Understanding the effects of floating solar panels in Andijk
Solar energy is a popular clean energy source to realise the energy transition. In the Netherlands, solar panels on roofs of houses and buildings are already commonplace. Meadows are also popular for accommodating solar panels. However, space for large-scale generation in the Netherlands is scarce. Increasingly, floating solar panels are seen as an option for sustainable energy generation in the water-rich Netherlands. Drinking water company PWN has come up with the plan to use their reservoirs in Andijk not only for drinking water, but also for a floating solar farm. The solar farm is an important part of their ambition to produce CO2-neutral drinking water by 2050. At the moment, it consists of three 140-metre diameter islands. One of the ideas is to expand this to 11 islands with a total of 67,000 solar panels with a combined capacity of over 22 MW. The question is, however, when floating solar farms are deployed on a large scale, what is the potential effect on the surrounding water quality and ecology?
3D hydrodynamic modelling of the impact of FPV systems on temperature and mixing of a reservoir
Deltares in cooperation with PWN, KWR and Rob Uittenbogaard (now Hydro-Key B.V.) assessed the possible effects of the Floating solar photovoltaic (FPV) systems on water temperature and mixing of the reservoir in Andijk. It is one of the studies of research on the impact of FPV systems on ecology and water quality. Miguel Dionisio, ecologist at Deltares: “Temperature is an important indicator for determining the ecological status of water. The focus of this study was to determine the potential adverse effect of FPV systems on the temperature in the reservoir and the water intake, and to look at the most beneficial configuration of the systems.” Water temperature and the mixing is determined by several factors. The FPV systems partially block incoming solar radiation, effectively cooling the water. However, solar panels can also increase the temperature under the panels by blocking wind. In addition, blocking the wind by the solar panels can reduce the wind shear stress on the water surface. This reduces both horizontal and vertical mixing of the water in the basin and potentially creates stagnant areas in the reservoir. In addition, the reservoir is equipped with a bubble screen so that there is vertical mixing of the water in the reservoir. These dynamics and interactions of water, wind, the solar panels, bubble screen and the changes in temperature are included in the 3D model. Different configurations of the FPV systems have also been modelled to gain insight into which configuration has the least impact on the temperature and mixing.
Animation of the simulated temperature for the situation with 11 circular FPV systems in place. The top figure shows the near-surface temperature and the two lower figures show the temperature for the W-E (left) and N-S (right) cross-sections.
The model simulations have shown that locally, near and below the FPV systems, some increase in water temperature may occur for the selected adverse upper-end estimates (large reduction in wind and limited reduction in solar radiation), which may be potentially relevant for water quality and ecology. Based on the model calculations, no substantial effect of the FPV systems on the temperature at the inlet is expected. Adjustments in the configuration of the FPV systems did not give a significant difference in temperature changes.
For this study, the Delft3D model of the reservoir was updated and applied. Roland Vlijm, hydraulic engineer at Deltares: “What is new in the numerical modelling approach is that we have explicitly taken into account the effect of FPV systems by applying spatially varying meteorological conditions for the change in air temperature, wind, solar radiation, light penetration, etc. based on the latest insights from the literature. This provides a more detailed impact assessment of the solar panels compared to more traditional modelling methods that completely block the heat exchange between the water and the atmosphere.”
Animation of the surface flow around the FPV systems including the existing bubble screen. The top figure shows the near-surface current and the two lower figures show the currents for the W-E (left) and N-S (right) cross-sections.
The 3D hydrodynamic simulations provided valuable insight into the complex impact of FPV systems on temperature and mixing. The 3D modelling made it possible to distinguish between the effect of FPV systems on the water temperature directly below the panels at the surface to the bottom and at the inlet. The analysis included not only the direct effect of FPV systems on the heat exchange under the panels, but also secondary effects such as the advective transport of temperature and horizontal and vertical mixing of temperature in areas not covered by the FPV systems. Nevertheless, PWN continues to monitor the effect of the FPV systems closely. This will provide valuable data for further validation of the modelling approach and the application of FPV systems in general.
This research was funded by PWN and by an Allowance for Top Consortia for Knowledge and Innovation (TKIs) from the Ministry of Economic Affairs (the Netherlands) (TKI Watertechnology research project “Zonnepanelen op spaarbekkens: innovatieve oplossingen voor multifunctioneel gebruik van het bekken). The TKI Watertechnology project was coordinated by KWR.