Powered by the Sun

Solar-power offers long-lasting lighting for bus stops and shelters

Sunday, September 1, 2002

Bus Ride Magazine - Sep 2002

Bus Ride Magazine

It seems like the simplest solution: instead of plugging in, look up to the sun for the newest powering options for outdoor applications.Solar illuminated bus shelters, bus stops and schedules promise to offer transit agencies easy installation with no digging, wiring, or electrical connections. Manufacturers says maintenance is so easy that the only thing transit agencies have to do is change a battery every five years or so.

By harnessing the power of the sun, manufacturers use a solar panel to convert daylight to electricity. The solar panel then works like an engine to charge long-life batteries, which store the energy until it is needed to power the lights. A solar panel, which is created with solar cell, or photovoltaic (PV) technology, has become more advanced over the years, making leaps and bounds since it began appearing in solar calculators decades ago.

Manufacturers say solar-powered lighting is so reliable that it can work even in cloudy places. Matt Hollister, account manager with Solar Outdoor Lighting of Palm City, FL, explains, "There's a variable we plug into an equation, it's called a sun hour. For instance, you have more available sun hours in Florida than you would in Illinois. The further north you go, typically the fewer sun hours are available to power the solar panels that charge the batteries each day for each evening's use. It really doesn't have anything to do with cloudiness, it has to do with latitude, the further away from the equator, the further we are from the sun, there's a different angle that the sun would hit the solar panels."

In essence, according to Hollister, the solar panel is able to receive the sun's rays much like we can still get sunburned on a cloudy day. "There are UV rays that are always coming through the cloud cover that will energize the solar panel to charge the battery," he says. "It's not as good as a very sunny day. However, charging will still take place." He also says that the system features a charge regulator that carefully monitors the charging and discharging of solar-generated electricity when the batteries have been fully re-charged.

Hollister says battery power for colder climates had to be "overengineered."

"In colder climates, we increase battery capacity, knowing that in winter months we are going to lose some of that capacity due to colder weather," he says. Additionally, the battery was engineered with a five-day back-up, so even if the solar panel was covered with a blanket and no charging took place, the system would still be able to work. An option to driving around at night and checking to see if the lights are still working properly is to use a test switch that can be turned on during the day.

Customers from Seattle, WA, to Erie, PA, have been testing the system and agree that the system still works even during the cloudiest seasons. Bill Macrino is a purchasing agent with Erie Metropolitan Transit Authority. He says that they have gotten more than their share of cloudy days since installing the lights, but the lights have worked well and offered their passengers in the downtown areas the necessary security lighting.

"Transit agencies are excited about this because they have a persistent problem with 'pass-bys,' where drivers miss picking up passengers because they can't see them at night," says Art Alyesworth, Carmanah's chief executive officer. Passengers waiting for a bus only need to press a button to activate the bus signaling device that is mounted at the top of the bus stop. The light is then automatically timed to shut itself off. The schedule case is operator-free because it uses a remote sensor to light up, and does so automatically when a person walks up to it, enabling it to be used any time during the day.

The highly-efficient LED

Carmanah's technology uses the integration of small solar panels, small batteries and light emitting diodes (LEDs). Aylesworth says the LEDs use a fraction of the power that a regular incandescent bulb uses. "Not that long ago, LEDs were just the small glowing red button on your stereo. They have gotten pretty advanced. They're much brighter and come in various colors and they have made lots of improvements and have gotten good enough that they can actually replace lightbulbs," he says.

He stresses the light source is so power efficient that it will last approximately 100,000 hours for about 27 years, assuming the LED is on for 10 hours a day. That's about 20 times longer than the life span of 5,000 hours of the best incandescent bulbs. He stresses an advantage to using LEDs as a light source is that almost no energy is wasted through heat dissipation. Furthermore, the LED focuses its light without using additional optical components.

Aylesworth says they have been monitoring the progress of its solar lights in a project with the city of London, England. He says if a system can be engineered to make it through the winter months when demand is higher because the days are shorter, then the system will be successful. "We have to design for the worst situation, which is December. If you can make your lights operate functionally during that time of year, the summer is easy," he says.

Aylesworth explains that the system was engineered to manage the extreme weather conditions and seasonal changes. He says that the lights are designed so that they can make decisions on how to manage their own power and how bright they need to be. For example, he says that in the winter when the system is getting less daylight, the lights can decide to turn down its brightness, thereby maximizing its battery power to last through the shorter days.

Carmanah also thought about what changes in temperature would do to the system, especially since its solar panels are enclosed in a polyurethane dome that refracts the light when it is low in the sky, allowing it to collect more sun. Aylesworth says this option, "is very vandal-resistant because curved surfaces are very hard to break." Yet, engineers also worked to ensure that the solar panel and the doming would expand and contract with the cold.

Another important factor is the ability to design a solar panel that not only offers durability, but optimal performance and a cost-effective price that can fit within any customer's budget.

Carmanah says that the potential demand for solar-powered bus stops, schedules and shelters exists, since they estimate that there are approximately one million bus stops in North America with 2,262 bus transit agencies in the U.S. spending one billion dollars annually on bus facilities.