## 1 Introduction
The intensive livestock farms in China produced about 205,000 tons of manure annually, of which 56% were not properly treated, which can lead to high levels of environmental pollution and a lack of compliance in the livestock sector under the stricter environmental protection regulations. The 13 th Five-year Plan for National Rural Biogas Development has set-up targets to increase biogas production capacity by the use of 8.64 million tons of crop straws as substrate to produce 26.5 million tons of digestate by 2020 and subsequently replace 1.14 million tons of chemical fertilizer [14], which means that the biogas sector in China will continue to expand in the coming years. Unlike the German FiT scheme, the Chinese government tended to invest funds primarily in the forms of subsidies or grants to households or livestock farms for the construction of biogas digesters or plants. As a result, BGPs were operating inefficiently or closed down [12] due to little investment in the final products and maintenance. The Chinese government acknowledged this issue and attempted to gradually switch the policy goal to focus more on quality and less on quantity. Since 2006, the government has issued several regulations to promote the subsidizing of biogas-power projects [17; 18]. However, the grid companies are not obligated by law to accept renewable power from biomass, and such biomass power projects require additional government approval before grid connection, further hindering the implementation of such regulations. Despite the recent impressive expansion in scale, a comprehensive evaluation of the sector's performance in China has not been conducted yet, neither by the government agencies nor research institutes. Significant data gaps exist, particularly in the actual biogas production, rather than the data always reported by official sources about the potential daily production [14; 19] or research studies [13; 20], as well as the substrate input amount, quantified economic costs, and benefits of biogas digesters, to confirm whether government subsidies are justified. Only a few previous studies have investigated BGPs on a full-scale, although neither chemical indicators nor actual operating data of BGPs have been tested in the laboratory. [PERSON] (2011) monitored the monthly operation of three BGPs in Northern China, and found that they have a stable anaerobic digestion process under mesophilic conditions (30-35 \({}^{\circ}\)C). However, the financial balance was only calculated for one BGP, which operated at a loss [21]. [PERSON] et al. (2014) conducted a contrastive analysis on the economy of pig farm biogas projects in China and Germany based on a biogas fermentation steady-state model. The results showed poor profitability of Chinese BGPs due to the low electricity tariff [22]. Overall, the BGP operation efficiency in China remains unclear to the public, which on the other hand, makes it difficult to provide sufficient and quantified feedback to the policymakers to improve the policies. Since October 2017, the authors' team has initiated the first BMP in China with the initial trial conducted on three BGPs based on (1) the substrate applied, (2) operation status, (3) sampling possibility, (4) data availability, and (5) the willingness of BGP operators to cooperate. Three BGPs from the current German BMP III were selected to conduct a general comparison of the BGP operation efficiency. The objectives of this study were: (1) To evaluate how the technical setup, operation conditions, and substrate compositions impact the operation of BGPs; (2) to evaluate the financial viability of these BGPs; (3) to discuss how different Germany (DE) and China (CN) policies have affected the financial sustainability of agricultural BGPs; and (4) to discuss how the DE BGPs can resist the coming auction market pricing.