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the case for solar-powered LED lighting
- Feb 07, 2018 -

Rapid developments in solar cells, LED lighting and energy storage are creating great opportunities for solar-powered solid-state lighting.

The outdoor lighting industry, as with so many other application-oriented industries, assumes that the power source is infinite and always available. This is a tribute to the reliability of the electric grid - at least in developed-world nations. It has certainly made life simpler for the lamp/lighting designers who, for the most part, are able to divorce the lamp characteristics from the energy source. The developed world is starting to learn that the power source is far from infinite.*

Some companies are not waiting to see the bottom of the barrel, and are exploring alternatives that range from replacement power sources to energy demand reduction. A number of companies are developing technologies that achieve both: working in solar-powered solid-state lighting under the NOMO brand name is an example of this.

[* Estimates indicate at current levels of energy usage, the earth has about 150 years of energy stored in the form of oil, coal and uranium. However, if the entire population of the earth consumed as much as Americans' do on a per capita basis, that amount drops to 15 or 20 years.]

integrated solar street light.png

Integrated solar street light.png

Solar-powered lighting

Solar electric lighting systems do in fact connect to a truly "infinite" power source - the sun. However, as we all know, this source is intermittent. In the case of solar outdoor lighting, the power source is inversely related to the load (the lights turn on when the sun goes down). This relationship leads to an important conclusion; the system must rely on energy storage (e.g. batteries), unless it remains connected to grid.

Now in order for a solar lighting system to perform reliably, the solar panel and battery must be sized for the period of longest nights, shortest days and cloudiest weather, all of which occur at the same time each year (see figure 2). Historically, the solar industry has addressed this worst-case scenario by seeking out the most efficient lumen per watt DC lamps and over-sizing the system for the rest of the year. That translated to DC fluorescent bulbs, bigger solar panels, more batteries, higher costs and less-than-appealing appearance.

This approach confined the market for solar lighting to areas closer to the equator with highest average levels of solar irradiation and temperatures that did not affect the performance and lifetime of the DC fluorescent bulbs. It also left the markets in the higher latitudes, typically with higher per capita wealth levels and greater lighting needs rather under-served.