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PostPosted: Thu Oct 02, 2014 11:21 pm 

Joined: Wed Jul 17, 2013 11:59 pm
Posts: 13

I ran a simulation on a site for a 1MWp project, and I found 1.9% for PV loss due to irradiance level. I was using PVsyst v.6.25 at that time (July, 3rd).

Today I ran the same project with PVsyst 6.3 (the new version) and I got 0.6% loss for the same parameter. I haven't change anything on the meteo parameters, so I was curious to know how come the results be so different?

I took a look at the software development at the web site, and I noticed that the following upgrade in version 6.27: "PV module Rserie default value: according to 200 W/m2 relative efficiency (-3%)."

I know that Rseries and Rshunt parameters affect this kind of loss, so is it possible that this could be the answer?

PS: I noticed the same situation for the temperature loss - but to a less extent (9.4% on the previous version to 8.8% on the new version).

Thank you so much for the help, and best regards,
Rafael Pereira Santos

PostPosted: Sat Oct 11, 2014 11:13 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1686
Yes, if your module has not an explicit specification of the Rserie in the database, this is certainly the effect of the new default choice for Rs, according to the relative efficiency instead of the diode quality factor.
The value of Rserie may also have an effect on the temperature behavior if muPmpp is not explicitely specified.
Try to resimulate with a same fixed Rserie.

PostPosted: Sun Nov 16, 2014 3:49 pm 

Joined: Wed Dec 18, 2013 12:36 pm
Posts: 8
i have same problem
i have simulation with panel BYD P6 36 285W
i dont have any idea how R shunt i need to write
i try to go back ( download old ver ) to pvsyst 6.25 not work
i have irradiance level 0.3% but in old version 1.9%
please help me

PostPosted: Tue Dec 02, 2014 5:56 pm 

Joined: Thu Aug 21, 2014 11:34 am
Posts: 18
Hi André,

I've noticed the same problem with the Phonosolar, PS240P - 20/U module. The pan file on PVsyst uses the default value of series resistance so its value - and consequently the gamma and the low irradiance loss - changes depending on whether I open my project in version 6.25 or version 6.32. Given that the pan file data source is 'Manufacturer 2013' is it best to stick with a 2013 version of PVsyst (i.e. the 6.2 series) which was the version that the manufacturer may have been working with?
The low irradiance loss for the project changes from -2.6% (v 6.25) to -1.6% (v 6.32) so this version change would have big implications for all projects going forward.

Thanks for your assistance,


PostPosted: Fri Dec 05, 2014 4:31 pm 

Joined: Thu Aug 21, 2014 11:34 am
Posts: 18
On a related note, why has this change in the definition of series resistance been implemented? Series resistance changes with illumination (e.g. http://www.ijetae.com/files/Volume4Issu ... 814_49.pdf) so why has 200 W/ m2 been used? Or is the two I-V curve method of determining series resistance the new method, using the 1000 W/m2 curve AND the 200 W/m2 curve?

Thank you for your help :)

PostPosted: Sat Dec 06, 2014 11:27 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1686
The default values (mainly of Rserie) is adjusted for being as close as possible to the performances of modern PV modules.
In the past (version 5), the default highly underestimated the low-light performances (based on a required gamma value of 1.30 or 1.35).
This had been corrected for the version 6, where the required Gamma was reduced to 1.1 (on the basis of Sandia large database).
But it appears now that this was not sufficient (at least for the recent modules), and I applied a value in a better accordance with all the Low-light measurements I have gathered from official measurements.
However this value is still a little bit conservative.

See the FAQ How should the Rserie be specified ?

PostPosted: Thu Dec 18, 2014 5:19 pm 

Joined: Thu Dec 18, 2014 4:19 pm
Posts: 3
I understand that the required Gamma must sometimes be reduced to values below 1 to better fit the results from todays indoor measurements.
But this also means going out of the physically meaningful range below 1.

As i now understand it, there are two possibilities to this problem:
1. The weaklight measurements are flawed and give false results.
2. The model (or better its limitiations) is not correct any more and needs to be adjusted.

The attention seems to be with point 1 at the moment, but isn't applying the one-diode model to a complete PV module a simplifcation which would justify dropping the Gamma limitations?

PostPosted: Sun Dec 21, 2014 9:02 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1686
The objective of the model is to reproduce the real behavior of the PV module, in any irradiance and temperature conditions.
Even when the Diode Ideality factor is below its "physical" value of one, nothing indicates that the model gives erroneous results.

Please see my work about validations of the model on our web site:
"Performance assessment of a simulation model for PV modules of any available technology", Mermoud, A. & Lejeune, T., 2010,
I would be very glad if someone does an equivalent measurement with modern PV modules.

PostPosted: Tue May 26, 2015 7:12 am 

Joined: Tue Oct 21, 2014 1:08 pm
Posts: 10
Location: Chennai
Hi Andre,

what is the reason behind some modules having (+ve) PV Loss due to irradiance level?

PostPosted: Thu May 28, 2015 5:31 pm 

Joined: Thu Aug 21, 2014 11:34 am
Posts: 18
Many modules exhibit better performance at irradiances just below 1000W/2 than at STC, e.g. see http://static.renesola.com/f/2014/07/12 ... on(US).pdf. So if the irradiance levels at your site are mainly around 600-100W/m2 then it's possible to observe a low irradiance gain.

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