New solar lighting is nearing market

ASHRAE Journal, July, 2007

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OAK RIDGE, Tenn. -- A hybrid solar lighting technology that delivers natural lighting to a building with 50% efficiency is expected to enter the market in 2008.

Developed at the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL), the technology uses a rooftop-mounted 48 in. (1200 mm) diameter collector and secondary mirror that tracks the sun throughout the day. The collector system focuses the sunlight into 127 optical fibers connected to special light fixtures equipped with diffusion rods similar to fluorescent lightbulbs. The rods spread light in all directions.

One collector can power eight to 10 hybrid light fixtures that can illuminate about 1,000 [ft.sup.2] (93 [m.sup.2]) of space. During times of little or no sunlight, a sensor controls the intensity of fluorescent lamps to maintain a constant level of illumination.

According to ORNL, the system is estimated to save about 6,000 kWh per year in lighting and another 2,000 kWh in reduced cooling needs for a total savings of 8,000 kWh per year. If PV panels were used to convert the sunlight to electricity and then to convert the electricity back into lighting, the conversions would result in only about 2% to 8% efficiency.

Currently, 21 hybrid lighting systems are being tested at various demonstration projects in the U.S. including the Wal-Mart in McKinney, Texas. Sunlight Direct is planning for the commercial release of the HSL technology in early 2008.