The mechanical and electrical development in dairy farming in China increases energy-related carbon emission (CE). To support the sustainable planning strategy of the department, this study calculated the CE and the carbon emission intensity (CI) of the direct energy consumed in dairy farms from 21 provinces in China. Through four dimensions analysis including the national level, farm scale, inter-provincial distribution, and main producing area, this study illustrates the impact of the environment, production, and management on CE. The total CE of nationwide dairy farming was about 2.4 Tg CO₂ eq. in 2019, and the CIs of the 21 provinces varied from 0.009 to 0.216 kg CO₂ eq. per kg of milk. The results indicate that the management mode applied in large-scale dairy farms (500 heads and above) varies considerably due to inadequate adaptation to climate. In general, semi-arid and semi-humid regions are more suitable for dairy farming than arid and humid regions. In the main milk-producing area, the spatial aggregation effect is visible in the carbon reduction potential. The present study suggests that further steps to promote sustainability and milk productivity are embodied when the replacement of fossil fuels and the management standardization are adapted to regional characteristics.

To enhance energy utilization efficiency, dairy farmers have increasingly adopted photovoltaic (PV) panels on barn roofs. However, there is currently a general separation between the barn construction and the additional aspects of the PV system. It is unclear to dairy farmers whether rooftop PV panels will have an impact on the dairy barn, particularly on the thermal environment. This study investigated the influence of air layer properties, specifically thickness and ventilation conditions, on the thermal performance of PV dairy barn roofs. Utilizing the harmonic analysis method, the study quantified its dynamic thermal properties. The results demonstrated that increasing the air layer thickness in ventilated roofs decreases heat flux and improves thermal resistance (1.67–2.15 times higher than non-PV roofs). In contrast, sealed air layers exhibit consistently high thermal resistance (up to 3.33 times higher). Optimizing ventilated air layer thickness (0.20–0.30 m) effectively minimizes heat ingress and prevents PV efficiency degradation. These results provide valuable insights for optimizing the design of energy-efficient PV dairy barns, enhancing thermal comfort, and contributing to low-carbon energy solutions in livestock facilities.