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China has been placing a substantial focus on biogas for reducing energy consumption and carbon dioxide (CO 2) emissions. The operation mode of biogas systems may make the CO 2 reduction target over-optimistic. There is limited research to investigate the influential factors that may be causing the gap between the actual and theoretical CO 2 reduction costs of biogas systems in China. In this research, by using field survey data of 209 biogas users and 489 non-biogas users from 19 villages in 2015, the gap between actual and theoretical unit CO 2 reduction cost is quantified at approximately 156 USD/t CO 2. By employing the Logarithmic Mean Divisia Index I (LMDI) model, it is found that both the cost effect (48%) and the reduction effect (52%) contribute to the unit CO 2 reduction cost gap. Four influential factors–household labor, accessibility to the energy resource, acceptance of biogas technology, and subsidy–significantly narrow the gap between actual and theoretical CO 2 reduction costs, while the levelized subsidy contributes to widening the gap. On average, biogas systems should be operated for at least four years and the substitution rate should be more than 67% in order to keep the gap between actual and theoretical CO 2 reduction costs under 50%. • Actual and theoretical CO 2 reduction costs of biogas systems are assessed. • The gaps are decomposed to the cost effect and the reduction effect. • Five key influential factors are investigated to narrow the gap. • The under-estimated CO 2 reduction costs of biogas systems are evaluated. [ABSTRACT FROM AUTHOR]

Biomass fermentation and gasification are two types of biomass utilization technologies for residential households. Government plays an essential role in the diffusion of improved technologies. Cost-effectiveness analysis can provide the cost and abatement potentials of each alternative under a single abatement strategy; however, it is difficult for policy-makers to make an integrated assessment when multiple objectives are involved. This paper evaluates the performance of three distributed alternatives and two centralized alternatives for residential biomass use in rural China, including centralized biogas and centralized gasifier systems. An integrated assessment approach is built, which combines cost-benefit analysis, an entropy-weighting method, and a preference-ranking organization method for enrichment evaluations using the PROMETHEE approach. A total of 686 sample households in three regions of China were surveyed in this study. The centralized gasifier system and distributed household biogas were the top two alternatives for further development to meet the government's 2020 development goal for biogas technology. The overall biomass utilization amount in the prioritized scenario is about three times that of the business-as-usual scenario by 2020. This study can provide significant insights for China's policy-makers to draft strategic policies and countermeasures that will promote the development of renewable energy in China. [ABSTRACT FROM AUTHOR]