Background

Fossil fuel prices have been rising sharply, and an increasingly viable alternative is woodfuel from arboricultural arisings produced from maintenance of the urban environment. If arboricultural arisings are to be used as fuel, space will be needed to dry the material, and specialised equipment will require an initial financial outlay. Grant schemes aimed at meeting some of this capital cost may be available.

Fossil fuel prices have risen sharply over the past 12 months. Domestic heating oil has risen from around 29 pence per litre in February 2007 to 49 pence per litre in January 2010; gas prices were unsettled throughout this period. The price of woodchips suitable for heating systems varies considerably depending on location, delivery distance and size of order. The range of prices end-users are likely to encounter is between £50 and £90 per tonne delivered. Price per kWh of various fuels is shown in the table.

It is difficult to provide accurate figures on woodfuel production costs in the urban and peri-urban environment, as much of the fuel will come from arboricultural arisings produced during the maintenance of parks, gardens and street trees. A market for this material may offset disposal costs currently incurred by urban land managers.

Practical considerations

If arboricultural arisings are to be used as fuel, space may be required to dry the material down to 30% moisture content (freshly cut wood has a moisture content in the region of 50–55%). A specialised chipper will also be required to produce woodfuel grade chips suitable for use in boilers. These items are expensive and start in the region of £25k. Grant schemes aimed at meeting some of this capital cost may be available. Standards describing the properties of biomass used for fuels have been agreed at European level.

Compared with fossil fuel boilers, biomass boilers are very expensive. As with the fuel-processing machinery, this capital cost may be offset through national or regional grant schemes.

Case studies

There are a number of projects using woodfuel produced from trees growing in the urban environment.

• Bristol City Council has recently installed a 400 kW woodfuel boiler at Blaise Nursery. This boiler is fuelled by wood chips produced from arboricultural arisings generated by council and tree surgery activity.
• The Croydon Tree Station, established by BioRegional, produces around 8000 tonnes of woodfuel each year. The raw material for this fuel is provided from arboricultural arisings produced during the management of Croydon’s trees. This offers the Council significant reductions in its green waste management bill, as well as potentially saving thousands of tonnes of greenhouse gas emissions.
• Thames Valley Energy announced the creation of a new Tree Station that will convert arboricultural arisings and other material into woodfuel, reducing the volume going to the region’s landfill sites or being burned on site.

Forest Research’s Technical Development Services have been involved in the evaluation of fuel-grade wood-chippers and other equipment for a number of years. Although not directly applicable to the urban environment, the Technical Note on small-scale harvesting systems for woodfuel products ^(PDF-398K) may be of interest to those considering establishing a biomass fuel supply chain in the urban environment.

Services

Forest Research has been studying and developing systems associated with the production, processing and end use of biomass and woodfuel for over two decades. This research track record, combined with a proven technology-transfer capability, ensures that Forest Research is well placed to develop a ‘national focus of knowledge and analysis on biomass energy’, as recommended to Government by the Biomass Task Force in October 2005.

As part of Government’s response to these recommendations, the Biomass Energy Centre was launched in April 2006. Managed by Forest Research on behalf of the Forestry Commission and Defra, the Biomass Energy Centre has provided impartial, up-to-date advice and guidance in response to thousands of enquiries and requests for information in its first year.

The Biomass Energy Centre has played an important part in initiatives aimed at developing a sustainable biomass sector, and is integral to the Woodfuel Strategy published by Forestry Commission England in March 2007. The Biomass Energy Centre also works with woodfuel officers employed by Forestry Commission Scotland and the Wood Energy Business Scheme team in Wales. The Biomass Energy Centre continues to develop links and information-delivery mechanisms with regional bodies and local organisations across the UK.