I thought this week’s announcement – proposals for the UK’s first large-scale district heating system based on geothermal energy to be built in the midlands city of Stoke-on-Trent – was a bit unlikely. But then I remembered that the biggest district energy scheme on Britain’s south coast, in Southampton, has a geothermal component too.
I went to its opening, over 25 years ago, and saw how the City Council was using the ‘free’ output from what had been a research borehole drilled to investigate geothermal aquifers in Britain. Southampton has since developed its network largely on natural gas-fuelled CHP plants.
However, this new proposal suggests that, even in Britain, hardly a hotspot for geothermal energy, there is scope for district heating schemes at least partly based on heat delivered from deep underground. And heat is one of the big energy subjects in the UK at the moment. Although heat policy lags well behind that for electricity, heat is hugely important. Almost half the total energy used in the UK is used to generate heat for buildings – that’s more than is used either for transport uses or to manufacture electricity.
Currently, the vast majority of that heat is produced by burning fuels, but the UK government is working on a series of policies to decarbonize heat; initially the Renewable Heat Incentive. The world’s first long-term financial support programme for renewable heat, the RHI was launched more than two years ago to provide support payments to industry, businesses and public sector organisations which switch to low carbon heat sources. The scheme is to be extended to the domestic sector this year.
So what will a largely decarbonized heat sector look like? Well, cogeneration will be important among an interesting mixture of heat pumps, direct-electric heating, biogas, CHP-based district heating systems (for high load density urban areas), solar thermal systems and micro-CHP (for suburban areas, possibly biogas-fuelled). By 2050, it is assumed that progress towards decarbonization of electricity will be well-advanced, so that electric heating would be a low carbon option. It may be that district energy systems will be largely fuelled with biomass, biogas and municipal waste.
The UK district heating sector certainly looks active at the moment. Aside from Stoke-on-Trent, construction is due to begin this year on an entirely new energy network, based on gas-fuelled CHP, for Gateshead in north east England that will supply local government offices and homes. And utility E.ON is building another new heating network to serve a range of public sector and commercial buildings in the east of Sheffield – a 29 MWe biomass-fuelled CHP scheme will be at its heart.
The distribution locally of what would otherwise be wasted heat is what makes CHP so efficient. In the UK, CHP, some of it based on geothermal energy, is to be at the heart of a major and long-term strategy to decarbonize not only electricity, but also heat.