Bulletin Board
Rants, Raves, Interesting Science & Awful Puns
November 9, 1997

Solar Realities

Correcting some myths

A few people have noted my earlier mentions of nuclear energy and asked why I don't think the future is with solar. I don't read newspapers since I long ago dismissed the mass media as a credible source of information on anything, and I didn't know that this fraud was still being pushed.

The thing to bear in mind when people start talking about how much energy comes from the sun and how free it is, is that what matters if you want to do smarter things more efficiently isn't so much the amount of energy as the density -- how concentrated it is. A 200 foot fall of water even ten feet wide can usefully turn a turbine and produce a worthwhile amount of power for the cost. A waterfall ten miles wide but with a drop of only one foot would release more energy, but the size and ungainliness of the contraption necessary to harness it would make the venture useless. Similarly, it's straightforward to calculate how much energy it takes to lift three hundred people across the Atlantic, and how much wood you'd need to burn to release that much energy. Now try building a wood-burning 747. It won't work. The mountain of logs would never get itself of the ground. For concentration enough to make it practicable, you need jet fuel.

Hydro power and wood are in fact examples of solar energy concentrated to a degree that becomes usable. With hydro, solar evaporation lifts billions of tons of water, which then release gravitational potential energy by falling as rain and running back down to sea level. In suitable locations, the terrain is such that the drainage of thousands of square miles gets brought together and funneled through a strategic point where it can be tapped by a dam. Wood concentrates solar energy in two ways, first over time by accumulating the sunshine of many years, and second over space through the human activities of cutting and gathering. But raw solar, as extolled by the activists, is far too dilute to be capable of more than a marginal contribution--and then only in exceptionally suitable and not-too- demanding circumstances.

The solar constant in places like Arizona is typically about 1 kilowatt per square meter (29% more than a square yard), which aside from heating the sun up or moving the Earth closer to it, you're not going to be able to change. 20% would be a good conversion efficiency, and allowing, say, the equivalent of 6 hours of collection per day to take account of nighttime, poor weather, and density being reduced when the sun is at low angles brings the figure down to 50 watts per square meter. Now, a kilowatt-hour of electricity can be produced by about a pound of coal. Estimating the cross-section at 15 square inches, or roughly a hundredth of a square meter, the sun would need to shine on that lump of coal for almost three months to deposit the amount of energy released in minutes by burning. For the average solar constant for the whole US, this comes close to a year. That's how dilute solar energy is.

What this means in real terms is that while there might not be any utility billing you for the fuel, an enormous amount of effort must be put into concentrating the energy to a usable degree, and this doesn't come free. Here are some figures for materials needed for the construction of a thousand megawatt (typical size for a large coal or nuclear plant) solar facility:


This is in the order of 1000 times the materials needed for a comparably rated nuke, spread over 50 to 100 square miles as opposed to something like 40 acres (a sixteenth of a square mile), with all the corresponding escalations in transportation and construction. All of these materials come from heavy, energy-hungry industries that produce large amounts of waste, a sizable proportion of it highly toxic.

And that's not the end of it. Normal power-industry practice is to design for peak ratings of several times the rated capacity of a plant, to allow for heavy-use periods and recharging storage systems. To compare like with like, we need to multiply the above figures by, say, 2.5 minimum for a solar facility capable of doing the same thing as what's meant when we say "a thousand megawatt nuke."

Current capacity of the USA is around 750 billion watts, which, multiplied by 2.5 gives 1.875 trillion watts for all-solar replacement. Based on the "Solar 2" demonstration at Barstow, California, which delivers 10MW for an outlay of $180M, this would require $33 trillion, equal to $118,000 per person or $472,000 for the average family--500 to 1000 times the cost of coal or nuclear (even with nuclear hiked by a factor of five as a result of political obstructionism). Your $200 per month utility bill just turned into $100,000. Still interested?

Good Book
A goldmine of information on all aspects of nuclear energy and related issues is The Nuclear Energy Option by Bernard L. Cohen, professor of physics and radiation health at the University of Pittsburgh, $24.95, 338 pp., Plenum Press, New York, 1990. ISBN 0-306-43567-5.

(See also Petr Beckmann's The Health Hazards of NOT Going Nuclear under RELATIVITY BOOK.)

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