Page 130 - Alternative Energy Systems in Building Design

106 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

The heating of the liquid is controlled by aluminium shadow plates. When one of
the canisters is exposed to the sun more than the other, its vapor pressure is increased,
forcing the liquid to the cooler, shaded side. The shifting weight of the liquid causes
the rack to rotate until the canisters are equally shaded.
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 axel movements by means pro-
grammable 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 mechanisms. Programs
within the control computational systems use a combination of solar movement algo-
rithms that adjust rotational axis movement in orientations that constantly maintain
minimal cosine angle throughout all seasons.

VERTICAL-AXLE TRACKERS
Vertical-axle trackers are constructed so as to allow pivotal movement of PV panels
mounted about a vertical axis. These types of trackers have a limited use and usually
are deployed in high latitudes, where the solar path travels in a long arc. PV panels
mounted on a vertical-axis system are suitable for operation during long summer days
in northern territories that have extended solar days. Figure 3.54 is a rendering of a
dual-axis solar power tracker installation.

Field Safety Recommendations

■ Do not attempt to service any portion of a PV system unless you understand the
electrical operation and are fully qualified to do so.
■ Use modules for their intended purpose only. Follow all module manufacturers’
instructions. Do not disassemble modules or remove any part installed by the
manufacturer.
■ Do not attempt to open the diode housing or junction box located on the backside
of any factory-wired modules.
■ Do not use modules in systems that can exceed 600 V open circuit under any cir-
cumstance or combination of solar and ambient temperature.
■ Do not connect or disconnect a module unless the array string is open or all the
modules in the series string are covered with nontransparent material.
■ Do not install during rainy or windy days.