Leif Gustavsson

Towards a standard methodology for greenhouse gas balances of bioenergy systems in comparison with fossil energy systems

In this paper, which was prepared as part of IEA Bioenergy Task XV (“Greenhouse Gas Balances of Bioenergy Systems”), we outline a standard methodology for comparing the greenhouse gas balances of bioenergy systems with those of fossil energy systems. Emphasis is on a careful definition of system boundaries. The following issues are dealt with in detail: time interval analysed and changes of carbon stocks; reference energy systems; energy inputs required to produce, process and transport fuels; mass and energy losses along the entire fuel chain; energy embodied in facility infrastructure; distribution systems; cogeneration systems; by-products; waste wood and other biomass waste for energy; reference land use; and other environmental issues. For each of these areas recommendations are given on how analyses of greenhouse gas balances should be performed. In some cases we also point out alternative ways of doing the greenhouse gas accounting. Finally, the paper gives some recommendations on how bioenergy systems should be optimized from a greenhouse-gas-emissions point of view.

Greenhouse gas balances in building construction: wood versus concrete from life-cycle and forest land-use perspectives

Greenhouse Gas Balances in Building Construction : Wood versus Concrete from Lifecycle and Forest Land-Use Perspectives

Integrated carbon analysis of forest management practices and wood substitution.

The complex fluxes between standing and harvested carbon stocks, and the linkage between harvested biomass and fossil fuel substitution, call for a holistic, system-wide analysis in a life-cycle perspective to evaluate the impacts of forest management and forest product use on carbon balances. We have analysed the net carbon emission under alternative forest management strategies and product uses, considering the carbon fluxes and stocks associated with tree biomass, soils, and forest products. Simulations were made using three Norway spruce (Picea abies (L.) Karst.) forest management regimes (traditional, intensive management, and intensive fertilization), three slash management practices (no removal, removal, and removal with stumps), two forest product uses (construction material and biofuel), and two reference fossil fuels (coal and natural gas). The greatest reduction of net carbon emission occurred when the forest was fertilized, slash and stumps were harvested, wood was used as construction materia...

REDUCING CO2 EMISSIONS BY SUBSTITUTING BIOMASS FOR FOSSIL FUELS

Replacing fossil fuels with sustainably-produced biomass will reduce the net flow of CO2 to the atmosphere. We express the efficiency of this substitution in reduced emissions per unit of used land or biomass and in costs of the substitution per tonne of C. The substitution costs are calculated as the cost difference between continued use of fossil fuels at current prices and the use of biomass, assuming that the biomass technologies are implemented when reinvestments in existing technologies are required. Energy inputs into biomass production and conversion are biomass-based, resulting in a CO2-neutral fuel cycle, while CO2 emissions from fossil fuels are estimated for the complete fuel cycles. Substituting biomass for fossil fuels in electricity and heat production is, in general, less costly and provides larger CO2 reduction per unit of biomass than substituting biomass for gasoline or diesel used in vehicles. For transportation, methanol or ethanol produced from short-rotation forests or logging residues provide larger CO2-emission reductions than rape methyl ester from rape seed, biogas from lucerne (alfalfa), or ethanol from wheat. Of these, methanol has the lowest emission-reduction costs. Increasing biomass used by 125 TWh/yr, the estimated potential for increased utilization of logging residues, straw and energy crops, would eliminate more than one-half of the Swedish CO2 emissions from fossil fuels of 15 Mtonnes C in 1992.

Regional production and utilization of biomass in Sweden

Regional production and utilization of biomass in Sweden is analysed, considering the potential of replacing fossil fuels and producing new electricity. Extensive utilization of biomass will decrease biomass-transportation distances. The average distance for biomass transportation to a large-scale conversion plant suitable for electricity or methanol production will be 30–42 km when the conversion plant is located in the centre of the biomass production area. The total energy efficiency of biomass production and transportation will be 95–97% and the emissions of air pollutants will be small. In areas where energy crops from agriculture constitute the main part of the biomass, the transportation distance will be two to three times shorter than in areas where logging residues from forestry dominate. When present Swedish fossil-fuel use for heat and electricity production is replaced, more than 75% of the biomass required can be produced locally within the county. The average transportation distance of the remaining part will be between 130 and 240 km, increasing the cost of this biomass by 15–20%. Increased use of biomass by 430 PJ/yr, the estimated potential for increased utilization of energy crops, logging residues and straw, will lead to an excess of about 200 PJ/yr biomass after fossil fuels for electricity and heat production have been replaced. This biomass could be used for methanol or electricity production. The production of biomass-based methanol will lead to a low demand for transportation, as the methanol produced from local biomass can mainly be used locally to replace petrol and diesel. If the biomass is used for electricity production, however, the need for transportation will increase if the electricity is cogenerated in district heating systems, as such systems are usually located in densely populated areas with a deficit of biomass. About 60% of the biomass used for cogenerated electricity must be transported, on average, 230 km. Changing transportation mode when transporting biomass over large distances, compared with short distances, however, will lead to rather low specific transportation costs and environmental impact, as well as high energy efficiency. Replacing fossil fuels with biomass for heat and electricity production is typically less costly and leads to a greater reduction in CO2 emission than substituting biomass for petrol and diesel used in vehicles. Also, cogeneration of electricity and heat is less costly and more energy efficient than separate electricity and heat production.

Future production and utilisation of biomass in Sweden: potentials and CO2 mitigation

Swedish biomass production potential could be increased significantly if new production methods, such as optimised fertilisation, were to be used. Optimised fertilisation on 25% of Swedish forest land and the use of stem wood could almost double the biomass potential from forestry compared with no fertilisation, as both logging residues and large quantities of excess stem wood not needed for industrial purposes could be used for energy purposes. Together with energy crops and straw from agriculture, the total Swedish biomass potential would be about 230 TWh/yr or half the current Swedish energy supply if the demand for stem wood for building and industrial purposes were the same as today. The new production methods are assumed not to cause any significant negative impact on the local environment. The cost of utilising stem wood produced with optimised fertilisation for energy purposes has not been analysed and needs further investigation. Besides replacing fossil fuels and, thus, reducing current Swedish CO2 emissions by about 65%, this amount of biomass is enough to produce electricity equivalent to 20% of current power production. Biomass-based electricity is produced preferably through co-generation using district heating systems in densely populated regions, and pulp industries in forest regions. Alcohols for transportation and stand-alone power production are preferably produced in less densely populated regions with excess biomass. A high intensity in biomass production would reduce biomass transportation demands. There are uncertainties regarding the future demand for stem wood for building and industrial purposes, the amount of arable land available for energy crop production and future yields. These factors will influence Swedish biomass potential and earlier estimates of the potential vary from 15 to 125 TWh/yr.

A System Perspective on the Heating of Detached Houses

Primary energy use, emission and the cost of whole energy system chains, from natural resource to end-User, were analysed, in a Swedish context,, hen heating detached houses. Both electricity-based systems employing heat Pumps. boilers. or resistance heaters. and local fuel-based systems (e.g. natural gas. oil and wood fuel) were considered. The base-load electricity was Produced in stand-alone power plants using wood fuel or natural vas, while peak-load electricity and fuel used For transportation were produced from crude oil. The heat Pump systems were most energy efficient. followed by the local fuel-based systems. Electricity production based on cogeneration instead of stand-alone power plants would improve the energy efficiency and reduce the cost of the electricity-based systems. The wood-fuel-based systems emitted about one tenth of the carbon dioxide emitted by the fossil-fuel systems. The acidic emission. however was higher for wood-fuel-based systems, especially compared with natural gas. Primary energy use and emission from the recovery. Production and transportation of fuels were limited compared with the primary energy use and emission for the whole energy system chains. Transportation of biofuels. for example, represented less than P. of the primary energy use. The heat pump systems and the local boiler systems. excluding the pellet boiler system exhibited the lowest cost. The cost of electricity-based systems. other than heat Pump Systems, was higher due to a lower overall coversion efficiency. The pellet boiler system exhibited almost as high cost Lis these electric-based systems. The difference in cost between the same type of wood-fuel- and fossil-fuel-based systems was less than 12%. All Swedish energy taxes and environmental fees were excluded in the Cost Calculations. The removal of carbon dioxide front the flue gases front large natural-gas-fired stand-alone power plants could reduce the carbon dioxide emission by about 70%. This will increase the primary energy use, the emission of other compounds and the cost. However, regarding heat pumps these increases are small due to the high coefficient of performance

Project-based greenhouse-gas accounting: guiding principles with a focus on baselines and additionality

Project-based Greenhouse Gas Accounting : guiding principles with a focus on baselines and additionality

Heating detached houses in urban areas

District heating systems using cogeneration, as well as local fuel-based and electric heating systems for detached houses, are analysed. The analysis includes the whole energy system, from the natural resource to the end user, with respect to primary energy use, emission and cost. The end-use technologies studied are heat pumps, resistance heaters and boilers. It was assumed that the base-load electricity, except for the cogenerated electricity, was produced in stand-alone power plants using wood chips or natural gas, while peak-load electricity and fuel used for transportation were produced from crude oil. The heat pump and district heating systems are found to be most energy efficient, followed by the local fuel-based systems. The wood-fuel-based systems emit about one tenth of the greenhouse gases emitted by the natural-gas-based systems. The sulphur and nitrogen oxide emission, however, is higher for wood-fuel-based systems. Systems based on natural gas are less expensive than the corresponding wood-fuel-based systems. Decarbonization and carbon dioxide sequestration, however, do not reduce the carbon dioxide emission to the low level of the wood-fuel-based systems and, in addition, make the natural-gas-based systems more expensive than the wood-fuel-based systems.

External costs and taxes in heat supply systems

A systems approach was used to compare different heating systems from a consumer perspective. The whole energy system was considered from natural resources to the required energy services. District ...