Before examining the means with which to create a BETTER solar street light specification, let’s start by taking a closer look at very bad solar street light specification from a recently released bid—as there is much to be learned in the process.
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Purchase and delivery of 10 solar street light systems with the following salient characteristics:
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Solar panel
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Sealed lead acid battery
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Solid state system controller that regulates batteries and has a low voltage disconnect
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Light fixture with LED lamp that produces good street lighting
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Light fixture mounting bracket
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Entire solar lighting system mounted to a pole
The primary reason why this specification is so bad is because it is too vague and thus open to a host of different interpretations. The net result will most likely lead to the purchase of cheap solar street lighting systems that offer poor performance, reliability and return on investment (all of which, quite frankly, gives the solar lighting industry as a whole a bad reputation).
The only sure way to avoid this situation is create a detailed specification that establishes precise solar street lighting system design and performance parameters including:
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Type and number of solar module(s) used in the array
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Single or Multiple Crystal solar panels
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Total solar array wattage
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How is solar array mounted to the pole
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Top of pole, side of pole, etc.
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Type of Light fixture (sometimes even including model or part number)
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Salient characteristics of light fixture
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Lumens per Watt provided by the fixture
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Type of lamping
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Light distribution pattern
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Light level requirements
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B/U/G rating and Dark Sky requirements
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Fixture bracket arm
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Fixture mounting height
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Specify area to be illuminated (ex. 2 lane street, each lane 12’ wide with no median, light pole set back 5’ from edge of street)
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Light level requirements—the more detail the better (ex. lighting on street must be .3 foot candle average with lighting uniformity rations under 10:1)
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Note: Never specify light levels according to ‘equivalency’ (i.e. LED fixture equivalent to 150 Watt metal halide) –as this type of spec lends itself to many different interpretations! Such is not the case with foot candle specification as a foot candle is a quantifiable measurement of light
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Type/description of system controller
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Detailed description of nightly system operation, which is critically important to ensure the solar lighting system meets needs since with adaptive lighting being installed on most systems, dusk to dawn is not always enough information. Examples:
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Dusk to dawn with no adaptive lighting features: Dusk at full intensity for the entire night
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Dusk to dawn with adaptive lighting features: Dusk + 6 hours at full 40 Watt fixture intensity…dimming to 20 Watt intensity…returning to full 40 Watt intensity 1 hour pre-dawn
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Split time lighting features: On for x number of hours after dusk, off, on again x number of hours before dawn
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Type of battery
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Total amp hours of battery
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Autonomous battery storage to ensure reliable year round system performance
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Note: 5 nights of battery storage should be a minimum. In certain parts of the world, more than 5 nights of autonomous battery storage needs to be specified to help ensure ultra-reliable year round system performance due to depth of discharge changes in climate conditions
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Salient characteristics of battery box and battery box mount such as NEMA rating, construction materials, etc.
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Type of pole: anchor base, direct burial, aluminum, steel, concrete, composite, etc.
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Light pole must support the total weight and EPA of the specified solar power street lighting system in AASHTO wind loads for your particular area
With these design and performance parameters incorporated woven into the specification, there is no question that the buyer will ultimately get high quality solar power street lighting systems at the best possible price.
