Regulators are catching up with doubts around the merit of burning wood and other solid biomass as a large-scale solution for cutting carbon emissions, which may see the renewable fuel dumped – along with diesel and conventional biofuels.

Burning biomass is supported in the UK as a low-carbon renewable fuel which can cut carbon emissions compared with burning gas and coal. Britain’s tough carbon emissions targets have made the country a massive importer of wood. Drax, the biggest biomass power plant, alone imported 6.5 million tonnes last year.

However, there are flaws in the assumption that it is carbon neutral. Burning wood obviously emits plenty of carbon dioxide. Whether it is overall carbon neutral will depend on sophisticated lifecycle analysis of the feedstock. In addition, biomass burning leads to particulate (fine smoke) emissions, which could impact air quality when burned at scale in cities.

Regarding its climate impact, supporters of burning biomass base their carbon emissions estimates on rather selective accounting, where we can take the example of Drax.

Drax reports its biomass carbon emissions as 34 grams per megajoule (MJ), a fraction of gas and coal. The trouble is, that figure counts the emissions from actually burning the fuel as zero – by assuming this process is entirely carbon neutral. In other words, Drax assumes that all the CO2 coming out of its smokestacks is reabsorbed by trees growing in the plantations where the company harvests wood. The question whether all of Drax’s carbon emissions are offset in this way, over the next several decades, is too complicated to wish away like this.

We also should not ignore the impact of burning wood on air quality. Figures demonstrating particulate emissions shouldn’t surprise us. Power plants at Drax, Wilton and Lynemouth all burn biomass, and are Britain’s 5th, 6th and 7th biggest point sources of very fine particulate matter (called PM2.5), as of 2014, show the latest available data from the UK’s National Atmospheric Emissions Inventory.

Particulate matter refers to smoke particles so small that they can penetrate the lungs. PM2.5 is one of the smallest, and most dangerous, of this class of air pollutants, according to the World Health Organisation, and is responsible for cardiovascular and respiratory diseases including lung cancer.

Credibility concerns should not be simply ignored because wood is a renewable fuel, or because of assumptions that it is carbon neutral, and regulators do appear to be catching up.

Regarding its climate impact, the European Commission last November proposed changes to the EU Renewable Energy Directive, requiring new biomass installations for the first time to achieve certain carbon emissions savings, as well as meet other “sustainability criteria”, catching up with existing rules controlling the use of biofuels.

Those draft proposals are presently under discussion by the European Union’s governments and the European Parliament. And this month, the environment committee of the European Parliament votes on an amendment to the Renewable Energy Directive that would ban subsidies for co-firing biomass and coal, given concerns that such support is effectively propping up coal generation in ageing power plants.

Regarding air quality impact, the Mayor of London on Wednesday last week stated that he: “wants to reduce emissions from wood burning through improved education about the types of fuel that should be used and when they should be used. He also wants a stricter set of emission standards on future sales of wood burning stoves to tackle this source of pollution.”

That followed new emissions monitoring which showed that every area of London exceeded WHO recommended guidelines for PM2.5, and that 7.9 million Londoners lived in areas exceeding the guidelines by at least 50 per cent. Of course there are other sources of PM2.5, including tyre wear and diesel cars – also once touted as a low-carbon technology.

The European Commission and London Mayor are common sense regulator moves which draw more attention to well-understood carbon emission and air quality impacts of burning biomass. The dieselgate scandal which engulfed Volkswagen showed the dangers of ignoring well-understood problems – in that case the NOX emissions associated with burning diesel – in favour of other policy priorities, in that case its superior fuel efficiency. The particulate and carbon emissions associated with burning biomass are also well understood, if complex, and regulators must reflect these flaws when writing rules supporting its use as a green renewable fuel.    Send article as PDF   
  • Tags:
  • Biomass ,
  • Britain ,
  • CO2 ,
  • Diesel ,
  • Drax ,
  • NOx ,
  • PM2.5 ,
  • power generation ,
  • renewables ,

Leave a Reply