To be able to supply PV power that satisfies customer demand at all times, there is need for the generating plant to be available at all time. However, with the increased age and usage of the components, the component’s reliability reduces resulting to failure. These failures were due to a range of causes such as degradation and electrical wiring aging and cuts leading to a reduced performance efficiency and reliability. Therefore, to ameliorate the reliability of the system, a combined selective and preventive maintenance actions were planned by determining the best combination (optimal preventive maintenance intervals, optimal replaced components). In this work, an optimal preventive maintenance strategy with minimal repair was developed using iterative numerical technique for a photovoltaic (PV) plant with and without considering the influence of environmental condition on the system. An algorithm was developed on MATLAB to determine the optimal number of preventive maintenance actions that yields maximum availability by selecting the components to be maintained based on the reliability threshold without considering the environmental impact on the components. The environmental elements’ criticality was introduced and the reliability reiterated based on the new technique. Finally, by maximizing the availability of the system, an optimal preventive maintenance for a finite horizon was established.