add missing area parameter for eta_m arg (#1182)
add missing area parameter for eta_m arg (#1182)

* add missing area parameter for eta_m arg

* Remove trailing whitespace

* Add LaTeX for formatting

* Fix line too long

* Remove trailing whitespace

* Correct formula

Co-authored-by: Cliff Hansen <66c1097fe20c117aa7739c81f9654d6d6bdec1f1@sandia.gov>

* Improve presentation of the formula

Co-authored-by: Cliff Hansen <66c1097fe20c117aa7739c81f9654d6d6bdec1f1@sandia.gov>
wholmgren/pvlib-python,pvlib/pvlib-python,mikofski/pvlib-python,cwhanse/pvlib-python