<p>The global energy crisis and climate challenges urgently require a transition to safer, cleaner, and more diverse energy sources, and hybrid renewable energy systems have considerable scope for development as one of the best responses. However, there are fewer studies on hybrid renewable energy systems applied to farms, and the unused roofs of farms are not fully utilized. Therefore, this paper innovatively applies biogas-rooftop photovoltaic hybrid system (BRPHS) to farms and establishes a research framework based on life cycle cost and considering environmental benefits to explore whether it can bring good economic benefits. Meanwhile, power generation, organic fertilizer production, and greenhouse gas (GHG) emission reduction potentials were measured. Calculations based on a typical farm showed that the farm BRPHS is environmentally friendly and economically superior, which not only solves the problems of environmental pollution and GHG emissions caused by farm manure but also makes full use of idle resources and renewable energy sources, with an annual electricity generation of up to 42,851.92 MWh, an organic fertilizer production potential of 541.66 t per year, and a net present value of 1376.91. The net present value is 1376.91 thousand US dollars, with an internal rate of return of 19.46%, while the whole life cycle can reduce GHG emissions by 188,414.89 t CO₂e.</p>