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PostPosted: Mon Jun 19, 2017 12:15 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1665
I can see two topics for which the treatment of floating systems may be different from normal systems:

- The 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 way to determine these conditions is to measure them: 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 if you want to decrease the operating 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 4%.

- The albedo: curiously, when you measure the albedo on a water plane, it is very low (perhaps 0.1, i.e. much less than the 0.2 usual value for "normal" ground). By the way fo 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.

Tracking

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


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