• Energy Research

Abstract To understand the resource and environmental costs of bioethanol production, this study estimates the water and farmland use and CO2 emissions in China due to first- and second-generation bioethanol production technologies using a multi-regional input-output-based hybrid life cycle assessment model. Sensitivity analysis and structural path analysis are combined to investigate the key pathways for bioethanol production impact mitigation. Results show that the first-generation technology has higher resource-use and environmental impacts compared to the second-generation technology. The gasoline-to-bioethanol transition enables CO2 emission reductions, but at the cost of increased water and farmland use. Key impact mitigation pathways are then investigated for the first four production layers (PL0→3) in bioethanol industries because these layers contribute to a significant environmental footprint. For PL0, water-saving technologies must be developed to reduce direct water use in first-generation bioethanol production. For PL1, the primary production material suppliers of the bioethanol industry, such as biomass feedstock, food and tobacco, and water supply industries were ascertained with high potential for impact mitigation. For PL2→3, key pathways are investigated by combining their sensitivity and impact values. The results highlight the significance and necessity of cross-sectoral collaboration for resource and environmental impact reduction.

Abstract In this study, we investigated whether wood pellets were more sustainable than coal for heating buildings in China by presenting a “fuel-to-heat” energy, environmental and economic comparison for both energy sources. Pellet and coal heating systems were modeled using a process-based life cycle inventory modeling approach, and the energy consumption and air pollutant emissions were calculated in Gigajoules (GJ). Wood pellets were also analyzed for their costs and market competitiveness against coal and other fossil fuel heating alternatives. The results showed that the energy saving potential from using pellets instead of coal was 1382 MJ for every 1-GJ of heat generated. Greenhouse gas emissions from pellets were 11.76 kg CO 2 -eq GJ −1 heat, which were approximately 94% less than emissions from coal heating systems. Also, the wood pellet systems reduced SO 2 , NO x and PM emissions by 86%, 56% and 33%. However, the cost of pellets is significantly higher than the cost for coal, and is the primary impediment for the transition from coal to pellets in China. In addition, multiple consumers of wood residue, unstable heat values of pellet, limited supplies, and the lack of product and heating equipment standards also render the transition from coal to pellets impractical.

Abstract As China continues to focus on renewable energy in its future development, the energy performance of biofuels has become a hot research topic. However, existing bioenergy assessments have used diverse indexes and inconsistent system boundaries, hindering the comparative analysis of different technologies. Generally, improvements in energy quality (e.g., from solid to gaseous fuel) are accompanied by increases in nonrenewable energy investment. To quantify this trade-off, this study examined the energy return on investment (EROI) of typical biomass conversion systems in China—namely, biomass compression, biodiesel, bioethanol, biogas, biomass gasification, and biomass power generation. Various feedstocks were considered, including first-generation (e.g., corn), second-generation (e.g., corn straw), and third-generation (e.g., algae) feedstock options. The system boundaries of previous biomass footprint calculations are unified to make the results comparable. The results showed that converting raw biomass feedstock to solid fuel had the highest EROI (8.06-24.13), followed by biomass power (2.07-16.48), biogas (1.24-11.05), biodiesel (1.28-2.23), second-generation bioethanol (1.18-9.90), first-generation bioethanol (0.68-3.12), and biomass gasification (1.12-1.57). Compared with fossil fuels (e.g., gasoline, diesel), biofuels had a higher average EROI, indicating obvious energy-saving benefits. Among all biomass conversion pathways, pyrolysis gasification had the highest EROI opportunity cost for both straw and wood residues. This study's findings highlight the need for consistent system boundaries in bioenergy technology deployment to quantify the EROI opportunity cost of each biomass conversion pathway, and recognize the importance of energy efficiency promotion to enhance the economic feasibility of biomass energy industries.

Abstract Geothermal power has received a great deal of attention in China as the country strives to be less dependent on coal energy and to seek stable and base load renewable power. The country's 13th Five-Year Plan for geothermal energy calls for an additional 500 MW by 2020. To assess whether this ambitious target can be achieved, this paper provides an overview of the environmental and economic performance of geothermal power based on an emergy evaluation and economic analysis of the Yangbajain plant in Tibet, the largest working geothermal power plant in China. The results indicate that the full flow system that the plant currently uses has a much higher production efficiency than the dry steam geothermal power plant in Italy. In addition, the system exhibits a relatively good environmental sustainability compared to other renewable energy generation technologies. However, it is still not economically feasible without government subsidies. Labor is expensive due to the high demand for trained professionals and the harsh working conditions in Tibet. Since China's high-quality geothermal resources are mainly located in Tibet, it would be quite challenging to achieve the ambitious 500 MW target by 2020. However, considering its environmental competitiveness, attractive subsidy policies and support for scientific research to promote technological innovations are proposed in this study to encourage the growth of the geothermal power industry in China, which would provide the country with another valuable alternative to coal.

Existing policies of household biogas projects focus mainly on supports on construction, but less consider management and maintenance, resulting in high scrap rate and waste of resources. Alternative policies must be explored to balance construction and operation. Taking the costs and benefits from a typical rural household biogas project, this paper assesses the economic performance at three different subsidy levels, i.e., no subsidy, existing standard and positive externality based standard. Furthermore three subsidy alternatives, one-time, annual and combined option are applied to the externality based standard. The results show that household biogas digesters have unsatisfactory economic performance without any subsidy and even in current subsidy policies. Environmental benefits of the digester were estimated as 2732 Chinese Yuan, significantly larger than existing subsidy standard. To keep continuous work during the 20-year lifespans of digesters, the income disparity of farmers among regions must be considered for policy application. With the increasing of labor costs, the ratio of initial subsidies must be reduced. These results provide policy implications to the future development of biogas projects in terms of both their construction and follow-up management, reuse of the abandoned digesters as well as the exploitation of other emerging renewable energy projects.

Abstract Systematically quantifying the greenhouse gas (GHG) emissions of biomass power generation is a prerequisite for robust decision-makings associated with the technology's scale deployment. This study compared the planting-to-wire GHG emissions of a typical corn-stover-based power generation system in China, estimated using one process-based and two hybrid life-cycle assessment (LCA) models. Results showed that emissions calculated by process-based LCA were 11% lower than that of hybrid models because of the truncations on services and accessory equipment. The two tiered hybrid approaches yielded total-supply-chain GHG footprints of material and equipment with a negligible difference (0.7%). The parameter settings varied by time and regions/countries resulted in temporal and spatial uncertainties of process-based LCA at 4%–10% and 0.1%–16% respectively. We proposed adopting hybrid LCA models for footprint calculation because of their strength in comprehensive accounting coverage, less dependence on data acquisition, and reduced temporal and spatial uncertainties. As the GHG footprint of biomass energy utilization is region-specific and determined by multiple factors, such as supply-chain configurations and landscape of power generation technology, results of this study help to understand the uncertainties and trade-offs associated with different LCA model deployments in China, and thus, contribute to advancing the country's biomass power sector moving forward.

Abstract Although endowed with abundant tidal resources, China's tidal power generation industry has been largely lagging behind other renewable energy alternatives such as small hydropower, photovoltaic power, wind power and biomass-based power. To probe the reasons behind this slow pace of development, an emergy evaluation and an economic analysis were conducted on the Jiangxia Tidal Power Station (JTPS), which has an installed capacity of 4.1 MW. The JTPS is the largest tidal power station in China and the fourth largest in the world. The evaluation results exhibited a total power conversion system emergy use of 1.59E+19 sej to generate 5.90E+13 J of electricity in 2014. Tidal energy only accounts for 16.54% of the total energy budget. The rest of the resources were invested to capture and convert tidal energy to electricity, thereby generating a relatively low efficiency or high transformity of 2.69E+05 sej/J. The results revealed a JTPS emergy loading ratio (ELR) and energy sustainability index (ESI) of 3.72 and 0.41, respectively, which indicates poorer environmental performance compared to other renewable energy power plants, with the exception of photovoltaic power. In addition, the economic analysis revealed a JTPS power generation cost of 2.41 CNY/kWh, which is even higher than that of concentrating solar power (CSP). The JTPS is less competitive because tidal energy has a lower quality and is more decentralized when generating electricity compared to other renewable resources. This inefficiency was exacerbated in the JTPS case due to the original multipurpose design and consequential poor site selection with respect to tidal electricity generation. These results further highlight the importance of dam site selection and the tidal range, as they are critical for the improvement of the tidal power generation environmental performance. More importantly, R&D is essential to promote the development of this technology and to ultimately utilize abundant tidal resources in an efficient and sustainable way.

Small-scale bio-energy projects have been launched in rural areas of China and are considered as alternatives to fossil-fuel energy. However, energetic and environmental evaluation of these projects has rarely been carried out, though it is necessary for their long-term development. A village-level biomass gasification project provides an example. A hybrid life-cycle assessment (LCA) of its total nonrenewable energy (NE) cost and associated greenhouse gas (GHG) emissions is presented in this paper. The results show that the total energy cost for one joule of biomass gas output from the project is 2.93 J, of which 0.89 J is from nonrenewable energy, and the related GHG emission cost is 1.17 × 10−4 g CO2-eq over its designed life cycle of 20 years. To provide equivalent effective calorific value for cooking work, the utilization of one joule of biomass gas will lead to more life cycle NE cost by 0.07 J and more GHG emissions by 8.92 × 10−5 g CO2-eq compared to natural gas taking into consideration of the difference in combustion efficiency and calorific value. The small-scale bio-energy project has fallen into dilemma, i.e., struggling for survival, and for a more successful future development of village-level gasification projects, much effort is needed to tide over the plight of its development, such as high cost and low efficiency caused by decentralized construction, technical shortcomings and low utilization rate of by-products.