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.     

Life cycle assessment study of solar PV systems: An example of a 2.7 kWp distributed solar PV system in Singapore

In life cycle assessment (LCA) of solar PV systems, energy pay back time (EPBT) is the commonly used indicator to justify its primary energy use. However, EPBT is a function of competing energy sources with which electricity from solar PV is compared, and amount of electricity generated from the solar PV system which varies with local irradiation and ambient conditions. Therefore, it is more appropriate to use site-specific EPBT for major decision-making in power generation planning. LCA and life cycle cost analysis are performed for a distributed 2.7 kW_p grid-connected mono-crystalline solar PV system operating in Singapore. This paper presents various EPBT analyses of the solar PV system with reference to a fuel oil-fired steam turbine and their greenhouse gas (GHG) emissions and costs are also compared. The study reveals that GHG emission from electricity generation from the solar PV system is less than one-fourth that from an oil-fired steam turbine plant and one-half that from a gas-fired combined cycle plant. However, the cost of electricity is about five to seven times higher than that from the oil or gas fired power plant. The environmental uncertainties of the solar PV system are also critically reviewed and presented.     

Cofiring versus biomass-fired power plants: GHG (Greenhouse Gases) emissions savings comparison by means of LCA (Life Cycle Assessment) methodology

One way of producing nearly CO₂ free electricity is by using biomass as a combustible. In many cases, removal of CO₂ in biomass grown is almost the same as the emissions for the bioelectricity production at the power plant. For this reason, bioelectricity is generally considered CO₂ neutral. For large-scale biomass electricity generation two alternatives can be considered: biomass-only fired power plants, or cofiring in an existing coal power plant. Among other factors, two important aspects should be analyzed in order to choose between the two options. Firstly, which is the most appealing alternative if their Greenhouse Gases (GHG) Emissions savings are taken into account. Secondly, which biomass resource is the best, if the highest impact reduction is sought. In order to quantify all the GHG emissions related to each system, a Life Cycle Assessment (LCA) methodology has been performed and all the processes involved in each alternative have been assessed in a cradle-to-grave manner. Sensitivity analyses of the most dominant parameters affecting GHG emissions, and comparisons between the obtained results, have also been carried out.     

Life cycle sustainability assessment of hydrogen from biomass gasification: A comparison with conventional hydrogen

Hydrogen is a key product for a cleaner energy sector. However, the suitability of the different hydrogen production options should be checked from a life-cycle perspective. The Life Cycle Sustainability Assessment (LCSA) methodology is helpful for this purpose, allowing a thorough interpretation of a product system's performance by integrating economic, environmental and social indicators. This work presents an LCSA of renewable hydrogen from biomass gasification, and its sustainability benchmarking against conventional hydrogen from steam methane reforming. Environmental (global warming and acidification), economic (levelised cost) and social (child labour, gender wage gap, and health expenditure) life-cycle indicators are characterised and jointly interpreted. The results show that hydrogen from biomass gasification cannot yet be thoroughly considered a sustainable alternative to conventional hydrogen mainly due to economic and social concerns. However, improvement actions leading to an increase in process efficiency would significantly enhance the system's performance in each of the three sustainability dimensions.     

Exergy analysis of the woody biomass Stirling engine and PEM-FC combined system with exhaust heat reforming

The woody biomass Stirling engine (WB-SEG) is an external combustion engine that outputs high-temperature exhaust gases. It is necessary to improve the exergy efficiency of WB-SEG from the viewpoint of energy cascade utilization. So, a combined system that uses the exhaust heat of WB-SEG for the steam reforming of city gas and that supplies the produced reformed gas to a proton exchange membrane fuel cell (PEM-FC) is proposed. The energy flow and the exergy flow were analyzed for each WB-SEG, PEM-FC, and WB-SEG/PEM-FC combined system. Exhaust heat recovery to preheat fuel and combustion air was investigated in each system. As a result, (a) improvement of the heat exchange performance of the woody biomass combustion gas and engine is observed, (b) reduction in difference in the reaction temperature of each unit, and (c) removal of rapid temperature change of reformed gas are required in order to reduce exergy loss of the system. The exergy efficiency of the WB-SEG/PEM-FC combined system is superior to EM-FC.     

Blending blue hydrogen with natural gas for direct consumption: Examining the effect of hydrogen concentration on transportation and well-to-combustion greenhouse gas emissions

Jurisdictions are looking into mixing hydrogen into the natural gas (NG) system to reduce greenhouse gas (GHG) emissions. Earlier studies have focused on well-to-wheel analysis of H₂ fuel cell vehicles, using high-level estimates for transportation-based emissions. There is limited research on transportation emissions of hythane, a blend of H₂ and NG used for combustion. An in-depth analysis of the pipeline transportation system was performed for hythane and includes sensitivity and uncertainty analyses. When hythane with 15% H₂ is used, transportation GHG emissions (gCO2eq/GJ) increase by 8%, combustion GHG emissions (gCO2eq/GJ) decrease by 5%, and pipeline energy capacity (GJ/hr) decreases by 11% for 50–100 million m³/d pipelines. Well-to-combustion (WTC) emissions increase by 2.0% without CCS, stay the same with a 41% CCS rate, decrease by 2.8% for the 100% CCS scenario, and decrease by 3.6% in the optimal CO₂-free scenario. While hythane contains 15% H₂ by volume only 5% of the gas’ energy comes from H₂, limiting its GHG benefit.     

Comparative life cycle assessment of the integrated generation of solid fuel and biogas from biomass (IFBB) and whole crop digestion (WCD) in Germany

Today’s bioenergy systems are very different in cultivation, conservation, conversion of the biomass as well as in the form of the final energy. The assessment of bioenergy systems concerning environmental impacts is increasingly up for discussion. Future challenges will be the development of procedures which reconcile high-yielding and efficient approaches with environment friendly production. Against this background the system of Integrated Generation of Solid Fuel and Biogas from Biomass (IFBB) was suggested to increase net energy yields over a wide range of energy crops in order to obtain a higher biodiversity in energy crop cultivation. In the IFBB procedure the ensiled biomass is separated into a liquid phase for biogas production and into a solid fraction for combustion.This work is aimed at the assessment of the IFBB system in comparison to whole crop digestion (WCD). The assessment is based on crop production in a double-cropping system where winter rye and maize are grown subsequently within one growing season. The main parameters investigated are the efficiency of the whole process, primary energy and greenhouse gas savings as well as potentials of acidification and eutrophication according to principles of Life Cycle Assessment. The calculation of energy efficiency shows a superiority of the IFBB system due to a mainly thermal use of the biomass. Savings of fossil primary energy average at a similar level, whereas greenhouse gas savings are slightly higher for WCD. Investigations on acidification and eutrophication show that both bioenergy systems caused higher emissions compared to the fossil-based reference technique.     

Land use impacts of industries and products in the Finnish economy: A comparison of three indicators

The sustainability aspects of land use were assessed with an environmentally extended input-output model of Finland in 2002. The main economic industries and products causing land use were identified and the impacts were estimated with three indicators: biocapacity, human appropriation of net primary production (HANPP) and ecosystem degradation potential (EDP). The results correlated well with expert assessments on the threats to biodiversity, although the influence of animal farming was not clear in all indicators. Most of the domestic land use was caused by final demand outside Finland. Based on a simplified trade balance, Finland was a net exporter of land area, mainly through wood products. Two thirds of the domestic land use was driven by export production. Therefore a regional consumption based approach is not sufficient to mitigate and control the environmental impacts of land use even in a developed country like Finland.     

Life cycle energy consumption and GHG emissions of hydrogen production from underground coal gasification in comparison with surface coal gasification

Developing underground coal gasification (UCG)-based hydrogen production (UCG-H₂) is expected to alleviate hydrogen supply and demand contradiction, but its energy consumption and environmental impact need to be clarified. In this paper, comparative study of energy consumption and greenhouse gas (GHG) emissions between UCG-H₂ and typical surface coal gasification (SCG)-based hydrogen production (SCG-H₂) is carried out using life cycle assessment method. Result shows energy consumption of UCG-H₂ is only 61.2% of that of SCG-H₂, which is 1,327,261 and 2,170,263 MJ respectively, reflecting its obvious energy saving advantage. 80% capture rate can achieve an appropriate balance between energy consumption and emissions. Under this capture rate, emissions of UCG-H₂ and SCG-H₂ are roughly equivalent, which are 207,582 and 197,419 kg CO₂-eq respectively. Scenario analysis indicates energy consumption in hydrogen industry can reduce by 38.8% when hydrogen production is substituted by UCG with CCS to fully meet demand of 21 Mt in 2030.     

Development and environmental impact of hydrogen supply chain in Japan: Assessment by the CGE-LCA method in Japan with a discussion of the importance of biohydrogen

Hydrogen is an attractive and clean source of energy with a high energy content and environmentally friendly production using green power. Hydrogen is therefore considered to be one of the future alternatives to fossil fuels that can limit the damage done by climate change. A dynamic GTAP model with LCA method is utilized herein in this investigation to forecast the development of the hydrogen supply chain and CO₂ emissions in Japan. The supply chain incorporates six hydrogen-related industries – biohydrogen, steam reforming, electrolysis, hydrogen fuel cell vehicles (HFCV), hydrogen fuel cells (HFC), and hydrogen fueling stations.     

Technological-economic assessment and optimization of hydrogen-based transportation systems in China: A life cycle perspective

Hydrogen energy is increasingly incorporated into long-distance transportation systems. Whether the coupled hydrogen-based transportation system can achieve a sustainable business operation mode requires quantification of environmental and economic performance by a comprehensive cost-benefit analysis. This study proposes a cost-based life cycle assessment method to evaluate the environmental and economic benefits of hydrogen-based long-distance transportation systems. The innovative cost assessment method introduces internal and external economic costs to conduct a multi-scenario assessment. According to the key factors of mileage, government subsidies and hydrogen fuel prices, this research identifies the key cost component of the hydrogen-based transportation system in China by using a multilevel comparison with cell-driven and oil-fueled vehicles. The results show that hydrogen fuel cell electric vehicles are competitive in terms of both fuel costs and environmental costs. As hydrogen costs are expected to be gradually reduced by 43% in the future, hydrogen logistics vehicles and heavy trucks are expected to have better life-cycle economics than other energy vehicles by approximately 2030. Hydrogen buses will outperform other vehicles by approximately 2033, while hydrogen passenger cars will have a reduced life-cycle cost per kilometre within 0.1 CHY/km compared to other vehicles by approximately 2035. Ultimately, fuel consumption, average annual mileage, and hydrogen fuel cell electric vehicle policy are three factors that have greater impacts. Policy implications are put forward to implement optimal investment plan for hydrogen transportation systems.