Solar Powered Lights: Realistic Expectations

The Japanese always seem to be one step ahead in technological wizardry, and it is thus fitting that the Toki no Sumika Gotemba Kogen Resort has constructed a tunnel lit by 3.2 million individual solar powered Light Emitting Diodes (LEDs). One of the most interesting aspects of this tourist attraction is that this vast number of LEDs only lights up the tunnel with a soft luminescence and not a dazzling blaze of light.

The Japanese tunnel illustrates the essential problem with solar powered lights. The light levels that are able to be generated by individual LEDs is fairly low. It takes over 30 LEDs to provide the light of one 13 watt CFL lamp, and although solar technology is advancing swiftly, there are still limitations on how much electricity can be generated per square foot of PhotoVoltaic (PV) panel.

PV films are a new development which equal the energy gathering capability of PV panels but in a thin film utilizing just 1% of the semiconductor material. However, the capacity to produce electrical power remains the same on a surface basis. One square foot of PV film will produce just about the same electricity of the same size of PV panel. Fortunately PV film is far less expensive per square foot than PV panels, so its development should lead to wider adoption of low intensity solar lighting applications.

Higher intensity solar lighting may still be far in the future. A maximum of 100 watts per hour of sunlight hits one square foot of area at sea level under optimum equatorial noon conditions, but the most efficient commercial PV panels can only turn that into 35 watts per hour. If the various factors of day length, cloudiness and latitude are factored in, many solar systems are hard pressed to produce an average of 150 watts per day from each square foot.

Assuming that we wish to apply solar power to lighting purposes alone and considering that the average American house uses approximately 250 kilowatt hours per month, over 55 square feet of PV panels must be dedicated to lighting alone. Since lighting is about 20% of the average household's total electrical usage, almost 280 square feet of PV are required for meeting the requirements to provide solar energy for the entire house.

Solar powered lighting systems also have to incorporate superlative battery systems as the draw in a home is rarely steady. Depending on the home, mornings and early evening electric draw can spike to ten times the average use, which would theoretically require 2,800 square foot of PV panel, and almost double that if the house is electrically heated.

The number of LED light bulbs required to light a home is excessive as well. An average house contains thirty incandescent 60 watt light bulbs, but to match that lighting would take well over a thousand LEDs.

Solar lighting is becoming more common in niche outdoor applications and technological developments should continue to improve efficiencies in every component. If considered as an adjunct to conventional lighting, solar powered lights can be appealing, useful, and a conversation starter to boot.

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