Floating PV

26 June 2020

A new use for old pit lakes

Above: Bomhofsplas, 27.4 MWp floating PV power plant (photo: BayWa r.e.)


“Floating PV power plants are a relatively new concept, which have huge potential for electricity generation worldwide, not least because they allow land-neutral expansion of photovoltaic capacity,” says Dr Andreas Bett, director of Fraunhofer ISE (Institute of Solar Energy Systems). Depending on the scenario, estimates show that up to 500 GW of photovoltaic generating capacity may be required for a successful energy transition in Germany. But due to the limited amount of arable land, solutions must be developed that are less dependent on land availability. A large advantage of floating PV is its higher land-use efficiency (1.33 MW/hectare, Fraunhofer ISE estimates). The water on which the PV array floats also provides cooling, which results in somewhat higher energy yields. However, the electricity generation costs for floating PV systems are about 10 to 15% higher than the costs for conventional ground-mounted PV power plants.

Commissioned by the renewable energy developer BayWa r.e., Fraunhofer ISE has investigated the potential of locating floating PV on pit lakes in former lignite mines in Germany.

There are about 500 lignite mine pit lakes in Germany, covering a total area of 47 251 hectares. Most of the lakes are located in Brandenburg (29.8%), Saxony-Anhalt (28.2%) and Saxony (15.7%). In order to assess the potential for electricity generation on these lakes, researchers interviewed local authorities, stakeholders and experts in areas such as regulation, planning, installation and water resource protection. A theoretical potential of 56 GW was originally estimated. From this value, the projected area for recreational activities, tourism, nature and land conservation was then subtracted. Pit lakes smaller than one hectare, or with large fluctuations in depth or lacking possibilities for anchorage onshore were rejected on cost grounds. The realistic economic potential was determined to be about 4.9% of the theoretical lake area, corresponding to a floating PV installed capacity of about 2.74 GWp. The largest potential is located in Lusatia and the Middle German coal district of Saxony and Saxony-Anhalt. Other types of artificial water body and naturally occurring lakes were not considered in the study, so that the total potential for floating PV in Germany is probably much larger. In all, Germany has some 4474 man-made lakes, mostly formed by surface mining for building materials. This includes 725 quarry ponds and 354 gravel lakes. Pit lakes at former opencast lignite mines represent only 12.9% of the total.


Above: Sekdoorn, 14.5 MWp floating PV power plant (photo: BayWa r.e.)


In the Netherlands, remuneration for electricity generation is sufficient to make it economic to build and operate floating PV systems, and BayWa r.e. has already installed four floating PV facilities there, totalling 52.4 MWp and including Europe’s largest floating PV plant to date, Bomhofsplas, 27.4 MWp, completed in March 2020. The Netherlands is also the location of Vattenfall’s first floating PV project, 1.2 MW at a gravel pit, currently under construction.

Germany’s first floating PV power plant began operation in 2019, but its nominal power was only 750 kWp.

Because the investment costs for floating PV are somewhat higher than ground-mounted plants, they have trouble competing in local tenders. “It would therefore make sense to have innovation tenders specifically for floating PV and other innovative PV plants that still need a market boost. In order to avoid time-consuming changes to the land use plan, land-neutral floating PV technology should be given a privileged position, as is already the case today for the use of land for wind and nuclear power plants,” says Dr Harry Wirth, division director of photovoltaic modules and power plants at Fraunhofer ISE.

Meanwhile, what is thought to be the largest floating PV facility in sea water, a 5.8 MW installation to be located on a lagoon in the Seychelles, is under development by French independent power producer Qair.

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