Understand Your Electricity: which appliances use the most electricity?

Here are some numbers from the Energy Information Administration. They are from 2001, the most recent available.

The two biggest components of household electricity use are heating, ventilation and cooling, which go by the catchy acronym "HVAC," and kitchen appliances. HVAC accounts for 31% of the total household use and kitchen appliances account for another 26%.

Air-conditioning is the single biggest electricity user in American households, totaling more than 182 billion kWh. More than 85% of that is for central A/C.

Space heating alone accounts for more than 10% of U.S. household electricity use, more than 115.5 billion kWh; space heaters account for more energy use than either lighting or home electronics, even though space heaters are found in only 43% of all households.

After A/C, refrigerators are the biggest electricity users, requiring 156 billion kWh per year. The average fridge uses 1239 kWh per year. Current Energy Star models use between 400 and 500 kWh per year.

Stand-alone freezers use a remarkable 3.5 % of the household total, even though they are found in only 34% of all homes. Dishwashers, which are found in 56% of all homes, account for only 2% of the household total.

Lighting accounts for 8.8% of the U.S. household total, about 100 billion kWh.

All home electronics account for only 7.2%, or 82.3 billion kWh.

Not surprisingly, TVs are the most common household electronic item, averaging more than 2 per household; they account for about 33.1 billion kWh. or 2% of the total.

Way down on the list, cordless phones and answering machines each account for less than .2% of the household total, or about 4.4 billion kWh between the two of them.

Understand Your Electricity: Sleeping your work Computer

From the Alliance To Save Energy

New Report Highlights the Power of Powering Down

A new report on personal computer usage and power consumption released this month suggests US business could be saving billions of dollars simply by shutting down machines at night. The survey, commissioned jointly by the Alliance to Save Energy and power management software company, 1E, found that nearly half of all corporate computers (roughly 31 million PCs) are not regularly switched off at night. According to the study, this lack of inactivity is costing US businesses $1.72 billion annually and adding over 14 million tons of carbon dioxide to the atmosphere per year.

Comment: pulling out my handy calculator, and borrowing a few PC numbers from Mr. Electricity, we can estimate that an average workplace computer uses about 100 watts just sitting there. The Alliance estimates that as many as 31 million PCs are left on at night. Forgetting about weekends, let's assume each of these is on instead of off or asleep for 10 hours every day, four nights a week; each one would thus waste 1 kWh per day, or 208 kWh per year. For 31 million computers that adds up to more than 644 million kWh per year, or a year's electricity for 586,181 homes. (Using my 11,000 kWh/year average). Each computer that is left on for 60 hours over the weekend wastes another 312 kWh per year. If 15 million of these were left on over the weekend year round, they would waste more than 4.68 billion kWh, or enough electricity to power more than 4.25 million homes.

Let's hope that these companies are sensitive to the other green, cost: according to the EIA, the average commercial cost for electricity this year is 9.28 cents/kWh. Using my numbers, each computer left on overnight during the work week wastes about $19 a year and each one left on over the weekend wastes another $30 a year.

Understand your Electricity: Vampires Part 2

I just read yet another site that recommends that we unplug our electronic appliances: this writer claimed that 75% percent of household energy use goes to power items in standby mode—the site credits the Department of Energy of all places. Considering that according to the most recent Energy Information Administration figures available (2001), all household electronics—TVs, stereos, computers, peripherals, everything—accounted for just 7% of U.S. household electricity use, that number is not just incorrect but utterly insane.

The writer may have wanted to claim that 75% of the total power use of our electronics is used to power items on standby—that could be true: is your printer on all day? how much time do you spend printing? Is your VCR on right now? Is anyone watching it? So we could probably cut a significant proportion of that 7% by shutting these items down.

But let’s get a little proportion. Here are a few numbers from my trusty Kill-a-watt to cut through the green haze we are living in.

The computer system I am currently writing at includes the following components all plugged into a single power strip:
Apple desktop
cable modem
HP printer
external hard drive

That entire system uses between 90-115 watts of electricity, including when I am printing. Starting up, the whole system draws about 105 Watts. The printer draws 21 watts on standby and 27 watts when it is starting up. The cable modem, which many people leave on all the time, draws 7 watts.

That is to say, my whole computer system uses about the power of a single 100 watt bulb or 1.5 60 watt bulbs.

My Energy Star Air-conditioner uses between 700 and 1000 watts whenever it is cooling. It saves energy by alternating its cooling mode with a 0-watt low-energy mode.

As I noted in my previous "Vampire" post, unplugging standby appliances might save you about 72 kWh a year. Turning off your window air-conditioner could save you twice that each week. A central system running at full blast uses 3.5 kWh every hour.

The problem with the internet is that this misinformation tends to take on a life of its own: how many internet start-ups were funded because of the widely repeated but utterly baseless factoid that the number of people on the internet was doubling every three months?

Standby power is a problem on a national not a household scale. Its real solution is efficiency standards. It makes much more sense for the government to revise the codes to minimize standby power draw than for individual consumers to have to research the power use of a dozen electronics that use only a few watts each, or for them to have to walk around turning them off--something that only a small number of people are ever going to do.

Understand Your Electricity: Why Light Bulbs Matter

Leaving a 7-watt cable modem on 24/7 for a year uses about 63 kWh---.6% of the typical household's yearly total of 11,000 kWh.

Leaving a 60 Watt bulb on for a year uses 547 kWh--about 5% of the typical yearly total.

Our house has two modems and 50 light bulbs.

Understand Your Electricity: What is a kilowatt hour (kWh)

What is a kilowatt hour (kWh)?

Glad you asked. We measure the electricity we use at any given moment by watts: a 100 watt bulb is using 100 watts continuously while it is on.

We buy our electricity by the Kilowatt hour or kWh. A kilowatt hour is not a period of time but an amount of power. The dictionary definition of kWh is: a unit of energy equal to the work done by one kilowatt in one hour.

I find this a bit abstract; it is easier to make sense of via equivalences. A device's wattage determines how long it must run before it uses up 1 kWh's worth of power.

1 kWh = the amount of power a 100 watt device uses in 10 hours
1 kWh = the amount of power a 10 watt device uses in 100 hours
1 kWh = the amount of power a 1 watt device uses in 1000 hours

From another perspective:
1000 ÷ wattage = the number of hours the device must run to equal 1 kWh

To calculate how many kWh a device uses in a year, you must know its wattage and how many hours a day it is running.

For a 50 watt device that runs 4 hours a day:
1000 ÷ 50 = 20 hours to make 1 kWh
4 X 365 = 1460 = the hours the device runs in a year
1460 ÷ 20 = 73 kWh per year

As usual, Mr. Electricity has a helpful discussion of the wonders of the watt and kilowatt hour.

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.

Understand Your Electricity: Unplugging Vampires

Every "save the planet" list these days tells you to use CFL bulbs, unplug “vampire” appliances (those that draw electricity even when they are off), and sleep your computer. However, I have yet to see one that tells you the different impact of these activities.

So here it goes, thanks to the “Kill-a-Watt” watt-o-meter, a device that every would-be environmentalist should own. (See the previous post for where to buy this miracle device).

Unplugging Vampires: the only appliances in our house that draw measurable power when "off" are the DVD/VCR player (4 watts), the printer (11 watts), and the computer (2 watts). The toaster, mixer, food processor, TV, stereo, and lamps draw no power.

What then is the impact of unplugging these “vampires”? Rounding our total up to 20 watts and assuming that these guilty appliances would otherwise be off and plugged in 24/7, unplugging them for a month would save about 12 kWh or 144 kWh for the whole year. Respectable, certainly, but equal to about 1.3% of the average U.S. household's 11,000 kWh yearly usage. Obviously, in a more realistic scenario, if we consider our vampires as "off" only half the time, and running the other half, the savings goes down to 6 kWh/month and 72 kWh/year or a tiny .65 % of household usage.

Changing light bulbs: assuming a given light was running 6 hours per day, changing a 60 watt incandescent light bulb to an 18 watt CFL would save 7.5 kWh per month or 90.7 kWh for the year--per bulb. Multiply that number by 40, the number of bulb sockets in the average house, and you are saving 300 kWh/month or 3600 kWh/year, or 32% of the average household's yearly electric usage.

As I noted in an earlier post, changing half of our bulbs and being careful about turning off the lights immediately cut our electricity usage by 20%.

Simple Advice for saving the planet: Change those bulbs and get aggressive about turning out your lights.

Setting Priorities #1: Understand Your Electricity

The recent Live Earth concert series was an inspiring attempt to raise public awareness of global warming and help educate people about reducing their impact. The main problem is still these "save the planet" tips, which though full of our beloved factoids, do not actually help individuals understand where their carbon footprint really comes from.

Americans have become fixated on driving because we are so dependent on our cars and because of the evil “foreign oil.” You will get no argument from me about cutting our oil usage, for security and environmental reasons. But as far as global warming is concerned, coal-generated electricity is the bigger problem: coal pollutes much more per unit of energy than oil or natural gas. In 2006, more than 2.1 billion metric tons of emissions came from coal, or 36% of the total.

As a society, more of our emissions come from oil, but

for the average individual, the energy used in our homes is responsible for more than twice the greenhouse gas emissions as the energy used by our cars.

So first thing’s first: for Americans reducing electricity use should be the top priority, and to do that we need to understand the following:

1. where we use it
2. where we can cut it
3. where it comes from


Over the next few days, Green Factoids will take a look at our electricity use with the help of a handy device that every household should get: the “P3 International Kill-a-Watt Electricity Usage Monitor.” You simply plug your Kill-a-Watt into the outlet and plug your electric device into the Kill-a-watt to learn how many watts the device is drawing.

The device will also tell you the appliance’s kWh, volts, amps and other cool information.

Amazon currently sells the Kill-a-watt for about $23.

Thanks to our favorite blog, Michael Bluejay's Mr. Electricity, for recommending the Kill-a-watt.