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Shading losses applied after calculation of GPOA


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Taking a look to the project simulation losses graph and main results with which the PR is calculated some questions arise regarding GlobInc parameter.

While in the main resutls table I get a yearly value of 2483,9 kWh/m2.

The losses graph shows a value of 1849+34.4%=2485 kWh/m2. I understand it could be assumed as the same value though it is not exact.

But the main question involves the next losses on the graph such as far and near shadings, reflection, diffuse, etc. They are applied AFTER defining GlobInc value but in reality (on-site) what we will be measuring as GlobInc will be a value in which shading losses, reflection, diffuse irradiance, etc. are already applied.

To my understanding this has a big effect on the Performance Ratio value given by PVSyst as, in my opinion, the value of radiation used in the PR formula should be closer to the "Effective irradiation on collectors" value rather than "Global incident in coll. plane". Could anyone share their thoughts on this? 

Thank you!



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  • 4 months later...


What you measure on site should be as close as possible as this GlobInc. Meaning that pyranometers should be installed with the same orientation of the arrays and they should receive no shading.
Of course you can't avoid Far shadings from mountains and that is why, when comparing simulation and measured data, you should exclude that loss.

Hope this helps, best regards

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I agree with Jonipa here, for me the near shading especially in a utility scale project on trackers with backtracking, and potentially as well some of IAM factor loss which are already measured by our pyranometers in the plane of array (GPOA). 

Ultimately the question is what does my pyranometers installed in the plane of array directly on my trackers for utility scale of my site, cleaned daily, Bifacial modules and Backtracking scenario measure?

1- GPOA onsite= Global inc?

2- GPOA onsite= Global Inc - (near shading: Irradiance loss)+ ground reflection on front side?

3- GPOA onsite= Global Inc - near shading - IAM losses + ground reflection on front side

4- Other?

Does PVSYST have any opinion on this?

Thanks in advance,

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Assuming the pyranometers are really within your array

GPOA "on site" is roughly equivalent to GlobInc - Near shadings + ground reflection on front side.
However, there will be some error because a pyranometer is on a single point, but diffuse shadings in PVsyst are accounted over the whole table.

Pyranometers have (almost?) no IAM. Reference cells do. Therefore you should not remove IAM losses with pyranometers.


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