Page 150 - Applied Photovoltaics

Telecommunications has been the backbone of the Australian PV market for many
years. Telecom (now Telstra) first experimented with PV installations in 1972 and is
still a major PV customer. Costs fell from A$30 to A$2 per voice channel in the ten
years to 1989 (Mack & Lee, 1989). There is now over 3 MW of installed PV
p
capacity in the Telstra network (McKelliff, 2004). Telstra uses PV to power repeater
stations within communications systems that link major centres and for individual
customer services in remote and rural areas. Three different telecommunications
applications for PV are discussed below (Mack & Lee, 1989).

8.4.1 Transportable PV power supplies
Typical trunk microwave radio repeater loads have reduced from around 1000 W to
under 100 W over the past few decades, opening the market to photovoltaics. By
1976, Telecom had developed a transportable solar power supply which used a
standard shipping container to:
x house photovoltaic arrays during shipment
x house batteries in the working system
x provide facilities for maintenance crews
x provide a mount for solar panels.
These systems formed the basis of the first major telecommunications trunk link in
the world. The 500 km link from Alice Springs to Tennant Creek opened in 1979,
with 13 repeater stations powered entirely by photovoltaics. The systems are designed
for extremely high availabilities, typically including 15 days of battery storage. The
batteries used have:
x pure lead positive plates
x low self-discharge (typically 3% per month)
x long life (about 8 years).
The systems proved so successful that more than 70 similar microwave repeater
stations have subsequently been installed across the country, as shown in Fig. 8.1.
Reliability has been improved by the use of passively-cooled storage shelters for
batteries and electronic equipment. Although PV battery systems are preferred, hybrid
systems are sometimes used. These use a diesel generator to provide less than 10% of
the annual power requirement, but significantly reduce the necessary solar array and
battery size and ensure system availability approaches 100%. The resultant cost
reduction further increases the cost-effectiveness of photovoltaics, although increased
maintenance for such systems is inevitable, such that these hybrid systems are not
suited for use in very remote areas.

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