Page 169 - Solar Power in Building Design The Engineer's Complete Design Resource

SEMITROPIC OPEN FIELD SINGLE-AXIS TRACKING SYSTEM PV ARRAY 139

ELECTRICAL DESCRIPTION

As described in the preceding, the arrays are electrically divided into five equal subsec-
tions consisting of 1440 SQ160 modules, dc circuit combiners, one 225-kW inverter, and
a 225-kVA 208-12.47 kV step-up transformer. Thirty panels each containing four mod-
ules are used on each of the 60 single-axis tracking rows. Figure 5.19 depicts a solar track-
ing pilot insolation detection system, Semitropic Water District, Wasco, California.
The dc collectors feed underground current to each inverter’s dc interface, which
incorporate prefabricated fusing and a manually operated disconnect switch. The ac
output of the inverters also includes manually operated disconnect switches that feed the
low-voltage section of the step-up transformer. The low-voltage winding of the trans-
former includes a metering section that is fitted with an energy production meter. The
meter includes a cellular modem that can be read remotely. The electronic meters are
designed to store daily, weekly, and monthly energy production parameters.
The transformers step up the 208 V ac to 12.47 kV ac. The high-voltage output of
each transformer includes fusing and a hot stick disconnect. All five transformers are
loop-fed, and the final underground feed from the transformer pad extends 200 ft to
the north section of the array where it terminates at a riser pole.
The Xantrex inverters used in this installation meet IEEE 929 and UL1741 stan-
dards and as such do not require any anti-islanding hardware.

Figure 5.19 Solar tracking
pilot insolation detection sys-
tem, Semitropic Water District,
Wasco, California. Courtesy of Vector
Delta Design Group.