SMOOTHlNG THE POWER FLOW

One of the big problems that electric utililites have always been battling is the unevenness of the demand for electric power. It usually peaks in the late afternoon, but a power plant's capacity to meet the peak demand goes wasted in the small hours of the morning, when demand is quite small. This waste of capacity (not of energy) is described by the "plant factor," the ratio of the average supplied power to the capacity power. If demand were constant throughout the day, a much smaller plant could supply it, and the plant factor would be 100%; such a fictitious plant would be fully utilized all the time.

But demand is not constant, and the obvious remedy is to let the unwanted energy flow into a storage reservoir during periods of small demand (night), and then tap this reservoir during the peak hours. This is the most efficient way, but not the only one, and at present most plants use cruder methods. At first, most utilities simply resigned themselves to low plant factors, which entailed higher capital costs, but did not drastically affect operating costs. As demand grew, they added special machinery (such as gas turbines) to tide them over the peak hours. As demand increased further and fuel became shorter, they had to resort to brown outs (lowering voltage) during the peak hours. Last month, for example, Con Edison of New York cut the voltage by 5%, which corresponds to an almost 10% cut in power.

However, an increasing amount of utilities is using a better method to handle the peak hour: They use the power available at night to pump water into a higher reservoir, from which it rushes down through hydraulic turbines during the peak hour. This is called "pumped storage" and amounts to a hydroelectric plant in which the water resrvoir is not filled by a naturally flowing stream (ultimately powered by solar energy), but by pumps using the excess capacity of a power plant during light demand.

Pumped storage capacity has been increasing fast in the last fen years. At present, the biggest such plant is the Consumers Detroit Edison plant near Ludington, on the shores of Lake Michigan. The reservoir above the lake is filled by reversible hydraulic turbines (acting as turbines when driven by water, and as pums u hen turned the other way). During the peak hours, when the cater rushes back through six giant (24 ft diameter) penstocks into the turbines at 34 million gallons per minute the plant can deliver an awesome 1.900 MW of electric power.

Pumped storage plants with three times this power output are planned for the 1980's; but it is quite possible that by then large scale storage in superflywheels will have become commercially feasible.