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One Diode Model Linear or Non-Linear Temperature Correction
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Author:  cq.trac [ Fri Aug 23, 2019 9:17 pm ]
Post subject:  One Diode Model Linear or Non-Linear Temperature Correction

Hello All,

Does anyone know what parameter in a .pan file would cause a linear vs non-linear behaviour in the max power point of a module vs temperature in the one-diode model calculated by PVSyst? I have 3 modules from the same manufacturer that behave differently, 2 modules will have a linear behaviour and their maximum power point will increase with a decrease in temperature. The last one will behave linearly up to a point (about -10C), and then its power will start decreasing with temperature instead of increasing. I've checked a few more .pan files and about 45% of them have this non-linear behavior as well, all starting to decrease in power at around -10C.

Does anyone know how PVSysts decides to correct for temperature in a linear vs non-linear way? I looked at the .pan files, but no parameter really stood out that might isolate the modules with a non-linear performance, so I assume it might not have to do with the .pan file parameters and have more to do with PVSysts methods of correcting for temperature. If anyone has a potential answer to this, I'd greatly appreciate an explanation


Author:  André Mermoud [ Thu Aug 29, 2019 11:23 pm ]
Post subject:  Re: One Diode Model Linear or Non-Linear Temperature Correction

This is an artefact of the one-diode model.
For numeric reasons, I had to limit the Diode Saturation current at a threshold value of 0.01 pA. When limiting to this value, the muPmpp becomes positive.
This arises at very low temperatures, when you define a Rseries value close to its maximum RSMax.

I judged that below -10°C, this remains acceptable. By the way even if the muPmpp becomes positive the one-diode model still works correctly. Simply the Pmpp doesn't increase anymore when going towards lower temperatures.

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