Page 171 - Solar Power in Building Design The Engineer's Complete Design Resource

SEMITROPIC OPEN FIELD SINGLE-AXIS TRACKING SYSTEM PV ARRAY 141

Backtracking begins by adjusting the tilt angle of each row to 10 degrees east just before
the sun rises in the morning. As the sun rises, each row begins tracking east just enough so
that no row-to-row shading occurs. This backtracking continues until the tracker limit
angle of 45 degrees is reached, at which time, the tracker controller waits until the sun
catches up with the 45-degree tilt angle and then begins to follow the sun throughout the
day. In the afternoon, the controller will repeat the backtracking scheme until the sun sets.
Shell Solar is including typical energy profiles for tracking arrays in December and
June (the winter and summer solstices). These profiles illustrate the effects described
in the preceding and the impact they have on the annual energy production of a mul-
tirow single-axis tracking system. See Appendix C.
This project was constructed by Shell Solar Industries for customer Semitropic
Water District and placed in service in April 2005. Because of market conditions at the
time, Shell SQ-85 modules were used in place of the SQ-160 modules. Then because
of other project constraints (related to the state of California incentive funding program
at the time) the project size was ultimately reduced from 11,520 kW to 979.2 kW.
In July 2006, Shell Solar Industries and its projects and technology including the
Semitropic project and single-axis tracking technology was purchased by SolarWorld
Industries.
Installation of a comparable system with the present, more efficient SolarWorld
modules would require 6576 SW-175 modules = 1150.8 kW. The modules could
be assembled into 1096 prewired panels. The basic elements of the single-axis track-
ing system design and array would remain the same; however, because of the reduced
solar module surface area the system would require approximately 9 percent less
space. Figure 5.21 depicts the solar power inverter installation, Semitropic Water
District, Wasco, California.

Figure 5.21 Solar power inverter installation, Semitropic
Water District,Wasco, California. Photo courtesy of Vector Delta Design Group.