[Radiance-general] Irradiation on a Solyndra solar module

[Lovati Marco]

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:image003.png at 01D03B20.5C09C200]
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:image005.png at 01D03B20.5C09C200]

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

EURAC research
Institute for Renewable Energy
Via Luis Zuegg 11, I-39100 Bolzano
t +39 0471 055 667
marco.lovati at eurac.edu<mailto:marco.lovati at eurac.edu>
www.eurac.edu<http://www.eurac.edu/>

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