Introduction of photovoltaic (PV) systems, also known as solar cell systems, reduces greenhouse gasses (GHGs) emission, by substituting a part of the GHG intensive generation with GHG-free generation during effective daylight hours. Because power is generated from different kinds of power plants operated with momentarily changing proportion, consideration of resulting changes in the power mix is needed to correctly estimate the reduction potential of a large scale introduction scenario. In this paper, a linear mathematical programming model is constructed to simulate a power mix for a given power demand under a cost minimization objective. Using the model, GHG emission reduction potentials at different scales of PV introduction were calculated assuming an ideal solar irradiation. A comparison of daily power generation before and after the introduction indicates that reduction potentials calculated with averaged GHG emission factor could result in errors, because PV systems neither replace averaged nor the single kind of power generations, but affects the entire power mix and reduces fossil fuel consumption. It is shown that the GHG emission reduction per kWh of power generated by PV differs at different capacities of installation. Namely, for the initial introduction stage, reduction would be close to fossil fuel fired power plant average for an introduction range less than 1 GWp.