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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.
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