Page 129 - Applied Photovoltaics

Standards Australia (2005) also recommends that plugs, sockets and couplers should
be multipolar and rated for DC voltage at least 1.2 times the array open circuit
voltage. Their current rating should equal or exceed that of the associated cables.
Plugs and socket outlets normally used for AC mains power should not be used. Refer
to Standards Australia (2005) for details and further recommendations.

6.8.5 Earthing (grounding)
Earthing involves the provision of low resistance paths from selected points within
the PV system to earth (ground). Standards Australia (2005) provides a decision
flowchart to help determine the necessary equipment earthing. Earthing is not
required in some cases, including if double insulation is used. Equipment grounding
involves ensuring all metal enclosures and parts of the array frame that might be
touched by hands are well earthed.

System earthing (Ibid.) normally involves connecting one of the current-carrying
conductors (commonly the negative but possibly the positive or a centre tap) to earth.
The manufacturer’s requirements for power conditioning equipment, such as
inverters, should be taken into account in choosing the most suitable arrangement of
system earthing. This aspect is considered in detail by Standards Australia (2005).

Good contact with the earth is required via a ground rod. Contact with subterranean
water helps. Rocky soil may be a problem.

6.8.6 Lightning protection
Lightning protection is required when a system is deemed to be prone to lighting
(Standards Australia, 1999–2000a) but is usually not necessary (Standards Australia,
2002). Such protection may include clamping circuits, metal oxide varistors, transient
absorption zener diodes and/or circuit breakers. These act as open circuit devices until
the voltage across them rises above the rated threshold breakdown voltage, at which
point they provide a short-circuit to ground (see Florida Solar Energy Centre, 1987).
They will not protect against a direct lightning strike. The system design guidelines
(Standards Australia, 2002) include an informative appendix on lightning risk
assessment and protection, and common practices are described by the IEA-PVPS
(2003).

6.8.7 Metering and alarms

Battery terminal voltage, input current and, in the case of a system including a backup
generator, generator run hours, should be metered. Alarm indicators of high and low
battery voltage are desirable (Standards Australia, 2002).

6.8.8 Battery housing and signage

Batteries must be protected from the elements, whereas people, the natural
environment and equipment must be protected from acid and the risk of explosion of
evolved gas. Batteries can be buried below the frost line in water-tight enclosures,
with drain holes, if sub-zero temperatures are anticipated, or housed in a building
where temperatures remain above zero. The batteries themselves should never be
placed directly onto concrete, as this will increase the self-discharge rate, particularly

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