Tuesday, April 14, 2009

Biomass Could Release More Carbon than Coal.

Biofuels are often spoken of as "carbon neutral", meaning that only the same amount of carbon absorbed during their growth through photosynthesis is released when biofuels derived from them are burned. This is not strictly true since the fuel used to run tractors and processing machinery is not costed into this attractive but naive energy balance sheet. Furthermore, the impact of growing fuel crops on the soil itself is ignored, and a new study by the Environment Agency (EA) concludes that if pasture is ploughed over to grow energy crops, it might release more CO2 by 2030 than burning fossil fuels.

However, it is widely thought that peak oil is with us now, meaning that we will never be able to produce more oil than at the height of 2008, and by 2030 biofuels may be in demand simply on the basis of need for any fuel. Only around 20% of the nation's fuel could be provided even if all our pasture land were turned over to crop production and the amount of fuel possible is in any case limited. The only potential source of non-CO2 releasing biomass on this scale is algae, but growing it on the large scale poses considerable challenges, along with hydrothermal plants to convert the algal mass into gas and liquid fuels rather than the palaver of extracting oil from it and converting that into biodiesel by transesterfication as is done from e.g. rapeseed oil. Dried algae can be burned directly in power stations, co-fired with conventional fuel e.g. coal.

According to the EA, waste-wood and medium-density fibreboard (MDF) produce the least CO2 while willow, poplar and oilseed rape the most. This is significant because wood-burning stoves, boilers and even power-stations are seen as vital components of the system by which Brtain's renewable energy targets are to be met. The actual quantity of CO2 released was found to be highly dependent on the particular circumstances, and in the most favourable case a mere 27 kg of CO2/kilowatt hour was produced - 98% less than from coal - which could curb emissions by two million tonnes of CO2 per year. However, in other cases, the overall emissions were higher than they would be from burning coal.

The worst offenders were energy crops planted on permanent grassland, according to the report. Nonetheless, biomass is going to be essential probably well before the target year of 2030 and the efficient use of its energy by combining heat and power production is underlined, as it is a limited resource.

Tony Grayling, who is head of climate change and sustainable development at the EA said: "By 2030, biomass fuels will need to be produced using good practice simply to keep up with the average carbon intensity of the electricity grid."

Related Reading.
"Biomass 'could be major emitter'." http://news.bbc.co.uk/1/hi/sci/tech/7997398.stm

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