Heating: Part of the Problem or Part of the Solution?
Burning carbon-based fuels is not a good idea if we want to avoid emissions of carbon dioxide. Despite this, Europe (as an example) is burning a lot of fossil fuel in order to provide heat. Approximately 25 % of final energy use in the EU-28 goes to space heating and 15 % to process heating. Three quarters of the heat is produced directly with fossil fuels and a portion of the remainder comes partially from fossil-based electricity. It looks like heating is a big problem, but in this post I will posit that heating could become an important part of the solution instead.
Wind and solar power are the lowest cost sources of carbon-free energy with a large resource base. However, before we can have power systems dominated by wind and solar, we have to deal with their temporal variation. Storing electricity would be a big help, but is still expensive with the exception of reservoir hydropower. Are there other uses of energy where the storage could be more affordable and where we could get rid of carbon dioxide emissions? Yes, that is correct, heat.
Heating Can Offer Flexibility
Heat can be stored in hot water tanks of various sizes. Tanks that serve individual residential buildings are a bit pricy in terms of $/MWh, but if the tank is serving multiple buildings or blocks of apartment houses, hot water based heat storage gets really affordable. However, piping becomes more expensive, although the existing district heating systems demonstrate that the piping cost is surmountable. Another alternative is to store heat in building structures or in boreholes of various depths that also yield geothermal heat. All of these options are easier to implement in new buildings than in existing infrastructure, which indicates that we should really be thinking hard about how to design future buildings with power system flexibility in mind (and not just energy efficiency).
Heating can also offer flexibility without storage. In fact, Northern Europe has lots of experience with combined heat and power plants that can switch output between heat and electricity. However, CHP profitability is becoming a problem due to the low amount of full load hours in energy systems with significant variable power generation. In addition, CHP burns fuel and causes onsite carbon dioxide emissions (unless the fuel is hydrogen or ammonia). Therefore, an interesting alternative is to have hybrid systems, which generate heat from electricity most of the time, preferably with heat pumps, and only switch to fuels when necessary. Relying just on electricity would cause expensive ‘net load’ peaks that hybrid systems can help to avoid.
Hybrid systems can be used both for space heating and for some industrial processes. However, it is important to note that there are many industrial processes, and while some of them could be relatively easy to electrify (e.g. when there is a liquid heat carrier) others will not be so easy. Furthermore, most process heat is needed at temperatures well above the boiling point of water. Even if the process would allow using steam, it is not cheap to store and therefore hybrid systems might have a better economic chance.
Heating Has Some Roadblocks
As indicated above, there are potential roadblocks for the electrification of heat:
- Heat storage is not always easy, especially within existing infrastructure.
- Some uses of (process) heat are not easy to electrify.
- Energy efficiency and flexibility can be at odds in new buildings.
- Space heating demand is seasonal and that is a big drawback. In many climates, the seasonality of heating demand could promote the use of wind power over solar power. Cooling could compensate heating seasonality, but at least for now it is a much smaller energy demand (one percent of final energy use in the EU-28).
- Electrification of heat, together with an increasing share of electric vehicles, will contribute to bottlenecks, especially in the distribution grids, and this will not be cheap to mitigate. We could begin with some electrification of heating now, and continue when the grid infrastructure expands.
Low Cost Renewable Energy and the Future of Heating
In recent years, energy policy has been obsessed with reducing CO2 in the power sector, which has made sense. The low-hanging fruit has been to replace electricity generated with fossil fuel with renewable electricity. The falling cost of renewable electricity bears more fruit, but due to variability of wind and solar, the fruit starts to become more scarce as the share of variable power grows higher. Meanwhile, fossil fuel conversion for heating is more efficient and therefore a similar switch has not been so prevalent. However, wind and solar power are becoming so cheap that direct replacement in heating is also starting to make sense, especially with the help of heat pumps when this is possible. Therefore, I postulate that the replacement of fossil fuels with electricity for heating offers the next low-hanging fruit and we will see a lot of activity on this front in the near term. The potential for switching is large.
Juha Kiviluoma, PhD
VTT Technical Research Centre of Finland