Page 240 - Applied Photovoltaics

smaller sizes (Bucher, 1988). Fig. 11.12 also clearly shows the superior efficiency of
DC versus AC motors. Owing to the high cost of solar panels, it becomes justifiable
in many applications to use more expensive DC motors to gain an efficiency
advantage. However, the trend in photovoltaics is for steadily falling prices, with the
potential for a further cost reduction over the next decades (Poponi, 2003). This will
tend to shift priorities away from efficiency as being the dominating feature in motor
design, in favour of lower cost, lower maintenance machines. However, AC motors in
general tend to be cheaper, which often complicates the choice.

Figure 11.12. Performance of DC and AC motors as a function of size (Bucher,
1988, Used with kind permission from Springer Science and Business Media).

There have been significant developments with small (typically 1–3 kW continuous
rating) DC brushless permanent rare earth magnet motors. These developments have
been stimulated by the demands of highly competitive, high budget, international
solar car races. In the World Solar Challenge, motor efficiencies as high as 92–96%
were reported, although corresponding costs are high (Cotter et al., 2000). Heat losses

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