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Large differences between sunLoadConstant and sunLoadFairWeather models

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Old   January 3, 2022, 03:22
Default Large differences between sunLoadConstant and sunLoadFairWeather models
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Bushra Rasheed
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Hi!


I was using solar load model to calculate irradiance on a solar panel. With fair weather model, the qr (irradiance) comes out to be 880 W/m2 on front surface. Keeping all other parameters same i-e sun direction, start time and start day, when I use constant sun load with values:

Code:
   sunLoadModel          sunLoadConstant;

	directSolarRad		835;
	diffuseSolarRad	134;
It gives me qr value of 410 W/m2 on front surface.

I do not understand such large difference in irradiance even though in constant model, the direct solar radiation is 835 W/m2.

Please guide.

Thanks!
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Old   January 6, 2022, 02:17
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Bushra Rasheed
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Update:
So I found out that the direct solar radiation calculated by fair weather with default values of A, B and C in simple Solar Car comes out to be 1930 W/m2 which is very unrealistic and hence the high value of 880 W/m2 I was getting on panel surface. When I used values from table 7 from Chapter 30 of the 2001 ASHRAE Handbook of Fundamentals, the irradiance on solar panel surface through fair weather model came out to be 460 W/m2 with (2 1 ) spectral distribution and (0.3 0.7) panel absorptivity and emissitivity.

Weird that OpenFoam tutorial was not using values from table 7 of Ashrae handbook even though the guide says that fair weather model is taken from ASHRAE
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directsolarrad, solar load, solar load model, solar radiation

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