The German experience with integrating photovoltaic systems into the low-voltage grids

The integration of rooftop photovoltaic systems in the low-voltage distribution grids has become a major international trend, helped by the sinking prices for photovoltaics. One of the key questions revolves around the technical challenges brought about by the grid integration of these decentralized systems. This paper therefore analyzes the substantial practical experiences of ten representative German distribution system operators, who play a leading role in this field. Our findings show that grid expansion measures are primarily undertaken to ensure compliance with the permissible limits for voltage and current. Grid optimization measures represent the most economical initial step and include, for instance, changes in grid structure and wide-area control. Once their potential is maximized, classic grid expansion measures such as laying parallel cables are implemented. In individual cases, the low-voltage grid is reinforced by so-called intelligent operating equipment such as voltage regulators or voltage-regulated local distribution transformers. Moreover, improved grid planning measures lead to a better use of the available low-voltage grid capacity. The practical solutions successfully implemented by German distribution system operators should also prove relevant for other countries that are currently planning the deployment of decentralized renewable energies.