Page 117 - Solar Power in Building Design The Engineer's Complete Design Resource

ROOF-MOUNT INSTALLATIONS 87

Figure 3.22 Solar inten-
sity equation diagram.

by several bearings that are secured to some type of wooden, metallic, or concrete pylon
structure frame. The tubular axles are installed in a north-south orientation, whereas PV
panels are mounted on the tubular axle that rotates on an east-west axis and tracks the
apparent motion of the sun throughout daylight hours. Note that single-axis trackers do
not tilt toward the equator. As a result their power tracking efficiency is significantly
reduced in midwinter; however, their productivity increases substantially during the
spring and summer seasons when the sun path is directly overhead in the sky. Because
of the simplicity of their mechanism, horizontal-axle single-axis trackers are considered
to be very reliable, easy to clean and maintain, and not subject to self-shading.

Passive trackers The rotational mechanism of a passive tracker is based on the
use of low-boiling-point compressed gas fluids that are moved or displaced from the
east to the west side by solar heat that converts the liquid to gas causing the tracker to
tilt from one side to another. The imbalance created by the movement of the liquid-gas
material creates the fundamental principle of bidirectional movement. Note that various
climatic conditions such as temperature fluctuations, wind gusts, and solar clouding
adversely affect the performance of passive solar trackers. As such they are considered
to have unreliable tracking efficiency; however, they do provide better solar output per-
formance capability than fixed-angle solar support platforms. Figure 3.23 depicts
Zomeworks passive solar tracker component diagram.
One of the major passive solar tracker manufacturers is Zomeworks, which manu-
factures a series of tracking devices called Track Rack. Tracking devices begin track-
ing the sun by facing the racks westward. As the sun rises in the east, it heats an
unshielded west side liquid-gas filled canister, forcing the liquid into the shaded east-
side canister. As the liquid moves through a copper tube to the east-side canister, the
tracker rotates so that it faces east.