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PostPosted: Tue Aug 04, 2020 4:20 pm 

Joined: Sat Nov 17, 2018 7:37 am
Posts: 5
Hello,
I have a complete weather station from Davis and it also includes Solar Radiation Sensor (pyranometer).
(Vantage Pro2 Plus with 24-Hr Fan Aspirated Radiation Shield)

And I want to measure PR (Performance Ratio) daily/weekly/Monthly.

I am confused with installation of a pyranometer .

How should I install Pyranometer, shall I install straight horizontal (on a pole along with rain collector) or should I install at the same angle as Solar panels (on the solar structure as PoA mounting)

I guess, if I install a horizontal flat, then it would measure GHI, in that case, I need to convert GHI to PoA, which I do not know how to convert.

For PR calculation, which one is better method?

Horizontal or at same angle of solar panel?

I saw many solar installations and they almost always install at Panel angle. Like photo shown below.
But many of them are also recommending installing at horizontal and then convert it to PoA using a long and lengthy calculation.

Please suggest and help.

Thanks
Senk


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PostPosted: Fri Aug 07, 2020 11:25 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
This is indeed a delicate question.

The PR is defined on the basis of the GlobInc value (i.e. irradiance in the collector plane, also named POA for "plane of Array").

Therefore is seems natural that for the PR evaluation, you measure the irradiance in the POA.
However be careful to put your solarimeter in front of your installation (on the first shed), or eventually significantly above, otherwise it will not "see" the albedo contribution, and may have some shading on the diffuse from other sheds.
NB: Even if the albedo is not "seen" by the sheds behind, it should be part of the "official" GlobInc. This is taken into account in the transposition model and simulation.

But it can also be interesting to measure the irradiance in the horizontal plane, with a solarimeter positioned sufficiently high.
In this case you have the uncertainty of the transposition model for obtaining the GlobInc value.
However this is more comparable with usual Meteorologic data.
Moreover this is valid if you have several plane orientations in your system, for which you will have "transpositions" calculations suited for each orientation.

For tracking systems, many people use to position the solarimeter on the axis. In this case the mutual shading of trackers (on the diffuse and albedo) are not part of the measurement, but they are accounted in the simulation process. Therefore this POA value is not really the waited value for the simulation.
In the present time PVsyst doesn't give the opportunity of suppressing the mutual shadings calculations (usually a loss of the order of 2-3%). We should do that in a next version for simulating systems from this measured (but erroneous) POA value.
Without this correction, the measured PR will be "boosted" by 2-3% as the reference POA is lower.


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PostPosted: Fri Aug 28, 2020 11:21 pm 

Joined: Wed Jul 08, 2020 6:16 pm
Posts: 2
Hi Andrés,
The guaranteed PR is caclulated from PVSyst output and the reference irradiation could lead to mistake of inpretation.
In PVSyst, irriadiation on the plan of the collectors, being impacted by far and close shading are:
GlobHrz Global on collectors, corrected for horizon (far shadings)
GlobShd Global on collectors, corrected for horizon and near shadings

could you confirm what should be the reference computed irradiation values to use for the guaranteed PR for each of the following configuration:

Configuration 1: Fix tilt structure
- Pyranometer location: located in front of the installation (on the first shed) > in that case the pyranometer would "see" the Beam component, the Diffuse component and the Albedo component (impacted by the horizon).
- Tilt irradiation to use for the Guaranteed PR: According to me this should be "GlobHrz"

Configuration 2: Fix tilt structure
- Pyranometer location: located on a shed with neighbors rows > in that case the pyranometer would "see" the Beam component and the Diffuse component (impacted by the horizon) but not the albedo component (?)
- Tilt irradiation to use for the Guaranteed PR: According to me this should be "GlobShd"

Configuration 3: Tracker structure
- Pyranometer location: located on a shed with neighbors rows > in that case the pyranometer would "see" the Beam component and the Diffuse component (impacted by the horizon) but not the albedo component (?)
- Tilt irradiation to use for the Guaranteed PR: According to me this should be "GlobShd"

Could you let me know if those assumptions are correct?


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