Note:  I have decided to add questions and answers that I get via email to this page:

How can I determine the amount of solar shading for a potential solar site?

There is a simple device, a "Pathfinder". 

http://www.solarpathfinder.com/works.html 

You place this device at the potential location for the solar panels.

You then trace a line on the paper under the dome.  Once done, you will have a good idea of the total solar output year-round.  Of course, we can't predict the weather..