Irradiation on a Solyndra solar module

Dear Radiance guys,

                      i was trying to estimate the irradiation on a Solyndra solar module, I created the model in GrassHopper (attachment:Solyndra.gh,); the Solyndra pipes are modeled as 24 side regular polygons extruded, their length is not perfectly aligned north-south, but is oriented some 8.5° clockwise (I'm trying to match some experimental data).

I run the simulation 4 times every hour of one day (therefore 96 times) using gendaylit with a sky description like the following one:

# Sky Definition

!gendaylit 12 16 11.5 -W 828 39 -a 46.467 -o -11.333 -m -15 -O 1 # 828 and 39 are values i copied from weather data, the weather station is close to the real Solyndra

skyfunc glow sky_mat

0

0

4

1 1 1 0

sky_mat source sky

0

0

4

0 0 1 180

skyfunc glow ground_glow

0

0

4

.5 .5 .5 0

ground_glow source ground

0

0

4

0 0 -1 180
The command for Radiance is written like the following (I have chosen as example the one which utilizes the sky shown above):
cd C:\Users\MLovati\Documents\Solyndra\quarterofhour
oconv -f C:\Users\MLovati\Documents\Solyndra\quarterofhour\blue_skyes_over_my_head\Solyndra_sky46.rad C:\Users\MLovati\Documents\Solyndra\quarterofhour\Solyndramaterial.rad C:\Users\MLovati\Documents\Solyndra\quarterofhour\Solyndra.rad > Solyndra.oct #Solyndra_sky46.rad is the one shown above, (46/4 =11.5)
rtrace -I -h -dp 2048 -ms 0.063 -ds .2 -dt .05 -dc .75 -dr 3 -st .01 -lr 12 -lw .0005 -ab 2 -ad 1000 -as 20 -ar 300 -aa 0.1 Solyndra.oct < Solyndra.pts > _results\solyndra46.dat
    don't read: the folder name "blue_skyes_over_my_head" is in honour of a song from Tom Waits

in this way I can have a curve of the solar irradiation on the solyndra in one day (in this case the december 16th), and here it comes the puzzling part:
[cid:[email protected]]
Well, for those who think that the shape is strange: it's not, also the electricity production has that spike in the morning
The real question is: why it changes just a few from 10° to 9.25° (0.75°) and then abruptly from 9.25° to 8.5° (0.75°)
Does it makes sense? I didn't expect such a difference for 0.75°
for the sake of completeness: in the next chart this results are compared with the ones provided by a full deterministic model, please notice how there is not much difference, and they all are really similar to the 10° one, so the 8.5° clearly stands out of the group
[cid:[email protected]]

Hope somebody can give me a clue, I am clueless
Thank You much everybody for your kind attention.

Marco Lovati, MEng
Institute for Renewable Energy

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Solyndra.gh (28 KB)

Marco,

Puzzling. I'd suggest starting by adjusting the simulation parameters to
make sure all ambient rays and direct rays are traced.

Here are the simulation parameters you used:
-I -h -dp 2048 -ms 0.063 -ds .2 -dt .05 -dc .75 -dr 3 -st .01 -lr 12 -lw
.0005 -ab 2 -ad 1000 -as 20 -ar 300 -aa 0.1

Here are the parameters I recommend testing:
-I -h -dt 0 -dc 1 -lw 1e-5 -ab 2 -ad 2000 -as 1000 -aa 0

If that doesn't help I'd like to see your Solyndra.pts file.

On a side note, this is the second posting where someone is using the -ms
parameter. Are people really using mist in daylight simulations these days?

Andy

Dear Andy,
Thank You for your interest, I must apologize, as I simply copied the command from a diva grid based illuminance simulation: I changed the input parameters to -W (Global Horizontal, Diffuse Horizontal)and the output to irradiance "-O 1"(Watt/m2); of course having some mist doesn't make any sense as it is already accounted in the parameters I have as input (which are from a weather station nearby(meters away from the panel)).
About the approximations I just completely trust who wrote the code for Diva, now I will try without any and keep you up to date
Thank You very Much
                                                   Marco

···

From: Andrew McNeil [mailto:[email protected]]
Sent: 29 January 2015 20:11
To: Radiance general discussion
Subject: Re: [Radiance-general] Irradiation on a Solyndra solar module

Marco,

Puzzling. I'd suggest starting by adjusting the simulation parameters to make sure all ambient rays and direct rays are traced.

Here are the simulation parameters you used:
-I -h -dp 2048 -ms 0.063 -ds .2 -dt .05 -dc .75 -dr 3 -st .01 -lr 12 -lw .0005 -ab 2 -ad 1000 -as 20 -ar 300 -aa 0.1

Here are the parameters I recommend testing:
-I -h -dt 0 -dc 1 -lw 1e-5 -ab 2 -ad 2000 -as 1000 -aa 0

If that doesn't help I'd like to see your Solyndra.pts file.

On a side note, this is the second posting where someone is using the -ms parameter. Are people really using mist in daylight simulations these days?

Andy