Renewable heat in rural areas: what are the options?

Options

Energy efficiency is a necessary condition for successful heat decarbonisation, but investment in a combination of energy efficiency and low-carbon heat will usually be the most cost-effective and practical solution.  As energy efficiency has been discussed in more detail here this section focuses on different heat options.

The Climate Action Plan places significant emphasis on heat pumps as replacements for high carbon heating systems (with a target of installation of 400,000 heat pumps in existing buildings by 2030).  As discussed previously 23% (65,187) of existing homes (built before 2010) in the Western Region may be suitable for heat pump installation (using the lower energy efficiency standard of HLI ≤2.3 (read more here)). This leaves 237,894 homes requiring very significant energy efficiency upgrades and major heating system change (switching from oil boilers or solid fuel) if heat pumps are to be installed.  Therefore while heat pumps will be a key technology in the decarbonisation of heat, particularly in new or more recently built homes or those which are already quite efficient, other options also need to be explored.

For the 78% of homes in the region which are not heat pump ready, switching from oil boilers and solid fuel will be both expensive and disruptive and there are particular categories of ‘hard to treat’ homes where achieving the high energy efficiency requirements needed for effective heat pump use will be difficult or prohibitively expensive.

There are a range of different heat technologies which could be deployed to move these to low carbon home heating systems. The technology used should depend on the home’s characteristics, its location, and the features of the available technologies alongside consideration of capital and lifetime costs in the specific situation.  Broadly, renewable heating technologies can be categorised as electrical or bioenergy.  In this post some of the technologies which may be suitable for rural homes in each of these categories are briefly outlined.  In considering these it not so much about what the exact technology mix should be, but how uptake can be achieved at scale and in a sensible way that makes full use of the economic potential of energy efficiency while promoting the lowest carbon heating options available.

Electrical Heating Systems

There are a number of electric heating solutions such as Electric Heat Pumps, Hybrid Heat Pumps and Storage Heaters as well as other electric heating sources and storage.  A brief overview of these options with a particular focus on their potential use in rural homes is given here.

Heat pumps

Heat pumps are the key technology for decarbonising rural heat.  The general term ‘Heat Pump’ includes Air Source Heat Pumps (ASHP), Ground Source Heat Pumps (GSHP) and Water Source Heat Pumps (which are unusual).  The SEAI has a useful guide for homeowners here.  In general for existing homes Air Source Heat Pumps are most likely to be installed.  While more efficient, the retrofitted installation of GSHP is more expensive and more disruptive than the ASHP option.

While very efficient because they operate at low temperatures, for heat pumps to work effectively and not be too expensive a high level of energy efficiency is required (see more discussion here).  They are usually used in conjunction with underfloor heating or may require larger radiators than in fossil fuel systems.  They are operated in a different way to conventional fossil fuel heating systems, needing to be on for longer periods.  An additional electric water heating source may be necessary.  Air Source Heat Pumps are however relatively small and are usually attached to an external wall.  Maintenance costs are likely to be lower than for oil central heating and they should be cheaper to operate when installed in suitable homes.

High temperature heat pumps are also being developed and they may be more suitable in less energy efficient homes but they are likely to be more expensive to operate than other heat pumps.

Hybrid heat pumps may also be a short term option.  These hybrid systems combine a heat pump with an existing fossil fuel boiler with the heat pump acting as the background heat source and the boiler used for peak demand.  While not a long term answer to decarbonisation they may have a role to play in less energy efficient homes.

Heat pump technology is well established and it is used widely in other countries so there is significant experience of their effective operation.  Nonetheless, in addition to stringent energy efficiency requirements, heat pumps are sensitive to quality of design and installation.  It is important that supply chains and skills in this technology are developed so that the experience of widespread transition to this technology is good.

Storage Heaters

Storage heating has long been an important electric heating technology, allowing users to make the most of cheaper ‘night rate’ electricity.  Electricity is used to heat ceramic bricks which store the heat (at night or when electricity is cheap) and release it during the day.  They can be effective but, with traditional storage heating once the stored heat was used there was no other heating option.  They could also be expensive to run.  More efficient and controllable storage heaters are becoming available; these have more options for ensuring the heat is released when required.  Some models use a fan to circulate heat better or can include an electric heater to provide additional heat when needed (though this may not be very efficient).

Storage heaters, using renewable electricity, will be an important low carbon heat option in ‘hard to treat’ homes unsuitable for heat pumps.  Although less efficient than heat pumps they are not as expensive to buy and install.  As with other renewable heating options, there are likely to be further technological developments in the next decade as global demand for low carbon heat increases.

Other electricity heating and storage

Heat can be stored in a variety of forms, most commonly as hot water, either in the traditional hot water tank, in the heat pump buffer tank or in solid heat batteries which are becoming more available (see here for an overview).   Where solar PV panels are installed, hot water, thermal or battery storage may be options for making the most of the household’s solar generation.  The electricity may also be used directly in electricity resistance heaters or in certain situations infrared heaters but unfortunately the electricity generation pattern of solar PV does not fit with heat demand (which will be higher after sunset and on days with less solar radiation) so storage will be important.

With the shift to low carbon heating options and more use of electricity for heat alongside smart opportunities to purchase electricity more cheaply at different times (such as when there is significant wind generation), there will be an increase in battery and thermal storage options (read a more detailed study of domestic heat storage and energy flexibility here).  These opportunities again highlight the importance of new developments in domestic heat and ensuring that any strategy for transitioning to low carbon heating systems is responsive to new, effective technological opportunities.

Bioenergy

Different forms of bioenergy (solid biomass, liquid biofuels and biogas) can provide renewable alternatives to electrification.  Each is likely to be suitable in different situations and over different time periods.

Solid Biomass

Biomass (usually wood) can be used as a direct replacement to existing systems, a new boiler is required but as these are high temperature heat systems (like oil and gas) there is less likely to be a requirement to change the internal pipe and radiator systems and so there is less disruption.  Biomass is available in the form of pellets, wood chip or logs.  Pellet systems can be more automated and so require less user involvement, while log boilers require filling and more frequent ash disposal but are cheaper to run.  For all biomass it is important that dry wood or pellets are used to allow the boiler to operate efficiently and to reduce particulate emissions.  Given that biomass can be a direct replacement for heating systems already in use in rural areas (biomass boilers for oil boilers and solid biomass for coal or peat), it is important that biomass options are explored as part of any domestic renewable heat strategy and supported in the transition to low carbon heat in rural homes.

None of the options for moving to renewable heat are easy, biomass boilers are more expensive to install than oil boilers, and they require more on-going maintenance by user (e.g. ash disposal) and servicer.  Concerns about the availability of consistent feedstock can affect consumer confidence and there may be worries about the potential for fluctuation in fuel costs.  As part of any strategy to decarbonise heat with biomass  the  issue of emissions and clean air must be considered, with enforcement of stove and boiler standards and quality standards (such as the Wood Fuel Quality Assurance (WFQA) scheme) to ensure the traceability and quality of the fuel used.

However, a clear strategy to develop local bioenergy supply chains in rural areas, education of those supplying fuel, installing and servicing boilers and using them should mean that biomass is an important option for renewable heat in rural areas and one which will bring significant employment while keeping the money households spend on heat in the local economy.

In addition to the replacement of oil central heating with biomass heating, biomass can substitute for solid fuel in systems already in use (18 % of heating in the Western Region is from peat and coal).  In general wood is the most likely replacement fuel in stoves and ranges but novel low carbon bioenergy solid fuel substitutes are being developed in Ireland.  Read more about the fuels and how they are produced here and here.

In the last decade there has been an increase in the use of wood burning stoves instead of open fires.  These are generally secondary heating sources but where wood or other solid biofuel is used instead of fossil fuel they lower the carbon intensity of heating.  This is particularly the case if they are used to heat a single room rather than putting on the central heating throughout the house.  This is a common practice in larger or less energy efficient homes where the cost of heating can be substantial.

Liquid Biofuels

There may be liquid biofuel options too.  There has been a reduction in carbon emissions from transport with the Biofuels Obligation Scheme, where a portion of the fossil fuel in petrol and diesel is replaced with a biofuels (read more here).  There may be an option to do similar in home heating oil (kerosene) as a short term measure to reduce the carbon intensity of home heating.  A recent government consultation on biofuels discussed this possibility and sought feedback on how it might work, based on the level of use and availability of suitable biofuels.  The consultation document and the responses are available here.

BioLPG is a potential option, providing an easy switch for those already using LPG as a home heating fuel (0.8%[2] of homes with central heating in the Western Region).  It has been developed substitute for fossil fuel LPG (read more here).  There is however, limited domestic production and there may be difficulties in sourcing materials to significantly expand production of BioLPG.  Additionally, there may be greater demand for use in transport where alternatives to liquid fossil fuels are more limited.

Biogas

As most of the rural Western Region is not on the natural gas network, there are probably fewer opportunities for using biogas as a direct home heating fuel substitute than in areas on the natural gas network (biogas can be mixed with natural gas and in the longer term could potentially replace fossil fuel natural gas).  Biogas is produced in a number of ways but Anaerobic Digestion (AD) of feedstocks such as food waste, slurry, sewage, or grass is the most important option.  The production of biogas will take place in rural areas, and depending on the site of the AD plants, there are possibilities for small scale heat networks to use it.  However, this is only likely to be possible in the longer term and will be dependent on a complex range of factors.

There are clearly bioenergy options which may form part of the transition to low carbon rural home heating alongside electrification.  All biofuels need a sustainable long-term, domestic supply, and well developed supply chains and to be compatible with air quality standards and be sourced sustainably.  Nonetheless bioenergy needs to form part of the suite of options for the low carbon transition and we need a clear policy statement on role of bioenergy in decarbonising domestic heat.

Conclusion

To drive a successful low carbon transition we need to be open to different heating options.  Solid biomass, liquid fuel and modern electricity storage heating are important options for decarbonising heat in rural buildings. In certain situations they may have lower installation costs or running costs than heat pumps.

We should measure their real world performance, collect information on the economics of different technologies and keep up to date with newer or developing options.  In addition to research about the best real life solutions for heating rural homes with renewable energy, we need good, robust data on actual installation and running costs, and then guidance on how best to move the ‘hard to treat’ rural home to low carbon heating so that people can make the choices most appropriate to them and to their home.

We must consider the full range of low carbon technologies, their associated performance, cost and environmental benefits.  To successfully transition to low carbon rural home heating we need to support a range of low carbon heating technologies beyond heat pumps.

Helen McHenry

[1] This term is used in the very useful Scottish consultation document on low carbon heat in homes off the natural gas grid https://www.gov.scot/publications/energy-efficient-scotland-future-low-carbon-heat-gas-buildings-call-evidence/pages/6/

[2] CSO Census of Population 2016, StatBank / Profile 1 – Housing in Ireland / E1053