There's lots of ways to do this.  Assuming you want full tracking
(azimuth, elevation), and assuming the location is fixed, then I'd use
a simple RTC and sun camera.  The sun camera would be attached to the
solar array iteself (moves with the array so you don't have to
calibrate the motors).

Since you know the time and location, you can point to the sun.  The
elevation only needs to be adjusted perhaps once a week if you want
nearly perfect tracking, but even once a month or four times a year is
about as good.  Most trackers only do azimuth (horizon to horizon) and
are user adjustable for elevation since 4 times a year is within a few
percent of total energy output.

The sun camera is used to determine the location of the sun on clear
days, and can be used to set the RTC as well as the array.  It's not
needed if the motors are calibrated (ie, a known home position, like a
printer does) and you know the time is exact (GPS receiver).

You could use the phototransistors instead of a sun cam, and probably
get pretty good resolution.  It would certainly take less processing
if you went digital, and going digital gives you an easy way to reset
the array at the end of the day.

If you used a GPS receiver, a magnetic field detector, and had good
motors you could conceivably correctly track the sun on a moving
platform.

-Adam

On 8/21/06, Bob Axtell <engineer@neomailbox.com> wrote:
> To my delight, I have been given a shot at designing a solar tracking
> system,
> the arrays running at 24V. The arrays are very large, 14' sq and 18' sq. The
> user is UNCONNECTED from the AC mains, running his entire business
> from inverters attached to the system.
>
> Anybody have ideas? I know about (1) not allowing the moon to be tracked,
> (2) end the day by moving the array to immediately catch the dawn sun
> when it comes up, to minimize movement, and (3) the funny 4-diode array
> to determine where the sun is..
>
> --Bob
>
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