02 May 2012
It is a bizarre view: 47,250 modules mounted on the site of the former paper mill Muldenstein close to Bitterfeld, Germany. Because some parts of the former factory are listed as historic buildings, the 11.2MW of PV is embedded around the ruins of this factory. The PV power produced has been successfully feeding into the grid since October 2011.
What is remarkable from the technical view, however, is the fact that the operating company, Greenfield Solar Europa GmbH & Co KG, decided not to use a central inverter for the module area of 77,000 square meters, but instead a series of smaller three-phase inverters with three maximum power point (MPP) trackers each from Kaco New Energy.
The 11.2MW of PV is embedded in the ruins of the former paper mill.
Central inverters are commonly used in PV solar parks with several megawatts of power. Instead, for this project the project planners chose another combination for several reasons: Using the smaller units allows a higher distribution of risk, since a failure in a central inverter would mean a complete standstill of the whole power plant. Furthermore, the 290 smaller inverters not only guarantee a higher reliability, but can also control fewer modules with much more precision.
Small and robust
Compared to a central inverter solution, the more individual MPP-tracking can pay off in a large installation, despite the additional costs for cabling, etc. Robustness and size were other factors that lead Greenfield Solar to choose a decentralized solution: Because of their size, the compact inverters can be placed in the outside under the module lines (see picture) they are shielded from the wind, rain and other elements.
Certainly there is no key advantage to the central or distributed inverter approach, but rather the decision depends on individual factors of the specific project. Some of these factors include the situation on site, the project cost calculation, as well as priorities set by the project planners. In Muldenstein, the operating company estimated that it will achieve 1,000 kWh annual yield per installed kWp. Results are not yet in, but will be known when the energy output of the first full-size operating phase is analysed.
Written by Andreas Breyer, Contributing Editor, Germany, Solar Novus Today