With a diameter bigger than a hundred earths laid out in a line, the sun is big-really big. Solar power advocates thought that their technologies would be the correspondingly next big thing in the energy business. Instead, the costs are mammoth. Research suggests that one practical solution to the solar conundrum is concentration. Focusing sunlight into a tiny space can increase the amount of available energy and drive down the price per watt. In other words, to get big, the trick might be to think small.In this case, small is a parabolic mirror a little less than 20 centimeters on a side, developed by researchers at the Jacob Blaustein Institute for Desert Research of Ben-Gurion University of the Negev in Sede Boqer, Israel. The mirror focuses the reflected light to a small, flat reflector 12 centimeters away that, in turn, directs it down a 20 meter-long strand of optical fiber. Out the other end of the fiber comes an intense stream of heat that can cut like a knife-or a laser. “We’re taking the sunlight and concentrating it close to the fundamental limits, what it is at the surface of the sun,” says professor Jeffrey Gordon of the Blaustein Institute’s department of energy and environmental physics. Although just a prototype, in sunnier climes it could become a solar-powered mobile replacement for laser surgical instruments at a cost of as little as $1,000 in mass production. That compares favorably to the low six-figure price tag of the conventionally powered lasers now used in medicine. Experiments have progressed from dead animal tissue to tests by veterinarians.
The concept of concentrating solar power is as old as the first time a child grasped a magnifying glass and focused it on a leaf. And solar furnaces, like the one operated by the U.S. Department of Energy’s National Renewable Energy Laboratory in Golden, CO, have shown the effectiveness of concentrating energy on a large scale. That installation uses 32 square meters of mirrors to concentrate solar radiation by as much as 50,000 times, forming a ten-kilowatt heat source. Researchers have used that furnace to help deposit coatings on metals and ceramics, produce nanoscale materials, and detoxify hazardous wastes.
In a sense, concentrators restore sunlight to something a little closer to its original intensity. While the sun emits enormous energy, by the time it reaches the earth, that radiation is dispersed over a sphere with a radius of about 150 million kilometers. Moreover, many uses of solar energy, particularly conversion into electricity through photovoltaic (PV) cells, are highly inefficient: the world record for photovoltaic efficiency, currently claimed by BP Solar International, stands at a mere 18.3 percent. At that conversion rate, the kilowatt of solar power that, on average, strikes every square meter of sunlit land would produce just over 180 watts of electricity-barely enough to run a typical PC and monitor.