THE RICH MAN'S TOY

As the advertisement rightly says, it is "for the music box buff, the classroom instructor or the executive who has everything," and that is just about what direct conversion of sunlight to electricity amounts to at present - a rich man's toy which costs a lot of money for very little power.

The cost will come down, of course. Solar cells are mostly made from large single crystals of silicon, and at presents their cost per output watt runs $1.50 up. For, say, a pressing iron, you would have to invest $1,500 plus the cost of the iron to run it "for free" when the sun is out. Cells made from cadmium sulfide crystals are much cheaper (per unit area, not per output watt), but their efficiency is so poor that they are only used where it does not matter, for example, in through-the-lens metering systems for photo cameras.

Now a team at the U. of Delaware has succeeded in raising the efficiency of the cheaper CdS cells to almost %, though only in laboratory samples. They did this by growing a different type of crystal and reducing surface reflection, for much of the incident energy is lost by reflection. This puts ERDA's solar-electric program well on the way toward meeting its 1980 target of 10% efficiency.

The high cost of silicon cells is due to the need of growing its crystals. A thin film of amorphous (non-crystallic) silicon would be much cheaper to produce, but would it ever convert more than 10% of the incident sunlight into electricity? Teams at Scotland's U. of Dundee and at RCA's David Sarnoff Research Center in Princeton, N.J., think so. So far, they have produced efficiencies of 2.4% with the thin films, but by the right kind of "doping" (injecting impurities to make the material electrically conducting), they eventually hope to achieve 14 or l5%.

All of which is heartening, but not very. Suppose the cost per output watt did come down by a factor of 10 (which it won't in the near future), would you invest $150 to run a pressing iron "for free" when the sun is out?

And money, even when the sun is out, is not the only problem. More than 100 square feet of collecting area would be needed just for that one pressing iron. But there are other ways to go for solar energy.