Urgent search for alternative energy sources needs because of the fact that the rapid depletion of fossil fuel resources. Solar and wind energies are environment friendly potential resources. But it is investigated that neither a standalone solar nor a wind energy system can provide a continuous supply of energy due to seasonal and periodical fluctuations. Therefore, in order to satisfy the demand, hybrid energy systems are implemented as combination of solar and wind energy system.Sizing and optimization such a hybrid energy system is important for the performance and initial investment. In a typical hybrid energy system, one energy resource is at a lower supply level while the other one is usually at a higher supply level (in the winter seasons the wind speed is generally at its high level while the solar radiation is at its low level). Hence, simultaneous utilization of multiple energy resources greatly enhances the certainty of meeting demands. In this book, the main objective is sizing and optimization of a PV/wind hybrid energy system with the minimum cost as a function of PV size, wind turbine rotor swept area and battery capacity.