Module Model Differences pvsamv1 and pvwattsv5

Hello Paul,

I´m currently trying to understand on which pvsamv1 module model (if any) the pvwattsv5 module model is based on.

Is it a simplified version of the CEC model, of the Sandia Cell Temperature Module (perhaps even the Simple Efficiency model, itself already a simplification of the latter), or is it an altogether different approach? If so, which?

I´m looking over the PV SAM Technical Reference and the PV Watts V5 Manual (both very complete guides I should add), but can´t really come to a conclusion. Could you shed some light on this please?

I´m asking in order to better gauge the necessity to use the more complicated pvsamv1 or, if possible, pvwattsv5 in my calculations, and for that I need to establish the critical differences in the approach to the module calculations.

Thanks once again in advance for any and all help,
Kindest regards,

Miguel Duarte

Dear Miguel,

The pvwattsv5 compute module contains the code behind the online PVWatts calculator, and the PVWatts implementation in the desktop version of SAM. It models the photovoltaic system using the relatively simple set of equations described in the PVWatts V5 reference manual, and has a basic set of inputs for describing the system.

The pvsamv1 compute module, implemented as the Detailed Photovoltaic Model in the desktop version of SAM has separate models for the module and inverter, and includes several models for shade and other losses. It has more inputs than PVWatts for module and inverter parameters, shading and other losses, and for the system design.

When you design a system in PVWatts, you specify a system capacity along with a few other parameters. In the Detailed Photovoltaic model, you choose a module and inverter, and specify a number of modules per string, and number of strings in parallel, and then choose various options for modeling shading and other loss factors. It offers several model options for the module, including the single-diode CEC model, Sandia model, etc.

The best way to explore the difference between the two models might be to run the desktop version of SAM, and create a file with two cases: One for PVWatts, and one for the Detailed PV model. You can then compare the inputs, and run simulations to compare the results. Once you familiarize yourself with the models, you can refer to the documentation in SAM's help system, and the reference manuals you mention above to better understand their similarity and differences.

In general, PVWatts is best when you do not have detailed information about a system design or when you want quick results. Because it has fewer inputs, it takes less time to set up a simulation. The detailed PV model allows you to explore more involved questions about the system design.

Best regards,
Paul.

Thank you once again for your thorough explanation Paul. I´ll do as you suggest, if doubts remain I´ll get back in touch.
Kindest,
Miguel D.