Three out of the six 630 MW electricity generation units at the Drax power station have been converted to burning biomass in the form of wood pellets (BiofuelWatch, 2015; Drax, 2016). The generation from these units is now counted in the UK’s electricity generated from renewable sources, on the basis that wood is a renewable source because the CO2 generated when it is burnt originated from the atmosphere as the wood is grown. CarbonBrief (2015) investigated this, concluding that it was feasible to generate electricity within DECC’s definition of renewable energy but that other factors such as the size of trees being extracted and changes in land use may result in significant emissions.

As described in CarbonBrief (2015) in 2013 the UK got 5% of its energy needs from renewables of which biomass is reported to represent around one third. UK power plants used 3.4 million tonnes (Mt) of wood pellets and the UK was the world’s largest importer of wood pellets in 2013 – importing 3.9 Mt (expected to rise to 5.5 million tonnes in 2015) representing 28% of the global market. Drax is now the UK’s largest consumer of wood pellets at 7.5 Mt per year - more than half the global trade in wood pellets, increasing to 10 Mt per year when a fourth unit gets converted (CarbonBrief, 2015; Drax, 2016). In 2015 Drax reported generating 12% of the UK’s renewable electricity (Independent, 2016).

The debate around the status of Drax wood pellet burning generally takes place in the context of the DECC guidelines (DECC, 2013). Under the guidelines Drax electricity generation from wood pellets is treated as renewable and hence qualifies for RO (renewables obligation) certificates in the same way as wind and solar qualify – anticipated to amount to £660 million in 2016 (BiofuelWatch, 2015). The RO requirement is for less than 2851 kilogrammes of CO2 equivalent per megawatt hour (kg CO2(e) MWh-1) of electricity generated. This is planned to reduce in steps to 180 kg CO2(e) MWh-1 in 2030. Table 1 below shows estimates from various sources.

Table 1 - Carbon emissions from various sources.

Energy Source               Emissions / kg CO2(e) /MWh

Coal                                 1018

Natural Gas                      437 (1)

DECC biomass limit        285

Drax biomass                   122

Wind                                  3 to 41

Figures from Stephenson and Mackay (2014) and CarbonBrief (2015).

(1) This is just for burning natural gas, and does not account for the effect of ‘fugitive emissions’ when gas is extracted.

For biomass DECC rules dictate that these figures are calculated based on lifecycle analysis (LCA) which includes transport, processing and agricultural inputs such as fertilizer etc and ‘direct’ land use change. The CO2 emissions from burning the biomass are ignored because they are assumed to be balanced by CO2 extracted from the atmosphere as replacement trees are grown. Thus, on the face of it, while emissions exceed those from traditional renewable sources, significant savings seem possible with the added advantage of not being intermittent and weather-dependent (for example wind generation in the UK was unusually low in 2016). More details of the RO calculations are given in DECC (2015).

Most controversy around these assessments turns on the question of so-called ‘counterfactuals’ (Stephenson and Mackay, 2014) – i.e. what would have happened if Drax was not using wood pellets – which is not included in the LCA as prescribed by DECC (see above). For example, forest expansion might be faster, dead or waste wood may be left to decompose in place or be burnt either outside or in local incinerators, land may not be repurposed for wood pellet production (eg in the Amazon jungle), the wood may be used for other purposes. The carbon cost of these scenarios is very dependent on where the wood comes from. Drax reports that 81% of its wood pellets come from ‘sawmill residues, forest residues and thinnings’ (CarbonBrief, 2015). In 2017 23.4% was from thinnings (, 2017). While sawmill residues are relatively uncontroversial and residues are meant to represent wood that would otherwise be left to rot or be burnt in-situ, the definition of thinnings can include whole trees and lacks precision about the types of trees being taken (CarbonBrief, 2015).

To address this David Mackay’s team (working for DECC) created the Bioenergy Emissions and Counterfactual calculator (BEAC) to estimate the carbon emissions from each source, looking specifically at scenarios in the southern United States where around 58% of the pellets originate (Stephenson and Mackay, 2014). This effort did not attempt to match Drax consumption to these scenarios but DECC commissioned a report to look at this (Ricardo Energy and Environment, 2014). The report, based on a questionnaire and literature review, attempted to match Drax data on American wood pellet consumption to the scenarios identified in the BEAC model (and some additional scenarios) to estimate any emissions. The report then went on to consider how likely various ‘high GHG’ (high greenhouse gas) scenarios were, both in Canada and the South-East United States, finding that several were likely. Of the many estimation problems here, the existence of more than one counterfactual for a given scenario (eg forest expansion vs reversion to grassland) with widely different results and the fact that many scenarios were not recognized by actual timber producers are significant. The most important factor considered was the effect of wood pellet burning on the growth of North American forests (i.e. the change in carbon storage in North American forests over time) where it was concluded that some scenarios could result in more emissions than coal.


A considerable proportion of the UK’s reported renewable electricity generation (12% in 2015) comes from wood pellets burnt at Drax. These wood pellets represent a large proportion of world production and this practice is being subsidized under the RO regime by hundreds of millions of pounds a year. While wood pellet burning at Drax has a higher carbon footprint than traditional renewables such as wind, it still falls well within DECC guidelines using LCA prescribed by DECC. Unlike traditional renewables there is considerable uncertainty about the total carbon emissions of wood pellet burning when alternative scenarios are considered.

Robin Speed, WinACC August 2017


BiofuelWatch (2015) Open letter - End support for Drax power station

CarbonBrief (2015) Investigation: Does the UK’s biomass burning help solve climate change?

DECC (2013) Government Response to the consultation on proposals to enhance the sustainability criteria for the use of biomass feedstocks under the Renewables Obligation (RO)

ADECC (2015) The Renewables Obligation for 2016/17 [Online]. (2016) Renewables: Better Together (2017) ‘Reporting’ Sustainability

Independent (2016) Green energy: How one power plant chips away at the UK's carbon footprint

Ricardo Energy & Environment (2014) Use of North American woody biomass in UK electricity generation: Assessment of high carbon biomass fuel sourcing scenarios

Stephenson A L and Mackay D J C (2014) Scenarios for assessing the greenhouse gas impacts and energy input requirements of using North American woody biomass for electricity generation in the UK


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