SOLAR POWER, NOT SOLAR PIDDLING

No matter how much money the Congressional sunworshippers spend on solar energy, the sun will never give more than 1 kW per square meter (about 0.088 BTU/squ.ft/sec another good reason to go metric). The large collecting areas needed to provide sizable amounts of power are one of the great (and permanent) handicaps of solar power.

Sometimes people come out with comparatively small collecting areas, but usually they forget about efficiency and spacing, and almost invariably they forget the plant factor.

A 10 MW conventional plant has a maximum capacity of 10 MW and can supply them when needed; a 10 MW solar plant also has a capacity of 10 MW, but is able to supply them when the sun cooperates, i.e., when it stands high in a cloudless sky. In either case, the plant factor is the ratio of average power supplied to capacity power. For a conventional plant, the average power supplied depends only on the demand; for a solar plant, it depends on both the demand and the sun, and therefore its plant factor is far lower than the roughly 50 to 7SS usual in conventional plants. To characterize a solar plant by its maximum capacity is entirely misleading, because that maximum could (and usually will) be achieved when it is not needed. A fairer characteristic is the power that a plant can supply whenever needed. For a conventional plant, this is the capacity of the plant itself, but for a solar plant, it is the (power) capacity of its storage reservoir, which is being drained by the consumers and replenished by the solar generator. Typically. a solar plant wiffi 10% efficient collectors and 50% spacing between them would need 50 square miles of collecting area to provide 1,000 MW on demand.

There have recently been some new developments in large-scale solar energy conversion. For one thing, the Sandia Labs in Albuquerque, N.M., working for ERDA, last July demonstrated a turbo-generator driven by solar-produced steam at 32 kW. Now 32 kW is not very much power not quite enough to run six 20-lb clothes dryers. And yet those 32 kW represent the largest amount of power ever produced by a solar-thermal-electric process. The price per kW is, of course, nowhere near competitive with conventional sources of electricity, but it's a start.

ERDA is also looking for a site in the sun-belt states for a solar-thermal-electric plant producing some real power 10 MW. Southern California Edison and the Los Angeles Dept. of Water and Power have offered a 130-acre site plus equipment and other resources toward the total cost of $100 million. The site is in the Mojave desert and receives l5% more sunlight than the minimum specified by ERDA. The proposal envisions a 100-acre field of guided mirrors (i.e., mirrors tracking the sun) to focus the incident rays onto a boiler on top of a 300 to 400 ft tower in the center of the field. The steam produced in the boiler would then run a conventional 10 MW power plant, which would, together with other auxiliary facilities, occupy the remaining 30 acres.

Very nice, and a worthwhile experimental project; but as SCE, owner of the San Onofre nuclear plant, well knows, 30 acres can by themselves support a conventional power plant producing not 10, but 1,300 MW and more; and we are back to the drawback of large land areas needed for comparatively little solar power. They can be spared in the desert (though even there, no doubt, the inevitable environmentalists will complain about laying the desert waste), but transmission over long distances always affects economy adversely, even if it is there to start with.

Which once again leads us to the type of solar power that is already being collected all the time by vast areas the earth's oceans. It can be harnessed in sizable amounts by Ocean Thermal Energy Conversion, and here, too, we were going to report on progress but we have run out of space and have to leave it until next month.

In the meantime Happy New Year!