Utilities are looking for the holy grail: reliable baseload electricity derived from a sustainable, low carbon source and available around the clock, whatever the weather. Biomass, despite the rapid growth in its use, is still not ticking all of these boxes. It has also recently received bad press from environmental and scientific agencies as they question whether it reduces greenhouse gas emissions compared with fossil fuels. In November 2012, the UK's Royal Society for the Protection of Birds (RSPB), Friends of the Earth and Greenpeace called on the UK government to cancel plans to subsidise the burning of trees in coal power stations. The RSPB report 'Dirtier Than Coal?' says that generating power from typical conifer trees results in 49 per cent more emissions than burning coal, and calls on the government to withdraw public subsidy for generating from feedstock derived from tree trunks. Binding climate change targets and government support for low-carbon energy are bringing about widespread use of biomass in electricity. Coal power stations are co-firing biomass, and dedicated biomass facilities are springing up. As the sector develops, so does understanding of the impact of the large-scale use of fuel made from recently living plant material. It is increasingly clear that the diverse forms of biomass come with different life-cycle carbon emissions and varying green credentials.Initial national policies were based on the assumption that biomass energy is carbon neutral. Biomass has been included in energy portfolios as an infinitely renewable energy source like wind and solar, so it has been eligible for the same support. But closer study of the net greenhouse gas benefits of burning biomass shows that a more complex model of carbon accounting is required. This should include factors relating to the type, source and treatment of the biomass, modelling of forest growth, transport of the biomass and timing of emissions and sequestration.
The Drax power plant will no longer be the UK's biggest polluter Credit: Drax Burning biomass to generate a unit of electricity does release CO2. It initially liberates up to twice as much carbon dioxide as coal and up to four times as much as gas used to generate a similar unit of power. The idea of carbon neutrality arises because replacing the combusted vegetation with new trees will lead to the re-absorption of the CO2. The time it takes for a new plant to absorb the same amount of CO2 released during the harvest, transport and combustion of the felled plant is termed the carbon payback. Biomass feedstocks Biomass is available from sources such as: conventional forestry management: thinning, felling and coppicing of sustainably-managed forests and trees conventional agricultural crops and crops grown for use in energy generation. These include short-rotation coppice, such as willow and miscanthus (elephant grass), which can be grown on land unsuitable for food crops biodegradable wastes and residues, including wood processing residues - for example, sawmill residues and parts of trees unsuitable for the wood industry; agricultural waste such as straw and husks; sewage sludge; animal manure; waste wood from construction; and food waste algae, which is not yet viable on a commercial scale but could be an important source of liquid biofuel and solid biomass in the future Biomass generation is booming on the back of climate change legislation and incentives, such as subsidies and FiTs designed to reduce greenhouse gas emissions.