Reliability is an essential factor in Photovoltaic (PV) systems. Solar power has become one of the most popular renewable power resources in recent years. Solar power has drawn attention because it is free and almost available worldwide. Moreover, the price of maintenance is lower than other power resources. Since there are no moving parts in PV systems, their reliability is relatively high. It is assumed that a typical PV system can operate 20–25 years with minimum possible interruptions. However, solar power systems may fail, the same as any other systems. It is indicated by several studies that the PV inverters are responsible for major failures in PV systems, as other components are almost passive. Hence, the reliability of the inverter has maximum impact on the reliability of the whole PV system. Thus, not only assessing and calculating the reliability value of inverter is highly crucial, but also increasing its value is essential, as well. This paper calculates and evaluates the reliability of PV single-stage inverters exclusively. Furthermore, there are suggestions that improve their reliability value.