commercial heating demand is largely met with the direct burning of methane in boilers and the aggregate combustion products from these methane boilers is the single biggest contributor to UK greenhouse gas emissions1. This methane is delivered to almost every home and business in the UK via an extensive national gas grid.
Although it’s difficult to directly compare, the gas grid is something of the order of two times bigger than the power grid in terms of raw capacity to deliver energy2. Whilst I think we would all agree that the roadmap to decarbonise power and transport is clear, the heat sector is currently in a vicious battle for capacity dominance.
There are four great powers fighting in the heat capacity war: Big Gas, Big Heat Networks, Big Heat Pumps and Big Insulation. Big Gas wants to replace methane boilers with clean burning hydrogen boilers, Big Heat Networks wants hot water pumped to every house in every city, Big Heat Pumps wants a state-subsidised heat pump in every home and Big Insulation wants teams of retrofit co-ordinators working on every street. Whilst these incumbents fight it out to either defend, of eradicate, the UK national gas grid, the big question for us is, how can solar heat possibly compete against these great powers?
The good news for solar heat is that solar does not have to compete with anyone, we can just let them fight it out. Solar works just as well with a hydrogen gas grid as it does with a natural gas grid (in fact even better given the likely higher gas prices). Solar works great with heat networks, especially at the 20% level as commonly found in Denmark 3. Solar works great with heat pumps and solar works great in highly insulated houses. Solar even works great in a future where heat is simply directly electrified (think smart hot water tanks).
Although solar heat maybe a neutral party in the next capacity war, we do have to make the case that adding some solar capacity to the system will be beneficial in terms of energy security, affordability, and providing meaningful emissions reduction. Given the somewhat difficult past of solar thermal in the UK, it will not be that easy to persuade policy makers that solar has a role in heat decarbonisation.
Ultimately, the ability of the Solar Heat Working Group to come together to make a coherent case will define if solar will have the kind of positive impact on the national gas grid in this decade, that it had on the power grid in the last decade.
 BEIS, ‘Heat decarbonisation: overview of current evidence base’, GOV.UK, 2018. https://www.gov.uk/government/publications/heat-decarbonisation-overview-of-current-evidence-base.
 S. D. Watson, K. J. Lomas, and R. A. Buswell, ‘Decarbonising domestic heating: What is the peak GB demand?’, Energy Policy, vol. 126, pp. 533–544, Mar. 2019, doi: 10.1016/j.enpol.2018.11.001.
 R. Hall, ‘Solar Heat Networks’, 2020. https://wiki.energytransitions.uk/wiki/Solar_Heat_Networks.