Electricity generation through renewable energy sources such as wind energy has been growing in recent years due to several reasons including free and infinite resources as well as their considerable impact on the reduction of fossil fuels consumptions as well as CO2 emissions. This paper aims to assess the impact of grid-connected large-scale wind farms in a region located in Iran, on the reduction of natural gas as well as gasoil fuel consumptions in heat-cycle power plants and their related CO2 emissions as a practical case study. The wind farms under study comprise about 51% of the total grid connected capacity of wind power generation in Iran by the end of March 2021. The total energy yielded by the studied wind farms are first extracted over a two-year period from April 2019 to March 2021 based on a detailed practical data and then, its impact is investigated on the reduction of natural gas and gasoil consumptions in a real heat-cycle power plant due to its practical fuel intake data. Finally, the reduction of CO2 emission is calculated as the result of reduction in the natural gas and gasoil consumptions of the considered heat-cycle power plant. The results of this practical case study well demonstrate the effective role of wind farms energy yields on the reduction of fossil fuels consumption in heat-cycle power plants and thus, the significant reduction of CO2 emission as one of the most crucial aspects of decarbonization and fossil fuel phase out plans.