Technology
Outdoor Photovoltaic Lighting
What do a highway billboard, a campground parking lot, and your front
walk have in common? Not a great deal at first glance, but they are
all possible locations for outdoor solar photovoltaic (PV) lighting.
Outdoor PV lighting is easy to install, virtually maintenance free,
and in many applications very economical, as long as the system(s) will
receive the manufacturer's recommended hours of sunlight.
Outdoor PV lighting systems use PV panels (or modules), which convert
sunlight to electricity. The electricity is stored in batteries for
use at night. They can be cost effective relative to installing power
cables
and/or step down transformers for relatively small lighting loads.
A few examples of outdoor PV lighting applications include:
 Billboards and Highway Guide Signs
In 1989 the Florida Department
of Transportation used PV lighting to illuminate an important guide
sign
on an isolated section of interstate highway, several miles from the
nearest utility service. Even in less isolated areas the cost of hooking
into
and installing traditional utility power for road signs and billboards
can be two or three times the cost of a PV system.  Campground and Recreation Area Entrance Signs and Restroom
Lighting
The U.S. Bureau of Land Management, National Park Service, and State
Parks
Departments have installed numerous PV lighting systems on campground
and visitor facilities around the country.  Exterior Home Lighting
Several companies now
market units for marking or decoratively highlighting driveways, walkways,
and patios. Many of
these designs are totally self-contained units that need only to be
staked into the ground in a sunny location. Others have the lights
separate from
the PV panel(s) so it can be placed in a sunny location. Units vary
in size from small eight-inch red glowing pathway markers to pole-mounted
patio and high-beam security lights.  Municipal Park Lighting
In Indiana, a PV lighting system installed
to light restrooms and a parking lot in a county park saved thousands
of
dollars. It also avoided the trenching and disturbance to trees and
shrubs required to run a mile-long utility cable to the park. In North
Miami
Beach, Florida, PV nighttime park lighting cost $900, instead of the
$3,000 to bring in utility power. Streetlights
The Bent Tree Community Association,
located in a west Miami, Florida suburb, installed 26 PV powered streetlights
in the summer
of 1991. Two 48-watt PV modules charge two batteries. The battery capacity
enables the lights to operate from a full charge for 12 hours a night
for four nights without recharging.
 Home outdoor PV lighting systems are often available in hardware, lighting,
and discount stores as well as through environmentally oriented mail
order companies. Home outdoor PV lighting is practical for all parts
of the
country, though it is important to consider geographic and site specific
variables when choosing a product. The key factor is that the PV panel
or unit must be in a place where it will receive sunlight.
The "nightly run time" listings on most "off-the-shelf" products
are based on specific sunlight conditions. Systems located in places
that receive less sunlight than the system is designed for will operate
for
fewer hours per night than expected. Nightly run times may also vary
depending on how clear the sky is on any given day. Operating times in
the winter
months may vary as much as 30% to 50%. Unless the PV system has been
sized specifically for winter operation, the system will not operate for
the
specified number of hours per night in a given location. Shading of
the PV panel by landscape features (vegetation, buildings, etc) will also
have a large impact on battery charging and performance. Bird droppings
on the PV panels can also negatively affect performance. Insufficient
battery charging will significantly affect performance and may reduce
the life of the battery.
 Nickel cadmium, sealed lead acid, and lead acid batteries are most commonly
used for outdoor PV applications. The bulb and the battery are the
two components that are most likely to need servicing. Check with the
manufacturer
to be sure that replacement bulbs or batteries are available before
you buy the unit. Also determine whether you will be able to recycle
the batteries
or how they can be disposed of properly. Some units do not provide
the option of replacing batteries, so the entire unit may need replacing.
Be sure that a safe recycling or disposal option is available.
Systems for large area lighting, such as for parking lots and billboards,
may be available through outdoor lighting contractors or through
PV system suppliers.
This brief was reviewed for accuracy and updated in November 2007.
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