Page 149 - Applied Photovoltaics

Cells used in space are not protected by the earth’s magnetic field and atmosphere
and are subject to high energy particles and radiation, which reduce life expectancy to
about seven years. The ability of a solar cell to withstand such bombardment in space
without serious degradation is known as radiation hardness.

Research priorities for the next generation of space cells include weight and cost
reduction, since the PV panels can account for 10–20% of a satellite’s weight and 10–
30% of its cost (Allen, 1991). Also important is the ability to pack the array into a
small area for launching. Many space cells are made from gallium arsenide and
related compounds, rather than silicon, yielding higher efficiency but at much higher
cost.

8.3 MARINE NAVIGATIONAL AIDS

The use of photovoltaic cells to power marine navigational aids became economical
many years ago, owing to the high cost of replacing primary batteries. Since the loads
are small, photovoltaic cells are well suited to this application, provided the lamps
and lenses have high efficiency. A system typically comprises:
x 10–100 W p of solar cells
x low-maintenance battery in weatherproof storage box
x voltage regulator or self-regulation
x military specification timing and motor control circuitry
x automatic lamp changer with military specification DC motor.

Environmental protection of system components is of prime importance and is
achieved by:
x weatherproof and salt-resistant battery housing and photovoltaic module
encapsulation
x salt and water resistant wiring
x lens and circuitry housing seals
x use of spikes to prevent birds perching on and fouling light lenses and PV
module surfaces.
A high system availability is required, since navigational aids are a critical
application. However, obsolete circuitry is still used, with hundreds of components
that could be replaced by a single microprocessor or microcomputer chip. Since
navigational aids require military certification, it will take many years for the system
designs to be modernised. Photovoltaics are the standard choice for powering remote
lighthouses around the coast of Australia, as well as signal buoys in harbours and
rivers.

8.4 TELECOMMUNICATIONS

Repeater stations for telecommunications are powered by photovoltaic cells in
numerous countries. These systems are well suited to harsh terrains, such as Papua
New Guinea or countries where there are vast unpopulated areas without grid support,
such as Australia. The latter was one of the first countries to substantially use
photovoltaics for these purposes, with the involvement documented in the following
sections.

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