Page 120 - Solar Power in Building Design The Engineer's Complete Design Resource

90 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

Figure 3.27 Position of tracker after completing
daily cycle.

As the sun moves, the rack follows at approximately 15 degrees per hour continu-
ally seeking equilibrium as the liquid moves from one side of the track to the other.
The rack completes its daily cycle facing west. It remains in this position overnight
until it is awakened by the rising sun the following morning.

Active trackers Active trackers use motors and gear trains to control axle move-
ments by means of programmable controlled timers, programmable logic controllers,
and microprocessor-based controllers or global-positioning-based control devices that
provide precise power drive data to a variety of electromechanical movement mecha-
nisms. Programs within the control computational systems use a combination of solar
movement algorithms that adjust rotational axis movement in orientations that con-
stantly maintain a minimal cosine angle throughout all seasons.

Vertical-axle trackers Vertical-axle trackers are constructed in such a manner as to
allow pivotal movement of PV panels mounted about a vertical axis. These types of track-
ers have a limited use and are usually deployed in high latitudes, where the solar path trav-
els in a long arc. PV panels mounted on a vertical-axle system are suitable for operation
during long summer days in northern territories, which have extended solar days.

Electric Shock Hazard and

Safety Considerations

Power arrays, when exposed to the sun, can produce several hundred volts of dc power.
Any contact with an exposed or uninsulated component of the PV array can produce
serious burns and fatal electric shock. The electrical wiring design and installation