Page 229 - Applied Photovoltaics

level and small bores, which place constraints on motor and pump sizes and types.
The particular case of water pumping for livestock is treated in detail by Stokes et al.,
(1993). Fig. 11.1 gives some of the common water pumping terms.

Figure 11.1. Common water pumping terms (after Sandia National Laboratories,
1991, used with permission).

11.2 SYSTEM CONFIGURATIONS
There is a range of possible components and configurations for photovoltaic water
pumping systems, as shown in Fig. 11.2. Selection of the most suitable components
and configurations for each specific application and site is critical to the economic
viability and the long-term performance of the system (Sharma et al., 1995).
In the simplest photovoltaic water pumping systems, the solar panels are directly
connected to a DC motor that drives the water pump. For such simplified systems,
DC motors and centrifugal pumps are virtually mandatory, because of their ability to
be matched to the output of the solar panels.

Volumetric pumps, often referred to as (positive) displacement pumps, have
completely different torque-speed characteristics and are not well suited to being
directly coupled to solar panels. Therefore when volumetric pumps are used, power
conditioning or maximum power point tracking circuitry is commonly included
between the solar panels and the motor/pump, to convert the electrical energy into a
suitable useable form.
Similarly, a range of motor types is used for water pumping systems, including DC
series motors, DC permanent magnet motors, DC permanent magnet brushless
motors, AC asynchronous induction motors and AC synchronous motors. As with the

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