Page 252 - Applied Photovoltaics

operators to redirect the panels whenever they wish. The mechanical structures for the
latter tend to be more complicated, less robust and more prone to failure. Of course,
the option of manually redirecting the solar panels depends on the availability of an
operator, which for some remote or inaccessible locations may not be feasible nor
practical. However, to give an appreciation of the potential benefits, in 1981 the
World Bank, using one of the most efficient photovoltaic water pumping systems
then available (Arco Solar System), added a simple manual tracking system requiring
two adjustments per day. The result was that a 30% relative improvement in the daily
efficiency of the system was achieved (Halcrow & Partners, 1981b).

EXE RCI S ES
11.1 (a) Discuss the use of solar cells in water pumping systems.
(b) What are the alternative techniques for water pumping and how does
the use of solar cells compare to each of these?
11.2 (a) What are the advantages and disadvantages of a directly-coupled
photovoltaic-powered water pumping system (where the solar panels
are directly connected to the motor/pump, with no interface circuitry
or batteries)?
(b) What limitations does such a configuration impose on choice of
pumps?

(c) In what situations or applications would such a configurations be:
(i) preferred
(ii) unacceptable?
11.3 Can you tell the difference between a permanent magnet, brushless DC
motor, and a synchronous AC motor?
11.4 (a) Outline the potential range in water pumping system configurations,
using AC and DC motors, the wide variety of water pump types and
power conditioning circuitry.

(b) Obtain information on the availability, price, operating performance
and characteristics of the different components that make up a
photovoltaic-powered water pumping system.

(c) Are there problems in matching these components, from efficiency
and compatibility perspectives, within such a system?
(d) Discuss the suitability of the different configurations for specific
pumping applications, indicating the relevant strengths and
weaknesses of each.

11.5 (a) What are the advantages and disadvantages of photovoltaics for water
pumping?

(b) Discuss the variability in types of water sources and their
characteristics.

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