By Dave Elliott
Imperial College has looked at Heat System Decarbonisation (PDF) in the UK in a new report. Provocatively it says solar and biomass heat can only play limited roles for direct space heating, and focuses mainly on three other low carbon system options: a shift to using hydrogen in the gas grid, the use of decarbonized electricity to run heat pumps, and the creation of local heat networks.
As a consequence of the investment in the gas Iron Mains Replacement Programme (IMRP), it says the repurposing of the gas grids for use with hydrogen has become feasible, and ‘could be an attractive option especially for properties in urban and suburban environments, which comprise 80% of households’, with the cost and disruption of conversion optimised ‘by regulating for the installation of hydrogen-ready appliances as early as possible’.
It notes that hydrogen has the advantage that it can be stored in similar facilities to those used for natural gas, i.e. salt caverns, disused gas fields and aquifers, albeit needing about three times the volume (or three times the pressure) due to its lower energy volume density. However, it says the most important precondition for using hydrogen ‘would be the development of large scale, low cost production facilities’. This it says could be by electrolysis of water, though this is ‘currently very expensive and not yet suited to large scale production, or through conversion of natural gas by steam methane reformation (SMR)’. This is currently less expensive, but still more costly than natural gas. SMR produces carbon dioxide as a by-product and its use would therefore, it says, be ‘very dependent on the availability of CCS, which is currently not commercially or technically proven in the UK’. To keep this option open, pilot studies should, according to the report, be carried out to determine the feasibility of each of the hydrogen production processes and, for steam methane reformation, the viability of CCS.
That’s what’s now planned in Leeds – with the focus on SMR conversion from natural gas, with CCS. The resultant hydrogen will be fed into the gas main. ITM’s Power to Gas option will be looked at, although it’s not seen as likely to be a major option for now even though it would avoid having to use CCS!
The Imperial College report’s second focus is on decarbonising the electricity sector, which could provide ‘considerable future optionality for decarbonising the heat and transport sectors once sufficient extra low carbon generating capacity is in place.’ Electrification, using highly efficient heat pumps, can ‘be suitable for less densely populated environments, where access and traffic disruption from electricity system upgrades can be minimised. Disruption and cost to the householder could be a significant barrier to their adoption, but can be reduced by focusing on applications where no major energy efficiency improvements or radiator replacements are required’.
It notes that ‘the electrical effects of heat pumps will be particularly significant in the local, low voltage networks and their 11kV feeder circuits, since the ability to smooth out their impacts are much more limited than in the higher voltage distribution and transmission systems. For reasons of network capacity and, more often, to avoid short term fluctuations in service quality, local networks could need upgrading to accommodate even modest penetrations of heat pumps’. However, it says that ‘direct electric heating is suited to well-insulated properties, particularly flats and maisonettes in high rise buildings, where gas-fired boilers are not used and the space heating requirements are low’.
The report also notes that ‘since there is a high probability that electrification of heat and transport is likely to be a significant route for decarbonisation, a low voltage mains upgrade programme along the lines of the gas IMRP could be considered in those areas suitable for electrification. The justification for this could be stronger in areas that also have a high potential for solar PV roll-out where network upgrades may also be required’. It says that ‘electricity is more difficult and expensive to store than gas, so consideration must be given at the design stage to storage, demand side management and back-up solutions that will provide a low cost, low carbon capacity, capable of dealing with the seasonal space heating requirements’. Absolutely! Electrification shouldn’t always be the primary goal. Gas can be better for heating and so can directly supplied and stored heat.
Which brings us to district heating, the third area covered by Imperial College. It says district heating ‘can supply heat very efficiently and at low cost, although there are currently only limited sources of low carbon heat production, even at limited scale – sustainable biomass, geothermal, waste heat and heat pumps – for this paper, the latter was used.’ It is well suited to areas of mixed use with ‘strong anchor clients, such as municipal buildings, offices and leisure centres’.
Though most readily installed as part of new projects, ‘district heating can also be suitable in less populated areas as part of community energy schemes as well as for flats and maisonettes in multi-storey buildings’. It adds that ‘the seasonal fluctuations in space heating requirements can be reduced for mixed use district heating schemes and heat storage can be less expensive than electricity storage’. Nevertheless, as in the electricity system, Imperial says ‘consideration should be given at the design stage to storage, demand side management and back-up solutions’.
The report’s detailed focus on the infrastructure and new management approach needed for green heat is very welcome : it can’t all just be grafted on to the existing system: ‘Most of what currently exists relates to the centralised supply of fuel and energy – gas and electricity – and these current governance arrangements are not fit for purpose in relation to the new and different challenges of heat decarbonisation, where arrangements may, more often than not, be determined by regional and local requirements, and could reach into every home and business. Future arrangements, which should also include national and local system design capability, will be needed to ensure that key decisions are made, delivery frameworks are put in place, and that the interests of residents, businesses and consumers are properly considered’.
However, not everyone will agree with all of the report’s technology choices. While the proposed shift to hydrogen/syngas and district heating is likely to be applauded, the downplaying of solar and biomass may raise hackles, especially, since (see my earlier post) the government has decided to cut support for solar heating and rethink its approach to biomass boilers. For example, solar can be linked to efficient heat storage options at various scales, including community-scaled inter-seasonal heat stores, and, although there may well be some land-use limits on solid biomass availability, as DECC has accepted, easily stored biogas from wastes has its attractions and can be used for heating, not just to make electricity.
Certainly green gas is moving up the agenda. The Labour party has been pushing it hard via a new report, the Green Gas Book, with a series of essays exploring the various biomethane, hydrogen, bioSNG and biopropane options. It notes National Grid’s rather optimistic view that up to a third of current UK domestic gas demand could be met from bioSNG and that this gas demand can be cut by a third by 2050, so we just need to find the last third, with AD biogas and Power to Gas conversion of surplus renewable electricity being options.
I’ll be looking at that in my next post, hopefully re-energised after the upcoming three-day Radical Technology Revisited conference in Bristol.