Power electronics is the enabling technology for optimizing energy harvesting from renewable systems like Photovoltaic(PV) and wind power systems, and also for interfacing grid-friendly energy systems. Advancements in the power semiconductor technology(e.g., wide band-gap devices) have pushed the conversion efficiency of power electronics to above 98%, where however the reliability of power electronics is becoming of high concern. Therefore, it is important to design for reliable power electronic systems to lower the risks of many failures during operation; otherwise will increase the cost for maintenance and reputation, thus affecting the cost of PV energy. Today’s PV power conversion applications require the power electronic systems with low failure rates during a service life of 20 years or even more. To achieve so, it is vital to know the main life-limiting factors of power electronic systems as well as to design for high reliability at an early stage. Knowhow of the loading in power electronics in harsh operating environments(e.g., fluctuating ambient temperature and solar irradiance) is important for life-time prediction, as the prerequisite of Design for Reliability(DfR). Hence, in this paper, the technological challenges in DfR of power electronics for grid-connected PV systems will be addressed, where how the power converters are stressed considering real-field mission profiles. Furthermore, the DfR technology will be systematically exemplified on practical power electronic systems(i.e., grid-connected PV systems).