Scientists from the Copernicus Institute at Utrecht University in the Netherlands have claimed offshore PV plants could be more productive than ground-mounted arrays after running a simulation comparing a North Sea project to a conventional system at the Utrecht Photovoltaic Outdoor Test field.
Simulation measurements accounted for average ambient and water surface temperatures and the effect of waves over a year. The model included seawater functioning as a natural cooling system as well as wind speed and relative humidity and the researchers observed big swings in ambient air temperatures during the year that was simulated contrasted with gradual changes in water temperature.
“[The] minimum air temperature at [the] land-based PV installation is −1.1 degrees Celsius, which is roughly 4 degrees Celsius higher than the minimum temperature at the floating PV location,” stated the Utrecht team. “Similarly, the maximum air temperature is higher at the land-based PV location. The minimum and maximum sea surface temperature are 1.8 degrees Celsius and 16.7 degrees Celsius, respectively.”
The temperature at sea was much lower at the floating installation due to higher relative humidity and wind speeds, the researchers observed.
Sea surface temperature, the scientists noted, was close to the PV system equilibrium level.
Both simulated projects comprised 12 solar panels for generation capacities of 3.72 kW. The floating project modeled was placed on a steel pontoon fixed by four wire ropes to four buoys. “The wire ropes limit the degree of freedom for the pontoon, in this way dealing with impact from sea waves,” said the Utrecht group.
For the floating system model, the estimate of the total amount of solar irradiation to hit panels with a defined tilt angle – the global tilted irradiance (GTI) figure – was based on a tilt angle affected by sea waves. Both simulated installations were based on use of a SmartSolar MPPT 75/15 solar charge controller manufactured by Victron Energy.
Under simulation, the ground-mounted array generated 1,192 kWh annually, per kilowatt installed. The floating system was 12.96% more productive, with 1,346 kWh, according to the model. The researchers also noted global horizontal irradiance (GHI) – the total irradiance received on a horizontal surface – was 8.54% higher for the floating system.
“Although the wind speed simultaneously changes the tilt angle and, as a result, the panels are not always positioned at the optimum angle, the existence of water around the pontoon is a big advantage for improving the efficiency, as the panel temperature is lower and more constant as well,“ the researchers stated.
The simulation did not compare the installation costs of the systems or the levelized cost of energy for the solar electricity they would generate.
The findings of the simulation were presented in the paper Simulation of performance differences between offshore and land‐based photovoltaic systems, published in Progress in Photovoltaics.
The Oceans of Energy company spun out of the Delft University of Technology, in the Netherlands, operates a pilot 8.5 kW offshore solar project in the North Sea which is set to be expanded to 50 kW for a year-long testing phase. The plan is to subsequently expand the site to 1 MW and, eventually, 100 MW.
A Belgian consortium including the Tractebel engineering subsidiary of French energy company Engie, is working on another offshore solar project in the North Sea. The group, which also includes Dredging, Environmental and Marine Engineering NV; solar installer Soltech NV; and Ghent University, is planning to install the €2 million array near an aquaculture farm and offshore wind project.
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