Here Comes the Sun


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Dr. Mahmoud Huleihil. Keeping the mirrors true
Not everyone gets the opportunity to work at his passion. Even as a child in Safed, one of the oldest cities in Israel, Mahmoud Huleihil treasured the purity of his natural surroundings. As an adult, he ventured to another pristine place, Sde Boker in the Negev desert, where he performed research on solar energy. What attracts him to that particular kind of energy? "It's pure," he says, as if this should be obvious to anyone who would compare a day on the beach to a walk in a smog-filled city.

But it's purely expensive, too. Arriving six months ago as a postdoctoral fellow at the Weizmann Institute, Dr. Mahmoud Huleihil of the Environmental Sciences and Energy Research Department is working to solve this kink in solar energy. "We've got to convince politicians," says Dr. Huleihil, "...and that's usually done through the pocketbook."

The divisive factor is the construction of a new solar power plant: Why invest money in building an additional plant when the old system works just fine, thank you? Simulating solar power plant construction on his computer, and programming it to suit experimental needs, the objective is to bring cost, as well as sunlight, down to earth.

The heliostat, a type of mirror, accounts for about 50 percent of the plant's total cost, according to senior scientist Dr. Abraham Kribus, Dr. Huleihil's postdoctoral advisor. [Dr. Kribus holds the Recanati Career Development Chair of Energy Research.] Maximizing the mirrors' efficiency will make it possible to minimize their cost. The solar plant's field area, occupied principally by the mirrors, would shrink proportionately.

One of Huleihil's challenges is to address the mirrors' tendency to deviate slightly from their set position. When this happens, the mirrors miss their target: the solar receiver, which absorbs their sum energies. But in a field of hundreds of mirrors, how can you find the one that's "faking" it?
The computer, which sets the mirrors' angles according to the time of day, can't tell the difference; judging by its screen, you wouldn't even know anything was amiss. Solution: Dr.Huleihil is working on a computer program which will spot deviant behavior by calculating the different light intensities shone on four "smart cameras" placed around the receiver.

Solar energy may, in fact, be even more efficient than other forms of energy. One of the basic precepts of thermodynamics is this: The higher the temperature, the greater the efficiency. The sun's temperature is approximately 6,000° C (10,832° F). Using solar energy, scientists can draw the sun's heat to earth at a temperature of 2,000° C (3,632° F), much higher than the temperature obtained when heating with fossil fuel. (Preliminary calculations to determine whether using solar energy in this way is worthwhile are currently being carried out by Weizmann scientists.) Yet, even with its advantages in mind, solar energy is costly.

However, as Dr.Huleihil points out, in assessing the price of an energy source, one must not look only at the accounts book ­ one must look at nature and the environment as well.