We still don’t know enough about new heat technologies to decide the best way forward

Posted on 2 March, 2021 by Green Alliance blog

This post is a reblog of an article by Dr Robert Sansom, independent consultant and member of the IET’s Energy Policy Panel.

Recently, Professor Cebon wrote on this blog that pursuing the hydrogen economy would be a mistake. I am neither an advocate of hydrogen nor am I associated with the oil and gas industry, but I was the lead author of a report, produced by the IET in 2019, which focused on the engineering questions that need to be addressed if the UK is to transition to hydrogen.  There are also major questions around the electrification of heat. Until these questions are dealt with, I do not believe anyone can say that one technology is better than another.

Ruling hydrogen out would be unwise
Let me start with hydrogen.  Often the focus seems to be on two hydrogen production methods, ie natural gas reforming versus electrolysis.  The criticisms made by Professor Cebon and others is that even with carbon capture and storage (CCS), reforming using natural gas as a feedstock, is not very green, that it is only promoted by the oil and gas industry and that the technology for large scale production has yet to be developed.  Whereas production of hydrogen from electrolysis requires huge investment in renewable generation, coupled with electrolysis plant, and is very inefficient.

But there are other choices for hydrogen production.  For example, from biomass gasification.  This is important because, to achieve net zero, the UK must have a strategy for greenhouse gas removals.  Possibly, in future, we might be able to decarbonise without the need for removals but that is not the case at present.  The key technology here is biomass with CCS (or BECCS).  The Climate Change Committee’s (CCC’s) sixth carbon budget report has 250TWh of energy bioenergy and waste by 2050 in its Balanced Net Zero Pathway, most of which is indigenous.  In addition there is scope for imported hydrogen, produced using solar PV, which also has substantial potential.

These options warrant further investigation before a decision can be made. Ruling them out at this stage would be unwise.  For example, it is possible that gas reforming using a combination of autothermal reformers and gas thermal reformers could achieve high levels of conversion efficiency with extremely high levels of carbon capture.  We should certainly do more to find out if that is the case.  Similarly, the cost of wind power has dropped considerably and there is optimism that the cost and efficiency of electrolysers will also improve in the near future, to be on par with, or possibly better than, gas reforming for hydrogen production.  Likewise, we should find out more.  There are challenges with importing hydrogen, particularly in terms of losses, but again it is worth testing.

There are significant obstacles to adopting heat pumps
The argument for air source heat pumps can be very persuasive, the conversion efficiency of heat from electric heat pumps is will  be much higher than that from hydrogen.  However, the main obstacles to heat pumps come from the changes required to the UK’s housing stock, electricity network upgrades and the provision of hot water. 

Without significant energy efficiency improvements to most of the UK’s housing stock, domestic heat pumps will underperform.  Heat pumps will also increase electricity demand by a lot, which is likely to require the street circuit network to be upgraded.  This is estimated to take about one month per circuit.  Typically, a street circuit will supply 100 to 200 houses and so the scale of the reinforcement programme will be enormous, costly and very disruptive.  

A typical heat pump is likely to be between 5kWth to 10kWth and incapable of supplying hot water on demand, so some form of hot water storage will be required.  Retrofitting hot water storage to the many properties that don’t have hot water tanks will be expensive and is unlikely to be welcomed by householders if it involves a loss of storage space.  In addition, the amount of hot water storage required will need to take account of the longer time it takes to heat water, particularly if the pump is also heating the home.  This may mean that more storage is required to compensate.  The alternative is to heat water directly using immersion heaters and electric showers.  But these operate at a much lower efficiency and higher cost, and would also possibly further increase the need for network reinforcement.

The main point is that we still don’t know enough about these alternative heating technologies, so we should certainly not rule any of them out at this stage.  Our focus over the next few years should be to find out more about how they can work, particularly in terms of cost, performance, implementation logistics, as well as consumer needs.  This can only be done by trialling them at scale so that we are able to make the best decisions on the way forward.

This is not an excuse for procrastination.  In the meantime, we should get going on a nationwide programme of housing insulation improvements.  The UK’s housing stock is shocking, not just in terms of energy efficiency but also in terms of the impact on householders’ health and comfort.  We can start that immediately with a target housing insulation improvement of 30 per cent, roughly equivalent to increasing the average rating to EPC C across the UK.  For heat pumps, this is essential, particularly for older buildings, but it is also necessary for hydrogen, as it will reduce the volume required if it is adopted for heating.