Q: How much energy does a typical laptop and desktop use in standby mode? How has this been reduced over time by changes in technology?

Asked by Shiva Swaminathan, Fremont, Calif.

It turns out that computers are like cars: the more powerful they are, the more energy they use. And, like automobiles, new computers are far more efficient than older models. However, even in standby mode many of your computer’s internal parts are still operating and consuming energy. In fact, depending on how old your computer is, it could be using anywhere from 1 to 60 watts even while “asleep.”

How do you tell whether your computer is an energy sipper or a watt hog? I decided to use a wattmeter to test how much energy computers in my laboratory at Stanford wasted during standby mode. To my surprise, I found that the desktops used 5 to 6 watts and the laptops 1 to 2 watts. This was much lower than I had expected, and was probably because all the computers I tested were fairly new. Still, if you consider that there are about 35,000 computers on the Stanford campus, a standby energy usage of even a few watts can add up quickly.

A good way to identify energy-efficient computers is to see if they are “Energy Star” compliant. If you have such a computer, you will need to enable its power management settings to actually save energy. To ensure the right settings for all its computers, Stanford deployed the “BigFix Power Management Tool” in 2007. This downloadable tool can switch off monitors and put computers in standby mode. Sustainable Stanford, a University-wide effort to reduce environmental impact, estimates that this could save individual departments up to $17 per computer per year. Based on 24,000 computers on campus with BigFix installed, this reflects more than $400,000 in annual electricity savings. Importantly, this also represents 28,000 tons of CO2 kept from entering the atmosphere, or the equivalent of taking 4,600 cars off the road for a year.

The only way to eliminate all energy consumption by a computer and its peripherals is to disconnect them. Using a power strip is a convenient way to do this, and newer models can automatically turn off power to peripherals when the computer is shut down. And some manufacturers make “zero-watt” models that completely disconnect their power supply when they go into standby.

Energy wasted while computers are on but unused is still a problem, but advances in computer technology and changes in behavior should be able to resolve it in the near future.

Sandeep Ravindran is a PhD candidate in microbiology and immunology.