Pysolar: staring directly at the sun since 2007

Pysolar is a collection of Python libraries for simulating the irradiation of any point on earth by the sun. It includes code for extremely precise ephemeris calculations, and more

Pysolar has two parts:

A library that, given a date, time, and and earthly location, calculates the location of the sun
A library that, given a panel spacing and dimensions, calculates the shading percentage as a function of time for a row of 2-axis tracked panels

Download

Pysolar used to be hosted at Sourceforge, but since March 2008, it's been hosted at Github. Releases 0.2.0 and previous are still available on Sourceforge, but you should not use them for anything new-- all versions before 0.4.1 have known, albeit minor, bugs.

Release 0.4.3 (If you're not sure, download this one.)

Prerequisites

Pysolar requires Python, which comes preinstalled on most Unix machines, including Apple's OS X. You can check to see if you have it installed on a Unix machine by typing python at a command prompt. If the result is something like
Python 2.5.1c1 (release25-maint, Apr 12 2007, 21:00:25) [GCC 4.1.2 (Ubuntu 4.1.2-0ubuntu4)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> you have Python. (You can escape from the Python prompt with Ctrl-D.)

If the result is more like
bash: python: command not found you probably don't have Python.

If you need to, you can download Python fromthe Python.org download page.

Examples of usage

Several examples of how to use pysolar can be found onthe examples pageon Github.

References

Abstract 1.1 MB PDF I. Reda and A. Andreas, "Solar Position Algorithm for Solar Radiation Applications," National Renewable Energy Laboratory, NREL/TP-560-34302, revised November 2005.
G. Masters, "Renewable and Efficient Electric Power Systems," Wiley-IEEE Press, 2004.
Abstract 4.6 MB PDF J. K. B. Bishop, W. B. Rossow, and E. G. Dutton, "Surface solar irradiance from the International Satellite Cloud Climatology Project 1983-1991," Journal of Geophysical Research, vol. 102, no. D6, March 27, 1997, pp. 6883-6910.