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renewable energy > features > renewable options 3: biomass

Renewable options 3: Biomass
Bringing biomass up-to-date

Posted: 01 Nov 2000

by David Hall

There is now nearly-universal recognition that wood and other vegetation is an important source of energy. Altogether biomass supplies 14 per cent of all the energy used in the world. In developing countries it is the single most important source providing more than a third of all the energy used.

In total, the use of biomass is not declining, though growing world population means that there is less of it to go round on a per capita basis. Indeed, the World Bank stated in 1996 that "energy policies will need to be as concerned about the supply and use of biofuels as they are about modern fuels."

In this situation, it is crucial to ensure that the mostly traditional use of biomass is carried out in the most environmentally and health-friendly way, using improved stoves, charcoal kilns, steam plants and other methods.

At the same time biomass is being actively promoted in a number of countries as an environmentally friendly fuel, which does not increase the level of carbon dioxide in the atmosphere, and is low in sulphur, so that it does not contribute to acid rain. This is happening, for example, in Scandinavia, Austria, USA and UK, where regulations, carbon taxes and incentives are promoting biomass to high per capita use levels.

Indeed, a number of studies by the International Intergovernmental Panel on Climate Change (IPCC), the International Energy Agency (IEA), Greenpeace and Shell Oil have all predicted a major role for modernised biomass in the next century.

© Mark Edwards/Still Pictures

Of course, biomass is not a perfect source of energy: but it is probably "more perfect" than most other sources. To be available in reasonable quantities for community and industrial use, it requires land for agriculture and forests, as well as transport and conversion into the solid, liquid and gaseous fuels.

All these operations must be part of a sustainable cycle which produces net benefits to local people, the country and the global environment. This is a stiff requirement which is hardly met by any other energy system where life cycle analysis and external costs of pollution and degradation are usually not considered. At least in the case of biomass it is possible to ensure long-term sustainability, with the right incentives for sustainable production and use. Groups in the United States, Europe, India and Brazil have proposed guidelines for producers and users to encourage communities and agroindustries to accept the necessary disciplines.

In the past, questions have been raised about the sustainability of biomass energy systems. These have queried the net energy benefits, the food versus fuel priorities in land use, the extent of land required to produce sufficient quantities of energy, the nutrient balances, and the effects on biodiversity. All these concerns have been answered over the last decade or so by small and large scale bioenergy systems from all around the world.

Successful examples have come from Austria with district heating, Brazil with sugarcane ethanol and industrial charcoal plantations, China with family biogas digesters, India with mixed plantations for gasifiers for local electricity production, Sweden and Finland with combined heat and power from forest residues and now new large scale gasifiers, the United States with industrial scale electricity production using all types of residues, and from Zimbabwe, Kenya and Malawi, where ethanol is being produced for transport fuels. Hopefully in the next century ethanol and methanol will be produced from woody plants.

It should, in the future, be possible to adapt such experiences to local requirements in many different settings, although this is often easier said than done because of the very diversity of options and requirements.

With the onset of the Kyoto Protocol to ameliorate global warming the future use of biomass takes on a wider role. It has been recognised, for at least a decade, that growing and using biomass on a continuous basis as a substitute for fossil fuels has clear advantages compared to using the biomass solely as a means to sequester (store) carbon to create a carbon sink.

The biomass is grown perennially to generate energy so that environmental benefits such as soil conservation and biodiversity protection accrue in comparison to annual crops. In addition, rural communities gain jobs rather than losing them when land is removed from productive use, simply to sequester carbon.

Naturally, where mature forests exist they should be conserved as both carbon sinks and deposits of biodiversity. Also, where biomass energy plantations are grown probably on degraded and excess arable land they must follow ecological guidelines to serve the same purpose.

David Hall, Professor of Plant Biology at Kings College, London, contributed this article shortly before his death in 2000. He was author with Dr H. N. Ravindranath of Biomass, Energy and Environment, published by Oxford University Press (1995).

Poultry power

The largest biomass-fired electricity generating plant in Europe has now begun commercial operation at Thetford, Norfolk, UK.
© Fibrowatt
Built at a cost of some �69m ($110m), the Thetford plant produces 38.5 MW of electricity (enough to supply 70,000 homes) from burning poultry litter (a mixture of straw, wood chippings and poultry droppings) to generate steam.

The plant and two smaller plants operated by the same company, Fibrowatt, are so far the only generating plants in the world using this fuel. Over 300 gigawatt-hours of energy will be exported annually to the national grid.

The Thetford plant will burn up to 450,000 tonnes of poultry litter per year. A nitrogen-free fertiliser, rich in phosphates and potash with trace elements, is produced as a by-product of the clean-burning technology. Among the environmental benefits are:

  • The reduction of CO2 emissions by recycling carbon rather than producing new CO2
  • The elimination of methane emissions from stored poultry litter reduces greenhouse gases
  • Levels of noxious gases released, such as sulphur dioxide and nitrogen oxides, are a fraction of those emitted by coal-fired power stations
  • Farmers are paid more for drier poultry litter an incentive for them to improve the conditions under which they rear their birds.

The project has been financed by a consortium of banks and the debt will be repaid over 12 years on a straight amortization basis at a commercial interest rate.

Peter Fraenkel

Contact: CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, UK.

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