# Energy or power? Take your pick. (News From Hench).

It has been said that power is the ability to make things happen and energy is what it takes to do it. This answer will not get you a passing grade in an engineering class, but it might work in a Political Science class.

These two words are often interchanged, even by people who should know better. A lot of ink is being used these days in newspapers and magazines about the country's "Power Crisis", or "Energy Crisis". Which one is it, or is it both? This month's Control Update will address these two words and what they mean. Then you can decide.

Power -- Power is the instantaneous value of the rate of doing work, measured in kilowatts (kW). A car's engine might have 200 horsepower, for example. This means that this engine can accelerate the same car twice as fast as a 100 horsepower engine. If you are in a situation where you need only 100 horsepower, and your engine has 200 horsepower, you can just use half the engine's capacity, by not jamming your foot to the floor. On the other hand, if you need (want) 300 horsepower when your engine is rated for 200, there is nothing you can do but go slower.

Automobile power is a pretty good analogy for electrical power. A kilowatt is roughly three-fourths of a horsepower. If an electrical utility has the ability to make 4000 kilowatts of power, and its customers need (want) 5000, the utility cannot do a thing to make up the missing 1000 Kilowatts. This is the crux of the current "Energy Crisis". The electric utilities are running short of installed capacity, which means they need to build more power plants to meet the current demand. So the country's current crisis is a "Power Crisis".

Energy -- Energy is the way to measure how much work or equivalent work is done. In electrical terms, energy is kilowatt-hours (kWh). A kilowatt-hour can be used up by consuming one kilowatt for one hour, or by consuming two kilowatts for a half-hour. The electric utility would rather you consumed a half kilowatt for two hours, because then they would have less money tied up in power generation equipment. Also, as the power used in a geographic region goes up, the cost of power goes up, too, because the most efficient power plants are used first, and as demand (kW) goes up the older, less efficient (and more expensive) power plants are used, which means their profit margins go down.

Electric utilities have come up with many ways of encouraging their customers to consume energy more evenly, rather than in short spurts. One is the use of Time of Day rates. Utilities charge you more for power in the afternoon when demand is high to keep you from using power in the afternoon, when their costs are the highest, or their ability to supply it is limited. Another technique for spreading out power use is through demand charges, in which they charge you for the highest power (kW) you used in a month. In some parts of the U.S., demand charges are half of the monthly electrical utility bill.

In some areas, the utilities use a "Time of Day Rate", which means that the utility downloads the rates for the next day into a computer at the customer's site, and the customer then decides how to use power on an hour-by-hour basis, depending upon its cost. The rates in a Time of Day scheme might vary between 2 cents/kWh and 2 dollars/kWh. This approach eliminates the need for demand charges, on peakloff peak rates and summer/winter-rate schedules. With Time of Day Rates, the utilities are charging their customers for energy at prices proportional to what it costs them.
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