IVP wrote:
> I'm working on a solar tracker and would like to calculate the
> sunrise/sunset position. The aim is to use a PIC controlling a
> pair of steppers and gear trains

If this is just to point a flat solar panel in the right direction, then yo=
u
don't need much accuracy.  For example if you ignore the earth's tilt and
point the panel parallel to the equator plane then you're down to only 92%
of maximum at the solstices, with the yearly average being better.  So
simply making the panel go around in a circle every 24 hours, although you
generally don't implement the nighttime part of the circle, is going to get
pretty close to maximum efficiency.

If your system focuses the sunlight, then you do have to track more
accurately.  That could be done closed loop with a light sensor, which
alleviates the need for the PIC to know the absolute position of the panel
from the stepper outputs.

Most flat solar panels are just pointed to the noon equanox position and
left at that.  Unless you're doing something unusual, the extra cost of the
mechanics, installation, and maintainence aren't paid back by the little
extra efficiency you gain.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.