Page 168 - Applied Photovoltaics

while portable systems can be turned away from the sun, or covered, to cease
operation.

8.16 ELECTRIC FENCES
There are enormous fenced areas in Australia, many of which are away from power
grids. Electric fences have been found to be extremely effective in preventing
intrusion from wild animals, such as dingos and kangaroos, while simultaneously
preventing farm stock, such as cattle, from escaping. A detailed guide to electric
fence design is given by Hurley (2004).
Stand-alone photovoltaic systems are well suited to powering the very small loads
associated with electric fences. A typical system would comprise:
x photovoltaic panels
x battery
x blocking diode
x high voltage, current limiting circuitry, which constitutes the load (converting
low DC voltage of panels to high voltages)
x power conditioning circuitry as necessary.
A high voltage with a very low current is applied to the metal wires in the fence. This
type of system is good for protecting long lengths of fence since it has virtually a zero
current draw under normal conditions. Photovoltaics is considered a suitable power
source since it is:
x cheap, relative to alternatives
x effective
x reliable
x relatively free from maintenance requirements
x portable, for temporary fencing.

EXE RCI S ES

8.1 (a) Give an overview of solar cell applications, past, present and future.
(b) Give specific details as to why solar cells are well suited to each
application.

(c) Why is there sometimes resistance to using solar cells in applications
already considered economical for photovoltaics?
(d) How substantial a contribution are photovoltaics likely to make to the
world’s electrical requirements in the future?

8.2 Discuss the suitability of photovoltaic powered systems for third world
countries. Consider:
x a range of applications
x feasibility and practicality

155