Hayes Time-Dependent Module Temperature Model should be added to temperature API.

[stephenjkaplan]

Description
A paper in JPV written by William Hayes in 2014 proposed a time-dependent module temperature model for fixed tilt utility-scale systems. (If anyone wants a copy of the paper, let me know). It's main strengths are that it can model temperature at sub-hourly intervals because if factors in the time dependency of module temperature on its heat capacity. The paper claims higher accuracy than other models.

Proposed Solution

• This would be added as a function to the API, as pvlib.temperature.hayes. The goal is to translate the paper into a function.
• Unit tests would be fairly straightforward. Inputs/expected outputs & any potential failure modes
• Validate against other models, or if there happens to be any available MST data.

Potential Obstacles

• As far as I can tell, there isn't anything in the paper that describes what initial condition to use. Each temperature is calculated based on the previous temperature in this model: so, what would be the initial module temperature?
• Some concern over validation. I don't have access to the data used to validate this model.

Additional Notes
I have started to prototype the API function for this and have discussed this feature with @wholmgren

[mikofski]

I would like to see Matt Prillman's weighted moving average temperature model implemented as well. Stephen, can you comment on differences between the models? Please see NREL/ssc#261

[cwhanse]

I think there's room and use for both models in pvlib

[cwhanse]

About the initial temperature - if in doubt, make it a user input. I'll look through the paper and look forward to the PR.

[mikofski]

As far as I can tell, there isn't anything in the paper that describes what initial condition to use

I believe if running a simulation that starts at midnight, then you can assume the panels are at steady-state in equilibrium with the environment, and therefore use the ambient dry-bulb temperature as the initial condition, otherwise, if starting the simulation when the sun is already up, then I agree with @cwhanse and let the user set the initial temperature.

[stephenjkaplan]

I would like to see Matt Prillman's weighted moving average temperature model implemented as well. Stephen, can you comment on differences between the models? Please see NREL/ssc#261

I haven't dug too deep into that paper, but from what I can tell, both of these models share very similar motivations, but involve different computations. Looks interesting, and sounds like both could be implemented without conflict.

[stephenjkaplan]

@mikofski @cwhanse thank you for the input on initial condition.

any recommendations on the best way to validate my implementation (with limited resources)?

[cwhanse]

pvlib relies on the published sources for validation of the algorithm. If you are asking about functional testing for pvlib, we test for correct calculation, and its OK to create a test input and corresponding output by hand. Or with a separate implementation in e.g. Matlab.

[stephenjkaplan]

@cwhanse yea, that's what I meant. I'm trying to talk to some people at First Solar (I've since left) to try and get my hands on the original implementation, but no luck so far.

[cwhanse]

If you can't get some code from FS, I could implement in Matlab. If our two calculations agree, that's enough evidence for me that the calculation is correct.

[stephenjkaplan]

one of the inputs to the model is effective POA (accounting for optical losses). is it conventional in pvlib to take care of those kinds of calculations within a function, or for the user to calculate effective POA separately with another API function and then use that as input?

[wholmgren]

Convention is for users to do that kind of prep. Keeps functions simple and maximizes user flexibility. If it were intimately tied to the model then we'd include it in the function, but I doubt that's the case here.

[stephenjkaplan]

another question: I have to perform the calculation for long wave radiation using view factors 3 separate times. this seems suited for a utility function. If I want to break out that functionality into a separate function, should I put it within temperature.py as a "private" underscored function? what is conventional?

[wholmgren]

should I put it within temperature.py as a "private" underscored function?

I suggest starting this way and we'll reevaluate once we see the pull request.

[wholmgren]

On that note, be sure to check out the contributing guidelines and perhaps review the discussion on some open and recently closed PRs. Lots of approaches to PRs and PR review, but in short everything is up for debate so don't worry about getting it perfect on the first try.