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The Lunch Table: Are Apples Really More Energy Efficient Than Dells?

Occasionally, we will post informal commentaries based on the lunch-time conversations around our conference table. Some may wander into marketing, engineering, politics, or psychology, but they’ll always be focused on energy.

Here’s the true sign that you’re at an energy-geek conference: instead of the usual schwag like a logo sweatshirt or carry-on bag, the organizers hand out Kill-A-Watts. (A Kill-A-Watt, pictured below, is a small device that you can plug into a normal outlet to measure the electricity used by whatever you plug into the device.)  This is exactly what we did several years ago at our summer research workshop.

Our Kill-A-Watts helped settle a recent lunch-time bet. Severin had plugged his home computer, a Dell, into his Kill-A-Watt and checked it after he’d turned off the monitor and stopped using the computer: 50 Watts. My husband, who was convinced by our kids to buy an iMac several years ago, thought he had noticed a drop in our monthly electricity bills after we made the switch. (We leave our computer on all the time, a habit we adopted as PC users since it could take so long to reboot.) I wagered on my husband’s off-hand impression and bet Severin that our iMac used less power when not in use.

Well, it turns out that the iMac was far, far superior, in a way that even annoying Apple aficionados may not realize. Ten minutes after my son and I had stopped using the computer, it was drawing 1 Watt, one FIFTIETH the power of the Dell.

My son figured out that, compared to a PC, we were saving a dollar every three and a half days. Sure that’s less than his allowance, but real money nonetheless.

I asked several colleagues why this might be the case. Here’s the explanation that makes the most sense to me, courtesy of David Jacobowitz, who knows more than most about computer energy efficiency:

When a machine is “asleep” (technically, “suspended”) the processor is stopped and most peripherals are turned off. The hard drive is stopped. Only the memory is being refreshed to keep it from losing data. The result is that the machine should draw very near nothing. I have measured a lot of machines in sleep mode and not a single one was over 1.5 W, Apple or otherwise.

On the other hand, Apple selects higher quality power supplies than most PC manufacturers and in general spends more time to make sure all the peripherals don’t interfere with sleep (a common problem — a peripheral or device driver forces the machine to remain awake).

So, it sounds like the iMac may be better at putting itself to sleep, while the Dell is more of an insomniac.

If you’re technically inclined, you can tell your computer when to go to sleep by adjusting the power management settings. (Click here for a detailed set of instructions for several different operating systems.)

Is this another victory for Apples? How much does the manufacturer matter? It sounds like they matter a little, but they’re not the whole story. For one, manufacturers choose the default power management settings, which the vast majority of us never change. Also, the user interface may influence how many of us venture to change the power management settings, so the operating systems could make a difference. Finally, the speed with which the computer “wakes up” from sleep mode impacts how willing we are to put the computer to sleep in the first place.

Surprisingly, EnergyStar ratings, which are supposed to help consumers make decisions about the energy efficiency of their purchases, are just beginning to address sleep mode for computers. We can discuss the economics behind EnergyStar in another post, but this certainly seems like an area where information from the government could help consumers save energy and money.



Catherine Wolfram View All

Catherine Wolfram is Associate Dean for Academic Affairs and the Cora Jane Flood Professor of Business Administration at the Haas School of Business, University of California, Berkeley. ​She is the Program Director of the National Bureau of Economic Research's Environment and Energy Economics Program, Faculty Director of The E2e Project, a research organization focused on energy efficiency and a research affiliate at the Energy Institute at Haas. She is also an affiliated faculty member of in the Agriculture and Resource Economics department and the Energy and Resources Group at Berkeley.

Wolfram has published extensively on the economics of energy markets. Her work has analyzed rural electrification programs in the developing world, energy efficiency programs in the US, the effects of environmental regulation on energy markets and the impact of privatization and restructuring in the US and UK. She is currently implementing several randomized controlled trials to evaluate energy programs in the U.S., Ghana, and Kenya.

She received a PhD in Economics from MIT in 1996 and an AB from Harvard in 1989. Before joining the faculty at UC Berkeley, she was an Assistant Professor of Economics at Harvard.

7 thoughts on “The Lunch Table: Are Apples Really More Energy Efficient Than Dells? Leave a comment

  1. Hi Christopher, I provided the E* data to Catherine and it looks like I provided bad data.

    I meant to state that E* does not require a certain power level for sleep (at least for Desktops; other classes do have such a requirement.) Instead, E* has a “total energy consumption” (TEC) requirement, of which sleep is one component.

    For example in E* 5.0, a “Category A” desktop PC must consume less than 148 kWh/yr. That could be achieved with a 36 W sleep mode, 37 W idle mode, and 0 W off mode — even though a mere 1 W drop would be pretty awful sleep performance. Unless I’m missing something, my read of the spec would not preclude this.

  2. Interesting. I really hope this doesn’t get picked up on any of the Mac and PC sites, otherwise you’re going to get crazy flamewars in these comments….

  3. I’m not sure where you get the data to support the claim “EnergyStar (sic) ratings … are just beginning to address sleep mode for computers.” The ENERGY STAR specification for desktop computers was the first ENERGY STAR rating for any product, and v1.0 dealt *solely* with sleep mode. This was, in fact, the great realization that spurred the development of energy-efficient desktop PCs – the idea that a desktop machine could conserve power in the same way that laptop systems had been designed to do so. The “sleep” mode was the technology transferred from laptop to desktop, made prevalent by the ENERGY STAR program.

    • Hi there-

      Thanks for the clarification on both content and spacing of ENERGY STAR. To my mind, the way the regulations account for sleep isn’t all that useful since they assume that all computers spend the same amount of time in different modes (5% at sleep).

      For instance, Severin followed the instructions on the climatesavers site to reset his default, but is still finding that the machine isn’t always sleeping when it should be, perhaps because of network activity? Any chance future regulations will somehow account for how computers are behaving, which presumably varies?


  4. Strange comparison made without giving more of the details. I am sure Apple does an overall better job at power management but to get 1/50th is less Apple and much more likely the fact that the Apple has a few advantages by just being newer: 1) Using Intel’s newer Sandy Bridge processors which are MUCH more energy efficient (especially when at idle) than even last generation and 2) Most iMacs use laptop graphics parts to help conserve power but their 3D performance isn’t ideal for everyone.

  5. I hope that Severin gets his power settings sorted, so that he too will enjoy peace of mind that comes with knowing that his PC is not waiting at all hours for his next keystroke!

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