A subscale test model of the unmanned Centurion rests on the bed of El Mirage Dry Lake after test flight in March 1997. © 1997, NASA/Brent Wood
You may not have heard much from the solar energy folks lately, but that doesn't mean the sun has quit shining. The Why Files found these cool inventions for using the priceless rays.
Cruising like Icarus
Trust the military to come up with an imaginative but costly use for the sun. They're now working on the 220-foot wide Centurion drone, a flying wing that is designed to fly to 100,000 feet. That's high -- double the existing record for a solar-powered drone and three times as high as the average jetliner. With a total weight of about 1,000 pounds, Centurion will have 10 to 14 electric motors. The solar cells alone cost more than half a million bucks (see "Giant Solar-Powered Drone" in the bibliography).
And no, they're not selling tix to this flying wing yet. Can't figure out where first class goes in a plane without a fuselage, I guess.
Soggy solar sprinters
You're familiar, we trust, with the "Tour de Sol," an annual race for solar-powered cars. Turns out that solar cells can also move boats. The winner of the 1996 Solar Splash Boat Race was the Kanazawa Institute of Technology, in Japan. A University of Michigan craft won the sprint, sloshing through a 300-meter course in 25.73 seconds. (See "Solar Boating Gains Its Sea Legs" in the bibliography). What's next -- photovoltaic cells on the canoe paddles?
Back in the dawn of the WWW -- gosh, way back in early 1996 -- The Why Files covered the electric car controversy.
Still awake, day and night
Think about the sun -- it's a daytime thing -- got this habit of sleeping the night away -- just when we'd like to put it to work. To neutralize this fundamental drawback, in 1996 engineers began testing Solar Two near Daggett, California. The plant focus the sun's glare with thousands of mirrors on a container of salt. Molten salt -- hot salt (at 1050 degrees Celsius) -- is stored and used to make steam that is put through a turbine to make electricity day or night. If the test project works, it could provide juice 24/7 at a price competitive with fossil fuels -- in a decade or so. (See "Solar Energy 24 Hours a Day" in the bibliography).
Ray gun zaps pollution
Sometimes the best ideas come from left field. Sometimes they come from Florida. We're going to talk about one that came from Florida -- or at least is being advanced in the Sunshine State. It's no secret that stuff degrades in sunlight -- paints fade, wood crumbles, and bacteria actually croak.
What if that decomposing power could be put to use breaking down organic pollutants like trichloroethylene (TCE), a cleaning solvent that is a persistent groundwater pollutant? Solar-powered detoxifiers could be handy indeed in a country that has more than 30,000 hazardous waste sites polluting the groundwater.
The reaction, called -- take a deep breath and repeat after me: "photocatalytic oxidation" -- starts when a semiconducting material absorbs a photon, a particle of light. The semiconductor begins to act like a catalyst and produces hydroxyl OH- radicals. These radicals react chemically with pollutants, stripping them of their toxicity and forming simple and less dangerous byproducts. (Catalysts are materials that accelerate a chemical reaction without being consumed in it.)
Field tests of the technology have been performed at Tyndall Air Force Base in Florida. In a test at Lawrence Livermore National Laboratory, the TCE concentration in groundwater was reduced from 200 parts per billion (ppb) to 5 ppb. But there have been few demonstrations, and engineeing problems remain to be solved. (See "Cleaning up with Sunshine" in the bibliography)
