Draft PPS 18: Renewable Energy
Annex 1 Technology: Fuel Sources
B11. Although this section deals with the planning implications of the energy conversion plant itself, and not of the fuel supply, some reference to the different sources is important. There are five main sources of biomass fuel:
- material from forestry harvesting;
- material from timber processing;
- agricultural residues;
- energy crops; and
- waste streams.
A large biomass scheme may use fuel from one or more sources, in order to ensure security of supply.
B12. All the ‘dry’ biomass fuels listed above have a broadly similar gross energy content. How much of this energy content can be exploited depends on the process, the technology employed, and the moisture content. Some direct combustion technologies can use fuel with a high moisture content (up to 50%), but gasification and pyrolysis generally require fuel to have a moisture content of less than 30%, and fuel may have to be dried as part of the process.
B13. Biomass material from forestry harvesting, agricultural residues and energy crops may have a similar supply strategy. Most biomass plants require fuel to be in a chipped form, and chipping often occurs close to where the crop is grown. Once chipped, fuel tends to deteriorate fairly quickly, hence fuel in long term storage (e.g. inter-seasonal) is usually left in the ‘as harvested’ state, either in situ, or in converted agricultural buildings. Chipped fuel is often loaded directly onto lorries for delivery to the energy plant. Generally, only short term storage facilities are provided at the energy plant, and regular fuel deliveries are needed. A useful rule of thumb for fuel deliveries is two 38 tonne lorry deliveries per day, per MW thermal continuous heat input. Thus, a 250kW boiler operating for half of the time (a duty cycle of 50%), supplying heat to a leisure development would require 1 or 2 deliveries a week, and a 10MW plant producing electricity continuously would require around 20 deliveries a day.
B14. Existing large coal fired power stations can use biomass to augment the traditional fuel. This is known as ‘co-firing’. Although this may not have implications for the planning system, it is an important way of increasing the critical mass of producers in the fuel supply chain.