**Is your feature request related to a problem? Please describe.** PVWatts uses a temperature model, Fuentes, that's not implemented in pvlib python. **Describe the solution you'd like** Add the Fuentes model described in this pdf: [850330.pdf](https://github.com/pvlib/pvlib-python/files/5124949/850330.pdf) **Describe alternatives you've considered** Continue to use `sapm`. **Additional context** Originally discussed in https://github.com/pvlib/pvlib-python/pull/1022#discussion_r473559969