Choosing the right safety sign: A/C vs. solar power
Radar speed check signs have become popular devices for slowing traffic and increasing worker safety. Thanks to new technologies, these signs have become more effective and easier to deploy than ever before. For instance, improvements in sign designs that make it easier to use solar technology now also make it possible to set up and use electronic signs in places where they were once impossible or impractical.
In fact, solar-powered signs are now used in many places that aren’t typically considered solar-power friendly.
“Even here in Alaska, where we receive long periods of sunshine and darkness depending on the season, our solar panel signs combined with battery backup power are used year-round,” said Michael Cobbold, safety manager and sustainability coordinator, Denali National Park. “Our calculations showed that the technology we needed to employ solar power was still more cost effective than it would have been to actually run a hard-wired connection to A/C power.”
But there are several issues that must be considered in order to choose the right equipment. The specific application, the environment and location where the sign is to be used and specific sign features all play a role in selecting the best setup.
Is solar the right choice?
The first thing to decide is whether A/C or solar-powered signs make the most sense for the particular situation. Conservation issues aside, the choice typically comes down to two concerns: cost and flexibility.
Solar-powered signs offer increased flexibility that plug-in signs simply can’t. Often times signs are needed in locations where hard-wired power sources aren’t readily available. In these cases, pure battery-operated signs are one alternative, but these require constant recharging — at least every week — which can be both costly and resource intensive. Also, overall battery life in these types of applications is typically short, so ongoing sign maintenance becomes a considering factor.
On the other hand, solar-powered signs can provide years of virtually maintenance-free service. They can easily be installed along roadways, loading docks, remote construction sites and other locations where access to A/C power is limited.
But what about the cost? Whether it’s connected to A/C or powered by the sun, driver feedback signs consume very little power — on average, about as much as a night-light. While the energy cost of operating these signs is negligible, the difference in installation costs can be dramatic.
Even when power is available nearby it may be necessary to tear up roads, sidewalks and landscapes in order to run the wiring necessary for an A/C connection. An A/C hook up may also require installation of a meter to measure the amount of energy used. Ask the utility company if it can bill a fl at rate for the energy used instead. Th is will save the cost of the meter and will reduce the overall cost of installation. A local utility company can lay out the specific requirements for the installation. With this information, a contractor can provide an estimate for overall construction costs.
Of course, with solar power one does not have to be concerned with meters or power runs. Once construction estimates for A/C power installation come in, it’s time to determine the cost of the particular solar power needs. By comparing the two a department can make an informed decision.
There are several things to consider when determining the cost of solar power. To begin with, ensure that the right equipment is being considered for the specific application. This is a matter of analyzing information concerning two things: the amount of power needed and the amount of available sunlight.
All electronic signs are not created equal. Different design features and functionality can have a significant impact on the amount of energy drawn. The more energy the sign requires to operate, the bigger the solar panel that will be needed.
For instance, some signs are made to focus light only where it is needed. Besides the advantage of preventing the distraction of other drivers, the focused viewing means less light is wasted and less power is used to achieve the same light intensity. High-end contrast enhancement technology can also reduce power requirements by providing a very dark background that permits excellent visibility with lower light output. Advanced glare management techniques can further improve the contrast ratio, again making them easier to see at lower light output.
Next, consider the specific application. The percentage of time the sign is illuminated will have a large effect on overall power consumption. High-traffic areas will cause the sign to draw more power than areas with occasional traffic. Similarly, signs used around the clock will require more power than those that utilize a timer to operate only during school hours or commute times.
Most significantly, one must determine the amount of sunlight that will be available — often referred to as units of solar irradiance or solar kilowatt-hours per square meter (kwh/m2). Since solar power signs rely entirely on the sun for their energy source, it’s critical that this information be accurate.
The most common mistake made when calculating solar irradiance is — using data based upon solar radiation averaged over many years. This may be fine for large solar power installations that include backup generators or power grid connections, but since electronic signs rely solely on the sun for power, it’s important the device get enough energy from the sun even during the most cloudy and miserable days of the year. Calculations must be based on worst-case scenarios rather than averaged data.
The most reliable data regarding worstcase weather conditions is provided by the U.S. Department of Energy in its 30-year Incident Solar Radiation charts. View this data at rredc.nrel.gov/solar. Be sure the provider is using this information to determine proper solar panel size.
It’s also important to consider the specific environment where the sign is to be used. Large overhanging trees, roofs or other obstructions can play a major role in the size and number of solar panels that will be required.
Using the correct data will also have an impact on battery life. Virtually all solarpower systems include a battery backup. A system that is undersized will require the battery to run for extended periods at less than full charge, dramatically reduce battery life.
Battery size is also a factor in system longevity. A battery that is drained more completely before each recharge will have a much shorter lifespan than one that is used only a little. For instance, a backup battery that is completely discharged each night will typically have a lifespan of approximately 300 cycles and would need to be replaced in less than a year’s time. A much larger battery would cost only a fraction more relative to the cost of the whole system, but a battery sized so that it is discharged only 10 percent every night will last closer to 3,600 cycles — potentially 10 years or more.
Understanding the data required to make an accurate calculation makes it possible to determine and compare the total cost of solar vs. A/C powered installations. Gather the information collected: traffic conditions, length and time of intended operations, regional solar data and local conditions; and share them with one or two sign dealers. Remember, resulting costs can differ dramatically depending upon the efficiency of the dealer’s products and the use of proper data.
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