Where my watts go

I like to conduct experiments and measure things. My monthly electricity bill tells me how many kilowatts I’m consuming, but not at a very interesting or useful granularity. Which devices consume the most? Where could I make the most impact, in terms of turning things off or putting them on timers? What I really want is the equivalent of top, but reporting electricity consumption instead of CPU usage, for all currently active processes (devices).

Since no such thing exists, I instead went out and bought a Kill A Watt, which monitors all consumption of anything that is plugged (through it) into the wall. This is a nifty device; not only does it give you instantaneous consumption, but it will also record the total usage over time. The packaging contained a bit of over-selling, though:

Perfect for detecting voltage drops and brownout conditions before they damage delicate equipment.

Perfect, that is, if you’re sitting there ready to yank it out of the wall if the line quality drops below 120 V. It doesn’t have any automatic shutoff or power surge protection.

Once I got the Kill A Watt, I went around the house plugging everything I could find into it. Here are some of the highlights of what I learned:

  • The largest instantaneous consumption comes from my microwave, at 1600 W.
  • I confirmed that CFLs really do consume less energy than incandescent bulbs. :)
  • My stereo uses about 40 W, whether playing the radio or playing a CD—and this amount increases with volume, as more power goes to the speakers. Same with the TV (a 19″ Samsung, 40 W, increases with volume).
  • My laptop consumes 2 W when sleeping, 27 W awake with low load, 36 W charging (asleep), and 60 W charging (awake). My wireless router consumes 14 W.
  • My front-loading high-efficiency washer uses 20 W when filling with water, 100 W when tumbling, and 460 W when spinning. The total consumption for one load is 0.14 kWh, which costs me all of 1.7 cents (not including the cost of the water).
  • My gas dryer uses 750 W when first heating (and tumbling), then settles into 260 W once it’s hot. One load consumes 0.17 kWh, or 2.1 cents (not including the cost of the gas).
  • Bottom line: I was surprised to realize that, based on this data, my biggest ongoing consumption might well be my dining room light fixture (2 75-W bulbs = 150 W), which has a dimmer switch and therefore isn’t amenable to regular CFLs. It might be worth the (more expensive) dimmer CFLs to address this, once the current bulbs burn out. However, my study was not comprehensive; I was unable to measure my fridge’s consumption, for example, nor do I have numbers for the oven, water heater, or air conditioner (which I know is a heavy consumer simply based on the seasonal change in my total bill). More study is merited!

Philip Torrone has posted instructions for how to convert your Kill A Watt into a Tweet-a-watt. That’s right, you can now tweet your consumption, for the edification of all. From the project description: “We feel there is a social imperative and joy in publishing one’s own daily KWH.” I’m content just sharing the preceding analysis, thanks!

5 of 5 people learned something from this entry.

  1. Terran said,

    June 28, 2009 at 2:39 pm

    (Learned something new!)

    Wow! This is nifty. And useful.

    It feels to me like we’re so close to having the really fully instrumented home. The monitoring and control electronics are close to dirt cheap now, and they’re small enough that you might as well just stuff them into all new devices. One of my friends here works in power systems design and he tells me that this stuff is already in all the widgets that they’re buying for industrial buildings (e.g., all the coolers, motors, and so on that go into running the environment control and all the lighting control panels). That’s higher end than consumer, but I can see that we’re heading in the right direction. Hopefully in the next, say, five years, you’ll be able to get fully instrumented sockets and switches and widgets for all points in your house.

    And the incentives are there for it from both a consumer and a power supplier point of view too. The power producers would absolutely love to have finer-grained monitoring and control of usage. One of the biggest things they can do to help production is to encourage people to shift usage (e.g., running high-demand appliances at night, when demand is traditionally low and power supply is plentiful). The idea is that they’ll offer cut-rate for people to buy power at night and put a premium on it in mid-afternoon and so on.

    So I think that the incentives are there across the spectrum. I think that in the next few years we’ll be able to get a detailed breakdown of where all the power is going in our house and do trade-offs like scheduling our power usage. With detailed control and monitoring, I could see that you’d, say, have a web widget for your house that lets you log in from work and twiddle which devices are running and so on.

  2. wkiri said,

    June 28, 2009 at 3:48 pm

    I agree. Some baby steps are being made in that direction: My sister, who lives near Phoenix, AZ, was approached by her power company to offer the installation of a device that reports usage back to the company on at least a daily basis. Benefit to them: they don’t have to send out a meter reader. Benefit to her: she now has a webpage she can go to and see her daily consumption. She’s been able to tweak different thermostat settings and test, e.g., whether it’s better to let the house heat up during the day and then cool it before you get home from work, or to keep it at a more constant temperature all day. Admittedly, she could do this by walking outside and checking her own meter daily—but then she’d have to record and track the results herself.

    As for remote configuration, I used to have Speakeasy’s VOIP service and it has the ultimate web interface; you can specify one or more numbers to forward your VOIP calls to, or send straight to voicemail, based on the time of day or day of week, and so on. So you could twiddle that remotely (not for power reasons, but for convenience). I remember thinking, “Ah, now THIS is a 21st century phone!” because you control where the signal (information) goes and when, rather than it being tied to a physical wire. I kind of miss it now. Is there any reason a cell phone provider couldn’t also offer that?

  3. Marcy said,

    June 28, 2009 at 3:51 pm

    (Learned something new!)

    I have always wanted to test out this stuff for myself. Specifically the volume on a stereo question. Thank you SO much for sharing your findings!

  4. Sen said,

    June 29, 2009 at 3:55 pm

    (Learned something new!)

    Why can’t you measure the power consumption for your fridge?

  5. Jim said,

    July 8, 2009 at 8:00 am

    (Learned something new!)

    Does it take more power to play a Cat Stevens song, or a CSN song?

  6. Geoff said,

    July 13, 2009 at 3:49 am

    (Learned something new!)

    Great post – I’ve been wanting to pinpoint my electricity use for some time now.

    I’m curious where the vacuum cleaner stacks up, if you tried it.

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