Government research examining emissions from biomass power generation seems unlikely to settle arguments over how polluting it is. But as campaigners and industry continue to argue about whether biomass could cut greenhouse gas emissions, the government has ambitious plans to increase the amount in the UK's energy mix. 

Biomass - carbon neutral power?

Plants, trees and crops can all be burned to generate electricity. One advantage of such 'biomass power' is that the greenhouse gases emissions from burning plants get reabsorbed as more plants grow. In theory, this means biomass power could be effectively carbon neutral.

This should make biomass an attractive option for the government, as it aims to reduce UK greenhouse gas emissions 80 per cent by 2050. The government has outlined proposals to get up to 11 per cent of the UK's total primary energy demand from biomass by 2020, and last week passed an amendment adding new subsidies for biomass generation, if it can emit 60 per cent less than fossil fuels. 

Calculating biomass emissions

That's all fine in theory, but projecting actual biomass emissions is quite complicated, and very dependent on assumptions about what is going to be burned and where it comes from. 

For example, one of the main sources of biomass is wood. Trees take a long time to grow, which can produce a significant time lag between emissions being released and being absorbed. This has to be factored into calculations about emission reductions. Or, if wood is burned that otherwise would have been used for building, it could also result in extra emissions.

This is why the Department of Energy and Climate Change (DECC) has developed a calculator, which considers twelve different scenarios for producing and burning biomass and works out the associated emissions. But startlingly, the preliminary results suggest biomass generation actually produces more emissions than burning coal in five out of the twelve scenarios. 

Calculation controversy

This issue hasn't come out of nowhere, as calculating biomass emissions has previously proved controversial. 

Environmental NGOs released a report last year claiming biomass can be "dirtier than coal", largely based on a paper by Princeton academic Timothy Searchinger. It argues that DECC's bioenergy strategy doesn't adequately account emissions from biomass, meaning the government is "significantly overestimating the climate benefits of generating electricity from wood".

Searchinger actually calculates that over a 20 year time period, the emissions from power generation using wood are 80 per cent higher than from coal - meaning biomass is obviously far from being a carbon neutral power source.

But the analysis is based on using whole trees as biomass. This prompted a firm response from the Forestry Commission's Biomass Energy Centre, which says Searchinger's paper "bases its main contention on the (rejected) worst case scenario, and the "Dirtier than Coal" report appears to base its fundamental arguments on this misleading and uninformed contribution". 

Trade body the Renewable Energy Association (REA), which represents the biomass lobby, says Searchinger's paper overlooks the fact that selling whole trees as biomass "would not be financially viable" for landowners. By-products from forestry such as sawdust, bark and thinnings - known as residues - are more likely to be used, as they can't be used for anything else. The market should largely take care of excluding the types of materials Searchinger envisages being used for fuels, REA argues. 

Continuing controversy

The new calculator captures this disagreement. It suggests that burning biomass from residues produces less emissions than burning coal or gas, while burning whole trees produces far higher emissions than burning fossil fuels. 

But if the government was hoping to bring some harmony to the debate, it seems to have failed. Friends of the Earth says the calculator provides further evidence that burning biomass can be dirtier than coal, and that it "changes everything" when it comes to thinking about the future of biomass in the UK's energy mix. It argues the calculator should be used to exclude high polluting forms of biomass from renewable energy subsidies. 

But the Renewable Energy Association's Back Biomass campaign says the calculator is still in the development phase and it expects "fundamental revisions" before the final version is released. A spokesperson tells us:

"Far from 'changing everything', Friends of the Earth is once again using data that doesn't reflect the real world of biomass supply chains and forestry governed by strict Sustainability Criteria."

So the argument looks set to rumble on until it is clear how the final version of the calculator and the scenarios it envisages fit into the government's bioenergy strategy. That probably won't be any time soon. 

If the government can guarantee residues will be used - not whole trees - then biomass generation will presumably help it achieve climate goals. But the research does highlight that sometimes calculating emissions can be much more complicated than it first seems.