Woodfuel

 

Using wood for fuel is hardly a new idea, but the recent upsurge in interest in renewable energy in the UK means that woodfuel is experiencing a renaissance. Using woodfuel reduces our reliance on fossil fuels, which in turn, helps to lower carbon emissions. Biomass fuels can be cheaper to use than fossil fuels in many circumstances. This is reflected in the rapidly increasing number of installations used in domestic, commercial and public sector buildings.

Woodfuel can come from conifer forests and broadleaved woodlands. It is very unlikely that high value material – such as good quality, large timber – for which there is an alternative market in construction, will be available for energy applications. Nevertheless woodfuel can be obtained from a wide range of forest products: early thinnings, small dimension roundwood, poor quality final crops, the side branches and very top of trees harvested for their stem wood. Short rotation coppice, where high-yielding species such as willow and poplar are planted at high density and harvested at three-year intervals, is another source of woodfuel. Urban and roadside trees can be used as well as clean by-products of wood processing.

Climate change benefits

The principal benefit of using woodfuel rather than fossil fuels is a reduction in carbon dioxide emissions. Emissions associated with energy projects in the UK Emissions Trading Scheme are listed for different fuels: consumption of 1kWh of electricity gives 0.43 kg carbon dioxide, 0.33 for the consumption of 1kWh from coal and 0.19 from natural gas whereas the emission factor for renewables is zero.

In reality, fossil fuel is used to produce woodfuel but it is a very small fraction of the energy it contains – woodfuel is more accurately described as carbon lean rather than carbon neutral. Standard methods have been developed to compare the greenhouse gas benefits of using woodfuel and fossil fuels for particular end uses. The comparison includes all the activities and processes involved in managing land, producing the biomass, setting up and running the system over its working life so gives a complete picture of the emissions. For a small farm in southwest England for example, use of woodfuel from its long-established broadleaved woodland and some recently planted confier stands in a 150 kW woodchip heating system required only 0.1kWh of non-renewable energy for every 1kWh heat delivered. Greenhouse gases emissions were estimated at 52 g carbon dioxide equivalent per kWh compared to 307 g carbon dioxide equivalent per kWh for the reference (efficient oil) system. Thus the emissions were cut by 90% compared to conventional fossil fuel heating systems. Over a 25–year life cycle the woodfuel system is predicted to reduce total emissions by 40 tCO2e. This gives an indication of the potential climate change benefits of using home-produced woodfuel at a local scale for heat production.

Wider benefits

Correctly managed, woodfuel is a sustainable fuel that can offer many ancillary benefits:

• Biomass can be sourced locally, from within the UK, on an indefinite basis, contributing to security of supply.
• UK-sourced biomass can offer local business opportunities and support the rural economy. The social benefits of wood fuel will accrue largely to rural areas. Increasing the use of wood for fuel will require more active management of woodlands. This should increase the number of jobs in the countryside. Setting up generating plants in rural areas should provide further employment opportunities.
• The establishment of local networks of production and usage, allows financial and environmental costs of transport to be minimized. There is no region in the UK that cannot be a producer of biomass, although some have greater productivities than others.
• Woodfuel also offers potential economic benefits. Prices for traditional forest products such as timber are currently low. Wood fuel provides an alternative and possibly more valuable market, and it also offers a new option for farmers to diversify away from agriculture.
• Woodlands, forestry and agriculture are generally perceived to be an environmentally and socially attractive amenity by the UK population, providing opportunities for recreation and leisure activities.
• Many biomass fuels generate lower levels of atmospheric pollutants such as sulphur dioxide that contribute to 'acid rain'. Modern biomass combustion systems are highly sophisticated, offering combustion efficiency and emission levels comparable with the best fossil fuel boilers.
• Biomass residues, arisings, co-products and waste not used for energy may be consigned to landfill. This imposes costs for disposal, an additional burden on limited landfill resources, and also contributes to global warming by the creation of landfill gas, including a high proportion of methane (CH4), a greenhouse gas 21 times more potent that carbon dioxide.