POA import diffuse and global in module plane

[MNE]

Dear Forum User,

i have actually measured diffuse and global irradiation in module plane and would like to use exactly these values for calculation.

Could you please implement the possibility of this import.

Greetings

Martin

[André Mermoud]

This is not possible in PVsyst.

The Horizontal global and diffuse components are computed by a retro-transposition, in order that the recalculation of the POA value will be the same as specified.

Now I don't have an explicit model for performing the retro-transposition from a diffuse component measured in the collector plane.

This is a non-standard problem, which would require some modelling work. I can't envisage such a development until several months, but I pout it on my to-do list.

[MNE]

Dear Mr. Mermoud,

we actually measure global irradiation and diffuse irradiation in module plane.

When i do use the ascii import for global irradiation in module plane, PVsyst converts to horrizontal data and back in to module plane.

Comparing the PVsyst Output file variable DiffSInc with the measured diffuse irradiation in module plane the values deviate in my specific calculation on a daily basis from -17,2% to +72,4%.

These deviations occure on days with low irradiation as well as on days with high irradiation.

For a specific performance calculation these deviations end up in an uncertainty of results.

Would it be possible to fasten the implementation anyhow?

[moonlite]

Andre, please confirm that in order to validate the production of an installation using onsite irradiance is to import the hourly global irradiance in the plane of the array and ambient temperature.

Also I have taken a screen shot of the options to choose when importing the hourly values. Which is the difference between the two selections in the drop-down menu, "POA_GHI_Tempe. : PVsyst standard, POA, temperature" and "PVsyst_Standard_P: PVsyst standard, POA, temperature"?

Thank you!

Screen shot of the options available when importing hourly values.

[André Mermoud]

Yes you can import data from your own measurements using POA (but you can't use a diffuse measured in the plane of Array).

In this case be careful with the time definition, already at the import time (see "My transposed POA values don't match the imported values").

PVsyst will then calculate (for each hour) GlobH and DiffH values which will restitute exactly your measured POA values if you use the Hay model.

For the second question, it is just an example (DEMO).

In the data of PVsyst (folder \UserData\), I have included 2 meteo files Geneva_PVsyst_Std_GHI.csv and Geneva_PVsyst_Std_GPI.csv with respectively Global horiz. and Global plane(POA) values, as examples.

These format protocols are the particular ones suited for reading each of them.

NB: these files are also here as an example of the specific standard format I have specified for meteo import in PVsyst.

[deblynn]

Hello,

It appears that I cannot import site measured meteo data starting with POA if it is a single-axis tracking array (not fixed tilt). Is this correct? Because I don't see any opportunity to specify that this is POA for a tracking array in the ascii or PVsyst standard format procedures.

However, if I export "Transposition factor GlobInc/GlobHor from my model that I wish to test with measured data, can I use that to back-calculate from measured POA to GHI? Does this make sense? Are there some risks in doing this?

Thanks very much!

[André Mermoud]

Yes, in the present time PVsyst is not able to import POA values measured with a tracking sensor.

And I don't see any possibility to do this "manually": the transposition factor depends on the GlobHor, but also on the DiffHor irradiance values.

When importing POA data, PVsyst performs an adjustment for retrieving a set of (GlobHor, DiffHor) values, which will exactly represent your POA data when transposed to the tilted plane (with the Hay model).

We intend to extend the importing tool for tracking systems in the future. But sorry, I don't know when we will have time to do that.

This requires that in the importing format, all Tracking parameters (including mode ans stroke limoits) should be carefully defined.

[Behzad]

Hi Andre,

A file has been referred to in the manual under the section "Importing Meteo Data from an ASCII file". The file is "DEMO_Import_Geneva_POA.CSV" which I might have deleted it from the UserData. Is there any way to obtain the file? Thanks,

[André Mermoud]

This file is in your installation location: C:\Program Files (x86)\PVsyst6.2.9\DataRO\

It will be recovered when you will update or reinstall PVsyst.

[jbennett]

Dr. Mermoud,

Have there been any updates to PVsyst's capabilities with regard to retro-transposition of POA irradiance to GHI for single-axis trackers? If yes, can you provide instruction on how the tracker type should be indicated when using the DEMO files you referenced previously?

Many thanks,

John

[André Mermoud]

No sorry, we did not yet have time for developing this.

[johank]

Stumbled upon this post after running into issues importing measured POA data (GlobInc) from a tracking system.

The reverse-Hay transposition is giving very high AM DHI readings, see att.

Is this something that isn't fully implemented yet or am I doing something wrong?

The "measured global" shown in the chart looks correct.

Thanks!

[johank]

Never mind, I re-created the conversion protocol (.mef) from scratch and now all appears to be well. Apologies for briefly reviving this thread, didn't appreciate how old it was.

[skrhee]

Hey @johank, 

Thanks for that information, do you know if PVSyst is using the imported POA or the retro-transposed POA when modeling your tracking system?  I was wanting to import custom POA for a custom backtracking schedule and I wasn't sure if PVSyst will use my imported values or the retro-transposed then transposed values.