Biomass can emit more CO2 per unit of energy than most fossil fuels, according to a report from think tank Chatham House, which warns against assumptions that the organic matter is carbon neutral.
Most renewable energy policies treat biomass as though it has a zero carbon footprint at the point of combustion, the report notes. The EU Renewable Energy Directive, for example, considers only supply-chain emissions from biomass and counts combustion emissions as zero.
The methodology assumes carbon has been absorbed during the growth of the trees or that the timber is harvested from a sustainably managed forest or from one that is growing.
However, these ignore what happens to the wood after it is harvested, and the carbon sequestration that would have occurred if the trees were not chopped down. Also, the efficiency of dedicated biomass plants can be lower than those running on fossil-fuels, depending on their age and size.
The report was written by policy analyst Duncan Brack, who was previously special adviser to former energy secretary Chris Huhne. Black concluded that only wood residues that otherwise would have been burned as waste or would have been left in the forest and decayed rapidly could be considered to be carbon-neutral over the short to medium-term.
The Renewable Energy Association said the report was misleading. Dr Nina Skorupska, chief executive of the trade body, said: ‘This report hangs on the fallacy that it takes decades for a forest to recapture carbon. That isn’t true. A well-managed forest is continually growing and it locks in carbon at an optimal rate.’ The biomass supply chain is monitored in detail to ensure greenhouse gases are cut by at least 60% compared to fossil fuels, though in reality reductions are often closer to 80%, she added.
The UK’s largest power station, Drax, is converting from coal to biomass.
