Page 251 - Applied Photovoltaics

in conjunction with their longer life expectancy, robustness, greater reliability and
freedom from requiring ongoing maintenance, make them well suited for such use. To
use float type lead-acid batteries under such conditions will cause problems with
excessive charging and discharging rates, and deep cycling. More conventional fork
lift lead-acid batteries are better suited to such use since the high self-discharge rates
become relatively unimportant, while their ability to charge and discharge quickly is
necessary.

11.7 ARRAY WIRING AND MOUNTING

11.7.1 Array wiring
Reference should be made to the stand-alone system design guidelines mentioned in
Chapter 6 (Standards Australia, 2002). Array cables should be heavy duty, with all
connections in water-tight junction boxes with strain relief connectors (Ball & Risser,
1988). The gauge of wire should be selected so as to keep resistive losses to less than
2.5%. For reliability, splicing of the leads from the motor to the array output cable
should utilise crimp-on connectors with resin-filled heat shrink tubing or equivalent,
to ensure long lasting, dry connections. All wiring should be attached to support
structures with, for example, nylon cable ties. PVC conduit should be used for the
array output wiring to the motor/pump, regulator or batteries. For a submersed
motor/pump, heavy duty double-insulated cable is essential. Also, the array and
mounting frames need to be grounded using substantial copper wire (Ibid.).
Grounding through the motor/pump and water source should not be relied on as the
system may be dismantled for various reasons. Lightning protection should be
considered, and bypass and blocking diodes should be included where appropriate.

11.7.2 Array mounting
All support structures should be anodised aluminium, galvanised steel or stainless
steel and need to be designed to withstand the maximum possible wind loading for
the particular location (Ibid.). Lock washers or equivalent should be used on all bolts
to remove risk of them coming loose during the subsequent 20 years. The structures
should be located as close as possible to the water source to minimise wire lengths,
and where necessary fencing may be used to protect from animals, theft, vandals etc.
(Ibid.).
Tracking support structures can be useful to enable the solar panels to point more
directly at the sun throughout most of the day. Motorised or passive tracking
mechanisms in Madrid, for example, have been calculated to boost annual water flow
by 40% or more. However, trackers operating outside for extended periods can
introduce considerable expense, maintenance and reliability problems (Illanes et al.,
2003). Vilela et al. (2003) calculate that tracking could increase the pumped water
volume by up to 53%, partly by allowing the pump to start earlier each morning. A
more affordable alternative is to use a manual tracking system, whereby a simple
adjustment by an operator can take advantage of the changing sun position. One such
regime is where a seasonal adjustment of the tilt angle is made a few times each year,
to compensate for the variations in the sun’s angle of declination. Another form of
adjustment allows for redirection of the solar panels twice a day to take greater
advantage of both the morning and afternoon sun. Yet another mechanism for
adjustment is a continuously-variable one, where it becomes the responsibility of the

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