Page 166 - Applied Photovoltaics

x domestic use.
Lamp efficiencies have increased enormously in recent years, but still tend to be
higher for higher powered lamps. Common lamp control techniques, which contribute
to higher efficiency include:
x photo cells (to turn the light on only when sufficiently dark, and turn it off
automatically when light levels are adequate)
x timers (for specific periods of operation or coding for identification)
x switches (to allow manual control, especially for domestic use)
x sensors, such as motion and infrared detectors (especially useful for security
systems).

Although gradually improving in quality, many of the photovoltaic-powered garden
lighting kits marketed over the last decade tend to be gimmicky and unsuitable for
their intended use for any reasonable period of time. Common problems include:
x use of low-efficiency amorphous silicon solar panels which degrade with time
and produce insufficient electricity
x use of low-efficiency lamps, which provide inadequate lighting
x poor encapsulation, which allows moisture to penetrate and corrode solar cell
contacts
x flimsy plastic moulding, which is easily broken and degrades with outdoor
exposure
x inadequate charge controllers, which permit overcharging and over-
discharging of batteries.
Most stand-alone photovoltaic lighting systems operate at 12 or 24 V dc . Since
fluorescent lamps are over four times more efficient than incandescent lamps, they
are preferred in photovoltaic systems. ‘White’ LED lighting is a recent innovation
that is gaining popularity for applications that require only low light outputs. They
can operate with very low energy requirements, and hence only need small PV
systems.

Most lighting systems are considered non-critical, except for warning devices and
security systems, so that availability, and hence cost, can be relatively low. Since
lighting is typically needed after sundown, all photovoltaic lighting systems need
batteries. Deep cycling, and preferably sealed, batteries are recommended.

From the customer’s perspective, price, ease of installation, clarity of instructions and
safety, as well as performance and reliability, are of key importance when purchasing
lighting kits (Servant & Aguillon, 1992).

8.14 REMOTE MONITORING
Of the 20,000 photovoltaic-powered monitoring (telemetry) systems installed in the
USA alone by the late 1980s, 84% were in the 0–50 W range, and almost all are
12 V dc (Ball & Risser, 1988). Their applications include monitoring of (Maycock,
2003):
x climatic conditions, including storm warnings
x highway conditions

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