The sun path analysis code in Pysolar is still pretty immature, but it’s also pretty cool. The basic deal is that you can start with a spherical picture of the sky and then calculate the path of the sun. This tells you when your photovoltaic panels will be shaded and when they’ll be in the sun.

A blog post describing basic usage is on Brandon’s blog. There is still more work to be done to develop a full shading analysis tool, but this at least makes cool pictures like the one below. The yellow lines estimate the path of the sun on June 21, September 21, and December 21, 2009.

(Click on the image for a larger version.)