Here Comes the Sun

By: David Banasiak

From the earliest days solar energy helped dry crops and produce salt from brines. In the 1950s, MIT built an experimental house that derived its energy from the sun through solar panels on its roof. However, early attempts to harness the power of the sun with solar cells and batteries proved expensive and not very practical.

Continued experimentation resulted in small advances, and slowly solar-powered products became available. Pocket calculators, hot-water heaters and battery rechargers for backpackers were some of the new products making use of solar power. However-for solar power to make an impact upon the energy needs of the country-other, more significant applications required development.

Another area where solar power began to make inroads was arrowboards and changeable message signs (CMS). In the late 1980s the first solar-powered arrowboard made its appearance followed by solar-powered CMSs in the early 1990s. David Wilfong, marketing representative for Precision Solar Controls explains," Arrow signs were introduced in 1987 and changeable message boards were introduced in 1991."

Off to a slow start, solar-powered arrowboards and CMSs have gained in popularity and are increasing in dominance over diesel-powered signs. Now, according to Wilfong, 90% of the signs used are solar powered. Ken Smith, national sales manager for American Signal Co. agrees that solar- powered signs will dominate the market; however, he does not feel they will totally replace diesel-powered signs. Smith says, "Solar CMS will replace about 95% of all diesel signs. It won't be 100% until there are rgulations in place to require their use." However, some states may grandfather the use of diesels and contractors who already own diesel may not purchase new solar equipment until the diesels wear out. For contractors who hold on to their diesel signs, conversion kits are available from some manufacturers, which allow a switch over to solar. Allmand Brothers, for instance, offers a kit to convert gasoline- and diesel-powered arrowboards to solar-powered.

Improved technology is the main factor in solar signs' rising popularity. "Solar wasn't used sooner because the technology was not there," explains Nathan Batson, president of American Electronic Sign. "The capability to charge the batteries has improved. A display that does not use a lot of power also was needed."

Since the mid-1970s great strides have been made in photovoltaic (PV) cell technology. PVs are devices that generate voltage when exposed to radiant energy. A PV solar cell is usually a thin wafer made of silicon, gallium arsenide, cadmium sulfide, or cadmium telluride. Solec International, a manufacturer of commercial PV, has concentrated its energy on improving crystalline silicon PV technology. Through its fast-pull crystal growth process, Solec has cut the growing time by 60% resulting in lower cost PVs. This improves the practicality of PV devices allowing for more widespread use. It also makes solar power more affordable.

Improvements in commercial PVs has allowed manufacturers to decrease the size of their panels without a corresponding loss of energy produced. Smith said that American Signal Co. first produced solar-powered signs with an array of solar panels that was about 6 ft ¥ 8 ft and now they are about half that size.

Another technological advance that helped the rise of solar-powered signs is high-intensity light-emitting diodes, commonly known as LEDs. An LED is made of a special semiconductor material usually gallium arsenide, gallium arsenide phosphide or gallium phosphide. This material gives off light when an electric current passes through it. LEDs are often used in pocket calculators and digital clocks, watches and radios. While LEDs are more expensive to produce than incandescent lights, they offer many advantages. They operate on very low voltages and can be designed to emit a specific light color. In contrast, an incandescent lamp emits a white light with a broad range of light frequencies. LEDs also are very rugged and more durable than incandescent devices. However, excessive voltage and heat will damage them. Resistors are used with LEDs, to limit the voltage to acceptable values, because of the LEDs' susceptibility to even a slight increase in voltage.

The combination of more efficient energy consumption, through the use of LEDs, and improvements in solar cells, have allowed solar-powered signs to gain an upper hand over diesel-powered signs and it appears that solar will eventually replace diesel. "Diesel power is fading. The new signs that we sell are all solar powered," says Batson. "Most states are now providing specs for solar CMSs. In a few years they will replace diesel boards," adds Wilfong. Bob Heinz, marketing manager for Addco Manufacturing Co. agrees, "Solar will most certainly replace diesel. The diesel market may not exist one year from now."

Solar-powered signs posses many advantages over diesel- or gasoline-powered signs. Diesel signs use an engine and a generator to produce its power; thus requiring more manpower in refueling, as well as fixing break-downs and performing maintenance to the engine and generator. Solar, on the other hand, requires a minimum amount of maintenance. "Solar only requires a periodic check of the battery banks," states Wilfong.

With more moving parts, and a reliance on consumable fuel, diesels have a greater potential for power failure, thus resulting in possible tort liability concerns. Relying on the sun, solar-powered signs have less chance for power failure, because their source of energy is endless. Their use of battery banks ensure that the sign will remain lit at night. Depending on the model most units can last 18 to 21 to 30 days without sunlight.

Contrary to some beliefs, overcast weather does not effect the signs to the degree some would believe, because solar energy is made up of visible light, infrared radiation and ultraviolet (UV) rays.

Heinz explains, "Overcast weather is not a factor because enough sunlight gets through to allow the system to charge the batteries." Addco's model also allows the user to tilt and rotate the solar panel in order to receive the full benefit of the free energy from the sun. In addition to recharging the batteries with the sun, solar signs also can be charged by plugging them into an AC outlet.

Some manufacturers provide fail-safe modes for their solar signs in case of a power failure. American Electronic Sign, for example, provides a retroreflective flap that displays a preprogrammed default message in the event of a power failure. This flap can also be used to conserve energy stored in the batteries.

Solar also has environmental benefits over diesel. It does not produce air pollution and it is quiet running. Smith comments, "Solar is socially, politically and environmentally more correct quieter and cleaner."

As its popularity increases, solar-powered CMSs are moving beyond the work-site to play a role in intelligent transportation systems (ITS) (see Portable Traffic Management System Shows Promise for Easing Congestion, October, p 36). The Kentucky Department of Highways worked with Addco to use solar-powered CMSs in its ITS. This ITS project will alleviate congestion and air pollution on I­p;64 and I­p;75, through Lexington. CMSs will inform travelers of upcoming incidents and guide them through route changes. The signs also are equipped with radar guns to warn motorists to slow down as they approach an incident.

Georgia DOT also is using CMSs in its ITS. American Signal Co.'s signs were used in the recent high-occupancy vehicle-lane construction in Atlanta. Now that the construction is complete the CMSs will be used for incident management and traffic control during the Olympics. "What was once a tool used exclusively for work-zones is now used as an incident and congestion management tool," said Smith.