Improving the greenhouse gas balances of bioenergy systems: The cases of Brazilian ethanol production and combined biofuel/district heat production in Europe
According to the Fourth Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change, the largest source of increased atmospheric CO2 concentration is fossil fuel use. The second largest is land-use change. Emissions from combustion of fossil fuels and land-use change will need to be reduced in order to reach ambitious climate targets. Biomass is one of the renewable energy sources that could be used to replace fossil fuels. While biomass is a renewable source, it is a limited and expected to become scarce compared to future demand; therefore, it is desirable to use it as efficiently as possible. Further, when biofuels expand into new areas resulting in land-use change, the total biospheric carbon stock (the sum of soil and above ground carbon) may increase or decrease, thereby influencing the net greenhouse gas savings achieved. The overall aim of this thesis is to investigate different options for improving greenhouse gas balances of different bioenergy systems.
The first paper studies second generation biofuels produced in Europe and integrated with district heating systems to improve the total efficiency of the biomass use. We find that each investigated country, except Italy, has a heat sink capacity in its district heating systems that is larger than the amount of heat that would be co-generated in plants producing biofuels volumes corresponding to national biofuel targets.
The second paper studies expansion of sugarcane ethanol production in Brazil. The expansion takes place in combination with improved milk production where sugarcane residues are used as animal feed. We find that the effects of sugarcane production on soil carbon content (which is different in, e.g., cropland and pasture) and the harvest practice for sugarcane both have a large influence on total GHG emissions from sugarcane-based ethanol production.
biofuels for transport