Residential heating and cooking consume about thirty percent of all energy used globally. To compare, producing electricity takes 20% while all transportation uses roughly 30%. As countries make progress with power sector decarbonization using renewables, attention is increasingly switching to decarbonizing the transport and heating sectors. Electric vehicles (EV) and hydrogen vehicles are expected to replace internal combustion vehicles in the transport sector, but the solution for heating is less well-defined. Most residential heating relies on electricity or fossil fuels, especially natural gas. In the United States, roughly 50% of homes currently use natural gas directly. This article looks at the low carbon options available in the residential heating sector, parts of which may be the most difficult areas of the global energy system to decarbonize.
Across many countries in high latitudes, where winter cold makes heating important, residential heating is largely provided by natural gas-fired boilers. Heating oil (a form of diesel) and coal boilers are also used. Electric and storage heaters make a major contribution as well, alongside district heating (distributed through pipes from centralized heat sources), especially in parts of northern Europe and Russia. Among these heating types, the electric options are relatively less efficient than the gas-powered options. However in some cases, the efficiency of electric heating can be enhanced by installing air or ground heat pumps. Electric options also have the potential to decarbonize if they use renewable power. District heating too, can be decarbonized by utilizing waste heat or renewable sources, such as solar and biomass.
There is another green alternative in the form of decarbonized gases that can replace natural gas while still being supplied using the same distribution network. Decarbonized or carbon-neutral gases include biogas, syngas, and blue and green hydrogen. In many cases, these gases can be added gradually to the natural gas supply using existing infrastructure and appliances to meet interim decarbonization targets. Compared to electrification, which involves replacing an existing boiler with a more expensive heat pump, using decarbonized gases can be less expensive and disruptive to the consumer. Sometime new boiler installations may be required to utilize decarbonized gases, but usually not at low hydrogen concentrations.
There have been calls for the European Union, via its 2021 Gas Directive, to encourage the introduction of zero-carbon gases by setting a goal to reduce the baseline carbon intensity of natural gas systems by 2030. This policy would encourage the blending of low carbon gases such as biogas and hydrogen into the conventional supply. Similarly, biofuels could be used to replace heating oil, although this has its own environmental impact and is not possible at the needed scale. Eventually hydrogen-based liquid fuels, such as methanol and ammonia, may become available, but, for the time being, heating oil and especially coal need to be replaced with green electricity or lower carbon gases.
Both gas and electric options have their unique advantages, but it appears a combination of the two represents the most efficient solution to decarbonize the residential heating sector.
The Pros and Cons
Buildings would need to be more energy efficient and better insulated for heat pumps to be effective due to their lower energy density. Other issues with heat pumps are their high up-front cost and the limitations of installation. In Europe many houses cannot have a ground source heat pump (more powerful than air source) because they require significant outdoor space. Still, when available, heat pumps can be safer than systems based on combustion, such as boilers. They can be fueled by rooftop solar panels, thus making residences more self-sufficient and lower-carbon. They are normally cheaper to run than oil and gas boilers, depending on the local price of power, and have an efficient conversion rate of energy to heat. They also incur less maintenance, and, critically, can provide cooling during the summer like an air conditioner. This is increasingly relevant as high latitude summer city temperatures rise with higher atmospheric CO2 levels.
However, electric appliances do not have the energy concentration that gas has and are simply not as powerful. This is an issue when poorly insulated properties need to be heated quickly and becomes critical at the systems-level. For example, in a UK snowstorm in March of 2018, the gas heating system carried six times the energy content of the electric power system—a peak demand that the power system could not have handled without massive, unfeasible expansion.
It is also difficult to store green electricity easily since batteries are expensive and not designed for seasonal demand variations. However, you can store the energy in a gaseous form such as green hydrogen by converting the renewable power into hydrogen using electrolysis. This is critical when matching grid-level supply and demand in a renewables-dominated power system. Blue hydrogen can also be produced from the natural gas itself through reformation, with the CO2 by-product sent to Carbon Capture and Storage (CCS). This provides a longer-term market for natural gas, extends the life of existing storage and pipeline infrastructure, and is currently the cheapest way of producing low-carbon hydrogen at scale.
So, while electrification may replace coal and fuel oil heating outside of the natural gas grid, low carbon gases can deliver centralized, undisruptive heating system decarbonization through the existing gas network with some possible modifications. Most boilers can handle a mix of biogas, natural gas, and hydrogen, so the transition can be gradual. The UK is considering a 20% hydrogen mix by 2030. However, many boilers may need to be replaced if the concentration rises towards 100% hydrogen. Even still, this option would be cheaper and more reliable than just replacing all boilers with heat pumps, storage heaters, and heavy insulation which risks overloading the power system during periods of peak cold. The UK and other European countries are already trying out the addition of hydrogen as well as some biogas in their natural gas systems.
Currently the world uses about thirty percent of all its gas in the residential sector, mostly for heating with some for cooking. This rises to about forty percent in the UK. The energy transition means there will be a decrease in natural gas use in the residential sector over time. However, some of this displaced natural gas may find a home as feedstock for blue hydrogen production. It will have to compete with natural gas displaced by the expansion of renewables in the power generation market as well.
Similar energy transition scenarios as imagined for the residential sector are also anticipated for the industrial sector. The industrial sector also uses natural gas as its primary fuel for the primary purpose of heating—often to very high temperatures. Hydrogen is a far better replacement for natural gas than electric heating to produce very high temperatures in industries such as steel. There are three blue hydrogen projects nearing approval in the UK, while a major two gigawatt wind-driven green hydrogen project (SeaH2Land) has just been given the go-ahead by Orsted in Holland - at this stage, these are primarily driven by industrial customers, but could also supply the gas grid.
Some areas of both residential and industrial heating are seen as the most difficult to decarbonize, although with low-carbon gases and electrification (alongside expanded green generation), it should be possible. Some environmental purists remain keen on one hundred percent electrification because they see it as the optimum minimum energy solution. They reject blue hydrogen which maintains fossil fuel extraction and existing fossil fuel infrastructure, particularly the pipeline and gas storage system. However, using hydrogen-blended gas is popular with most energy companies and is likely to be a lot cheaper and more achievable in combination with renewables-based electrification than one hundred percent electrification alone. Plus, as carbon capture technology develops and the ratio of natural gas is diminished, zero carbon heating can still be achieved.
*Jeremy Bowden is a freelance journalist, analyst, and editor, specializing in the energy sector. He serves a variety of clients across the world, with work ranging from features and interviews, to ghost-writing, in-depth reports and public relations material. Prior to turning freelance about ten years ago, his full-time experience spanned over fifteen years in the energy, specialist energy media and utility sectors in a variety of positions in both Europe and Asia with companies including IHS, Dow Jones and Argus Media.