Thursday, May 6, 2010

Cutting your electricity bills - the "Kill A Watt" is your weapon of choice

I think it is a pretty safe bet that our energy bills are going nowhere but up in the future.  Cutting down on wasted energy is a no-brainer and preserves our natural resources.

As electricity fuels our love for technology, it makes sense to take a hard look at how much our toys are consuming.  Of course you can look at the power ratings of your devices, but these are only hints (and usually maximum) numbers.  How can we really tell how much they are using?

The P3 International P4400 "Kill A Watt"

A couple of years ago a friend of mine (thanks Kevin!) recommended a neat tech toy that was so cool I bought one based on his description alone.  The  "Kill A Watt" is a simple, single purpose digital meter that plugs into your household power outlet and measures the power consumed by anything you plug into it.

Note that while there are more expensive models of the "Kill A Watt", I find that the basic P4400 version works just fine for me.  Also, it is only $20, so that makes it a decent bargain compared to how much you can save when you become aware of your power usage.

First, let's go over a few reasons why you should care about this...

What is a Watt?

The electric company bills you in units called KiloWatt hours (abbreviated kWh).  This is a fancy way of saying 1,000 Watts used continuously for one hour.  A Watt is simply a measure of energy consumption.  You pay for KiloWatt hours just like you pay for any other service.

The easiest way to relate to a Watt is to think of the rating of a light bulb.  The higher the number, the more energy needed (and usually light it produces).

What is a Watt Worth?
Typical electric company rates for a kWh vary significantly around the US and usually with usage.  Currently in my area (served by Pacific Gas and Electric), rates start at 12 cents per kWh and go up depending upon how much you use (there are 5 pricing tiers for regular residential service).   Any energy that you save (or use) will be calculated at the highest tier that you are in (possibly as high as 50 cents per kWh!)  This is one reason why your electric bills get so high in the summer.  It isn't just that you use more energy, it is also that the additional energy that you use costs significantly more than your "baseline" usage (a double whammy!).  Don't make the mistake of assuming that your savings are simply based on your average.

Let's put this into perspective

A simple 100 Watt incandescent light bulb (which would light up a medium sized room) used 24 hours a day for a year would consume (100 Watts / 1000 * 24 * 365) or 876 kWh.  If you had no other electricity usage and your rate was at the lowest tier of 12 cents , that "light" would cost you 876 * .12 or $105 per year (ouch!).  On the other hand, if you were using a lot of energy already and were in the top tier, that "light" would jump to 876 * .50 or $438 per year (yikes!).

Turn off that light and you would save at least $105 (probably much more!).  And this is just one light!

BTW: This should also make it clear why incandescent bulbs are being phased out in favor of much more energy efficient choices.  However, that is a topic for another post.

We aren't done yet, "Smart" meters are now here!

A good friend of mine (hey Renato!) just discovered that PG&E installed a new Smart meter in his home (without his permission I might add), replacing the old "spinning wheel" electric meter.  These new meters can be read electronically (saving the electric company a bunch of labor).  However, they also offer the ability for PG&E to charge you based on "when" you use electricity as well.  This rewards customers who use energy "off-peak" (and conversely penalizes those who must use it during peak time).  I'll blog about about this Smart meter and it's impact on your energy bill separately.

So, you have lots of good reasons to pay attention to your electricity usage

Now that your electric company knows how much electricity you use and soon will know when you use it, what tools do you have to fight the inevitable increases in your bill?

This is where the simple "Kill A Watt" meter comes in.  Simply plug it into the wall and plug anything that you want to measure into it.

Media PC power usage

Computers are a big electricity hog, let's see how much my Media PC (designed specifically to be fairly power efficient) uses.  I plugged the power cord into the Kill O Watt and put the Media PC into four different states.  The first was "OFF" with no lights on, the second was Standby / Sleep with no fans turning and the power light flashing, the third was idle running Windows just displaying the desktop, and the last was playing pre-recorded High Definition broadcast TV in Media Center:

In each of the cases, the display is indicating Watts used (not KiloWatts).

What is most interesting about this:
  • At 50 Watts idle and 66 while in use, my Media PC is not too bad of a power hog.  Typical PCs can be 100 Watts or higher.
  • PCs consume dramatically less power when in standby/sleep/hibernate mode.  This is why I make sure every PC I own is in Standby (or off) when not in use.
  • PCs (like almost all devices) consume some power even when supposedly off!
How much does it cost to toast a piece of bread?

Ok, so perhaps this isn't a question that keeps you up late at night, but my kids love sour dough toast and Eggo waffles.  As a result, we run our toaster all the time so it is reasonable to ask how much it costs.  It is nice to know that the Kill A Watt can test even power hungry appliances.  In fact, it can handle up to 15 amps (or roughly 1800 Watts).  My toaster oven says it is rated at 1500 Watts, so lets find out for sure:

So far I have just been measuring "Watts" currently being used.  Just press the center button and it toggles between Watts and PA.  Don't worry about PA, it isn't very useful.

However on the far right is a pink button labeled KWH and Hour.  Push this button and it toggles between the total kWh used by the device and the total time that the Kill A Watt is plugged in.  This is great for testing devices like mini-refrigerators which cycle on and off several times during the day.  Since we usually only care about the total kWh used over a period of time, this is a great feature.  In fact, this works EXACTLY like your electricity meter attached to your house (only allowing you to measure the usage of a single appliance over time).

Back to the toaster....  I toasted that piece of bread in 6 minutes, using 1600 Watts of power with a total usage of about .12 kWh.  If my electric rate is 16 cents per kWh, that piece of bread cost me 2 cents to toast (more if you like it crispy)!  At the top-tier of electric rates, it would have been 6 cents.

Okay, that isn't a huge amount, but if you are baking something for a long time it will add up fast (of course a full sized oven uses way more power than a toaster).


So go get a Kill A Watt and start trimming your electric bills!


  1. I would like to kill my electric bill. However, the electric company added on additional fees (customer service $6.00 per month), etc. I figured out that added on fees are roughly 40-50% of the actual electricity bill. Bummer! Why bother to save electricity....when that much of the actual bill is ....nothing but added on fees!

  2. Good point, and BTW the same issue applies with other utilities like water.

    Sadly saving electricity (or water) at low usage levels really comes down to doing it on principle. It is kind of the same reason why I try to recycle and reuse whenever possible. It doesn't save me any money, but it is the right thing to do.

    I'm with you, If I made the rules for utility companies I'd make sure that everyone at every usage level was encouraged and rewarded for consuming wisely.

  3. F-a-n-t-a-s-t-i-c ! I was looking for similar projects last week, and now i see this post. I normally use breadboard to do this type of work, with one of these, job will be more easy. I was thinking, and searching others projects to do my own PCB. So, let me try my luck, maybe i can win.
    Warning led lights


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