Robin McAlpine – September 23rd 2021
One of the most encouraging recent developments on climate change in Scotland is that there is a clearly-discernable rise in people saying ‘but how?’. As in ‘great, nice target – but how are you going to meet it? What are you going to do?’
Much of this discussion reverts back to the things that people do know how to do, like moving to renewable electricity. That’s fairly straightforward and easy to understand. In other instances it causes people to focus on the one bit they are familiar with at the expense of the rest (for example ‘reusable coffee cups’ rather than a consistent circular economy).
And then we get to decarbonising heating. On this people tend to trail off with a mumble of ‘Air Source Heat Pumps or something…’ before moving on. This is an understandable response because decarbonising heating is one of the most difficult things to do.
But we simply can’t ignore it and with the current fears about the impact of gas price rises, there hasn’t been a better time to start this debate.
So why is it so difficult? Put simply, we built Scotland around cheap gas heating and the infrastructure to go with it (from gas pipelines to the kinds of central heating we have). If we don’t use carbon-emitting gas and we can’t find a direct replacement, the infrastructure won’t support a warm Scotland.
There is one direct replacement – kind of. You can use hydrogen (probably mixed with another inert gas) almost like-for-like, but it is very expensive and chunks of the gas infrastructure would fail if it wasn’t upgraded (hydrogen gradually causes metal to become brittle and vulnerable). It is just a very bad use of available hydrogen.
The only other theoretical replacement is organically-produced gas, but we can’t produce anything like enough of it. Combined this means we can’t easily just piggyback on the existing infrastructure.
So what about the fabled Air Source Heat Pumps (ASHP)? For policymakers this looks like a very attractive option because you can force the cost onto households directly. On a properly-constructed new-build an ASHP can work wonders. But it is a pretty major task to retrofit them and they simply aren’t up to the job of providing all the heat and hot water for a house not designed for them.
(Note that ASHP is being hard-sold by the electricity companies because it traps you into electric top-up heating which hands them the heating market…)
What about electric heating? It too has problems. First, it is pretty expensive – probably about three times the cost of gas. To use it efficiently you really need to switch from water radiators to efficient modern electric heaters – which is another big job for most households. And it uses a lot of electricity which means we’d need to invest serious money into reinforcing the electricity grid if we don’t want it to fall down every morning when heating goes on and people have showers (and kettles and toasters crank up…).
None of these options are cheap to put in place and only ASHP offers the promise of reduced energy costs (though it seldom truly delivers these in retrofit). We’d be spending a lot to deliver expensive or unreliable heating.
And yet heat is the simplest form of energy there is – we actually have loads of it. But it’s in the water, the ground, coming from the sky… If only we could grab and use all that heat then heating your house would be cheap and easy.
But few houses can, on their own, grab enough of that heat for their own need. And that is why Common Weal has been pushing hard at the idea of district heating. This causes people to scratch their heads because we’re just so unfamiliar with it here. But both the principle and the practice is simple. It’s just a way to distribute heat.
Basically you send hot water to houses in insulated pipes. The houses don’t use the water directly. They use something called a heat exchanger which takes some of the heat out of the distributed water (which is very hot) and transfers it to their domestic water for their own use.
The main infrastructure is basically the same as a water main – a large ring main going round a town or city and smaller mains coming off that serve a neighbourhood (perhaps about ten blocks or so). This is sometimes called a heating grid because that’s exactly what it is.
So where does the heat come from? That’s the real beauty of district heating – anywhere you want. As long as the heat can be connected to the ring main anywhere it can be used. For example perhaps as much as half Glasgow’s heat could be extracted from the Clyde, more from disused mineshafts.
Solar thermal panels (solar panels for heat) are very cheap and much more efficient than Solar PV (electricity) so large arrays of them (or even a lot of roof-mounted ones) can produce a lot of the demand. Other sources could be industrial heat capture (using waste heat from factories), geothermal (heat from rock sources) and biomass (burning wood fuel).
But any source can be used – if a new technology comes along in the future it can simply be plugged in. The oldest still-working district heating system is nearly a hundred years old, so this really is future-proofing.
The remaining piece of the puzzle is storage. We get our renewable heat when we need it least (the summer) and not when we need it most (winter). But storing heat is really easy. You dig a big pit, fill it with gravel and water and put an insulated cap on it. In the summer you take all spare heat and put it into the store and then you take it out again in the winter. It’s that straightforward.
District heating is the least disruptive option for your house but it is certainly disruptive getting heat there, because you have to dig pipes to every house (basically anywhere on the gas grid is feasible to be on a heating grid) and ring mains round towns, and install heating technologies. This is absolutely not a small job, but none of the options is.
Common Weal modelled and costed the job; it is the single biggest cost included in the Common Home Plan. It’ll cost about £9 billion in ring mains, £25 billion from the ring main to the house (including replacing the gas boiler with a heat exchanger) and, depending on the technologies used, about £17 billion to generate and store the heat. So something like £50 billion to do in total.
It’s a lot, but none of the other options comes in at less than half that total so we’re going to be spending something like that one way or another. And once the system is in, heating becomes very cheap indeed, won’t need replaced and is 100 per cent self-sufficient and carbon-free in operation.
This will take time to do, so the longer we wait, the longer we’ll be trapped into using natural gas. District heating is simple, reliable, ‘just works’ and produces really inexpensive heat. There is a one-off cost and a one-off burst of disruption.
We’re going to have to do this somehow and no option is easy. So ask yourself this simple question – how would you want your own house heated? Explosive, enormously-expensive hydrogen? Pricey electricity with massive up-front costs and the need to rip out and replace your current heating system? The expensive (and ugly) retrofit of questionable ASHP?
Or clean, cheap, plentiful heat delivered invisibly to your house which will leave us entirely self-sufficient in heating basically forever?