rethink module-level model parameters dictionaries

[wholmgren]

#783 is adding a iam.IAM_MODEL_PARAMS dict that's simply sets of required parameters for IAM models.

#682 added temperature.TEMPERATURE_MODEL_PARAMETERS that includes default values.

#548 added pvsystem.DC_MODEL_PARAMS that's also only sets of required parameters.

We should reconsider if we want to expose these dictionaries to users.

These dictionaries are used by methods in PVSystem and ModelChain to automagically determine what functions to call. In principle, user code might do something similar with them, but I doubt that happens.

The TEMPERATURE_MODEL_PARAMETERS dictionary with default values is probably the most useful to an end user because the default parameters are useful when calling temperature module functions directly (i.e. not through ModelChain/PVSystem).

My short term recommendation is to:

• deprecate pvsystem.DC_MODEL_PARAMS into pvsystem._DC_MODEL_PARAMS. I'd also be ok with just changing it without deprecation because 1. 0.7 is a big release and 2. this change won't effect many people and 3. My time is limited.
• change iam.IAM_MODEL_PARAMS to iam._IAM_MODEL_PARAMS to prevent problems before they start
• leave TEMPERATURE_MODEL_PARAMETERS alone

[veronicaguo]

Hi Will, I opened a short PR to make DC_MODEL_PARAMS and IAM_MODEL_PARAMS private. Please let me know what you think and if I missed anything. Thanks!

[wholmgren]

Thanks @veronicaguo! I'm hoping that others will let us know what they think of these API choices and if the public dictionaries are actually useful to them or not...