Page 157 - Applied Photovoltaics

Future CP systems
Markets for photovoltaic-powered cathodic protection systems will continue to grow
as a better understanding of photovoltaic systems is gained, as photovoltaic prices fall
and as metal coatings improve in quality. The latter result in higher integrity factors,
which would therefore reduce loads, making photovoltaic systems more economical.

8.6 WATER PUMPING
Photovoltaics are increasingly meeting the needs for water pumping systems in the
range between the very small systems, where hand pumps dominate, and the large
generator-powered systems (Ball & Risser, 1988). They are also becoming
increasingly popular in very remote areas where reliability, long life and freedom
from refuelling provide significant advantages over windmills or diesel-powered
systems. They offer low maintenance, cleanliness, ease of use and installation,
reliability, long life, unattended operation, and can be easily matched to any need.
Table 8.1 gives the breakdown in sizes of photovoltaic-powered water pumping
systems in use in the late 1980s. These systems are primarily used for rural water
supply, and to a lesser extent for irrigation, stock watering, and commercial and
industrial use (McNelis et al., 1988). By 2000, more than 20,000 PV-powered water
pumps were installed in developing countries, notably India, Ethiopia, Thailand,
Mali, the Philippines and Morocco (Martinot, 2003). A market overview and
comparison of commercially-available photovoltaic pumps has been published (von
Aichberger, 2003), and Short and Thompson (2003) discuss the positive and
potentially negative effects on communities in developing countries.

Table 8.1. Estimated number of photovoltaic-powered water pumping systems in
use by 1988 (Ball & Risser, 1988).
size no. systems
(W p)
0–500 11,000
500–1,000 100
1,000–2,000 8,000
>2,000 2,000

The most significant disadvantages of photovoltaic-powered systems are the high
initial cost, the variation of solar insolation, the diffuse nature of solar energy (low
energy density, which necessitates relatively large systems), and the relative
immaturity of the industry with regard to system design experience and system
component development, although the latter is rapidly being overcome.
On a life-cycle-cost basis, photovoltaic water pumping systems of less than 2 kW p are
becoming quite economical, relative to diesel-powered systems (Halcrow & Partners,
1981), while PV systems less than 1 kW p are always cheaper than diesel (Bucher,
1991). Fig. 8.5 shows typical unit water costs as a function of volume pumped per
day for both photovoltaic-powered water pumping and diesel-driven pumps. In
addition, Fig. 8.6 shows the unit water costs as a function of pumping head. The costs
of course vary from installation to installation, depending on the specific
characteristics, requirements, configurations and type of components used.

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