Wednesday, July 11, 2007

Understand Your Electricity: Sleeping your Computer

One of the most common tips on the “save the planet" lists is to change the settings on your computer so it goes to "sleep" when it is not being used. How much electricity does this save?

Getting out my handy "kill-a-watt" meter, I discover that my Apple Desktop uses about 60 watts for regular functions. I should add that I am not what the tech writers would characterize as a heavy user, no “hard-core gaming” etc., just the usual word-processing, surfing, and email.

While sleeping, my computer’s power draw drops to about 4 watts, just a smidge more than it draws when turned off. Using these numbers, sleeping produces a power savings of about 56 Watts. For simplicity's sake, let's round that to 50 watts.

Assuming a 50 watt savings, every 20 hours that the computer is sleeping rather than running saves 1 kWh of power.

Let’s say that the sleep function was reducing power use 4 hours a day throughout the year. What then is the yearly savings?
4 hours X 365 days = 1460
1460 ÷ 20 = 73

That would save 73 kWh a year. Again using our average American household use of 11,000 kWh per year, eliminating 73 kWh would save about .66% of the year’s total.

Okay, so that is not so impressive from the household perspective. But from a nationwide perspective the numbers are more meaningful.

Again using my Apple numbers, every 50 computers that sleep instead of run for 1 hour save 1 kWh. Every million computers that sleep instead of run for 1 hour save 20 megawatt hours of power. Every 25 million computers that sleep instead of run for 1 hour save 500 megawatt hours of power, or the generation capacity of the typical coal-fired plant.

The most recent census data (2003) put the number of home computers in the U.S. at about 70 million.

If each one of these computers slept for 3 hours a day instead of running, we would save 1,533,000 megawatt hours per year, or 1.533 billion kWh: that's the yearly power use of about 139,000 typical American homes--I would be impressed by that.

A Caveat: Before we all get too excited, I should note that lap-tops use less electricity than desktops so they also save less when they sleep. My husband's Dell uses about 30 watts for normal operations and 2 watts when asleep. Hence, sleeping only saves 28 watts, and the computer requires more than 35 hours in the sleep function to save 1 kWh.

The Bottom Line: this one wins the no-brainer award. Resetting your computer sleep function takes about 30 seconds and will save energy as long as that computer is operating. It is definitely one of the easiest ways for the average person to help the planet.

Beginning this year, a group of technology companies has joined forces to form Climate Savers: Computing to increase computer efficiency. Their goal is admirable as well as achievable:

By 2010, we seek to reduce global CO2 emissions from the operation of computers by 54 million tons per year, equivalent to the annual output of 11 million cars or 10–20 coal-fired power plants. With your help, this effort will lead to a 50% reduction in power consumption by computers by 2010, and committed participants could collectively save $5.5 billion in energy costs.

Take a look at their statement of their initiative.

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