Energy, or renewable energy sources, is currently a frequently discussed topic. This paper focuses mainly on the economics of photovoltaic energy, specifically valuation of this technology. First, photovoltaic power systems are described, followed by a description of the method of analysis of photovoltaic project efficiency used in the case study. The main part is devoted to a specific case study of a power plant photovoltaic project valuation (using the Net Present Value). The authors have tried to answer the questions of guaranteed redemption prices as well as the "green bonus". A sensitivity analysis of the NPV to changes in some input parameters is calculated in the discussion. The principal final findings and legislative changes concerning photovoltaics in the Czech Republic (valid from 2011) are mentioned in the conclusion. These changes should restrict the increase in the prices of electric energy for the final consumer and, of course, ensure revenues for the state budget.