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Other microgeneration technologies
Along with solar, wind and hydro technologies, there are three other technologies that people can use to generate energy in their own homes – ground source heat pumps, bio-energy and micro-combined heat and power (micro-CHP). These forms of generation also allow users to cut their dependence on fossil fuels and may even save on utility bills.
Ground source heat pumps
Ground source heat pumps (GSHPs) transfer heat from the ground into a building to provide space heating and, in some cases, to pre-heat domestic hot water.
It uses a large pipe full of water and anti-freeze, called a ground loop, to capture this ground heat. The heat is then transferred – rather like the opposite of what a fridge does – to underfloor heating, radiators or hot water.
The Energy Saving Trust points out a few issues when considering a ground source heat pump:
- GSHPs can be combined with radiators but under floor heating is better
- you need space and suitable ground available for a trench or hole to accommodate a ground loop
- you may need a back-up heating system
- combining the installation with other building works can reduce costs
- wall, floor and loft insulation installed before the GHSP will lower your heat demand
A typical six to eight kilowatt (kW) system costs £7,300 to £11,800, plus the price of connection to the distribution system. This can vary with property and location.
Bio-energy
Bio-energy uses biomass - organic matter, but not fossil fuels - to generate energy. The CO2 released when energy is generated from biomass is balanced by the CO2 absorbed during the fuel's production – what’s called a carbon neutral process.
These biofuels fall into two main categories:
- woody biomass such as forest products, untreated wood products, coppice wood (such as willow)
- non-woody biomass such as animal waste, industrial and biodegradable municipal products from food processing and high energy crops (such as rape, sugar cane, maize)
For small-scale domestic biomass situations the fuel usually takes the form of wood pellets, wood chips and wood logs. There are two main ways of using biomass to heat a domestic property:
- stand-alone stoves providing heating for a room. These can be fuelled by logs or pellets. Generally they are 6 to 12kW in output, and some models can be fitted with a back boiler to provide water heating
- boilers connected to central heating and hot water systems. These are suitable for pellets, logs or chips – which must be loaded by hand - and are generally larger than 15kW
The Energy Saving Trust says you should consider the following issues if you're thinking about a biomass boiler or stove. An accredited installer will be able to provide more detailed advice and guidance on further issues to consider.
- it's important to have storage space for the fuel, good access to the boiler for loading and a local fuel supplier
- there must be enough air movement for proper operation of the stove
- the installation must comply with all safety and building regulations (see Part J of the Building Regulations)
- wood can only be burnt on exempted appliances, under the Clean Air Act. This mainly applies to domestic appliances
- if the building is listed or in an area of outstanding natural beauty (AONB), then you will need to check with your Local Authority planning department before a flue is fitted
Stand alone room heaters generally cost around £3,000 installed. The cost for boilers varies depending on the fuel choice. A typical 20kW pellet boiler would cost around £5,500 to £12,000 installed. That size boiler will heat a three-bedroom semi-detached house all year. A manual log feed system of the same size would be slightly cheaper.
Unlike other forms of renewable energy, with biomass systems you need to pay for the fuel. Fuel costs generally depend on the distance from your supplier. The running costs will be cheaper if you live in an area that doesn't have a gas supply.
Micro combined heat and power (Micro-CHP)
Micro-CHP is a new technology which recovers and uses the heat produced when electricity is generated. A micro-CHP unit resembling a gas-fired boiler will provide both heat for space and water heating, as does a boiler, but also electricity to power domestic lights and appliances.
Potentially, it could be a very efficient way of using fossil fuels, such as natural gas. As well as gas, a significant proportion burn alternative, renewable fuels. Not only is micro-CHP more efficient because it uses heat, but it also avoids transmission and distribution losses.
The current generation of micro-CHP systems is best suited to larger homes with three or more bedrooms, or older houses where it would be hard to improve insulation, such as housing with solid brick walls. In such homes micro-CHP can potentially deliver carbon savings of between five and ten per cent – with typical reductions between 200kg and 800kg of CO2 each year. But the systems currently available offer fewer benefits for smaller and newer houses.
To exploit the technology fully, heat networks (usually using piped water) must be installed, and these carry high costs - £500 to £800 per KW installed generating capacity. Typically the payback time on the investment in micro-CHP is more than five years. However, micro-CHP’s high efficiency leads to a reduction in the use of fuels. And less fuel used means significantly lower energy costs.
It’s worth remembering that this technology is still in development and it is not an all-purpose solution. So, its suitability needs to be checked carefully.
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