Words by Andrew Welfle, University of Manchester
The UK’s greenhouse gas (GHG) emission reduction and renewable energy generation targets have led to increased focus on low carbon renewable energy technologies to decarbonise the energy sector. Bioenergy is energy pathway that provides a major contribution to the UK’s current renewable energy mix and increased generation is targeted. UK Government energy statistics for 2015 (BEIS, 2016) showed that renewable energy contributed 22.3% of total UK power generation (bioenergy reflecting 13.7% of total power generation); 5.6% of total UK heat generation (bioenergy reflecting 5.3% of total heat generation); and 4.2% of total UK non-air transport fuel energy (all from biofuels). Large power stations fuelled by woody based materials from the forestry sector are the predominant contributor of bioenergy generated in the UK. The biomass fuel demand for these power stations is large and already far beyond the availability of woody biomass available from UK forests (Welfle et al., 2014). As a result the UK has a growing network of international supply chains importing biomass fuels such as pellets sourced from North American forests. The UK bioenergy sector currently consumes about 25% of global forest-based wood pellet production, making it the largest consumer worldwide. Over 90% of these wood pellets are imported making the UK the largest importer of wood pellets, reflecting over 40% of the globally traded feedstock (FAO, 2016).
For bioenergy to be a viable low carbon renewable energy option and replace fossil fuel generation, it is fundamental that the energy generated provides genuine reductions in GHG emissions. As a result there has been much discussion about the accuracy of GHG accounting systems and applied methodologies for forest-based bioenergy. As the scale of traded biomass has increased and international supply chains have become more complex, the scrutiny of the GHG impact of bioenergy has rightly also increased.
GHG Accounting Methodologies – Where Does Bioenergy Fit?
Bioenergy is an attractive renewable energy option for the nations like the UK as it can be easily transported and stored, is compatible with many elements of existing energy infrastructure and the important notion that it delivers carbon neutral energy – CO2 emitted through the combustion of the biomass, balances with the CO2 taken up by plants/ forests as they have grown. This concept of carbon neutrality has become the focus of much current debate; and therefore demonstrating that bioenergy pathways deliver energy with reduced GHG emissions compared fossil fuels is a barrier needing attention if bioenergy is to be truly regarded as a low carbon renewable energy.
The Intergovernmental Panel on Climate Change (IPCC) oversaw the development of the universally adopted methodologies and guidelines for accounting GHG emissions (IPCC, 2014, 2006). Within this framework nations are required to individually account all their emissions within a series of GHG inventories, including emissions from: Energy Generation; Industrial Processes & Product Use; Agriculture; Land-Use & Land-Use Change (LULUCF); and Wastes. Using a case study example of a bioenergy pathway where the UK generates bioenergy from pellets imported from Canada, within the IPCC’s accounting framework this bioenergy pathway will leave a different GHG footprint in both the UK and Canada, but also a different footprint across each GHG inventory within each country. Figure 1 has been developed to provide a stylised demonstration of how the GHG inventories of both the UK and Canada may be impacted through the UK generating bioenergy from imported Canadian forestry biomass.
Figure 1: Stylised Representation of the Life Cycle GHG Emissions Resulting from the Generation of UK Bioenergy from Resource Imported from Canada: Highlighting the Potential Emission Footprint as Attributed to UK & Canadian GHG Inventories under the IPCC GHG Reporting Framework
The bioenergy pathway documented in Figure 1 shows that overall Canada will benefit in GHG accounting terms as a consequence of producing biomass pellets for export. Within Canada’s LULUCF GHG Inventory the production of biomass for bioenergy can generate large-scale uptake of CO2 from the atmosphere. The biomass pellets (classified as wood products) represent a sink locking up carbon from the atmosphere, whilst the growth and regeneration of forests following successive harvest cycles provide a further mechanism for storing carbon. Any energy expended in Canada in producing, processing or transporting the biomass will generate GHG emissions accounted within Canada’s Energy GHG Inventory, and emissions released as a result of the degradation/ management of wastes will be accounted within Canada’s Waste GHG Inventory. The Canadian biomass pellets may then be exported where under the IPCC’s accounting framework any transport ‘bunker fuel’ emissions are accounted but not attributed to any national GHG inventories (UNFCCC, 2017).
Once landed in the UK any further energy expended transporting or processing the pellets will generate emissions allocated to the UK’s Energy GHG Inventory. Finally the pellets are combusted to generate bioenergy and in the process the stored carbon is released back to the atmosphere. Within the IPCC’s accounting framework non-CO2 bioenergy combustion emissions will be allocated to the UK’s Energy GHG Inventory, whilst released CO2 combustion emissions (assumed to balance those taken up during the growth of the biomass) are estimated but only recorded as a memo item within national GHG Inventory Reports (MacCarthy et al., 2015). Therefore in GHG accounting terms bioenergy provide an attractive alternative for the nation generating bioenergy in comparison to energy generated from high GHG emitting fossil fuels.
The IPPC’s accounting framework of allocating emissions to different national inventories, or not to any inventory can make bioenergy a highly attractive option for nations decarbonising their different GHG inventories – but the accounting framework doesn’t provide the true overall GHG performance of bioenergy. The reality is that in order to evaluate the GHG performance of a given bioenergy pathway, all emissions from the biomass supply chain, from the transportation steps, and from each bioenergy process need to be accounted collectively regardless to where they are geographically emitted.
A Better Approach for Accounting Bioenergy GHG Performance
Life Cycle Assessment (LCA) is a well developed and widely implemented technique for analysing the whole life cycle emissions of bioenergy pathways, where the respective balance of emissions from all the processes and activities within a given bioenergy pathways are calculated and summed up to provide an indication overall GHG performance. Again using Figure 1 as a stylised demonstration of GHG emissions across a bioenergy pathway – the overall GHG performance of this pathway would equate to the sum of all emissions emitted to the atmosphere minus those taken up from the atmosphere during the growth of the plants/ forests. Using this logic it is clear that achieving desired levels of GHG performance from forestry bioenergy pathways will rely heavily on the forestry production processes providing a favourable balance of carbon being locked up from the atmosphere.
Examples of specific LCA research where this is demonstrated include the UK Government’s analysis of UK power bioenergy pathways using North American pellets (MacKay and Stephenson, 2014). This research has been much publicised and widely used to discredit the choice of bioenergy as a low carbon renewable energy option. What this research actually shows is that where pellets are produced for bioenergy using bad practice techniques such as the intensification of forestry harvests or where land-use change occurs resulting in the large releases GHG emissions from carbon sinks, the resulting bioenergy was found to reflect poor GHG performance – the results of these bad practice bioenergy pathways being much publicised. The research also highlights that where pellets are produced for bioenergy using good practice techniques the resulting bioenergy was found to reflect highly attractive GHG performances compared to fossil fuel generation. The true message from such research is not to stop bioenergy, but to develop policies, regulations and supply chain reporting that stamps out bad practice.
BEIS, 2016. Digest of United Kingdom Energy Statistics (DUKES) 2016. London.
FAO, 2016. 2015 Global Forest Products Facts and Figures. Rome.
IPCC, 2014. Revised Supplementary Methods and Good Practice Guidance Arising from the Kyoto Protocol. Geneva.
IPCC, 2006. Guidelines for National Greenhouse Gas Inventories, in: Agriculture, Forestry and Other Land Use. Intergovernmental Panel on Climate Change, Geneva, Japan.
MacCarthy, J., Broomfield, M., Brown, P., Buys, G., Cardenas, L., Murrells, T., Pang, Y., Passant, N., Thistlethwaite, G., Watterson, J., 2015. UK Greenhouse Gas Inventory 1990 to 2013. London.
MacKay, D., Stephenson, A., 2014. Life Cycle Impacts of Biomass Electricity in 2020. London.
UNFCCC, 2017. Emissions from Fuel used for International Aviation and Maritime Transport (international bunker fuels). New York.
Welfle, A., Gilbert, P., Thornley, P., 2014. Securing a Bioenergy Future without Imports. Energy Policy 68, 1–14. doi:10.1016/j.enpol.2013.11.079