Across the range of renewable energy resources, bioenergy is probably the most complex, as using biomass to support energy services ties into a number of fields; climate change, food production, rural development, biodiversity and environmental protection.
Biomass offer several options for displacing fossil resources and is perceived as one of the main pillars of a future low-carbon or no-carbon energy supply. However, biomass, renewable as it is, is for any relevant, time horizon to be considered a finite resource as it replenishes at a finite rate.
Conscientious stewardship of this finite resource requires not only disciplined research, but also a multidisciplinary approach in the development of viable solutions.
It has been suggested that society can neither afford to miss out on global climate change mitigation and local development offered by bioenergy done right nor accept the undesirable impacts of bioenergy done wrong. However, doing bioenergy right is a significant challenge due to the ties into other fields of society.
Fundamentally plant biomass is temporary storage of solar radiation energy and chemically bound energy from nutrients. Bioenergy is a tool to harness solar radiation to do useful work for society. In a bioenergy system the ability to do useful work stems from the difference in entropy between the relatively low entropy visible light used by photosynthesis in plants and the higher entropy heat radiation from earth to space; the final state for all (bio)energy applications.
The main objective of the work presented here has been to explore the options for increasing the use of biomass in energy systems and how to optimise the use of biomass in energy systems.
Main findings
Residues from agriculture and forestry, dedicated energy crops and waste make up the primary sources of biomass for energy purposes in the European Union. Estimation of European biomass resources is associated with significant uncertainty, and it is not sure if the European Union can meet its 2020 energy policy targets with biomass produced in the EU, although some countries hold sway over significant biomass resources. The only resource exhibiting substantial future potential to increase is energy crops on former agricultural or degraded lands. Energy crop
production is estimated to have a potential to increase from its current (2010) level of 2-3 EJ per year to 22-34 EJ per year by 2100.
With emphasis on the potential of bioenergy from agricultural crop residues the production of residues from six major crops are analysed on global scale. Crops included are barley, maize, rice, soy bean, sugar cane and wheat, which together cover approximately 50 % of the world’s arable land. The analysis finds a total production of residues from these six crops of ~3.7 billion tonnes dry matter annually. North and South America; Eastern, South-Eastern and Southern Asia and
Eastern Europe each produce more than 200 million tonnes dry matter annually. The theoretical energy potential from the selected crop residues is estimated to 65 EJ per year corresponding to 15 % of the global primary energy consumption. With widespread intensification of agricultural production, not only the production of food can increase, also the production of crop residues can be increased with 1.3 billion ton dry matter (~23 EJ) annually.
A case study on bio-ethanol based on winter wheat straw (2nd generation) and/or grain (1st generation) draws a profile of different technological option’s impact on energy consumption, feed/fodder production and land use. Most notable differences between 1st and 2nd generation bio-ethanol production are their energy balances and feed/fodder production. Due to substantially lower process energy requirement 1st generation bio-ethanol has a more favourable energy balance than 2nd generation. On feed/fodder production 2nd generation is more favourable than 1st generation. Integrated production, where bio-ethanol production is integrated with combined heat and power production may improve the energy balance with about 30 % point and reach energy efficiencies almost comparable to those seen for conversion of petroleum into gasoline.
Minimisation of GHG emissions from bioenergy production is studied for a resource constrained model energy system. Optimal allocation of biomass in the energy system is much dependent on the availability of biomass resources and technical substitution between biomass resources. In most cases mixed strategies, where different biomass resources are used for a variety of energy services, are the best way to minimise the total greenhouse gas emissions. The analyses also demonstrate that exploiting a constrained biomass resource to its full potential is a sub-optimal
solution. Even if a resource appears superior to others in terms of technical performance and convertibility it is better to relax the exploitation of the superior resource and blend in other biomass resources in the energy resource mix.