SHAVE ITAND SAVE IT

One of the problems facing electric utilities is that they must work at full capacity (or even resort to brown-outs) during peak demand hours, but their full capacity goes unused during most of the remaining 24 hours. To combat this, they store energy during the hours of low demand and then draw on it during peak hours. This is called peak shaving and is achieved by methods (some of which we have described in past issues) such as pumped storage and compressed air; in the future, flywheels and superconductivity may also join the list.

Apart from technological measures, utilities also use purse strings to shave the peaks. For large industrial users, they monitor consumption and charge not only for the kilowatt-hours consumed, but also for the peak kilowatts demanded during certain half-hours. For industrial plants alsing electric power by the megawatt, a demand charge of $3.30 per kW, or $3,300/MW on top of the cost of the consumed energy, this is quite a penalty.

But many industrial users are now doing more than squirm. They are installing computers to shave their own peaks. The computer monitors consumption during the first 15 minutes of each half-hour, and then decides what machinery, if any, to disconnect (it is hooked to relay switches). It first cuts nonessential services such as air conditioning (a 10 minute cut will raise the temperature only by 2°F), then services in increasing order of importance, until in final desperation (if it comes to that) it flashes warnings that it is about to cut the big machinery.

TRW's Tapco plant in Cleveland, for example, has found it can cut as much as 4 MW from penalization by delaying the load to the next half-hour; and last May, it saved no less than $11,000 on its monthly electricity bill.

The utilities do not feel outsmarted; they are glad consumers are helping them to shave the peaks.