Can anyone tell me the formulas for passive solar design? I need to calculate roof overhang, etc. I Live in Illinois right outside of St Louis, Mo Lat 38, Long -89 degrees. I think. LOL I have looked everywhere and there isnt anything that I have found that I can understand.

Try this link:

http://susdesign.com/tools.php

It works perfectly. Thank you very much :)

Sure wish I would have known about this 10 months ago! I did my overhang design using solar path info from Oregon solar lab, or whoever it is, and TurboCAD. Checked my design with the tools in the link, and glory be!, I'm going to have a well shaded SW facing window in the summer, and quite well exposed in the winter. Sometimes life is really good!

Here are some more links to DIY passive solar design calculators:

http://www.builditsolar.com/References/SunChartRS.htm

Borst Passive Solar Roof Overhang Design Calculator

You can use the free software Sketchup to draw the house and it will draw sun shadows for any date/time at your location.