The Burning Question: is biomass really sustainable?

Drax, the biomass fuelled power station in North Yorkshire was in the news again earlier this year. This time it was over from where it sources its wood pellets and the wider environmental impact that may have.

Within the BBC article and on Drax’s own website the company is at pains to point out that the biomass they use “is sustainable and compliant with relevant legislation”. But it is possible to be legal and still do harm. So the Grantham Centre thought this would be a good opportunity to address some of the issues around the burning of biomass for power generation and whether it has a place in a sustainable electricity generation mix.

Woody biomass, whatever its final form, typically starts life from two main sources, either end-of-life or virgin wood. End-of-life refers to waste or scrap wood from manufacturing processes that would otherwise end up in landfill. Virgin wood is harvested for the purpose of burning. It is the virgin wood used by Drax which BBC Panorama programme alleges can come with questionable ecological credentials.

What are the supposed benefits of biomass fuel?

The end goal of renewable power is to reduce the quantity of greenhouse gases which end up in the atmosphere. This can be achieved by zero operating emission technologies like wind or solar. Substituting fossil fuel burning facilities for those that burn biofuels could also help reduce greenhouse gas emissions.

When accounting for carbon these biomass plants are permitted to declare themselves low or zero carbon. This is because carbon dioxide will be reabsorbed by regrowing the trees or other biocrops used. This “Biogenic Carbon” was originally removed from the atmosphere by photosynthesis and, under natural conditions, will eventually cycle back to the atmosphere as CO2 due to degradation processes.

So the argument is that these power stations don’t cause any more emissions than the biomass would have done if it had been left to rot, but have the added benefit of generating electricity along the way. However, accelerating this process means that these emissions happen much sooner and more quickly than in the natural process.

The confusing rules behind carbon accounting and biomass

The complex international carbon accounting rules mean that when the growing and felling happens in a different territory to the burning then it impacts on the carbon accounts of more than one country.

In the UK government’s consultation on its 2023 Biomass Strategy, the paper recognises the conflicts and contradictions that exist in the biomass value chain.

Carbon life cycle assessments (LCA and carbon accounting: Concerns were raised about the accuracy of carbon accounting, and whether carbon emissions are accurately reflected in the correct sectors. (e.g., whether emissions from land use change can be verified to be accounted for in the Land Use, Land Use Change and Forestry (LULUCF) sector for imported feedstock).
A full LCA [Life Cycle Analysis] accounting for temporal and spatial variations in carbon emissions was required by some stakeholders. The need to introduce accounting for negative emissions in GGR [Greenhouse Gas Removal] technologies, such as BECCS [Bio Energy, Carbon Capture and Storage], was also raised.

Grantham Centre’s own Green Watch team has concerns about the UK’s reliance on biomass and future BECCS technologies in the delivery of its net zero targets, particularly the use of virgin wood.

Over a long term combusting bio materials might be near neutral in emissions. But the timescales involved do not align with the carbon budgets required to meet the Paris Agreement.

This graph is based on emissions rates data published by the UK Government’s Department for Energy Security and Net Zero. It shows for every tonne of wood burned there are approximately 1.9 tonnes of CO2 equivalent emissions. Some come directly from the combustion process and others from the harvesting, processing and transport.

A tree planted simultaneously will slowly sequester carbon from the atmosphere taking approximately 35 years to reach maturity. By this time it will have captured nearly 1.7 tonnes of CO2e, leaving a residual 200kg.

This disparity can be addressed by planting an additional 14% of woodland per unit area that is felled for burning. However, this does not solve the time delay issue. As the old saying goes: the second best time to plant a tree is today. But in this scenario today is too late.

End-of-life vs virgin wood

An alternative to burning virgin wood is to take waste that would otherwise need to be disposed of in landfill. The argument here goes that this material will degrade overtime, releasing carbon dioxide and methane. So burning it is a way of disposing of that waste stream and releasing energy from it with no additional greenhouse gas cost.

Although studies, such as this one from Eunomia in 2011, have been conducted into the volumes of greenhouse gases emitted by waste in landfills, there are many variables that make this simple comparison difficult. The Grantham Centre would welcome opportunities to investigate this further. This way we could build a clearer picture of the role end-of-life wood should play in our future energy mix.

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Main image credit: Getty Images / BBC