The overwhelming growth in energy consumption in Iran is to the extent that in the coming years, it will turn Iran from an energy-exporting country into an energy-importing country. The use of renewable energy is essential to address this threat. In this research, the energy and economic analysis of solar energy-based cogeneration system for a building in Saveh City has been studied. The main purpose of this study is to determine the optimal size of photovoltaic cell and solar water heater by considering environmental parameters and fuel saving. In this regard, the amount of solar radiation intensity and the required loads of the building under study were determined. Then, using the SAM and TSOL relationships and software, results such as the supply of electric and thermal loads of six panels of 327 W and 3.2 m2, respectively, are needed. This system will save more than 75% energy.