How to adapt PVsyst to floating PV systems ?

[André Mermoud]

The development of a floating system is very similar to a normal terrestrial systems.

We can identify two topics for which the treatment of floating systems may be slightly different:

Temperature of the modules

Unfortunately we don't have any information nor measurements about the temperature on the water. Due to the evaporation, the ambient temperature could eventually be slightly lower than the temperature measured on the ground area using the "Meteo standard" measurment (i.e. measure in a shelted box, at 2m above a ground of grass of at least 100 m2). Or the U-value could be slightly different. The module temperature may be strongly dependent on the technology of the supports: are the modules directly "seein" the water, or on a platform? etc...

The only reliable way to determine these conditions would be to measure them on-site: see How is evaluated the Module temperature during simulation?

NB: If you get such measured data, we (and the PV community) would be very interested to get the results !

Now in the simulation, if you want to decrease the operating array temperature you have to increase the Uc value in "Detailed Losses > Thermal Parameter". There is a limit to this parameter (50 W/m²K). If really necessary, you can increase it in the "Hidden Parameters", topic "System design parameters", item "Heat loss factor Maximum value".

If necessary, we could indeed modify the thermal model for this specific situation, where the backside is "seiing" the water: perhaps develop a model involving the water temperature. We think about such a model, but we don't have any experimental data for establishing or assessing it in the present time.

Remember that for crystalline modules, a decrease of 10 °C of the array temperature will increase the yield by about 3.5% to 4%.

Albedo of a water surface

The water absorbs a big part of the incident light.

As amazing as it sounds, the albedo of the water is very low, some people propose about 0.06.

Only when the sun is very low on the horizon, there is an important reflexion, but this is specular and its duration is rather short.

By the way for a big installation in rows, the albedo is not significant as it is only "seen" by the first row. The shading factor on the albedo for the whole plant is (n-1)/n, where n is the number of rows. As an example a system of 100 rows will have a shading factor of 99%, i.e. it will "see" only 1% of the albedo contribution. Therefore the definition of the albedo parameter has no real importance.

Tracking systems

If your system is a floating disc following the azimuth of the sun during the day, you should use the option "Tracking with Vertical axis".

From the future version 7.3, it will be possible to define a backtracking strategy for this situation.