I was asked the following question in a comment replying to my last article looking at the carbon emissions factor of electricity in the UK, and the implications of a shift to direct electric heating that the SAP 10 is likely to encourage. My reply wouldn’t fit in a post so here’s another article!

Electric heating alternatives

Hi Emma

This is a super hard question, that we struggle with daily at Greengauge! Despite the concerns I raise about the way SAP is promoting electric heating, this is ultimately the way we will end up going. It is also important to acknowledge the difference between direct electric heating and heat pumps; the latter ‘leverage’ electrical energy via renewable, low-grade ambient heat (mostly in the air or ground). The thing I worry about is SAP 10 effectively encouraging developers to fit direct electric heating, which is cheap to install, but expensive and not necessarily low-carbon to run.

If in the medium term we have to discount all fossil fuels and leave then in the ground (which we do), and we acknowledge the problems of biomass (air pollution, the ‘carbon burp’, ecological footprint) at least on a large scale, it’s got to be electricity. So we’ve got to come up with ways of making that work, that don’t involve higher carbon impact during peak hours and the winter. That can’t be done with renewables alone, so storage technologies come into play, both inter-seasonal and diurnal. The former is only feasible at large scale, but the sheer amount of energy necessary to heat our buildings currently means this would be an enormous infrastructure project. Enormous as in orders of magnitude bigger than anything ever done before.

You asked for stats: Dinorwig can deliver 11GWh – I’ve just done a back of the envelope calc; let’s assume a reasonably efficient new home at 50kWh/m2 p.a. of heat demand, at 100m2, over a 200 day heating season would need 25kWh of heat input on an average day (not a peak demand, cold winter day). On that basis Dinorwig will do about half a million reasonably efficient homes for one average day. So then there’s a further 24.5 million homes, many of which are much less efficient than my assumption, and the rest of the year to consider…

In terms of local storage, the newer Tesla Powerwall has a 13.5 kWh capacity, so not enough but not a million miles away, and if we leverage that via a heat pump, we might be onto something. However, we’ve not started thinking about hot water, lighting and so on yet. And don’t forget all these electric cars we’re all being encouraged to switch to. There’s also the cost. The powerwall is currently listed at about £6,000, and a simple ASHP install would be at least £4,000, often a lot more.

Neither of these solutions (pumped storage hydro or domestic scale batteries) are appropriate for inter-seasonal storage which is necessary to harness the huge amounts of PV we’re installing, which tend to generate exactly when we don’t need to do space heating.

Load-shifting via demand response is another possible way of mitigating the impacts. a simple way of doing that is the old Economy 7 tariffs and storage heaters, but most people would agree storage heaters are not a great solution. Home batteries could play a role here, but again, we’re talking 24 hours or maybe a few days if throw money at it – these options don’t address inter-seasonal issues.

Currently, I’m not aware of any technology that has got off the drawing board that could be scaled up to provide a meaningful contribution to inter-seasonal storage of electricity – even with heat the feasibility for scale just isn’t really there. For the new Primary Energy (renewable) factors in PHPP, I believe the Passivhaus institute looked at underground storage of synthesised gas as the most feasible idea, but even that is an unproven technology.

Simply put, I can’t currently see a feasible way of heating our buildings via renewable electricity. I would therefore argue that rather than trying to match the national space heating demand, we crush it.

To do this we could immediately crank up new-build standards so that the amount of space heat energy required is close to zero. This is possible – we, and other designers, have delivered new housing in the last few years in which the occupants have yet to, or rarely, switch on the heating. That’s a real game changer, because all the feasibility problems associated with scale become much more solvable. Again, part of the problem with this is policy design, and how this can be set up by government to avoid the performance gap.

This does not of course address the challenge of the existing stock, which is much more difficult. It is possible to retrofit many, but not all of our buildings to the levels of insulation necessary, but it’s not cheap, and in the wake of the green deal fiasco, there is not the political will to go there. There are also technical risks, many to do with moisture, with retrofitting, which are not widely enough understood in the industry. There are however some really exciting projects being delivered at the moment, that suggest for the >£10k you might spend on a battery and a heat pump, an impressive energy saving can be achieved. Take a look at Energiesprong if you’re not already familiar. The pilot projects are coming in more expensive but they will come down in cost as they are scaled up.

Recommended Posts