Renewable Energy in Energy-Efficient, Low-Pollution Systems

Abstract: Energy use accounts for the dominating fraction of total sulphur dioxide (SO2), nitrogen oxide (NOx), volatile organic compounds (VOCs) and carbon dioxide (CO2) emissions. In this thesis, different strategies for reducing these emissions are evaluated, using a bottom-up approach. The thesis is divided in two parts. Part I (two articles) deals with how energy efficiency improvements and the increased use of renewable energy sources together can contribute to the reduction of emissions from energy use. Part II (four articles) focuses on energy from biomass as a potential option to reduce net CO2 emissions from energy systems. CO2 emissions from electricity and heat production in western Scania, Sweden, can be reduced by 25% and the emissions of acidifying gases (SO2 and NOx) by 50% by the year 2010, compared with 1988 levels, using energy systems based on efficient end-use technologies, cogeneration of heat and electricity, renewable energy sources and low-pollution energy conversion technologies (Article I). Exhaust-pipe NOx emissions from the Swedish transportation sector can be reduced by 50 percent by the year 2015, compared with 1991, by implementing the best available vehicle technologies (Article II). Exhaust-pipe emissions of CO2 can be stabilized at the 1991 level. With further technical development and the use of fuels from renewable sources of energy, NOx emissions can be reduced by 75 percent and CO2 emissions by 80 percent compared with 1991 levels. Swedish biomass resources are large, and, assuming production conditions around 2015, about 200 TWh/yr could be utilised for energy (Articles III-VI). Major reductions in CO2 emissions could be achieved by substituting biomass for fossil fuels in heat, electricity and transportation fuel production (Articles IV and VI). The cost of CO2 reduction would be about US$50-150/tonne C when replacing fossil fuels used for heat production, US$50-175/tonne C when substituting fossil fuels used for electricity production, and US$180-340/tonne C when substituting fossil transportation fuels with biomass (Articles IV and V). Transportation fuels produced from cellulosic biomass are likely to be less expensive than transportation fuels from conventional biomass feedstocks such as oil plants, sugar-beet and cereals.