In the choice between heat pump and combustion heating, the answer might be: both. Recent studies in the UK shows that the best heating source alternative could be a hybrid heat pump running on renewable electricity and bio-methane or hydrogen. That would be a highly decarbonised system.

In a hybrid system, the heat pump satisfies a constrained base level of demand. During high-demand periods such as daily peaks or low outdoors temperature, extra thermal energy is provided by a complementary system, e.g. a gas boiler. That boiler would initially use natural gas but low-carbon fuels such as bio-methane or hydrogen could be phased in over time and at different locations. The use of hydrogen is probably more likely in areas where there are industrial markets and probably close to natural gas feedstock supplies, with access to depleted gas fields for carbon capture and storage.

For the user, moving from a boiler to a hybrid system instead of a heat pump comes with both benefits and drawbacks. One advantage is that the electricity need during the cold season will not be as high, and thus the need to expand the electricity supply system is lower. Also, there is probably no need to modify the existing radiators. On the minus side is the higher up-front cost for the installation. But first of all, consumers need to be convinced that a hybrid system actually will provide them with secure and economical heating.

At the systemic level, the energy prices are a hindrance for a large deployment of hybrid heat pumps. The running costs are not competitive while natural gas remains the backup fuel. To change this scenario, a carbon cost could be added to the price of natural gas. Another possibility is to look into the pricing structure of renewable electricity.

Hybrid systems have been demonstrated, and the other elements needed in a hybrid/low-carbon gas energy infrastructure are also being evaluated. The hybrid approach potentially offers a path towards decarbonised heat with relatively few barriers to market acceptance. It also provides a degree of policy flexibility in the face of the inevitable uncertainties of applying relatively untried technologies at scale.

Roger Hitchin, Independent Energy and Buildings Consultant, UK.

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