Retrofitting of PV systems to solve 50.2 Hz problem

Published: 20/09/2011

A study made by Ecofys and IFK on behalf of the FNN/VDE recommends the retrofitting of some solar power systems to solve the so-called 50.2-hertz problem. Until the introduction of a temporary arrangement in April 2011, generators connected to the low-voltage grid – including solar power systems – were required to disconnect from the public grid as soon as the grid frequency exceeded 50.2 hertz. In normal operations (50.0 hertz), this level has not been reached so far, and is not likely to be reached. However, in the rare case that an overfrequency occured given today's installed PV capacity, on a sunny day with a high level of infeed from solar power systems, the infeed from those systems would at that moment suddenly be lost. The recommendation to retrofit older PV systems that are connected to the low-voltage grid is meant as a precautionary measure for such a case, and will optimize approximately 9 GW of installed PV capacity.

The study, which is entitled "Effects of a high proportion of decentralized power generators on system/network stability in the event of overfrequency, and the development of proposals to overcome those effects" was carried out by Ecofys and the Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart. It was commissioned by the four German transmission grid operators, represented by EnBW Transportnetze AG, the German Solar Industry Association (BSW-Solar) and the Forum network technology/ network operation in the VDE (FNN). On 1 September 2011, the recommendations were presented to the Federal Ministry for the Environment and the Federal Ministry of Economics.

More information on the FNN/VDE on: www.vde.com

Please see our related conference paper on the potential frequency stability problem and possible mitigation measures.