We think of renewable energy technologies as being new, but people have been using biomass as a source of heat for centuries.
In the UK it has perhaps the lowest profile of all the green sources of energy but there are very significant attributes, including the fact that it is not dependent on climate (wind, sun or heat) and therefore can be used in any part of the country.
Biomass is quite simply the burning of organic matter (other than fossil fuels) in stoves and boilers to create heat and, in larger plants, power. The difference is that modern technologies make the process far more efficient, with heat extraction reaching 80% or more.
The fuel is produced from organic material, either grown as crops or gathered from industrial or commercial waste. Using waste to produce heat and energy reduces the amount sent to landfill and biomass is the only renewable technology that uses waste.
The most commonly used forms of fuel for heat production are wood chips, wood pellets and logs. Wood pellets are a compact form of wood with a low moisture content and a high energy density. Though more expensive, they are easier to handle and more appropriate for appliances with automated loading systems, particularly smaller scale domestic appliances or where storage space is limited.
Generally, stand-alone stoves provide space heating, although some of the higher output versions can be fitted with a back boiler for water heating and central heating. Fuelled by logs or pellets, they generate between 6-12kW heat. Boilers connected to central heating and hot water systems are generally larger (15kW and above) and again use logs, pellets or wood chips for fuel. They have an integral hot water energy storage tank or accumulator tank that stores water up to 90OC. Whichever system is used, it is important that it is correctly sized: running an oversized boiler at low output will result in incomplete combustion and cause tar to form in the flues.
Back-up systems
Like other forms of renewable energy, the energy or heat generated may not be sufficient for peak loads. A back-up system (either fossil fuel or green) will therefore be needed to cope with shortfalls and to provide hot water in the summer when heating isn’t required. A biomass heating system can be run in conjunction with solar thermal if the site is good and summer water heating demand can be met. The biomass stove or boiler can then be shut down and only used when heating is needed. It can also be combined with other renewable technology depending on the specific energy requirements.
Biomass is most cost-effective and environmentally-friendly when fuels are sourced locally. Transport costs and related CO2 emissions are then kept to a minimum, also benefiting the local economy and creating employment. But there are a few issues that need be considered. There must be enough dry space to store the fuel and there must be access for loading. Boilers and stoves should be fitted by a certificated installer, who will be able to provide the right advice about sizing and ensure that installation complies with safety and Building Regulations. Chimneys may need to be fitted with a lined flue and if the building is listed or in an area of outstanding natural beauty, the local authority planning department will need to be consulted about this.
Costs
Costs will depend on the type and size of system chosen, but installation and commissioning costs are roughly fixed. Stand-alone room heaters generally cost £1,500-3,000 installed. For boilers the cost varies according to the fuel used: a 15kW automated feed pellet boiler (sufficient for a three-bedroom semi, for example) would cost £4,000-12,000, including the cost of the flue and commissioning. A manual log feed boiler would be slightly cheaper. Payback will depend on the type of fuel used but, using wood chip, this is estimated at 5-10 years.
