Any observer of the alternate energy arena can be constantly frustrated by the continued announcement of the megawatt capacity of this solar array or that wind machine. What a wind machine will do at its design condition at, say, a 28 mile-per-hour wind, or what a solar array will produce on a clear day at high noon is interesting information, but of little relevance.

What counts are the kilowatt-hours produced in a year. That is, what turns the electric meter – that is what puts money in the bank. And this is almost never mentioned. The latest issue of Renewable Energy World, published in the United Kingdom, came to the rescue. A solar array in Germany that produces one kilowatt peak will deliver 1,000 kilowatt-hours per year. That same collector in Greece will produce 1,500 kilowatt-hours per year. There are 8,760 hours in a year; a solar collector in Germany will produce, on the average, 11 percent of its peak output; the same collector in Greece will produce its peak output 17 percent of the time.

Richard C. Hill is a retired emeritus professor of engineering at the University of Maine.