Dear DIVA guys,

                      i was trying to estimate the irradiation on a Solyndra solar module, I created the model in GrassHopper (,); 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




1 1 1 0


sky_mat source sky




0 0 1 180


skyfunc glow ground_glow




.5 .5 .5 0


ground_glow source ground




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

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:

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

Hope somebody can give me a clue, I am clueless

Thank You much everybody for your kind attention.


Tags: Solyndra, angle, energy, gendaylit, grid, grid based, irradiation, photovoltaic, rtrace, solar

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Hi Marco,

Apologies for not replying to you before, but I do not have a very good answer to your query. I saw Andy's comments on the Radiance list, and would be curious to know if his parameter adjustments help your cause. If so, we obviously have some changes to make.

Essentially Andy's suggestion uses a bit of higher quality parameters, but for something relatively unshaded like PV panels, I don't think they should make a difference. FWIW, the mist parameters should be ignored by the simulation as long as there are no mist materials in your scene.



Dear Alstan,

thank You for the reply, actually the geometry of that panel is pretty complicated as it is made by many parallel pipes as in this image

the value you read in the charts is influenced also by the solar radiation reflected from the ground (the value is the average radiation on each single pipe, and is averaged between the 24 values of the 24 faces, some of them are facing the ground, some are facing the sky). My computer is too slow, so im currently trying to run the simulation with the parameters suggested by Andy on a Server.

Unfortunately i made a minor change in the diameter of the pipes, and on the distance between one pipe and the other, and the problem seems to have disappeared, or became smaller, and i no longer have the old geometry.

here you can see the last results still without the corrections suggested by Andy.

Now it seems more consistent although i still didn't change parameters:

anyway when i have the possibility to run the same simulation in the server i will upgrade the new results...i can get the old geometry (the one that causes the error) by downloading it from here.

Thank You to everyone of you, i hope we will figure out the cause of this


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