Near Shadings: Irradiance Loss

[how]

Hello,

I am doing the experiment test on the effect of near shading to the energy production of PV modules over a year.

Situation 1: I put the PV modules without near shading 3D scene, the loss diagram result shows that "Near Shadings: Irradiance Loss" is 0.3%

Situation 2: I put the PV modules with near shading 3D scene, but the building block never caused any shadow on PV module, the loss diagram result shows that "Near Shadings: Irradiance Loss" is 2.4%

Situation 3: I put the PV modules with near shading 3D scene, the shadow cover part of the PV modules in the morning (8am to 11am), the loss diagram result shows that "Near Shadings: Irradiance Loss" is 3.0%

I wonder to know why i adding a building block but dont have any shadow on the PV modules that can caused a 2.4% of near shading: irradiance loss. What is the parameter that affect the losses due to near shading.

Thank you in advanced.

[André Mermoud]

The shading is accounted for the beam component (the shade what you see), but also on the diffuse and albedo components, which are integrals of the shading factor over all the directions "seen" by the PV module.

[rouge26]

This makes sense to me as far as additional shading loss considered due to lower diffuse irradiance but could you expand on the Albedo effect. Is the Albedo factor from a nearby object necessary a loss? what if the object has a white high reflecting surface?

Thanks.

[bapossatto]

On 4/28/2017 at 5:38 PM, André Mermoud said:

The shading is accounted for the beam component (the shade what you see), but also on the diffuse and albedo components, which are integrals of the shading factor over all the directions "seen" by the PV module.

Dear Mr. Mermoud,

Considering the "diffuse shadows" losses, should I consider this fact in a PR test for example?

Because when taking into account the value of GlobInc for the determination of the reference PR, it would be ignoring the losses due to diffuse shadows that the pyranometer will measure during its operation. In this sense, I understand that it would be correct to use the value "GPOA = GlobInc - Near Shadings: irradiance loss + Ground reflection on front side" as a reference for calculating the PR.

Thanks,

Benhur Possatto

[Pierre Chatenay]

Dear Bapossatto, 

I also believe that the pyranometers onsite are reading something in between Global Inc and Glob Eff and i would like to know more from PVSYST about this split.  If i am not mistaken, GlobInc= Glob Eff+ Near Shadings: irradiance loss + IAM + Soiling +/- Ground reflection on front side. I am not sure though if this near shading loss would have an impact on a tracking system with backtracking since the near shading loss due to the diffuse and albedo component might be minor. Also for soiling, the pyranometer needs to be cleaned daily to be able to consider GlobInc as you pyranometer reading (particularly in desert conditions).

Could someone enlighten us on this?

Thanks,

On 5/12/2022 at 7:09 PM, bapossatto said:

Dear Mr. Mermoud,

Considering the "diffuse shadows" losses, should I consider this fact in a PR test for example?

Because when taking into account the value of GlobInc for the determination of the reference PR, it would be ignoring the losses due to diffuse shadows that the pyranometer will measure during its operation. In this sense, I understand that it would be correct to use the value "GPOA = GlobInc - Near Shadings: irradiance loss + Ground reflection on front side" as a reference for calculating the PR.

Thanks,

Benhur Possatto

 

[André Mermoud]

Sorry, your understanding about GlobInc seems erroneous.

In the simulation, GlobInc is the result of the transposition from the horizontal plane (i.e. from GlobHor and DiffHor, taking the Albedo contribution into account).

GlobEff is the resulting irradiance on the PV modules, after several optical losses like shadings, IAM, soiling, etc.

Now when defining the PR from the measured POA data, you should make sure that these losses (especially the mutual shading on the diffuse when tracking) are not affecting your POA measurement. For this you should ideally position your solarimeter on the tracking axis, but far from the PV system for avoiding shades of the neighbour trackers.

If not, the measured POA will be underevaluated, so that the PR will be increased. 

NB: The POA measurement may indeed be affected especially by the shading loss on diffuse/albedo. If needed, your final PR calculation result  should be evaluated by correcting the  measured POA. i.e.  by adding the  shading losses calculated by PVsyst.