Power generation on the water

The floating PV system generates electricity for the gravel works. "The system generates around 700,000 kWh of electricity per year, which we can use directly for the sustainable and climate-neutral supply of the Dettelbach gravel plant. This saves around 280 tons of CO2 per year," says Thomas Wittmann, Managing Director of Heidelberg Materials Mineralik.

Around 150 kilometers to the east in Sengenthal near Neumarkt, the Max Bögl Group also relies on floating PV on its quarry pond. The system produces over 1.5 million kWh and largely uses the existing infrastructure on the lake without taking up additional land in the municipal area or interfering with the existing water ecology.

Multi-use of space and technical development

The increase in population growth is accompanied by an increased demand for resources, which leads to increasing competition for space. One strategy to counteract this effect is the principle of multiple land use. This involves equipping areas that are already in use with additional technical facilities that complement rather than hinder each other in their respective functions. One example of this is the use of floating PV systems, which can be placed on water surfaces with a substructure and therefore do not take up any agricultural land. Until a few years ago, this technology was only used in Asia. Increasingly, quarry ponds of disused gravel pits are now also being used in Europe. The coal phase-out with unused open-cast mining areas also offers a large potential area.

The identification of suitable areas depends on various factors: the body of water must be unshaded and as calm as possible with easy access to the water. The body of water should also be shallow and have a hard bottom for easy anchoring. Ideally, there should already be an electrical infrastructure and sufficient space for the use and placement of this infrastructure.

The PV modules of a floating PV system are installed on floats. The individual module parts are connected to each other via movable connectors, which ensures flexible adaptation to the water surface. The floating system is secured by an anchoring system, the robustness of which is crucial in order to withstand the weather. The PV system is connected to the power grid and the respective consumer via underwater cables (there are no water cables).

The Netherlands as a role model and large-scale projects in Germany

The largest plants outside of Asia are currently located in the Netherlands - BayWa r.e. holds the record for the largest floating PV projects outside of Asia with the Uivermeertjes solar plant (output of 29.8 MWp) and the 41.4 MWp Sellingen project. Germany's largest floating photovoltaic plant is now to be built in Lusatia. It has an output of almost 30 MW and is part of the "Cottbuser Ostsee" megaproject. It is due to be connected to the grid at the end of 2024. The conversion of the former Cottbus-Nord open-cast mine into a 1,900-hectare artificial lake follows the coal extraction in the open-cast mine, which ended in 2015. Since 2019, the former open-cast mine has been flooded with water from the River Spree.

According to calculations by the Fraunhofer Institute for Solar Energy Systems ISE, suitable areas on artificial lakes in Germany have a technical potential of 44 GWp. Floating PV systems could also be installed in maritime environments, e.g. in brackish water areas in estuaries.

Challenges and advantages

From an ecological perspective, there are currently still some challenges with the use of floating PV, as Dr. Andreas von Lindeiner, State Nature Conservation Officer, Landesbund für Vogel- und Naturschutz in Bayern e.V. (LBV) in Hilpoltstein explains: "As there is still little sound knowledge about the long-term effects on nature, it is important to set a few guard rails: For example, there must be no loss of resting and feeding areas for waterfowl and therefore no turbines should be installed on waterfowl-rich bodies of water. Furthermore, measures are required to maintain 'healthy' physical and chemical properties of the water body, e.g. mixing and oxygen content under the modules. Qualified and mandatory monitoring of hydrological and biological parameters must be used to gain experience in the operation of such systems."

In addition to the unresolved environmental aspects, the biggest challenges in Germany for the expansion of floating photovoltaics are the current legal framework conditions: "Floating PV systems can be a valuable building block on the path to the energy transition. They are a very climate-friendly and sustainable method of generating electricity with solar energy. However, legislation limits floating PV systems to 15 percent of the lake area at a distance of 40 meters from the shore. As a result, only around a tenth of the quarry ponds that have been or are being created by raw material extraction can be used," says Dr. Stephanie Gillhuber, Head of Raw Material Protection at the Bavarian Industrial Association for Building Materials, Stones and Earths in Munich. For the time being, however, no changes to the new regulations that only came into force in January 2023 are to be expected.

Floating PV also has various positive effects on the environment and wildlife. The shading reduces algae growth in the water in strong sunlight. The shading provided by the floating systems helps to prevent the water temperature from rising and also reduces the evaporation of water. Another advantage is the cooling effect. Contact with the water leads to better cooling of the solar modules and thus to an increase in efficiency. Electricity production increases by three to five percent.