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July 23, 2014 4:17 pm
Burning wood to generate electricity can produce as many of the carbon dioxide emissions responsible for climate change as a coal-fired power station, an energy department study seen by the Financial Times has found.
But the report also shows that under certain conditions it is possible to burn some types of wood waste in a way that produces fewer emissions than either a coal or gas power plant.
The report, co-authored by Professor David MacKay, the department’s chief scientific adviser, will add to the debate over the subsidies paid to power stations such as Yorkshire’s Drax, which is converting some of its boilers to burn wood pellets imported from the US instead of coal.
The subsidies are aimed at helping the UK meet EU targets requiring the bloc to obtain 20 per cent of its energy by 2020 from renewable sources, such as wind, solar or biomass, which includes wood and other plant materials.
Power companies receiving the subsidies are supposed to make sure they use biomass in a way that produces fewer carbon emissions than a gas or coal plant.
But environmental groups and some academics say the current system for measuring the impact of burning biomass is flawed because it does not fully account for how a forest’s ability to act as a natural store for carbon is reduced when, for example, trees are harvested faster to meet extra demand for wood pellets.
A number of distinguished US scientists wrote to Ed Davey, the energy secretary, earlier this year urging him to abandon the “misguided” subsidies, which they said would not reduce carbon emissions and were threatening important native forests.
The energy department study by Prof MacKay, which has taken more than two years to complete and was due to be released today, is designed to give a better picture of how overall emissions are affected by burning biomass.
The report shows there is a huge difference in emissions produced depending on the type of wood used and its source.
For example, using wood residues from a plantation that would otherwise be burned on the roadside is much better than using larger bits of wood waste that would otherwise be left to rot on a forest floor, which can produce as many emissions as a gas-fired power station.
Burning wood from a naturally regenerated forest that would otherwise be left to grow and store carbon for 40 years can produce as many emissions as a coal-fired power station, it says.
UK power companies using biomass will need between 9m and 16m tonnes of wood fuel a year by 2020, the report says, but the UK only harvested 5.3m tonnes of wood in 2012.
That means Drax, a leading wood pellet importer, will probably have to keep obtaining fuel from big markets such as North America, where 210m tonnes were harvested in 2012.
Prof MacKay said the “most promising” form of biomass was forest residues currently being burned as waste at the roadside and it appeared that North America had plenty of this type of fuel to supply the UK.
While some of the 29 scenarios assessed in the report showed some types of biomass burning could produce more emissions than a coal plant, he said, it was not possible to say if this would actually occur.
“This work is not a detailed assessment of which scenarios will come to pass, it’s not predicting the likelihood of the alternative scenarios,” he said.
“The industry itself has expressed a commitment to sourcing sustainable biomass and we view this as a tool to help them do that.”
Dorothy Thompson, Drax chief executive, said she welcomed the report because it made a good contribution to the general public’s understanding about the use of biomass.
Asked how much of Drax’s wood pellets came from roadside waste the report identifies as being most sustainable, she said: “Definitely some of our supply chain includes waste residues that would have been burned on the roadside.”
Kenneth Richter, Friends of the Earth bioenergy campaigner, said the report showed how important it was for the government to now introduce full carbon accounting for biomass in the UK.
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