The production of renewable energy has been increasing in Poland in accordance with the EU mandate. Solar energy use, in particular, has been affected by regulations and the associated subsidy mechanism. The specific aim of the study was the verification of the influence exerted by renewable energy regulations on the amount of revenues and duration of the period when an investor can expect positive returns on operating a PV power plant. The analysis involved five scenarios and used financial and operational data shared by the existing PV power plant in Jadowniki, Poland. Two scenarios refer to plants operating under the support mechanism applied before July 1, 2016, while three scenarios consider plants operating under the auction system that became the support mechanism for renewable energy producers on July 1, 2016. Scenarios I and II generate a positive NPV and IRR under the assumed conditions including the use of green certificates. For PV power plants operating since July 1, 2016, Scenarios III and IV show that the return is dependent on the auction price and the size of NPV and IRR discourages investment. Scenario V assumes absence of support in the form of green certificates or through auction systems and generates loss. The continuing changes in the regulation of power generation from renewable energy sources, including solar energy, creates uncertainties that are likely to discourage investment in large commercial PV power plants in Poland.