Dr. Andrew Welfle

101 of the Intergovernmental Panel on Climate Change’s (IPCC) 116 scenarios for achieving the 2°C target are reliant on net negative emissions in the second half of this century. Bioenergy with carbon capture and storage (BECCS) is the targeted technology and mechanism for realising these net negative emissions. The negative emissions concept of BECCS is based on the principle that: atmospheric CO2 is absorbed during the growth cycles of biomass; if the CO2 produced during the combustion of the biomass to generate energy is captured and stored indefinitely; net removal of CO2 from the atmosphere can be achieved.

Dr. Andrew Welfle

Bioenergy differs from all other renewable and conventional energy pathways, as in many cases it is directly tied to the farms, forests and ecosystems from which biomass resources and feedstocks are produced and extracted. This close association within bioenergy systems and supply chains creates the potential for wide-ranging environmental and social impacts that can be both positive and negative. For bioenergy to be truly sustainable, there are many factors beyond the emission performance of a given bioenergy pathway that need to be considered. Many bioenergy ‘sustainability indicators’ have been developed to assess the performance of bioenergy based on social, economic and environmental themes, for example: assessing how bioenergy may impact or benefit communities using indicators such as changing land ownership; how bioenergy may influence economic performance such as the level of employment that bioenergy may generate; and how bioenergy may impact or benefit environmental systems measured through indicators related to water, emissions or ecosystem biodiversity. In general, criteria developed to assess the sustainability of bioenergy focus on performance of indicators related to: i) supply chains and the methods for sourcing bioenergy feedstocks; ii) characteristics of bioenergy deployment and the resulting scales, location and intensity of biomass resources that will be required, and; iii) the overall GHG emission performance of a bioenergy pathway and levels of potential GHG savings that may be saved compared to alternative energy systems.

Dr. Andrew Welfle

The UK’s GHG emission reduction and renewable energy generation targets have led to increased focus on low-carbon technologies to decarbonise the energy and transport sectors. Bioenergy with its vast array of feedstocks, conversion technologies and application pathways provides a major contribution to the UK’s current renewable energy mix, and the UK government is targeting an increased role for bioenergy. UK government energy statistics for 2018 showed that renewable energy contributed: 33% of total UK power generation (31.6% of total renewable power sourced from bioenergy); 11% of total UK heat generation (41% of total renewable heat sourced from bioenergy), and; bio-diesel and bio-ethanol accounted for 3.7% and 4.6% of the UK’s total transport fuels. Large power stations fuelled by wood-based materials from the forestry sector are the predominant contributor of bioenergy currently generated in the UK, but there are targets to increase the role of bioenergy from many different sources of biomass to decarbonise both the UK’s transport and heat sectors. The biomass feedstock demand for current and planned applications is large and in part supplied by a growing network of international supply chains importing biomass from different sources globally.

Dr. Andrew Welfle

When calculating the GHG performance of forestry bioenergy systems, it is simply a question of good management and timescales. Any counterfactuals used that assume that forests would alternatively have continued to grow locking up carbon will obviously demonstrate large net CO2 being taken from the atmosphere, which will look highly attractive compared to any scenario where large net CO2 is released to the atmosphere through bioenergy. However if you stretch out the timeline, there is a point where forests mature and the uptake of CO2 will slow and then reach an equilibrium as trees start to die and decay – at this point forests stop being the continual sinks of CO2. If forests are well managed through regular thinning and successive harvest rotations, the overall forest system may be kept in a phase where the maximum rates of CO2 taken up from the atmosphere are maintained (during the early life phases of trees). If the harvested resource from these well managed forests is also used for bioenergy, much life cycle assessment analyses such as that undertaken by the UK Supergen Bioenergy Hub highlight highly favourable GHG performances of forestry bioenergy.

Dr. Andrew Welfle

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 greenhouse gas (GHG) emissions in line with the mitigation effort to stay well-below 1.5°C. The concept of bioenergy providing low-carbon energy revolves around the transfers of biogenic carbon between the atmosphere and terrestrial systems: the carbon cycle. Biogenic carbon is defined as the emissions related to the natural carbon cycle in addition to emissions from activities such as combustion, harvesting or processing of biologically based materials. Bioenergy will be low carbon providing there is a close balance between emissions released to the atmosphere and the carbon stored as biomass materials (plants) grow. Accounting whole life cycle emissions from bioenergy systems and demonstrating that they deliver energy with reduced GHG emissions compared with fossil fuels is crucial if we are to meet national and international emissions reduction targets.