Can I save money on electricity by unplugging appliances and using capacitors?

March 13, 2009

Dear Cecil:

I once saw a man on Oprah who always unplugged appliances because he didn’t want to pay for “phantom” electricity that would leak through the plug even when the appliance wasn’t being used. Recently, a coworker told my husband he saved a lot of money unplugging TVs, computers, etc. Am I really wasting money leaving appliances plugged in even if I turn them off?

I’ve heard people are selling capacitors to lower electrical bills. Is that possible?

Cecil replies:

With everyone trying to economize these days, you’re going to hear a lot of dubious ideas about reducing energy costs. Here are a couple. We’ll start with the dumber one.

Capacitors. I think you’re referring to “power factor correction devices,” which are used to fix an obscure problem found in some AC electrical circuits. For example, a circuit used to run an induction motor sucks up a lot of juice to energize the coils, but only some of it is actually used to make the motor spin. The rest gets spit back out and flows back to the power company. It’s like the water circulating through a fish tank, which doesn’t get used up, just moved around a bunch. The power company doesn’t like this, because it has to go to the trouble of sending you all those amps but typically can only charge you for the part you actually consume. If you’re a big industrial energy user running all kinds of motorized equipment, you don’t like it either, because you have to install heavy-duty cabling and electrical apparatus to move power you’re not really using, and in the process some of the energy is lost as waste heat. (Also, big users often get charged a penalty for this inefficiency.) So you install power factor correction devices, typically capacitors, which magically allow you to sip only as much electricity as you genuinely use. (In geek terms, your power factor is corrected to more closely approach 1.0, the optimal value.)

However, chances are you’re not a big industrial energy user — you’re an ordinary civilian, and the biggest motor you’ve got runs the air conditioner or fridge. If your power factor isn’t 1.0, what do you care? The electric meter records only the juice you really use. If the house’s wiring is heavier than it needs to be, big deal, it’s already there. You lose some energy as waste heat, but experts say with correction devices you might save 2 percent on your electric bill. Every little bit helps, I guess, but you’d do better just shutting off lights you’re not using, installing compact fluorescent bulbs and energy-efficient appliances, etc.

Unplugging appliances. Here’s a more interesting question. The idea that plugged-in appliances leak phantom electricity is of course nuts. However, plenty of household devices do use energy in standby mode. The best-known example is a computer, but TVs also eat electricity while plugged in. (Generally it’s just a couple watts, but some high-def models use more than 40 watts.) Then you’ve got those electronic gadgets drawing power from a plug-in trans­former, the familiar black box known as a wall wart or brick. The box stays warm even when you’re not using the gadget. That’s waste heat, and it costs.

The question is how much. Some claim these energy vampires account for 4 percent of your home electricity usage, with total waste as high as 5 to 10 percent. However, here at the Straight Dope we don’t put much stock in mere claims. We want the facts. I assigned my assistant Una, a licensed professional engineer, to do a survey of her house with a Kill A Watt P4400 meter to see how much power was being wasted by wall warts and standby appliances. The total for her entire house was 12 watts, with half of that going to one old and rarely used VCR. While she did have a lot of wall warts plugged in, most of them drew so little power the meter wouldn’t display it. However, over a year that idling VCR projects to use more than 52 kilowatt-hours, costing about $5.17 at her electric rate. We’ll guess Una wastes maybe $10 annually for the whole house.

Now, you can multiply ten bucks by the number of households in the country and come up with an impressive number. Unplugging wall warts and turning off computers and such doesn’t cost anything. (Whether it increases wear and tear on the computer is a separate issue.) Far be it from me to encourage energy profligacy, so if you think it’s worth your while, go crazy, unplug everything in the house. Me, I’m a big-picture guy, and I figure energy is energy. My lifetime commitment to a better world consists of stuff like (a) insulating the hell out of my house, (b) buying little cars, and (c) taking the el (that’s the train, for you forest dwellers) when Mrs. Adams and I go out for our Valentine’s date.

 

 

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References

Commonwealth Sprague Capacitor, Inc. Power Factor Correction, A Guide for the Plant Engineer. 1987.

Consumer Product Safety Commission: Office of Information and Public Affairs "CPSC, Coast Energy Management Announce Recall of Power Saving Devices" Revised October 27, 2005.

International Energy Association Fact Sheet: Standby Power Use and the IEA "1-Watt Plan" April, 2007.

Square D Company. Low Voltage Power Factor Capacitors. 1985.

United States Department of Energy: Energy Matters Power Factor Correction: What it Can and Cannot Do Summer, 2008.

United States Department of Energy Industrial Power Factor Analysis Guidebook DOE/BP-42892-1, March, 1995.

United States Department of Energy Motor Challenge Fact Sheet: Reducing Power Factor Cost, 1996.

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