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Electricity is on track for decarbonisation – what about decarbonising heat?


The proportion of low carbon electricity generation in the UK has risen steeply over the years, such that DEFRA’s conversion factor (a measure of the CO2 in each kWh energy generated) for the National Grid has fallen by 35% since 1990, and is projected to fall by a further 50% by 2030, to below 100gCO2e/kWh. Even with short term policy movements, the direction of travel is clear, and technology is advancing faster than anyone expected.

Heat however has not had the same focus as power. Given that heat accounts for 48% of energy use in the UK and a third of all emissions1, failing to decarbonise the heat system in the UK is a serious problem. More must be done to decarbonise heat.

DECC’s latest figures2  reveal that we consume over 1250MWh heat per annum in the UK, and just 233MWh electricity, even with the shift to an electrified energy system. And yet, decarbonising the electricity grid has been the focus of policy and technological development, rather than decarbonising heat. 

There has been some gain through improving the energy efficiency of our homes – having risen to a peak in 2004 as more homes were connected to mains gas, domestic gas consumption has steadily fallen. However, while natural gas might be preferable to some other fuel sources, it is never going to be zero carbon, and 2014’s domestic gas consumption represents over 140m tCO2e in carbon emissions.

Low-carbon alternatives to individual gas boilers are plentiful. Heat networks are back into vogue in the UK – for example Islington’s Bunhill plant and the Queen Elizabeth Olympic Park scheme. Several policy and planning drivers (e.g. London Plan), as well as central Government support (e.g. Heat Network Delivery Unit) are nudging towards more uptake – but will it be enough? To date, only 2% of UK heat demand is supplied by heat networks1. Combined (Cooling) Heat and Power systems are also frequently specified for new build, and with gas-fired engines, do generate slightly lower carbon heat and electricity. But gas is not the silver bullet: it will not be widely available for consumption after 20303, is non-renewable, dependent on import, and subject to price volatility. 

This is where heat networks are a good investment now, with a view to exchanging the engine for biomass-driven when a local supply chain is established and air quality allow for combustion of biofuels. Typically, the bulk of the cost of a decentralised heat system, like a heat network with a local heat source, is in the capex cost and cost of civil works for piping required to distribute heat to the end users. But this infrastructure is long-lived: one pipe manufacturer claims that piping running under typical use conditions since the 1970s is still performing well. In most cases it is the engine that needs to be replaced before the pipework, which affords the opportunity to upgrade to a higher efficiency, lower carbon solution in time, without replacing the whole system. We are already seeing innovative low carbon heat solutions being trialled – including anaerobic digesters, energy from waste, and biomethane – any of which could be used as alternatives to natural gas as a heat source for networks in future.

There are immediate benefits to moving to biomass heating now. It would be a huge carbon saving for the 2.5m households currently off the gas grid4, who are often relying on heating oil and other higher carbon fuel sources. Small scale wood burners or larger syn-gas systems could supply domestic heat and hot water sustainably for these users. Ground source heat pumps are also a compelling application, as we improve the building fabric of our homes and underfloor heating becomes de rigeur for home owners.

While heating systems for individual buildings and ground source heat pumps are good solutions for regions of lower population density, our population nationally is increasingly concentrated in urban areas. Higher population density strengthens the case for heat networks: with a higher heat load and greater variation of use pattern over time, a single heat engine running continuously can supply a greater proportion of the total heat demand on the network. Rather than seeing urbanisation as a problem, the opportunities for a highly efficient, low carbon energy network within cities are great.

The role of policy makers is clear. Compare similar schemes Feed-in Tariffs for solar PV with the Renewable Heat Incentive: at the end of March 2016, 873,000 PV installations had been completed since January 2010, a total of over 9.7GW capacity5; yet only 14,000 renewable heat installations have been completed since its opening in 2011, with a total of 2.8GW capacity6. This urgently needs bolstering to accelerate the shift to low carbon heat.

Given the current state of play, the shift to gas-fired heat networks in urban areas is the logical next step as a short-term intermediary to zero carbon sources. But do we need a more radical shift? Incremental changes in building performance have produced a steady decline in gas consumption. Yet Passivhaus technologies have shown that domestic space heating can be met without any external energy supply – potentially cutting 750 GWh of energy demand from the energy system nationally7 – planners and developers should do more to promote this approach. 

Or why not completely abandon direct heat sources and electrify our heating supply? DECC quotes the capex cost of switching to electric heating at £175/kW for domestic users – a third of the capex of biomass boilers8. If we can improve energy efficiency of our buildings and appliances sufficiently, the higher lifetime cost of heating with electricity could be offset by the lower capex costs – provided we can also revolutionise the National Grid to cope with this increased demand.

Either way, the conclusion is clear: we cannot meet our renewable generation targets, let alone our decarbonisation targets, without addressing the carbon impacts of our heat consumption. Electricity has had huge effort applied and seen carbon intensity drop off dramatically – we now need to apply that same effort to decarbonising heat.



Helen Troup MPhys is Programme Manager for Renewable and Decentralised Energy Systems at Carbon Smart. Helen has extensive experience in advising local authorities, businesses, and third sector clients on energy strategy, energy reduction opportunities, local renewable and low carbon energy generation potential, and longer range trends analysis in the energy sector. 



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  8. The Potential and Costs of District Heating in the UK, Poyry, Faber Maunsell and Aecom for DECC 2009.

Posted 13/07/2016 by Michelle Fisher

Tagged under: Decarbonization , DECC , Carbon , Energy , Heat

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