Reactive power support by photovoltaic (PV) systems is of increasingly interest, when compared to the conventional reactive power compensation devices. PV inverters can exchange reactive power with the utility grid in a decentralized manner even outside feed-in operation, especially at nights when there is no solar irradiance. However, reactive power injection causes additional power losses in the switching components leading to a temperature rise in the devices. Thus, this paper analyses the impact of reactive power injection by PV inverters outside feed-in operation on the thermal performance of their power switching components. A thermal analysis based on the mission profile (i.e., solar irradiance and ambient temperature) has been incorporated, so as to determine the additional temperature rise in the components induced by the operation outside feed-in hours. An analytical lifetime model has been used. The damage produced on the transistors has been quantified using Palmgren Miner rule. A reliability analysis has been carried out on a PV inverter with and without the injection of reactive power into the utility grid at nights. Economic impacts of injecting reactive power from PV inverters outside feed-in operating hours have been analyzed thereafter. This analysis can be helpful to make a better choice while choosing between conventional reactive power devices or PV inverters for injecting reactive power to the grid.