Wednesday, October 25, 2006

Phantom Loads, Are They Really That Costly?

For those who don’t know, a phantom load is the use of electrical power by a device when it is turned off. TV’s, for example, require a constant source of power for the remote-control sensing circuitry. This wasteful use of electricity can be eliminated by unplugging the offending device from the wall. Off/On switches on power strips and surge protectors offer another convenient way to disconnect devices. The amount of power used by a turned-off device is usually small, and I’ve often wondered if eliminating this feature is worth the inconvenience it causes. For that reason I decided to do some tests to find out.

I suspect that older devices are more wasteful than newer ones, but I decided to test a flat-panel TV that I recently purchased. I used a Kill-A-Watt meter to measure the current with the TV turned off. Having recently read how wasteful phantom loads are, I was surprised to find a current flow of only 30-milliamperes (0.03-Ampere). Then I did some calculations. The phantom load on this TV ends up costing me about $3.00 per year on my electricity bill. Although this isn’t much over the course of a year, I probably have at least 9 more devices that also waste this much power. That brings the total to more than $30.00 per year. And, since older devices are probably more wasteful than newer ones, my actual total is probably in excess of $60.00 annually. While it’s not a lot of money, I like the idea of reducing my monthly bill by five dollars or more.

The increased cost of grid-supplied electricity is not my only concern. I want to be able to power my home with my solar PV system eventually. Reducing waste allows me to do so with a smaller, less expensive, solar PV system. A current flow of 30-milliamperes at 120-Volts AC is the equivalent of 3.6-watts. In a day, the power wasted by my TV is 86-watts. My solar PV array needs to be able to produce this power every day. And, if I have 9 more devices wasting power due to phantom loads, my array needs to generate 860-watts each day. By reducing this load, I can downsize my solar PV array by two to four solar panels. The result is a PV system that costs considerably less than it otherwise would.

In addition to reducing my system cost, I like the fact that my efforts have a positive environmental impact. If a million homes would eliminate their phantom loads as I’m doing, the load on electrical power plants would be reduced by 860 million watts each year. Since burning coal is the primary source of electricity production, this effort would result in a lot less carbon dioxide being pumped into the atmosphere. Let’s do it!


  • Consider replacing your doorbell and alarm clocks with mechanical devices that serve the same function.
  • Don't leave transformers (wall-warts), plugged in when the connected device is not in use.

Solar John


Anonymous said...

So, the only way to calculate phantom loads is to purchase a device that measures them, is that correct?

How about determining the starting watts on an appliance? Is that possible by looking at name plates or must one measure these too?

Solar John said...

Regarding Phantom Loads: You might find that information on the manufacturer's website for the particular device you're interested in. But at about $35.00 the Kill-A-Watt meter is an inexpensive and worthwhile investment.

Regarding Starting Watts: I've read that motor starting current is typically 2 to 4 times the running current. Motors that start up while under load will have the highest starting current.