Page 244 - Applied Photovoltaics

x high efficiencies
x no need for an inverter
x well suited to direct coupling to photovoltaic panels
x high reliability if brushless
x submersible if brushless.
2. Disadvantages:
x brushed type not submersible
x brushed type requires higher maintenance
x expensive
x not readily available in larger sizes.

Figure 11.15. Performance curves for typical low cost, low efficiency permanent
magnet DC motor (Used with permission of Halcrow & Partners, 1981).

11.4.3 AC motors
A wide range of AC motors are commercially available, owing to the wide range of
applications for which they have been used for many years. However, with most of
these, the emphasis has been on low cost rather than operating efficiency. In
particular, small motors of about 1 kW or less suffer from very low efficiencies,
making them not well suited to photovoltaic-powered systems. In addition, they
require costly inverters at their inputs, which can exacerbate reliability problems.
Furthermore, to provide high starting currents, additional power conditioning
circuitry is generally required. In general, however, AC motors are very reliable and
relatively inexpensive, being typically half the cost of an equivalent size DC motor.
The two basic types of AC motor available are asynchronous induction motors and
synchronous motors. However, standard induction motors produce extremely low
starting torques, making them suitable only for low starting torque pumps such as

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