Page 160 - Alternative Energy Systems in Building Design

136 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

to the motor) for up to about 15 hp, and the base-mounted type (where the separate pump
and motor fasten to a base and are connected by a coupling) is used for larger sizes.
The static lift is typically the distance between the operating level in the cold water
basin and the reservoir inlet near the top of the towers. When selecting a pump, it is
important to make sure the net available suction head exceeds the required net suction
head. This ensures that the application will not cause water to vaporize inside the pump,
resulting in a phenomenon called cavitation. Vaporization inside the pump occurs when
small water particles essentially “boil” on the suction side of the pump. These
“bubbles” collapse as they pass into the high-pressure side, producing the classic “marbles
sound” in the pump. If operated under this condition, pumps can be damaged.
Pumps are also required to operate under conditions of net positive suction head
(NPSH), which means that the pump lift must be able to cope with the local baromet-
ric pressure and handle the friction losses in the suction line and vapor pressure of the
water being pumped.

SEMITROPIC OPEN-FIELD SINGLE-AXIS TRACKING SYSTEM
PV ARRAY: TECHNICAL SPECIFICATIONS
The following project was designed and built by Shell Solar, which consists of a solar
farm configured from 1152-kW solar array modules (Fig. 3.71). The project, referred to
as the Semitropic Water District (SWD), is located in Wasco, California, approximately

Figure 3.71 A large-scale single-axis solar farming system, Semitropic Water
District, Wasco, California. Photo courtesy of SolarWorld.