Study Recommends Retrofitting of PV Power Plants to Solve 50.2 Hz Problem

A study conducted on behalf of the four German transmission system operators, the PV trade association BSW Solar and Forum network technology/network operation in the Association of Electrical, Electronic and Information Technologies (VDE/FNN) recommends retrofitting roughly 315,000 PV power plants to solve the mounting 50.2 Hz problem for networks due to rising decentralised input by PV systems.

With a share of renewable energy of 20% in the first half of 2011, 3.5% of which came from PV systems with a capacity of more than 19 GWp at the end of June 2011, maintaining the voltage in the German networks becomes increasingly difficult.  This is true especially in the low-voltage networks to which a large part of the installations are connected.

Until the introduction of temporary voluntarily applicable rules set by VDE in spring 2011, power generators connected to the low-voltage grid – including PV systems – were required to disconnect from the public grid as soon as the grid frequency exceeded 50.2 Hz. During normal operations (50.0 Hz), this level has so far not been reached, and was not likely to be reached. 

However, given today’s installed PV capacity, if the rare case of an over frequency occurred on a sunny day with a high level of input from PV systems, the power input from those systems would from one moment to the other cease.  This would result in a sudden power variation, VDE points out. 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 optimise approximately 9 GW of installed PV capacity, BSW Solar explains in its press release.

Much as conventional generation plants do, the inverters will lower the power input as the frequency increases. Should older inverters not support such a frequency-based power reduction, the shutdown frequencies of the systems are recommended to be spread in such a way that basically the same result will be attained. The study also recommends the system-compatible re-connection to the grid following the normalisation of the frequency.

Retrofitting is being recommended for all PV systems with a capacity of over 10 kWp that started operating after 1 September 2005. According to the study, retrofitting would in the vast majority of cases consist of a software update or a change of the parameter settings of the solar inverter. It is recommended to be carried out between 2012 and 2014 on around 315,000 mid- to large-sized solar power systems that are connected to the low-voltage grid. Thus, small roof-mounted systems on single-family homes would not be required to undergo retrofitting.

Initial estimates of the costs of updating the PV systems range from EUR 65 to 175 million. Additional costs of up to EUR 2 million would be incurred for the adjustment of emergency standby power systems, as well as for administrative costs for manufacturers and grid operators.

Agreement on the 50.2 Hz problem between the trade associations, manufacturers and TSOs ends when it comes to bearing the costs for retrofitting, the magazine photovoltaik points out. While BSW Solar’s managing director Jörg Mayer demanded raising the grid charges accordingly, predicting additional costs of 0.02 Cent/kWh, grid operators demanded raising the EEG reallocation charge, photovoltaik writes.

A decision will have to be made by the Federal Ministry of Economics and Technology (BMWi). The ministry that was involved in the study is currently in the process of drafting an ordinance regulating the retrofitting of PV systems. According to photovoltaik, it shall be presented by the beginning of next year.

Sources: VDEBSW Solarphotovoltaik

3 Responses to “Study Recommends Retrofitting of PV Power Plants to Solve 50.2 Hz Problem”


  • Question: is this 50.2 Hz Problem only in Germany, or could it be a problem elsewhere, for example in France, too ?
    Thanks for your imput.

  • Someone with a technical background would probably be better placed to respond to this. My understanding from the study is that the 50.2 Hz issue is connected to a technical requirement in the German standard DIN VDE V 0126-1-1 that was originally introduced in 2005/2006. At the time, German PV capacity was technically negligible. Since then, more than 12.7 GW in solar capacity have been connected on the low voltage grid level. In a worst case scenario, currently 9 GW of solar PV capacity could be disconnected when 50.2 Hz are reached. It is this quantity that may now create the problem.

  • Frequency regulation has always been a challenge for utilities. With increasing generation capacities of intermittent distributed renewable energies on the grid, such as wind and solar, but particularly solar due to the instant on/off nature from shading, the utilities must either invest in more ancillary services, storage, or throttle PV plant outputs as described in the above article. In most studies of this problem in the U.S., it’s generally shown that frequency regulation does not become a problem until reaching ~15 percent intermittent renewables on the grid. While Germany should be proud of its commitment to renewable energies, and the EEG that has fueled the revolution, I’m surprised no one is looking at storage solutions rather than throttling output at the inverter. Is there no discussion of the storage option in Germany, Matthias? In the U.S., although light years behind Germany in renewable energies, at least an innovative solution to intermittent renewables is already being developed through the ground breaking work of Dr. Willett Kempton at the University of Delaware. You can read about using electric vehicles as grid storage through vehicle-to-grid (V2G) technology here http://www.udel.edu/V2G/. And here’s a recent article on V2G http://gigaom.com/cleantech/nrg-energy-embraces-vehicle-to-grid-tech/, it seems the Danish are looking at it as a solution as well. Of course, Germany is way ahead in renewables and there are very few electric vehicles.

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