posted by Howard Fosdick on Tue 2nd Aug 2011 22:18 UTC
IconYour computer is an important energy consumer in your home. Can you save energy when using it? This article offers a few tips.

1. Buy a voltmeter

You only know how much electricity you use if you have a way to measure it. And only if you measure it can you minimize its use. A voltmeter gives you this ability. You can buy one for only $25 US at Amazon.

      A popular inexpensive Voltmeter

You plug the voltmeter into the wall socket, then plug the device you want to measure into the voltmeter. To measure how much electricity all your computer equipment uses, plug it all into a power strip, and plug the power strip into the voltmeter.

If you're like me, when you get your new voltmeter you'll run around the house and measure the power consumption of everything in sight. You'll quickly find ways to minimize your use of electricity, powering off some appliances and using others less. With your computer you'll discover:

1. Different configurations use different amounts of electricity.  How much electricity your system uses depends on the device type, the power consumption of the processor and motherboard, the number and type of memory sticks, how many disk drives, what peripherals you have, etc.

2. The same computer uses different amounts of electricity depending on how it's being used. Your computer uses less electricity at idle than when in use, and heavy use drives the power consumption higher than light use. Heavy disk I/O and maximum CPU utilization use more power, for example.

3. Your computer can be in different "power modes." When you're not using it, your computer drops into a low power mode. We'll discuss the Standby, Sleep, and Hibernate states below.

2. Use a laptop instead of a desktop. Or a tablet or smartphone.

It's tough to generalize about computer power consumption because it varies so widely. (That's why you bought the voltmeter!) Most desktop computer systems consume between 70 and 200 watts while in use, while laptops often burn between 15 and 60 watts. Both figures include typical LCD displays. View this power consumption chart to see how much electricity some typical systems use. This chart lists power consumption for displays alone.

A laptop in use always uses less electricity than a desktop in use. Often by a pretty significant ratio. If you're buying a computer and you're into saving electricity, go with a laptop. I'll show you a formula below so you can easily determine the energy cost savings you get with a laptop. (We're only talking ongoing energy consumption here. We're ignoring factors like whether laptops last as long as desktops, how much energy goes into their production, etc.)

If they meet your needs, consider moving to even more energy-stingy devices, like tablets or smartphones. (Here are example power specs for the iPad and iPhone.)  From least to greatest energy consumed, the device type hierarchy is:

smartphones and tablets   -->   laptops   -->   desktops


3. Use a flat panel display instead of a CRT monitor

Those big, bulky old CRT monitors use several times the power of space-saving, power-sipping flat panel displays. CRT's often consume between 60 and 110 watts, while most flat panels are down in the 15 to 60 watt range. No contest!

The energy savings you'll get might even pay you to buy a flat panel to replace an old CRT. You can calculate this yourself. Here's how.

My old Dell D1028L 17" CRT used about 100 watts of power, while my beautiful replacement Acer P205H 20" LCD/TFT display uses only 28 watts (and only 0.75 watts at Standby!).

Say I use the computer for 4 hours per day every day.  Here's the electricity calculation for these two displays:

4 hours/day * 365 days/year  =  1,460 hours of use per year

CRT = 1,460 hours * 100 watts/hour = 146,000 watt-hours/year
LCD = 1,460 hours *  28 watts/hour  =   40,880 watt-hours/year

Electric bills measure your usage in thousands of watts per hour, or kilowatt-hours. So the comparison is between 146 kWh versus 40.88 kWh. Your electric bill shows what your power company charges per kWh. Mine happens to be 15 cents per kWh. Just multiply it out:

CRT = 146 kWh   *  0.15 charge per kWh = $21.90 yearly cost
LCD = 40.88 kWh  *  0.15 charge per kWh =   $6.13 yearly cost

So I save $21.90 - $6.13 or $15.77 a year by using the LCD instead of the CRT. If the Acer costs me about $120, I can divide $120 by $15.77 to determine that it will pay for itself in under 8 years solely from electric bill savings.

The financial experts out there will point out I'm ignoring amortization, inflation, and lord knows what else, but this simple calculation suffices for most of us. Use it to compare electrical costs:

((watts * hours used)  /   1000)   *   charge per kilowatt-hour   =  total electricity cost

Laptop versus Desktop -- Redo

Let's use the formula to compare laptop to desktop energy costs.

Say I want to replace a Dell OptiPlex GX260 Pentium 4 and its 17" Dell LCD display from 2003 with an Apple MacBook Pro with 15" integral display from 2010. The Dell desktop and its display together consume 104 to 162 watts during moderate use. I'll assume 135 watts here. The MacBook clocks in at 55 to 58 watts for moderate use. I'll assume 55 watts. 

We'll again assume 4 hours of moderate use per day, or 1,460 hours annually. At 135 watts/hour, the Dell desktop consumes roughly 197.1 kWh per year. At 55 watts/hour the laptop consumes around 80.3 kWh per year. Assuming 15 cents per kWh, that prices the desktop's annual electrical bill at about $29.56 and the laptop's at $12.05. The difference is $17.51. I can use this number to help me decide whether buying the laptop is worth it.

I've made many assumptions here but the approach is valid. Use it to compare electrical costs
. Remember that we're excluding other factors like the energy used during manufacture, longevity (MTBF), disposal costs, etc.

4. Set your Power Management options

Measurements with your new voltmeter quickly expose a power consumption hierarchy. These are your computer's power usage levels, from greatest power consumption to least:

Heavy Use  ->  Light Use  ->  Idle  ->  Standby  ->  Hibernate  or  Turned Off

A heavily-used computer sucks more power than one at idle, while idling requires more power than standing by or hibernating.

There's lots of confusion between the terms standby, sleep, and hibernate. For good reason. How they work vary by operating system and by computer manufacturer! There is no industry-standard meaning for these terms. I'll use the U.S. Department of Energy definitions. These recognize two distinct states: hibernate and standby.

Hibernate means the computer saves its state, then turns itself off. It will reload its state when you turn it on again. Hibernate powers up faster than a regular boot. The computer uses zero power during hibernation.

means the computer still uses power but at a reduced level. Non-essential components are powered down. The computer can "awake" faster than from hibernate mode but uses some minimal power to enable this. This chart summarizes:

Energy Use:
1 to 5 watts
0 watts
0 watts
Time to Become Usable:
quickest (under 5 seconds)
intermediate (30 seconds to 2 minutes)
longest (2 or 3 minutes)
U.S. DOE definitions for Standby and Hibernate. Figures are approximate.

One quick word about screen savers. Many don't save energy. That's not their purpose. They may even use more electricity if they've got color graphics moving all around. (Pick the "Blank screen" as the most energy efficient screen saver.) To save energy either turn off your display or set its power management options.

To set your computer's Power Management options, in Windows you can right-click on the desktop, select Properties, then choose the Screen Saver tab. Here you set the screen saver attributes. Click on the Power button to set the power management options. In Ubuntu go to System -> Preferences -> Screensaver. You can click on the Power Management button from there.

      Typical Linux Screen Saver and Power Management Panels  (from openSUSE 11.4)

Always test your power management settings. It's not unusual to find quirks in how they work (or don't). This is doubly true if the operating system you're running was not manufacturer-installed.

Beyond OS-based power management, you can also install an intelligent power calibration tool like Granola. This free Windows & Linux product does dynamic voltage and frequency scaling (DVFS) for your system's CPUs. MiserWare's web site claims Granola can reduce your computer's electrical use from 15% to 35%. Monitor with your voltmeter over a period of time to see what results you get.

How much electricity can you save by proper power management? It depends on how you use your computer. This study cranks real numbers for office workers and finds that reducing annual energy consumption by 80% is not unusual. I think that what this means is that going from ignorance of power management to active power management is a huge win.

5. Turn off your computer when you're done for the day

From a power consumption standpoint, a computer turned OFF always uses less power than one that is still ON.

Some claim that the power required to start up a computer is greater than that consumed by leaving the computer on overnight. Not true. The power involved in start-up is about the same as power consumed during maximum regular use ("heavy use"). Measure it with your voltmeter. Or view the proof in this chart. The extra power consumed at start up will not exceed the power used by keeping the computer on all the time. Even if the computer is in standby status, which consumes just a few watts per hour.

This research study gives you the numbers on this and concludes that "... ensuring computers are turned off at night dramatically reduces their energy consumption."

Some claim that starting a computer "stresses it" due to a "power surge" and makes it more likely to fail sooner. They say you should leave your computer on overnight rather than switching if off and on.

Majority opinion among those who seriously research the issue is that "Hard drives and other components are now better built, so wear and tear through daily powering on and off of desktop computers is no longer a consideration."

The U.S. Department of Energy has it right for most of us:

"Most PCs reach the end of their "useful" life due to advances in technology long before the effects of being switched on and off multiple times have a negative impact on their service life. The less time a PC is on, the longer it will "last." PCs also produce heat, so turning them off reduces building cooling loads."

Of course, if you need your computer on at night to perform work, that's a whole different story. Some people perform updates or run batch processes overnight. Just set your power management options so that they take effect after the work completes.

6. Use an Ink Jet printer and turn it on only when printing

Printer energy consumption varies widely. You'll have to use your voltmeter to see how much electricity yours draws when printing and when turned on but idle.

From least to greatest energy consumed printer technologies order like this:

Dot Matrix   -->  Ink Jet   -->   Laser

Since dot matrixes are largely obsolete due to lesser print quality, this makes the ink jet is the best energy-conscious choice for most home users. An active laser printer uses several times more electricity than your computer!

Most home users only print occasionally. You can save electricity by turning on the printer only when you intend to print, then turning it off immediately afterwards. Don't leave it on all the time. Some people waste electricity because they put their printer on the same powerstrip as their computer so it's on whenever their computer is on. Energy savings will be dramatic for laser printers, which consume hundreds of watts when active and tens of watts even in standby mode.

7. Buy Energy Star equipment

Energy Star (or ES) is a joint program run by the U.S. Department of Energy and the Environmental Protection Agency. Computer equipment that meets ES energy efficiency standards display the Energy Star logo:

        The Energy Star Logo

Many countries beyond the U.S. have adopted the ES system and at least 40,000 appliances conform to it. Energy Star specs cover all kinds of computer components including system units, power supplies, batteries, displays, printers, and more. What's great about ES is that the program is strictly voluntary. It does not impose government regulation. Yet it saves billions of dollars per year in energy costs while minimizing our carbon footprint. The EPA estimates ES saved $14 billion in energy costs in 2006 alone.

The first ES specification for computer equipment was developed in 1992. The current computer specification is version 5.0 from 2009. The good news is that the ES specs keep moving forward and incrementally improving. The bad news is that the changes make it hard to compare power efficiency between systems released under different ES standards. ES is a great tool for buying new energy efficient hardware. It isn't so useful when comparing hardware across time.

How much will you save by buying Energy Star products? This article calculates a total lifecyle savings for a computer system of $161, or 18% of the initial purchase price. Even if that's on the high side, it pays to buy ES!

8. Keep your computer in service longer

In my articles on computer refurbishing I advocate keeping computers in service until either technological obsolescence or their natural end of life. Some readers have responded that this is a bad idea because older computers consume more electricity than newer ones. Actually, if you're talking consumer systems produced over the past decade, there has been but minor reduction in operational energy consumption in spite of the ES energy efficiency increases. You can't take a random new computer and assume it uses less electricity than one from 2005 or even 2000. The big change for consumer systems has come in displays. Not only do LCDs use way less energy than CRTs, but newer flat panel displays use less than older ones.

The key reason to keep consumer computers in service longer is environmental. It costs both natural resources and energy to make a computer. Lots. If your current machine still does the job, replacing it with a new computer of the same type (desktop or laptop) unnecessarily consumes resources.

According to a United Nations University study, the natural resources that go into making a computer are about 10 times its weight in fossil fuels and and chemicals, versus only 1 to 2 times their weight for a car or refrigerator. This is why your little laptop is so expensive compared to larger appliances in your house.

Then there's the huge problem of proper disposal of all the toxins computers contain when they're no longer usable.

What about energy? This research project found it takes about 1,778 kWh of electricity to produce a desktop computer and monitor as of 2004. This is as much energy as the typical household uses in two months. It's enough energy to keep your 100 watt desktop in active use for 17,780 hours. That's over 12 years of daily use at 4 hours per day. Given a typical lifespan of 3 to 5 years, this means that the energy cost to produce a computer greatly exceeds the energy it consumes during its operational lifespan.

This article underscores the point. Based on research recently published in the Journal of Cleaner Production, it concludes that "Computer factories eat way more energy than the devices they build." The study found that 70% of the energy a typical laptop will consume during its life span is used in manufacturing the computer!

If you buy two computers of the same type (desktop or laptop) over a decade, you use less total energy than if you had bought three in that same time span. The best way to reduce your computer energy use is to buy fewer computers. This is why research from sources as diverse as Fujitsu and the Gartner Group advocate device longevity.

What if you replace a device of one type with a device of another type that consumes less electricity? For example, say you replace your old desktop with a new laptop or a tablet. Or say you replace your laptop with a smartphone. Now you have a much more complicated comparison. I've shown in this article how to compute ongoing electrical costs. You can use the simple formula to predict and compare your electrical bills for different devices. However, we haven't compared the energy required to manufacture different kinds of devices. Nor have we explored how recycling costs might differ for device types. And these are just two of the factors you'd have to measure to make an accurate judgement.

For now let's stop at one useful conclusion. So long as it still does the job you need done, it is cheaper to keep your current computer in service than it is to replace it with a similar new one. This is true both from the standpoint of the total energy cost (energy cost to manufacture plus ongoing power consumption) and from the standpoint of natural resource consumption.

Refurbishing and reusing computers in the 3 to 10 year old range is without question good for the environment.

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Howard Fosdick (President, FCI) is an independent consultant who supports databases and operating systems. His hobby is refurbishing computers as a form of social work and environmental contribution. Read his other articles here or email him at contactfci at the domain name of sbcglobal (period) net.
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