Scottish Government

7. Conclusions and Recommendations

This chapter summarises the key findings for each of the major aspects of bioenergy systems considered in this study: 1) energy generation potential, 2) greenhouse gas ( GHG) and energy balances, 3) air quality and associated environmental impacts and 4) economics. Additionally, recommendations for further work are presented.

7.1 General Conclusions

Energy Generation Potential

• Wood fuel from forestry and sawmill co-products are Scotland's most readily available biomass feedstocks. There is estimated to be 800,000 - 1,200,000 odt available for bioenergy in 2020, according to the SDC and FREDS reports (2005), and refinement of these estimates is an ongoing process (not including additional sources such as brash and recycled timber).
• Of the energy crop options, short rotation coppice appears to be the most appropriate to Scotland, although there are still doubts regarding its economics in Scotland. Assuming a yield of 10 odt ha ^-1 and a planting area of 50,000 ha, an extra 500,000 (about 40% the projected available forestry volume) could be available by 2020.
• There is still very little practical experience of energy grass cultivation in Scotland, but reed canary grass appears to be the most suitable to Scottish conditions. Commercial uptake of this species is, however, currently deemed unlikely.
• Agricultural residues appear to have very limited energy generation potential for Scotland, due to alternative markets or uses.
• The overall potential of electricity production from biomass is much lower than that of wind energy and lower than marine energy.
• For transport biofuels, biodiesel is more promising for Scotland than bioethanol production under present market conditions, as Scotland has a diesel deficit and cheap bioethanol alternatives are available;
• If Scotland were to meet its RTFO requirements from indigenous sources, it is likely that crops such as oilseed rape would have to be planted to do so, as the volume of UCO and tallow available in Scotland is, at present, unlikely to be sufficient to meet targets on their own.

Greenhouse Gas and Energy Balances

• There is a considerable body of existing work on GHG balances for a range of biomass energy technologies that could be modified without major difficulty for Scottish conditions. Transparent LCA data are available for production of biodiesel from oilseed rape and the production of heat or electricity from wood chip from forestry sources, sawmill co-products and short rotation coppice, for example, which could be adjusted to reflect the situation in Scotland.
• Of all the LCA studies that have been published, the Biofuels Report (Elsayed et al, 2003) can provide relevant results for Scotland on the production of heat, electricity and combined heat and power by combustion, gasification and pyrolysis of wood chip from forestry residues, the production of heat, electricity and combined heat and power by the combustion of straw, and the production of biodiesel from recycled vegetable oil.
• Much of the existing data concerning fossil fuel baselines is not transparent, which affects comparisons of GHG balances of biomass systems against fossil fuel alternatives.

Although there are no LCA results specifically designed to represent Scottish conditions, some general trends could be observed among the studies reviewed. These are described briefly below:

• Biomass heat, electricity and CHP technologies result in significant GHG and depletable energy savings in relation to fossil-fuel based systems.
• GHG emissions and depletable energy savings from biomass heat and electricity systems are of the same order as those from other renewable systems such as wind and hydro. The difference between renewable systems is very small in comparison to the significant reductions obtained when replacing fossil fuel technologies.
• The GHG emissions and energy savings of more efficient gasification and pyrolysis biomass systems are greater than those of combustion-based biomass systems, but the technology is less well proven.
• The GHG and energy balances of transport biofuel technologies are heavily influenced by the source of the energy used in the production process, and by the end-use of the by-products (rape meal and DDGS). For example, use of straw-fired CHP and co-firing of by-products results in significantly improved GHG and energy balances compared with production based on fossil fuels for energy, and by-products sold for animal feed.

Air Quality and Other Environmental Impacts

Combustion

• The choice of fossil fuel that biomass energy technologies replace is very important in determining whether air pollution emissions increase or decrease. Displacement of coal results in significant reductions in SO₂, as well as reductions in CO, PM, NO_x and NMVOCs emissions, whereas displacement of oil tends to lead to decreases in SO₂ emissions, but increases in other emissions such as PM or NO_x. Substitution of natural gas with biomass, on the other hand, generally leads to increases in emissions of all major pollutants.
• Although emission of some pollutants is determined by fuel
  characteristics, the choice of electricity/heat generation technology, including abatement systems, can also have a significant impact on non-greenhouse emissions and, in some instances, the technology can be more relevant than fuel characteristcs.
• There are substantial gaps in reliable emission data for biomass combustion for energy. This is especially true of PM2.5, PAH, VOC, ultra-fine and trace element emissions.
• Changes in air pollutant emissions resulting from the uptake of 1.7 million tonnes of woodfuel for energy in Scotland in 2020 were projected for two biomass scenarios: 1) 50% small-scale heat and 50% large CHP and 2) 30% cofiring, 35% large CHP and 35% small-scale heat. Results showed that this would lead to reductions in SO_x equivalent to 2.8-3.8% of the UK baseline, increases in NO_x of 0.02-0.05% of the UK baseline and a decrease in total PM of between 0.43 - 0.63% of the UK baseline.
• The range of combustion emissions reported from transport biofuels is wide and there is much uncertainty associated with these estimates. The general trend in light duty vehicles is that in relation to fossil diesel, HC, PM and CO emissions are decreased while there tend to be increases in NO_x emissions. For bioethanol, there appear to be no major significant changes in emissions of NO_x and HC, although emissions of PM are found to be significantly decreased, while acetaldehyde emissions are greatly increased.
• Changes in air pollutant emissions arising from uptake of biofuels under two different scenarios to 2020 were projected: 1) all vehicles run on 5% biofuel, 2) all diesel vehicles run on 100% biodiesel and all petrol vehicles on 5% ethanol. The first scenario would result in an increase in NO_x emissions of 3.8% relative to Scotland's current road transport emissions and decrease in PM emissions of 4.6% relative to Scotland's current PM emissions, whereas the second scenario would lead to increases in PM emissions by 2.0% relative to Scotland's current total PM emissions. This is due to the disproportionate influence of heavy duty vehicles in this scenario.

LCA

• Compared to greenhouse gas and energy balances, there are very few LCA studies that include air pollutant balances, and none were identified that were directly representative of Scottish conditions.
• LCA studies that present results in terms of summed eutrophication and acidification impacts, often report that biomass systems based on energy crops are at a disadvantage to equivalent oil and gas-based systems, although there is less difference with forestry residue systems. In relation to most other renewable technologies, the overall acidification and eutrophication impacts of biomass energy systems are higher.
• Life cycle non- GHG impacts from transport biofuels produced from dedicated crops are consistently greater than those of reference fossil-fuel based systems. Fertiliser NH₃ emissions have a considerable bearing on this.

Economics

• The literature suggests that the economics of energy crops is not currently favourable, and suggests that energy crops are currently economically feasible only on set-aside land at moderate to high yields with current government incentives.
• Heat production is, on the whole, much more economically favourable than electricity production, and small-scale industrial/commercial heat, in particular, seems to provide the best returns.
• The literature indicates that the carbon abatement costs of biomass heat systems are generally much lower than those of biomass electricity systems. In addition, abatement costs of biomass heat systems are much lower than those from alternative renewable heat technologies.
• The carbon abatement costs of transport biofuels are high in comparison to other biomass end uses, although this depends upon the actual carbon balances of the technologies in question.
• In relation to other renewable energy technologies, biomass provides good prospects of creating new jobs.

7.2 Recommendations for Further Studies

Energy Generation Potential

• Assessments of wood fuel availability have recently been undertaken ( SDC 2005), and are currentely being refined ( FCS 2006). Such assessments are very important in guiding the development of the biomass energy sector in Scotland and should be regularly updated.
• Among lesser researched options, short rotation forestry may present additional potential to contribute to the bioenergy sector in Scotland, particularly through the utilization of existing on-farm woodland. This option is already being investigated by the Forestry Commission (Hardcastle et. al. 2006).
• There is very little in the literature about the potential of biogas production from anaerobic digestion of animal manures in Scotland, although experimental farm-scale AD plants are currently operating in the southwest of Scotland. There may be the possibility of developing a number of centralised AD facilities in Scotland, but this appears not to have been thoroughly investigated yet.

Greenhouse Gas and Energy Balances

• Some existing studies could be modified to determine GHG and energy balances for a number of technologies under Scottish conditions. In order to undertake these modifications, it would be necessary to identify, collect and incorporate appropriate Scottish data on key parameters such as fertiliser application rates, crop yields, transport distances, etc. Additionally, it would be necessary to ascertain the likely sources of process energy and the likely end uses for joint products by developers and operators of future plants which produce biodiesel and bioethanol from oilseed rape and wheat grain, respectively.
• To enable meaningful comparison, GHG and energy balances for conventional and other energy technologies would have to be prepared for Scotland by modifying existing LCA studies.
• New work would have to be conducted to determine the GHG and energy balances of a number of biomass energy technologies. These would include the production of heat, electricity and combined heat and power by combustion, gasification and pyrolysis of wood chips and wood pellets from short rotation forestry, the production of heat by combustion of biogas from the anaerobic digestion of animal slurry, the production of electricity and combined heat and power from combustion and gasification of poultry litter and meat and bonemeal, the production of biodiesel from tallow and the production of bioethanol from barley and potatoes.

Air Quality and Environmental Impacts

• To best understand changes in emissions resulting from increased biomass energy development in Scotland, LCA analyses tailored specifically for Scottish conditions need to be undertaken. Some of these could be modified from existing work although there are considerably fewer studies with information on air pollutant balances than carbon balances. Studies which take a similar approach to the Biofuels Report by Elsayed et al. (2003) should be conducted to address non- GHG environmental impacts.
• There is still much uncertainty regarding biofuel combustion emissions. No reliable data is available for biodiesel from tallow, for example. More work is necessary to understand what impact the future transport biofuel mix would have on combustion emissions from transport.

Economics

• Comparative studies of different renewable technologies with regards to electricity generation costs and carbon abatement costs for Scottish conditions should be encouraged.
• A comparative study of the economics of alternative carbon sequestration schemes of relevance to Scotland ( e.g. carbon sequestration through afforestation vs. bioenergy) would be very informative, provided it is carried out in a structured and transparent manner
• Integrated LCA and economic studies of the biomass chains which are likely to be of greatest relevance to Scotland should be undertaken for different biomass uptake scenarios involving different allocations for heat and electricity schemes of various scales. Such a study would provide data on economics aspects such as carbon abatement costs which are specific to Scottish conditions.