Frequently Asked Questions
We present these FAQs to help you draw up clear, concise specifications for our solar-powered traffic equipment. To further clarify your needs, please refer to Tech Support / Provide Your Requirements on this Web site.
What is Solar Traffic Controls (STC) basic product line?
Our product line consists of solar-powered crosswalk systems; flashing beacons for school zones; continuous-duty flashers; radio-activated systems; and sensor-activated flashers. We also offer engineering services for special traffic systems applications.
What are the baseline specifications for a solar-powered system?
The specifications remain consistent, i.e., you need to know three basic items:
1. Location - Specify the geographic location of the application site so respondents can provide accurate solar radiation data. For example, the State of Arizona is too general. The City of Flagstaff (in Arizona) would be more specific.
2. Load - Quantify the electrical load. A typical school zone flasher project may list either two 8-inch or 12-inch DC amber LED lamps, a time clock and a control circuit. The solar equipment provider usually furnishes these items and knows the power draw of each piece of equipment. You, the specifier, must identify the lamp configuration so the respondent can calculate the load's power draw.
3. Duty Cycle - The number of hours per day each piece of equipment in the load will be operated. For a school zone flasher this may break down to 2 to 4 hours per day for the lamps; for five school days with the controls being on continuously.
This critical information-location, load and duty cycle-enables the prospective vendor to submit an accurate sizing report. Details such as mounting the enclosure and solar array, type of door lock and days of battery autonomy should also be carefully itemized.
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What is a sizing report?
We input your basic requirements - location, load and duty cycle - into our database sizing program. The resultant sizing report will yield the solar array size and description for the location; the required battery subsystem needed; and the estimated performance for each month of the year.
The accuracy of the sizing report sustains your quote and forms the basis of your warranty. Be certain to obtain a sizing report as this is the necessary proof you need that the equipment being offered will work correctly.
What are the components of a solar-powered traffic control system?
A typical solar-powered flashing beacon system includes:
1. A solar array comprising a solar module which converts the sunlight to DC electricity; the mounting structure to hold the solar module and attach it to the pole; and the array output harness.
2. The system controls panel which consists of a charge regulator, flasher circuitry and, in a school zone system, a programmable timing device.
3. The battery for storing energy; most systems will consist of one to four batteries.
4. An enclosure which holds the electronic controls and batteries.
5. The LED lamp assemblies.
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What are the typical costs of a solar-powered traffic control system?
Our products and services are custom-engineered and manufactured. Typical costs range from $2,000 to $7,000. Solar-powered traffic systems are a viable, low-cost alternative to expensive hardwired installations; they allow you to stretch your budget to obtain the traffic control devices you need at affordable prices. Most systems are equivalent to the cost of obtaining an AC power drop. Solar power is a free energy source which eliminates the need for utility hook-up.
Most school zone systems include a single battery which may cost from $120 to $160 to replace once every four to seven years. Most AC powered systems will have their own meter which has a base monthly charge to operate of approximately $10 to $13. This means that the cost for powering the AC system during the same period will be on the order of $480-$1090.
How long will the battery bank last?
Battery life for our solar flasher systems is typically five to seven years: less expensive than grid electricity for the same period of run time. Battery life is subject to a number of factors. The three most critical things to consider are the average daily depth of discharge, the charging method and the temperatures to which the batteries are exposed. We have known gel batteries to last as long as seven years in cooler climates and as briefly as five years in hot climates. AGM batteries have shown a similar life span. It is safe to say the life of the system battery in a properly designed system should be on the order of five to seven years.
The cost to replace a sealed battery can be from $120 to $160 depending on its capacity. Since the actual battery life varies with environmental conditions, it is recommended that the flashing beacon systems be put on a preventive maintenance schedule and batteries replaced around the five-year mark. Some battery manufacturers can test batteries at their local distributors and provide you with an estimate of the life remaining in a battery.
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Will the system work in cloudy weather?
Cloudy weather should not preclude the use of solar electric in your next project.
A properly-designed solar flasher system can function in a cloudy environment and supply enough power to run the equipment for its duty cycle.
If you know the basic electrical performance of the solar module in full sunlight, you can calculate its productivity in cloudy weather. While it's true there is no direct sun on a cloudy day, sunlight penetrates the clouds in the form of diffused light. The cloud density dictates the percentage of sunlight which reaches the solar module. On a lightly overcast day, there may only be a loss of 10 percent. On a heavily overcast day, there may be only 50 percent of the equivalent solar radiation reaching the module. Nevertheless, there is some sunlight coming through which will produce electricity.
Systems for "cloudy" climates will obviously require larger solar arrays and battery banks than "Sunbelt" areas, yet may still offer a viable option over a traditionally hardwired system. Continuing improvements in solar module and LED technology will continue to decrease the costs of the systems and expand their useful range throughout all climates in the United States.
Will the system operate at night?
Yes, the battery bank is used to store energy produced by the solar modules during the day and to supply this power to the electrical loads as needed: during the night and periods of cloudy weather.
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Will the system perform reliably in a cold climate?
Solar modules actually generate more power at lower temperatures as the modules are basically electronic devices and the electricity is generated from light, not heat. Solar modules generate less energy in the winter than in the summer due to shorter days, lower sun angles and greater cloud cover, not cooler temperatures.
What type of maintenance is necessary?
A well-designed system will operate unattended and requires minimum periodic maintenance. The savings in labor costs and travel expenses can be significant.
Maintenance for solar modules is generally confined to shading from surrounding plants and accumulations of dirt or bird droppings on the modules. Modules installed at a tilt are usually washed clean of dirt and droppings by periodic rains. If a large bird, such as a hawk, uses your solar array as a convenient perch, you may need to periodically wash the droppings off the solar module.
Remember to check for shading from nearby trees, shrubs and buildings that may impact your solar power output. The best time to inspect your modules is between 10 a.m. and 2 p.m. when the majority of the day's charging takes place. Trees and shrubs may need to be trimmed periodically to prevent shade-related problems. Loss of even a half of a cell in polycrystalline or crystalline solar modules can cause significant power loss, and is easily prevented.
Electronic controls have become more reliable over the years yet issues arise which require maintenance. The most common is damage from lightning-related events; another could be failure of the timing device. Lightning strikes are unpredictable. We have seen entire control panels destroyed or a single lamp drive transistor fail. Agencies should plan to keep a spare control panel on hand if they have multiple systems. Regular maintenance should consist of checking connections to ensure they are clean and tight. Also check the timing device for time drift and that the system functions manually in the event of a time clock failure.
The system battery is the one component that will wear out and need regular replacement. Most manufacturers use only sealed, lead-acid batteries for flashing beacon systems. The all-important reasons: they're maintenance free so technicians need not add water periodically and there are no fumes or acid-related corrosion issues. These batteries cost substantially more yet appreciably reduce maintenance during the life of the system.
LED lamps have become less expensive over the years and have replaced incandescent light sources for most solar beacon systems. Individual LED elements have a rated life of 100,000 hours which translates to more than 11 years of continuous, reliable operation. Most DC lamps use a simple regulator circuit to maintain the optical output of the lamps. Consequently they do not experience the failure rates for their circuitry as with the far more complex AC lamps.
Because of their reliability, most LED lamps on the market include lengthy warranties: some up to five years. We have had only two DC LED lamps fail during the past four years-a small sample compared to the several hundred we ship every year. Aside from an occasional cleaning of the lens the LED lamp does not present a significant maintenance issue in the beacon system.
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We don't have an engineering crew to install these systems. Will STC assist us with the installation?
Our solar-powered systems are designed for quick and easy installation in the field; there's no power drop; no trenching; no boring; and no sweat. STC's careful front-end engineering performed at our manufacturing facility results in a high level of integration of the delivered system to your site. This minimizes your installation costs and provides years of trouble-free operation. Furthermore, a complete documentation package is included. If you have questions, please call us in Arizona at 480-449-0222.
How do I write specifications for a solar-powered system?
Go back to basics when writing specs for a solar-electric powered system: 1-2-3, location, load, duty cycle. Seek advice from those who have had success with solar-powered projects. Review basic solar design literature on the Internet. Does the spec for the equipment outlined make sense from a physical and electrical standpoint? Finally, if the responses you receive are vague, ask for a sizing report and a full technical outline of the items to be submitted. Low prices turn costly if the equipment meets a poorly designed spec and does not function as a system.
Joseph Wise, "Solar Flashers: How to draw up clear, concise specifications"
IMSA Journal, July / August 2004
Joseph Wise, "Maintenance and Long Term Costs of a Solar Beacon System"
IMSA Journal, April / May 2005
Joseph Wise, "Solar Flashers: Too Cloudy for You?"
IMSA Journal, November / December 2002
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