Using renewable energy sources is an efficient alternative to supply the electrical load of stand-alone remote areas. The main motivation of this paper is to optimize the size of a biomass-based PV power plant to supply the electrical power of agricultural wells located in Bardsir, Kerman, Iran. In an off-grid PV power plant, there must be a backup system to supply the demanded load in deficit conditions. Biomass energy generation systems could be complementary taking into account their different properties in reliability. As a result, the combination of PV and biomass systems could be an effective way to make a reliable and cost-effective hybrid energy system. In the proposed hybrid system, the area of the PV system and the size of the engine–generator of the biomass system are optimized for minimizing the total net present cost (TNPC) of the system during its lifetime. The reliability of the designed system is met by considering the loss of power supply probability (LPSP) concept. For the investigated region, the obtained results indicate that the PV/biomass generation system is more promising than a single PV system or a single biomass system.