Issue 366 (#383)

* fix for issue #343

Now, passed 'offset' parameter are used instead of it's default value.

* test for issue #343

* solar_position_method passed to basic_chain wasn't used causing
execution of solarposition.get_solarposition with default 'nrel_numpy'
value in all cases.

* Update modelchain.py

doc string fixes for modelchain.basic_chain function

* Update v0.5.1.rst

* Update v0.5.1.rst

* Update v0.5.1.rst

* According to 'Solar Position Algorithm for Solar Radiation Applications'
 by Ibrahim Reda and Afshin Andreas there is usage of alpha_prime.

* what's new update for issue #366

Author: KonstantinTr

docs/sphinx/source/whatsnew/v0.5.1.rst

@@ -12,6 +12,8 @@ Bug fixes
 * Remove condition causing Overflow warning from clearsky.haurwitz
 * modelchain.basic_chain now correctly passes 'solar_position_method'
   arg to solarposition.get_solarposition
+* Removed unnecessary calculations of alpha_prime in spa.solar_position_numpy
+  and spa.solar_position_loop
 
 Enhancements
 ~~~~~~~~~~~~

pvlib/spa.py

@@ -952,7 +952,6 @@ def solar_position_loop(unixtime, loc_args, out):
         x = xterm(u, lat, elev)
         y = yterm(u, lat, elev)
         delta_alpha = parallax_sun_right_ascension(x, xi, H, delta)
-        alpha_prime = topocentric_sun_right_ascension(alpha, delta_alpha)
         delta_prime = topocentric_sun_declination(delta, x, y, xi, delta_alpha,
                                                   H)
         H_prime = topocentric_local_hour_angle(H, delta_alpha)
@@ -1064,7 +1063,6 @@ def solar_position_numpy(unixtime, lat, lon, elev, pressure, temp, delta_t,
     x = xterm(u, lat, elev)
     y = yterm(u, lat, elev)
     delta_alpha = parallax_sun_right_ascension(x, xi, H, delta)
-    alpha_prime = topocentric_sun_right_ascension(alpha, delta_alpha)
     delta_prime = topocentric_sun_declination(delta, x, y, xi, delta_alpha, H)
     H_prime = topocentric_local_hour_angle(H, delta_alpha)
     e0 = topocentric_elevation_angle_without_atmosphere(lat, delta_prime,