Simulation Results - PR

[J0s3]

Hello.

I'm running some simulations now and I noticed something I would like you to help me understand, reading the definition of PR from PVsyst I build a calculations sheet in excel and so far all the PR from PVsyst simulation result where succesfully coincident with the ones in the calculations sheet. (refer to Image 1 to Image 3).

Values used to calculate PR where: PR = (E_Grid/E_AvailableMax) *100

E_AvailableMax = Efficiency Noct * A_collector * GlobInc

All those values got from Simulatios Results.

Image 1.

http://imageshack.com/a/img661/8889/1ONbUN.jpg

Image 2.

http://imageshack.com/a/img537/7571/nrrzVS.jpg

Image 3.

http://imageshack.com/a/img631/3183/U5IhU0.jpg

As you can see, all the PR values from Calculations match PR values from simulation results.

My concern came out when I separate the system to ran the simulations for each orientation then I got what you can see in Image 3 (oriented 0°, south) and 4 (oriented 180°, north).

Image 3. South

http://imageshack.com/a/img913/8961/hR62nB.jpg

Image 4. North

http://imageshack.com/a/img910/3527/ufHdFM.jpg

I was expeting for a result of PR from Image 3 to be greater than PR from Image 4, wich is not true because PVsyst calculated PR Image 3 = 69.2% < PR Image 4 = 70.2%

Then, I ran the calculations sheet to get the values as I did in the global system simulations and got different PR for each subsystem and got the values I was expecting.

http://imageshack.com/a/img673/664/y3Hh5h.jpg

http://imageshack.com/a/img911/5743/bHWznR.jpg

I realized that PVsyst calculates PR from the Yf / Yr relationship, I checked this in the Monthly tables results from simulation and the PR from those values matches the result from the simulations results, so I'm guessing the problem comes out from the Yf and Yr calculations wich a I have not checked how they were calculated.

Please help me clarify that.

[André Mermoud]

First, please have a look on the FAQ How is calculated the PR ?.

Your expression is the one used in PVsyst, except that the Effic (NOCT) is indeed the Effic at STC.

In fact, the definition in PVsyst is

PR = E_Grid / (GlobInc * Pnom) where Pnom is normally equal to Effic(STC) * module area.

Now as it is normalized to GlobInc, the PR is an indicator of the running quality of your system, independently of the orientation and the climate.

You have a south and a north orientation (with probably very little tilt, and a very low positive latitude - near to the equator).

The southern part is more exposed (higher incident irradiance): its temperature will be slightly higher than the northern orientation. Therefore its temperature losses will be slightly higher, i.e. the PR will be slightly lower.

[J0s3]

I'm really grateful for your concern and fast response :D

Thank you very much for your time.