Page 170 - Solar Power in Building Design The Engineer's Complete Design Resource

140 SOLAR POWER GENERATION PROJECT IMPLEMENTATION

ENERGY PERFORMANCE

Generally speaking, it is estimated that the annual energy production from a single-
axis tracking system can be as much as 20 percent higher when compared with that
of a comparable fixed-tilt system. In general, the single-axis tracking modeling soft-
ware used in this project calculates energy production of a single north-south axis
row of PV modules from sunrise to sunset (90 degrees east to 90 degrees west). The
most popular software currently used for calculating solar array output performance
such as PV Design Pro or PV watts use a 90-degrees east to 90-degrees west algo-
rithm to calculate the maximum available annual energy. As discussed in earlier
chapters, when calculating energy output performance, shadowing effects must be
accounted for in the annual energy production model. Figure 5.20 depicts the track-
ing tilt actuator mechanism at Semitropic Water District, Wasco, California.
When tracking multiple rows of solar panels, the higher the tracking limit angle (in this
case 90 degrees), the larger the shadow cast in the morning and afternoon hours. This
shadowing will effectively shut down energy production from all the rows located behind
the eastern-most row in the morning and the western-most row in the evening. This effect
can be reduced by limiting the tracking limit angle to 45 degrees. From a practical stand-
point, the linear actuators used in the most popular systems easily accommodate a 45-
degree limit angle and are the hardware used in the proposed system. To further improve
the energy performance of the system, a backtracking scheme is used in the morning and
evening hours of each day to eliminate the row-to-row shadowing.

Figure 5.20 Solar tracking
tilt actuator mechanism,
Semitropic Water District,
Wasco, California. Photo courtesy
of Vector Delta Design Group.