Energy by the Numbers

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.