The changing nature of heat

Within the EU recently there have been significant drops in carbon emissions, most notably in the electricity sector. The UK for example, has seen a 45% drop in carbon intensity (despite all the Tories anti-renewable dithering), with an average level of emissions of 250 gCO2/kWh. However Scotland is well on course to join the 100% club, with an 92% drop in carbon emissions since 1990 and an expected carbon intensity of 24-50 g/CO2/kWh beyond 2020.

While this still leaves some way to go, electricity of course being only 18% of total energy consumption, and the energy sector as a whole being only responsibly for 60% of emissions (the remaining 40% coming from industry, mining and most notably agriculture). However, it does show how the situation is rapidly changing. Which may require the need to re-evaluate certain policies.

For example, electric vehicles have long run the risk of simply shifting emissions from tailpipes to power plants. However, with a cleaned up grid in Europe, this is less of an issue any more. And, as I recently discussed, vehicle to grid technology can actually help balance a future renewables heavy electricity grid.

However, by far the biggest sector impacted will be in terms of heat generation. Traditionally in the UK gas fired central heating has been seen as more environmentally friendly. As gas boilers are about +90% efficient (while a power station is 55-33% efficient, with a further 10-25% lost during transfer via the grid and in end use appliances), they have a carbon intensity of about 290 gCO2/kWh, while electric heating was typically in the order of +450 gCO2/kWh. As a result gas boilers were often recommended on environmental grounds and governments spent quite a bit of money upgrading council flats, or offering grants to see more gas boilers installed. And gas central heating has become a must have commodity in UK homes (they often mention it in UK property ads as a selling point).

However these significant drops in the carbon intensity turns everything on its head. Now in fact, its the gas boilers that seem to be part of the problem, rather than the solution, with electric heating increasingly looking as the better choice. That said, there are other reasons why electric heating has long been looked down on. To be blunt, its kind of crap.

Traditionally, you’d be relying on electric storage heaters for space heating, which are good at storing heat, but aren’t great at actually releasing any (until about 3am when your in bed and wondering why the house is suddenly warm). And water heating was done by immersion heaters (essentially a giant kettle) which are energy intensive, inefficient to run and prone to leaking.

However, that is also now changing, with new combi electric boilers becoming available. These work just like a gas combi boiler, in that they provide instantaneous heat, only using electricity when there is demand for heat (thus, they don’t need a big tank). And they can run radiators as well as providing hot water. Hence you can swap one for a gas boiler, without changing the radiators. Furthermore, gas boilers come with various safety hazards (carbon monoxide poisoning) and need a flue installed to vent gases. This is not an issue with a electric boiler.

Indeed, I’ve kind of been caught up in all of this. My old gas boiler died recently and repairing it was going to be prohibitively expensive. Worse, refitting another gas boiler in the same location would have also been expensive (they’d have had to rip down the ceiling across half the flat to install a new flue). And the only spot where it could be relocated to an outside wall was in a bedroom (which is fine so long as you maintain it and have a mains powered CO alarm installed, but could be a showstopper if I tried to sell the place). So instead, I opted for the electric boiler option (which, given that I’m on a 100% renewable electricity tariff, makes mine a zero carbon home).

That said the other main reason why gas boilers have been preferred is cost. Gas is about ¼ to 1/5 the price of electricity in the UK. In my case, I live in a very energy efficient flat. About 25% of my annual heating costs was the gas standing charge, 20% the actual gas and the rest boiler maintenance. So in theory, by getting rid of the gas standing charge I should be only slightly worse off (or more than likely about the same or slightly better off, depending on how much the maintenance costs are).

Of course for people who don’t live in an energy efficient homes, this might not be an option (mind you that’s sort of why I went for one in the first place!). Hence other alternatives might need to be considered such as heat pumps, hydrogen (basically running those same gas boilers off hydrogen instead of natural gas), biomass or district heating systems.

One has to consider however, the enormous rise in energy demand over the winter in the UK. Hence whatever option is chosen it would have to be something storable. So in the case of heat pumps or direct electric heating, you’d need some sort of seasonal electric storage (possibly in the form of a large PHES system located in the highlands). Hydrogen could take the form of underground caverns filled with hydrogen, while district heating systems (and heat pumps) could look at heat storage underground.

I’d also further note the impact on the grid itself. In much the same why electric vehicles will likely force changes to how the grid is wired up and how bills are calculated, the same is likely to be true for future heating systems. Particularly if its heavily dependant on heat pumps or electric heating systems, as they too can be programmed to come on at certain times of the day, using off peak electricity (so a form of energy storage not unlike what’s possible with electric car batteries), de-rating during peak hours, to help even out the peaks and troughs.

Its worth noting that electric heating systems can be fitted with a surge tank to allow a few hours of energy storage (the issue is, this reduces their efficiency, but it would make still economic sense with the right electricity tariff’s). Furthermore that the main obstacle to installing electric combi heating is often the capacity of the building’s electricity system (some older buildings just can’t withstand the very high current draw such a boiler will require). A heat pump will require either a large garden for a ground coil, or a suitable spot on a wall onto which a fan coil unit (which will be making some noise 24/7) can be mounted (this was the problem in my place, neither of these were options, so I had to go for the electric boiler).

Either way, it does show how the situation isn’t as insurmountable as the naysayers would have us believe. There are solutions. Yes nothing will offer a like for like replacement for fossil fuels and likely it will be range of these different options that get implemented. But it shows that the situation is rapidly changing. How steady improvements in decarbonising the electric grid can be rolled out to other sectors.

About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
This entry was posted in Biomass, CHP, clean energy, climate change, efficiency, energy, environment, housing, news, Passivhaus, politics, power, renewables, sustainability, sustainable, technology and tagged , , , , , , . Bookmark the permalink.

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