There are an estimated 43 million street lights in the USA and at least 55 million parking lot and parkway lights. Since they combine to use about 10% of all the electricity consumed in the USA, taking them to LED is a step in the right direction but going all the way to zero energy use is even better.

Look, Ma No Wires!

Rob Aldridge | TellCo Europe USA

During the last five years, technologies have improved and converged to make “wireless” solar LED street, parking, green space and other external lights feasible.  Although the initial cost per light standard can be higher, the lifetime costs will generally be significantly lower.  For new construction, where the electrical grid has to be extended, solar LED lighting is often the cheaper short term as well as long term solution and with zero carbon emissions, more environmentally friendly.  If you or your customers are interested in solar LED lights, here are some considerations as to choosing a product.

Lighting Requirements - Safety

There are obviously different requirements as to “lumens on the pavement” as well as lighting coverage based upon usage.  Highways and heavily travelled roads, as an example, require more lighting than would a store parking lot.  A manufacturer of solar LED lights should be able to assist by modeling the installation, including calculating whether it might make sense to use fewer, more powerful lights spaced farther apart and thereby use fewer lights overall.  In any case, you will want to be sure that you meet or exceed relevant Building Code requirements.

Lighting Requirements - Quality

In addition to the intensity of the lighting, decisions must be made as to “color temperature” as well as “color rendering index”.  The temperature is generally expressed in degrees Kelvin and typically ranges from 2,700 to as much as 7,000 K.  Towards the lower end of this scale and the light results in “warm” lights which have a yellowish hue, like traditional incandescent bulbs.  5,000 K is equivalent to natural sunlight with higher “cool” levels taking on a bit of a bluish hue.  Most outdoor lights tend to stay in the 5,000 K range.  The color rendering index is a rating for how accurately colors are depicted when illuminated by the light in question. As an example, can a red car seen under a street light at 2 AM be accurately described as to the correct shade of red?  In most cases, CRI should be at 80 or above.

Reliability – Long Term

Solar LED has the advantage of being all low voltage DC based, which results in greater efficiencies than switching to higher voltage AC.  As to long term reliability, the prime consideration is the battery.  Although there are other options, the best balance of useful life at a reasonable cost seems to be using deep cycle gel based products, which require no maintenance and if sized correctly, should perform for 7 to 10 years before requiring replacement.  Because extreme heat or cold can negatively impact battery performance, consider using a buried vault at the base of the solar LED light, rather than an external battery box which would be subject to greater temperature fluctuations.

Reliability – Short Term

Solar irradiation varies based on latitude and local weather patterns, so a solar LED light’s PV panel and/or battery should be sized to provide enough reserve energy for three to six days of very cloudy weather.  Make sure that this reserve capacity is calculated at or near the winter solstice, when the days are short and the nights are long. Local weather patterns also come into play here, since a place like Portland, OR has far more cloudy days than does Pierre, SD while they are both at very similar latitudes.

Economics?

There is no argument that installing a new high pressure sodium street light is less expensive than a comparable solar LED light, provided that the electrical grid connection is already there.  While there are some variations based on pole height and lumen requirements, a HPS light and standard might cost $1,500 or so while a self-contained solar PV equivalent could be $4,000 or more.  When the grid needs to be extended, however, that can easily cost $3,000 or more per light for the wiring, trenching, conduit, electrical components and labor involved.  For new construction, therefore, solar LED is often comparable or can even less expensive than traditional lighting systems.

If installed prior to the end of 2016, the solar LED light also qualifies the Federal Energy Investment Tax Credit.  Based on a recent IRS Revenue Ruling, it would seem that the entire cost of the installed unit, other than the LED light itself, would qualify for the 30% credit.  Since this includes the pole, solar PV panel, battery, controller and installation, it should be safe to assume that 25% or so of the entire cost will be recovered from the ITC.

Another difference, of course, is that solar LED uses no grid power, ever and the lights last three times longer than most non LED alternatives.  This means no electricity bill and fewer service calls to replace light bulbs.  While it is true that the battery must be replaced in 7 to 10 years, this is probably about a $200 expense. When compared to high pressure sodium lights, a solar LED unit can easily save an additional $8,000 to $10,000 over the next 25 years due to energy and maintenance savings.

According to a 2012 study done for the Department of Energy, there are an estimated 43 million street lights in the USA and at least 55 million parking lot and parkway lights. Since they combine to use about 10% of all the electricity consumed in the USA, taking them to LED is a step in the right direction but going all the way to zero energy use is even better. 


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