Biogas projects have significant benefits, in particular, considerable reduction of the negative impact on atmospheric air. In order to highlight the benefits of biogas projects, it is necessary to consider the features of the source of heat or electricity generation and to compare it with the fossil fuel being replaced. Currently, the existing methodological tools do not consider the specifics of the use of various types of fuels, including alternative ones, when conducting an environmental assessment of energy projects. The purpose of this study is to develop methodological approach to the evaluation of biogas energy projects using integrated greenhouse gas (GHG) emission metrics. The indicator for the environmental efficiency assessment of an investment project with partial replacement of power consumption from the grid in terms of GHG emissions was proposed and tested on the regional energy facilities. The developed indicator considerably complements existing approaches to the efficiency assessment of biogas projects and allows to evaluate the performance of biogas projects using a single indicator that significantly simplifies the assessment procedure. It could also be paired with economic indicators such as net profit value, total capital costs in order to build a dependency matrix diagram for environmental and economic assessment of the projects. The proposed methodology could be especially useful for biogas projects implemented in countries and territories with large reserves of fossil fuels, when the profitability and economic efficiency of renewable energy projects are low.