Earth Day Tip - How to Save Energy When Your Computer is Not in Use

Vampire Computers

Vampire electronics are a well-known problem.  All those microwaves, set top boxes, and game consoles suck up lots of electricity even when they are turned off.

I decided to look at the problem for personal computers.  I have a Mac laptop at work, and a Dell desktop at home.  Both of them go into “sleep” or “standby” mode when I’m not using them, and both are still drawing power (presuming the laptop is plugged in, which it is most nights).  Part of my initial motivation was that the Dell in standby mode has a bright blue LED on the front panel that blinks, and when the rest of my house is dark that blinking light is bright and annoying.

Hibernate:  I made two improvements to both computers.  First improvement:  get the computer to really sleep.  What I mean by “real sleep” is like what Windows XP used to do in “hibernate” mode:  the computer saves a complete copy of all the programs that are running, then turns itself completely off, then when it restarts it can recover the states of all the programs that were running and all the windows that were open before it went to sleep.

Windows and Mac computers have different “sleep modes” that can be set by software, in ways that are unfortunately well hidden.  The terminology is also difficult.  The terms “sleep”, “standby”, “hibernate”, “safe sleep”, “hybrid sleep”, and others are used for different kinds of sleep, and have changed over the years, and are different between the Mac and Windows.   “Hibernate” seems to be the term that makes the computers do what I think is the right thing.  

Smart power strip:  the second improvement I made was to use a “smart power strip”.  Lots of computers have several peripheral devices attached: printer,  external monitor, powered speakers, etc.  The idea is to turn off all the peripheral devices when the computer is off, and turn them on when the computer is running.  Each peripheral device can be a vampire too, using a little bit of power all night even when the computer is turned off.

A smart power strip has one main device plugged into one of its plugs, and other devices in its other plugs.  When the main device is on, power goes to the other devices, and when the main device is turned off the power is shut off to all the other devices.   

Results:  here are the results I got, in watts:

	Running	Dumb sleep, normal power strip	Hibernate, smart power strip
Mac + monitor + printer	99	8	1
PC + monitor + printer	121	10	2

With all the improvements I made, there’s still a little bit of electricity being used.  The numbers in the right column are still not 0 watts.

Price of sleeping computer:  the PC+monitor+printer using the factory settings, sleeping at night, are using 10 watts of power.  That’s like having a lamp on all night, with a dim 10 watt bulb.  It’s not a huge amount of power but it’s something.

Doing the math, 8 watts * 24 hours * 365 days / 1000 = 70.08 kilowatts per year.  The price of residential electricity where I live is 14.81 cents per kWH, so the electricity cost savings per year for my sleeping PC is $10.37.  My computer isn’t really sleeping all year, but it’s sleeping a lot more hours than it’s awake.

Environment:  saving $10 per year on electricity for one computer is not huge, but it’s something.  If lots of people did it, it would add up to saving a lot of electricity and greenhouse gases and pollution.  On the other hand saving 80% of the electricity that the computer would otherwise be using during those off hours is big.

Vampire electronics suck.  Let’s kill some vampires!

To Microsoft and Apple:  I wish you would include “hibernate” as a default mode in the menus, along with “sleep”, the way it used to be on Windows XP.  It shouldn’t be such an obscure option.

Downside:  after hibernation the computer starts up more slowly.  It’s a little slower for the PC, a lot slower for the Mac.  The reason Microsoft and Apple have default sleep modes that aren’t very good for saving energy is market demand.  People want their computers to start up immediately.  Maybe that will change as people realize the cost to the environment of always-on “vampire” computers.

 

Details and References

Vampire electronics-#1

Vampire electronics-#2

Price of  electricity

Computers used for measurement:  MacBook Pro with Mac OS 10.5.8, Dell Inspiron 530 desktop with Windows 7 Pro, Dell 2407WFP monitor, HP Photosmart C4250 printer.

Explaining sleep & hibernate on Windows 7

Enabling hibernate on Windows 7

Enabling hibernate on Mac

Measuring power use of different electronic devices

Smart power strip

 

Mitch Gart, Principal Software Engineer