Safety considerations for a transformerless inverter in residential PV-systems

In photovoltaic AC-systems for residential applications influences the inverter's part load efficiency the average system efficiency to a high degree. This is due to the fact that the main energy in a typical stand-alone residential system is provided in a power range between 5% and 20% of peak load. In this part load range tare loss is the main parameter, which affects inverter efficiency. Transformerless inverters offer significantly lower tare loss and improved part load efficiency over designs employing a transformer. However, disposing of an isolating transformer necessitates careful consideration of personal safety and household equipment protection. Experiences with a transformerless inverter design, developed by the "Fraunhofer-Institute für Solare Energiesysteme", show that all requirements of the electric safety can be met by employing standard ground fault interrupters. Protection from DC-injection can also be adequately realized.