Energy from biomass residues - the present opportunity
Biomass energy has had its share of successes and failures, and now the industry must learn from its past by tapping into the free resource of waste wood - writes renewable energy researcher Dr. David Fulford of Reading University.
Successes and Failures
Certain sectors of biomass energy are commercially successful, particularly landfill gas and sewage gas. Some water authorities have installed electric generators in many of their sewage works to use the gas produced from digestion. The new Thames Water plant in Reading is a good example (1 MW from a population of about 230,000). The direct combustion steam generation plants built by the Fibrowatt Group and now run by EPR in the East of England, and more recently Scotland, to use chicken litter and straw have also proved successful.
All these systems generate electricity from biomass in a sustainable way, but receive very little publicity. There may be squeamishness in the media about such energy-from-waste plants. The biomass to energy plants that have received the most publicity have unfortunately been the ones that have subsequently failed, such as the ARBRE plant near Leeds, and the cattle dung digester at Holsworthy in Devon.
ARBRE was an 8 MW (net electrical) fluidised bed wood gasification system running gas turbine electric generators using short rotation coppice wood purchased from local farmers, supported by a EU THERMIE grant. The gasifier was built in 1998 by TPS of Sweden. However, the system experienced technical problems and the operators could not run it on the grid. The financiers were not willing to fund further tests and modifications, so withdrew support in 2001. Various attempts at reviving the plant seem to have failed.
The 2 MW (net) Holsworthy biogas plant was built in 2002 by Farmatic Biotech Energy, who already had several similar plants in Germany. The German government has an electricity tariff scheme that makes farm-scale generation look fairly profitable. Low electricity prices in the UK, combined with stricter regulations on processing wastes, meant that the plant ran at a loss, so the financiers forced its closure. A consortium of local farmers tried to run the plant, but also failed to make a profit. It has now been purchased in 2005 by Summerleaze Group, who are well experienced in running landfill gas sites.
There are examples of the use of both woody biomass fuels and anaerobic digestion that are commercial success stories in the UK.
The most obvious way to generate energy from biomass is direct combustion of either woody materials or wastes to generate heat. The steady, but quiet, growth of new institutional wood heating systems in various parts of the country can be seen as a success. Many councils are beginning to see the benefits of replacing old boilers in schools, office blocks and council flats with ones that run on wood chips or wood pellets. The best example is that of Barnsley Council, who replaced three such boilers in the last two years, with a total rating of 970 kW. They use wood from tree pruning and other woodland management wastes that were otherwise put in landfill, which won them an Ashden Award for renewable energy generation this year. The Marches Wood Energy Network Ltd has been installing boilers for organisations such as Worcester County Council and Telford and Wrekin Council as well as farms and small businesses. Similar companies are building similar such in many other parts of the UK, such as Sussex, the English/Scottish border, Yorkshire and Wales.
A supply system must also be in place to ensure a steady and convenient supply of wood chips. Barnsley Council have set up a wood supply scheme alongside the boiler installation. Midlands Wood Fuel Ltd supplies wood chips on a contract basis to customers of The Marches Wood Energy Network Ltd. Other groups, such as the BioRegional Development Group (another Ashden Awards winner) in co-operation with the London Borough of Croydon, have set up a wood chip supply business to make use of wood residues from a tree surgery business and the management of the borough's parkland and woodland management work. TV Bioenergy Ltd (a 2005 Ashden Awards winner) is a group that is setting up a wood chip fuel supply business in the region West of London.
Woody biomass fuels can also be used to generate electricity either by direct combustion or via gasification. Slough Heat & Power, part of Slough Estates plc, have been running a CHP system using fluidised bed combustors since 2001. They have used wood from pallets and packaging from the waste stream from the commercial operations on the estate. They are also a major customer for wood chips from both BioRegional and TV Bioenergy.
Anaerobic digestion of vegetable and farming wastes is taking longer to get commercialised. The farm-scale plants built in the 1980s have mainly gone into disuse. However Greenfinch Ltd have recently built a 5000 tonne a year plant in Ludlow, Shropshire to process kitchen and garden household wastes collected by South Shropshire Council. The system will run an engine to generate electricity and heat to run the process. As political pressure increases to reduce the putrescible wastes going to landfill, such schemes will be required by most councils. Other companies are close to bringing similar technology to commercial operation, such as Bioplex Ltd.
These examples demonstrate the way that biomass sources are becoming commercial in the UK. Firstly, they usually use a waste stream as a source of fuel, as it has a negative cost (people pay to have it taken away). This overcomes
the poor benefit-to-cost ratio of biomass energy systems in the absence of any subsidy support. This can be compared with solar pv, which has an even worse benefit-to-cost ratio, but is heavily (if erratically) subsidised in the UK.
The disposal of waste in the UK also seems to be a sensitive political issue (both locally and nationally), as landfill is being made more expensive and public pressure against incineration is increasing, so using a waste stream is not an ideal answer.
The second feature is that these initiatives are small-scale and local. The larger-scale, centrally inspired schemes are the ones that have failed. However, such small-scale and local schemes tend to be "under the radar" of government planners and the national media, which is why these types of biomass energy project tend to be ignored.
Perhaps the biomass industry should learn the lesson from the wind industry. In the late 1980s, wind turbines were small and seen as insignificant in terms of energy production. The British Wind Energy Group with support from UK DTI and EU installed two 2 MW prototype systems in Carmarthen bay (horizontal axis and vertical axis designs), both of which failed due to unforeseen technical problems. Vestas, a Danish Company, built up their business using small-scale (125 kW) machines, installing them for local communities in Denmark. In recent years, Vestas have bought out BWEG and now make 2 MW horizontal axis wind turbines as a standard product (their range goes up to 4.5 MW). An obsession with larger-scale systems not only lost the UK a place in the development of this technology, but also prevented us from being a world leader with the innovative vertical axis design that was being developed in the 1980s.
DTI missed one opportunity for the development of small-scale local biomass systems in 1995 in the 3rd NFFO call, when small-scale wood gasification systems (less than 1 MW) were dropped from the scheme. Let us hope that the outcome of the Energy Review is not to stifle the new initiatives that are emerging in the biomass energy field, but to encourage them.
More information on the work of the Energy Group at the University of Reading's School of Contruction Management and Engineering, of which Dr. Fulford is a member, can be found at www.reading.ac.uk/energy