Temperature coefficient units

[williamhobbs]

solarforecastarbiter.datamodel.PVModelingParameters takes in temperature_coefficient in units of %/C, while the temperature coefficients used in pvlib, typically gamma_pdc, are in units of 1/C. Additionally, the example from the workshop is in units of 1/C:

temperature_coefficient=-0.003, # 1/C

Is there a reason that the units are different in solarforecastarbiter?

[williamhobbs]

I just remembered that the units for site metadata in the web interface are %/C, and I was probably involved in that decision, or at least had the opportunity to comment on it...

[lboeman]

It looks like we neglected to update the workshop notebook with new values after adjusting the units. Thanks for bringing it to our attention. I know that the API documentation for these units was not updated until long after this change was implemented in the core library and dashboard.

The primary motivations for this change were that AC and DC loss factor are specified in units of % and temperature coefficients are typically available on datasheets in units of %/C as discussed here: SolarArbiter/solarforecastarbiter-core#350

Conversion to units of 1/C for use in pvlib occurs in the calculate_power function: https://github.com/SolarArbiter/solarforecastarbiter-core/blob/25fc4c97114f9750d9e1381cddbc783e7024e662/solarforecastarbiter/pvmodel.py#L270

[williamhobbs]

The reasoning behind using %/C makes sense to me.

Thanks.

[wholmgren]

I am certain this came out of the DOE workshop in October 2019 in DC, and I recall you had some good suggestions there...

I'll transfer the issue to the workshop repository so we don't forget to update the notebook.