modelchain.PVWATTS_CONFIG is incorrect

[cwhanse]

When modelchain.PVWATTS_CONFIG was first added, the Fuentes temperature model was not in pvlib so temperature.sapm was substituted. temperature.fuentes was added in v0.8.0.

Consider changing PVWATTS_CONFIG.temperature_model to 'fuentes' here.

[cwhanse]

FTR, I am opposed to making the change from sapm to fuentes if we don't also add a default for the fuentes parameter noct_installed. We don't know what user code would break without the default parameter. I think those using PVWATTS_CONFIG are likely choosing it primarily for convenience and not for replicating NREL's PVWatts.

[kandersolar]

I thought I remembered discussing this idea, but I couldn't find any relevant thread on GH...

I think those using PVWATTS_CONFIG are likely choosing it primarily for convenience and not for replicating NREL's PVWatts.

Along these lines, fuentes's rather slow speed is a mark against using it here.