Heat Pumps reappraised

Following a new review by the Energy Saving Trust, ten years on from its landmark report into the quality of heat pump installations in the UK, the EST now says ‘it’s time to reset your opinions on heat pumps -particularly air-source heat-pumps’. As it admits, there had been some serious criticism of heat pump performance, air source systems in particular, which seemed not to be well suited to often cold, damp UK.  However, improved technology and better installation evidently means that all is now well in most cases, with EST/ICAX noting that most users were happy with them.

Indeed, in a Blog (that sadly now seems to have been blocked for some reason), EST’s Ben Whittle was so enthused he said that we didn’t need to go for hybrid heat pump/gas heating system as proposed for home heating by the government and the Committee on Climate Change (CCC): ‘An all-electric heat pump has an auxiliary electric heater to assist in the coldest months - the vast majority of heat pumps available in the UK have this feature built in. So why would we carry on leaving a gas connection in place and maintaining two pieces of equipment when for the very large majority of houses, an all-electric heat pump will do the job?’  He went on ‘When we look at running costs, we are weighing up the very small number of days in the year where a heat pump might require assistance from an auxiliary source, versus the cost of maintaining the back-up heat source. Again, it will vary depending on where you are in the UK but many people won’t require much back-up heating at all’.

So, if that is right, it means there is no need for hydrogen for heating, although presumably there will be a need for more electricity, especially at peak demand times. But it seems, if that power can be delivered, heat pumps can use it flexibly to meet heat demand and cut emissions at reasonable cost. A Blog post on a RAB report relayed by the UKERC claimed that ‘heat electrification via heat pumps alongside energy efficiency upgrades, and the use of smart tariffs which reflect wholesale electricity costs and carbon intensity, can reduce greenhouse gas emissions immediately at limited consumer costs’.

However, not everyone thinks that this happy outcome is realistic. Heat pumps, especially ground sourced heat pumps, are expensive and installing them is disruptive.  The rival view is that it would be far easier to carry on using gas, delivered by the gas main, for home heating, but switch over to non-fossil or low carbon green gas. That certainly sounds easier, but there are issues. Biomethane, produced from anaerobic digestion of bio-wastes, is one possible green gas, but there is unlikely to be enough available to meet much of the UKs heating demand. Hydrogen is another option. It can be produced by the high temperature steam reformation of fossil methane (‘SMR’), but to make it low carbon means you have to capture and then store the resultant CO2, which makes it expensive and inefficient. By contrast, so called ‘green hydrogen’ production, by the electrolysis of water using renewable electricity, can be zero carbon, but it is currently an even more expensive process than the fossil gas SMR/CCS route to what is sometime called ‘blue hydrogen’.  Worse still, you can’t just pump hydrogen, however generated, into the gas grid at high percentages- some of the pipe work has to be upgraded and so do the devices using the hydrogen. All of which argues against going down the hydrogen gas route.

The case against blue hydrogen from SMR is certainly strong- it can be seen just as a way to keep using fossil gas, with CCS being far from proven at scale. In a critique,  Dr David Toke, Reader in Energy Politics at Aberdeen University, says that ‘the natural gas industry is now campaigning to save its business by extolling the alleged virtues of converting gas heating to supply by 'blue' hydrogen. This blue hydrogen production would be done using natural gas to produce the hydrogen whilst capturing and storing carbon dioxide produced in the process. But this is a facade that will delay transition to a sustainable clean energy economy and waste renewable energy into the bargain. Blue hydrogen is not a substitute for energy from renewable energy’

However, he is also unhappy with green hydrogen: ‘Even if the hydrogen was sourced from renewable energy (and not much of it will be) the result would be a grandiose waste of renewable energy. This is because using hydrogen from renewable energy to heat buildings is around four times less energy efficient compared to using heat pumps (using renewable electricity) to supply heating in buildings’.  The point is that, heat pumps can deliver 3-4 times more heat energy out than with direct use of power, whereas the efficiency of power-to-hydrogen gas conversion can be low, maybe 50-60%. On that basis, it seems clear that it’s best to go for heat pumps, not power-to-gas conversion. That is certainly how CCC and others see it, with most space heating being met in that way in their 2050 scenarios.

There is a problem with this. Even given the fact that heat pumps need 3-4 times need less power than would be needed to supply heat via the green hydrogen route, the power grid will find it hard to meet the UK heat needs, especially at peak demand times. At present the gas grid handles around 4 times more energy than the power grid- so if the latter has to take over (and also supply power for Electric Vehicle battery charging), it will have to be substantially expanded.  That will add to the cost. Of course so would going down the hydrogen route, including the need to install enough renewable capacity to supply the hydrogen – more than would be needed to run the heat pumps.  Set against that, the hydrogen gas route does offer flexible storage options, unlike the power-to-heat pump route. And the projected costs of green hydrogen gas production do seem to be falling while conversion efficiency is rising, so that interest in it remains strong. Indeed a recent FCH report on options in the EU sees the hydrogen route as avoiding key problems with the heat pump route, which, it says, would involve ‘costly or even impossible retrofits in old buildings, which account for 90% of buildings’ CO2 emissions’ and would also ‘lead to major seasonal imbalances in power demand that would, in turn, require a power storage mechanism at large scale’.

The UK government nevertheless has decided that, for the UK, the electric heat pump route is best, but only with the hybrid heat pump compromise- so as to be able to use a bit of gas to meet peak demands without having to expand the power grid massively. So it’s pipes and wires- a bit of a botch!  But it’s possibly the lowest cost option- unless there’s a local green heat network option. Though that’s another story- then storable solar heat might also play a role.