Photovoltaic surface odd values for self shading

Hello everybody,
I am doing a study with a shading system with photovoltaics integrated into it. Since now, for the calculation of the energy output, I am using the Ladybug_photovoltaic Surface component in combination with the Ladybug_Sunpath Shading component to generate a derate factor to take into account for the self-shading of PV on the upper side of the blinds. I am testing the consequence in PV production of adding more blinds to the system, but I am getting strange results out of it. I did a set of simulation with 10 louvres up to 25 and checking the PV production, there is a linear increase in it, which is unrealistic since the louvres are getting more and more close to each other and the self-shading effect should result in a drop or stabilisation in the production over a certain optimal threshold.

I, therefore, tried to run the same set of simulations with another method, using the Ladybug_radiation Analysis component and then converting the total radiation in PV production through a formula that takes into account the efficiency of the modules and another couple of penalty factors. Here the results follow a more reasonable trend in my opinion, where the addition of extra louvres does not bring any great advantage due to an increase in the overshadowing effect.

My question is: why the method with the Photovoltaic surface in combination with the Sunpath shading is not giving convincing results? I do not see where I am making a mistake in setting it up. Do you have any clue about where the error is? I would prefer to use that one since it gives me hourly PV production results that I would like to have for making the system dynamic in a second step.

Here a couple of pictures of the two methods I am describing and a table and chart of the series of results for the two. The louvres are 20cm wide and 45° tilted.

Thank you in advance for your help
Matteo

Did you already solve the problem?

Hi @Moritz,
I used the “radiation analysis method” that it was giving to me more convincing results. I still don’t know why using the photovoltaic surface component in combination with sun-path shading is not delivering consistent results when increasing the number of louvres (and reciprocal shadings).
I would still be glad if someone could come out with an explanation!

Best,
Matteo

I feel that it’s probably related to how your Grasshopper data trees are structured. I’m sorry that I can’t be of more help but I know @djordje wrote all of the renewables components and he could probably explain what is going on. He hasn’t been available for some time but maybe he might see this at some point.

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Hi Matteo,

Sorry for the late response.
Without the definition and all the required files attached, it is very difficult to identify the issue from the screenshots.
Even if those were attached, I would have to have all the same installed plugins, and spend some investigating.

Here is the help that I can provide:
If width of the window is larger, try splitting the PVsurfaces into smaller pieces, where each piece corresponds to some approximate PV module size.
Also read this topic for more explanation on how ‘Sun Path’ component works. Maybe this is causing the issue with results.

On PVsurface angles:
Depending on what is the priority in your project (energy consumption in the room behind the window or PV energy generation). If it is the second one, then to generate the louvers, you should use the ‘PV SWH system size’ component. Try searching for this component’s name here, and on the old forum as well, just to see how it can be used. You won’t be able to download majority of attached .3dm/.gh files from older topics on this discourse forum, thus you would have to search for them on the old one.
Essentially the ‘baseSurface_’ input of your ‘PV SWH system size’ component would represent the window opening.

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Thank you @djordje,
I will have a look at the solutions you are proposing in my coming projects!