Laptop Power

Kill-A-WattIt’s been a crazy day. I was up at four this morning to take Maggie and our friend Lindsey to the airport for their separate flights to the same place (Portland). We had some very interesting conversations, including some talk about investing sustainably that I hope to talk about when I’m more conscious.

Instead, let’s talk about something that I can explain even while brain-dead: the Kill-A-Watt (it’s pretty cheap right now on Amazon). Maggie’s parents gave one to me for Christmas and I’ve played with it several times since.

It resets when you unplug it, so it can sometimes be inconvenient to read when, say, you have it plugged in behind the refrigerator. Nevertheless, it’s fun and enlightening to see how much electricity things around the house actually use. I generally think about everything in terms of how long I could power a CFL (or how many CFLs I could power) for the same amount.

My first sample was my laptop. The power supply can draw 120 Watts (about ten CFLs), so I always assumed that was about how much it drew. It turns out that I was way off. Even though it has a big screen and uses WiFi constantly, my laptop only draws about 35 Watts (three CFLs) while in use or about twice that when charging and being used. While in “sleep” mode, it uses somewhere between 0 and 1 Watts, which is amazing.

My netbook uses even less electricity, which goes some way towards explaining the battery life. Running the netbook draws 15 Watts, which is about the same as a CFL. So far, though, Maggie has vetoed my plan to replace all of our light fixtures with netbooks. From reading the specs, the CPU uses 2.5-3 Watts, so most of that power is going to the backlight (which you can turn off while leaving the screen on, although it’s totally unreadable). It just goes to show how efficient LEDs are.

We’re currently using the Kill-A-Watt to determine whether we should keep our current fridge or swap it for the old one that Maggie’s parents have. It’s plugged in and running at their place right now, but we’ve already gotten the results on our current model. It uses about 950 Watts (about 73 CFLs) while not running the cooling pump and even more when actively cooling. It used 28kW over a typical period of 382 hours (a little over two weeks). That averages out to about 1.75 kWh per day. That certainly makes it hard to hit my 3 kWh a day target but it’s slightly better than my 2 kWh per day estimate.

Unfortunately, we can’t use the Kill-A-Watt to measure some of our biggest energy users (the dryer and the water heater) because it won’t work on 220-volt outlets. I’m hopeful that eventually we’ll have measured all of the other important stuff so that we can just subtract them out and get better estimates for them as well.

Once we’re done with the refrigerator, my plan is to check my TV and stereo to see how much phantom power they actually draw. We have them on power strips because we’ve heard a lot about the waste of phantom power, but I don’t know how much of a concern it actually is.

What about you? Is there anything you’re interested in hearing about now that I have the means to measure energy consumption? this!

2 Responses so far »

  1. 1

    Emily said,

    March 19, 2009 @ 4:16 pm

    We’ve been playing with our Kill-a-Watt and found that the older TV/DVD/converter drew 12w when OFF. The new one draws 4w when off.

    A couple other resources: Black and Decker is making a new tool that will read your electric meter “live” so you can see what your water heater or dryer draws. They also make a point-and-shoot thermal leak detector:

    I also did a bunch of calculations for as I drew up the One Stone Carbon Reduction Challenge – you might want to take a look and geek out at some figures with me. 🙂

  2. 2

    Will said,

    March 21, 2009 @ 6:05 pm

    Our TV is about 5 years old, so I think it shouldn’t be too bad, but we also have a DVD player and a Wii hooked up on the same power strip, so it might be a lot for our “entertainment center.”

    The electrical meter is right outside our back door, so I can usually figure out pretty easily how much power is being drawn at any particular time. The hard part is figuring out what’s drawing all that power, which is where the Kill-A-Watt and process of elmination come in.

    The One Stone Carbon Reduction Challenge seems very cool. I’ll have to look at it in more detail when I have more free time!

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