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Letter: Energy use

Who killed Mother Goose? Well, nobody really —she’s still going strong, but it’s a good mnemonic for talking about energy over time, which is power. WKMG? That’s power.

“W” is a watt, our most popular power unit. We have a feeling for the watt. We sense the basic difference between a 20-watt bulb and a 100-watt bulb, maybe because we pay for it.

“K” is a kilowatt, 1000 watts, familiar from the electric bill.

The electric company doesn’t measure how many 100 watt bulbs we have. It measures how much energy we use, reported in “kilowatt-hours.” Use 10 100-watt bulbs for 1 hour or one 100-watt bulb for 10 hours, you’ve used 1 kilowatt-hour. Use a kilowatt hour every hour all day, you’ve used 24 kilowatt-hours. All year? 365 times 24, or 8,760 kilowatt-hours of energy.

At that point things get wobbly, even for journalists. “M,” a megawatt, is 1,000 kilowatts. “G,” a gigawatt, is 1,000 megawatts. That’s about as far as we usually go. Sometimes we like to use zeros for emphasis. A “one thousand megawatt” installation may sound more impressive that a 1-gigawatt installation, but it isn’t. (A Terawatt, 1,000 gigawatts, is past imagining.)

As with the bulbs, the amount of energy actually used (or produced) depends on the amount of time the plant is actually running and how much of its rated capacity is actually being used. It’s nice to have a 1-megawatt installation, but if 80 percent of the plant is down 20 percent of the time ... you need to look at the measured data to know how much energy was actually in play over the time period you care about.



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