Robert Morein said:
I notice that most solar trackers seem to use either a photosensor or
mechanical servo system.
I find this surprising, since telescopes are driven by very small
synchronous motors.
Astronomical telescopes that are on equatorial mounts use a different sort
of gearing though. The mechanism is designed to track stars, not the sun.
Yes, yes, I know the sun is a star. But stars move across the night sky
based on a 'sidereal day', not a 'solar day'. The 'sidereal day' is several
about 4 minutes shorter than the 'solar day'. So you'd have to reset the
clock mechanism at least a couple of times a year.
And as Duane has pointed out, the local 'noon' is not always exactly 24
hours apart. As the earth travels around the sun, it sometimes is traveling
faster and slower (owing to the slightly eliptical orbit). If you study a
list of the sun-rise/sun-set times for your locale for an entire year, you
will see this variation. This will require resetting the clock mechanism
more often again.
Optical trackers are simple and 'automatically' compensate for these
variation. A 'clock' type of mechanism *could* be used, but it would
require more adjustments and wouldn't really be any simpler. Many optical
units don't draw any power at night or severely cloudy weather, whereas a
clock would all the time.
daestrom
