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Saving Electricity

Mr. Electricity is your guide to saving energy in your home. Saving Electricity 101: Start Here How much it costs / how they charge What's a Watt / Kilowatt? How much energy stuff uses How to measure electrical use General Electricity Myths Using elec. when off? Why is my bill so high? Capacity of an Outlet Electric Meters General Questions Specific Appliances Cooling Heating Lighting Refrigerators Washing Machines Clothes Dryers Water Heaters Computers Televisions Cooking Elevators Environment Carbon footprint calculator Carbon Offsets Solar Power Bicycle Power Alternative Energy Climate change Special Topics Compact Fluorescents Gas vs. Electric Standby power Surge Suppressors (TVSS) Power Factor Commercial Buildings Using devices overseas We're recommended by the government of Berks County, PA. Related sites: Watt Watt. News about efficiency and conservation, written by readers of the site. Home Power Magazine. All about renewable energy for the home. Thin House. Blog about a family committed to cutting its energy use by 80%. No-Impact Man. Blog about a family striving to have no net impact. (i.e., What little they use, they offset.) Inspirational. Off-Grid. News and resources about living without being connected to a utility company. If you like this site, you might also like some of my other sites: Battery Guide Which battery is best? We cover rechargeable and alkaline batteries to show you what's hot, what's not, and the best way to charge them. (visit now)

How much electricity costs, and how they charge you   What the heck is a kilowatt hour? Before we see how much electricity costs, we have to understand how it's measured. When you buy gas they charge you by the gallon. When you buy electricity they charge you by the kilowatt-hour (kWh). When you use 1000 watts for 1 hour, that's a kilowatt-hour. For example: Device wattage Device Hours used kWh medium window-unit AC 1000 watts one hour 1 kWh large window-unit AC 1500 watts one hour 1.5 kWh small window-unit AC 500 watts one hour 0.5 kWh 42" ceiling fan on low speed 24 watts ten hours 0.24 kWh light bulb 100 watts 730 hours (i.e., all month) 73 kWh CFL light bulb 25 watts 730 hours 18 kWh When the number is low we sometimes use watt-hours (Wh) instead of kWh. For example, we might say 240 watt-hours instead of 0.24 kWh.   Watts and watt-hours Watts is the measure of the rate of electrical use at any moment. For example, a laptop computer uses about 50 watts. On a separate page I have a list of how many watts various devices use. If your device lists amps instead of watts, then just multiply the amps times the voltage to get the watts. For example: 2.5 amps   x   120 volts   =   300 watts (If you're outside North America, your country probably uses 220 to 240 volts instead of 120.) Understand the difference between watts and watt-hours: Watts is the rate of use at this instant. Watt-hours is the total energy used over time. Here's a question I frequently get, which makes no sense: "You say that some device uses 100 watts. What period of time is that for?" It's not for any period of time, because watts is a rate at that instant. One might as well ask: "The speedometer in my car says I'm going 35 miles an hour. What period of time is that for?" It's not for any period of time. You're going 35 miles an hour at that instant. To measure use over a period of time, we use watt-hours, not watts. The way it works is, watts or kilowatts for the amount at a given instant, and watt-hours or kilowatt-hours for the amount over a period of time.   Trivia The average U.S. household used 920 kWh a month in 2006. (Dept. of Energy) The U.S. as a whole used 3,883 billion kWh in 2003, or 13,868 kwH per person based on a population of 280 million. (Dept. of Energy) On a peak day in 1999, California used 50,743 megawatt-hours of electricity, or 50,743,000,000 watt-hours.   How much does electricity cost? The cost of electricity depends on where you live, how much you use, and possibly when you use it. There are also fixed charges that you pay every month no matter how much electricity you use. For example, I pay $6/mo. for the privilege of being a customer of the electric company, no matter how much energy I use. Check your utility bill for the rates in your area. If it's not on your bill then look it up on the utility's website. The electric company measures how much electricity you use in kilowatt-hours, abbreviated kWh. Your bill might have multiple charges per kWh (e.g., one for the "base rate", another for "fuel") and you have to add them all up to get the total cost per kWh. Most utility companies charge a higher rate when you use more than a certain amount of energy, and they also charge more during summer months when electric use is higher. As an example, here are the residential electric rates for Austin, Texas (as of 11-03): First 500 kilowatt-hours 5.8¢ per kilowatt hour (kWh)   Additional kWh (May-Oct.) 10¢ per kilowatt hour   Additonal kWh (Nov.-Apr.) 8.3¢ per kilowatt hour Some utilities break their charges into two, a standard charge plus a fuel charge, each charged by kWh. The standard charge might change only infrequently, while the fuel charge goes up and down according to the local price of fuel for the power plant. Make sure you add both parts to get your total cost per kWh. The average cost of residential electricity was 12¢/kWh (DOE) in the U.S. in April 2009. The average household used 936 kWh/mo. in 2007 (DOE) and would pay about $108 for it based on the April 2009 average rate. DOE also has historical rates. The cost of electricity varies by region. In 2009 the price ranged from 7¢ in Idaho to 22¢ in Hawaii. The map shows average rates in 2003, and here's 2009 data in table form. (Your cost may differ, and I don't need to know if it does.)    Exercise #1. Go get your electricity bill and see how many kilowatt hours you used last month. Also see if it lists how much you're paying per kilowatt hour. Exercise #2. Assume that the lights in your kitchen and living room together use 400 watts. How much does it cost if the lights are on 24 hours a day, for a whole month? How much per year? Assume 12¢/kWh. (see answer) 400 watts x 24 hours/day x 30.5 days/month = 292,800 Total Watt-hours 292,800 Wh / 1000 Wh = 293 kWh 293 kWh x 12¢/kWh = $35.16/mo.; $422/yr. Exercise #3. Assume your window AC uses 1440 watts. How much does it cost to run it continuously for a month? How much per year? Assume 12¢/kWh. (see answer) 1440 watts x 24 hours/day x 30.5 days/monh = 1,054,080 Total Watt-hours 1,054,080 Wh / 1000 Wh = 1,054 kWh 1,054 kWh x 12¢/kWh = $126/mo.; $1518/yr. Demand Charges Some utility companies also impose an additional charge based on the maximum amount of electricity you draw at any one time. This is called a demand charge. The following chart from Wisconsin Electric illustrates the concept. The shaded area is how much electricity you used, and you know you get charged for that. But the black bar on top is the demand, how much energy you "demanded" at any given point throughout the day. If your utility company has a demand charge (ask them), then you can save money by spreading out your electrical use throughout the day. Running appliances one after the other rather than at the same time would reduce your demand. And better yet, running them when you're not using much electricity for other purposes (such as at night when the air conditioner is off) will reduce your demand even more.     Possibly cheaper in the evenings Some utilities have cheaper rates in the evenings. (Check with them to find out.) That's because it's harder for them to reach peak demand during the day when everyone's running AC. So they might charge less in the evenings to try to get you to move some of your consumption (like laundry machines) outside of those daytime hours. And even if your utility doesn't have cheaper rates at night, if your utility has a demand charge (see above), it could still pay to shift your laundry to the evenings, because running laundry + air conditioning at the same time results in a higher demand . »» Now let's examine how much electricity your appliances use. »» Saving Electricity 101: Start Here How much it costs / how they charge What's a Watt / Kilowatt? How much energy stuff uses How to measure electrical use Mr. Electricity is your guide to saving energy in your home. General Electricity Myths Using elec. when off? Why is my bill so high? Capacity of an Outlet Electric Meters General Questions Specific Appliances Cooling Heating Lighting Refrigerators Washing Machines Clothes Dryers Water Heaters Computers Televisions Cooking Elevators Environment Carbon footprint calculator Carbon offsets Solar Power Bicycle Power Alternative Energy Climate change Special Topics Standby power Compact Fluorescents/CFL Surge Suppressors (TVSS) Power Factor Commercial Buildings Using devices overseas

©1998-2009 Michael Bluejay, Inc. All Rights Reserved. Unauthorized reprinting is prohibited All advice is given in good faith. We're not responsible for any errors or omissions. Electricity can kill you; if you're not competent to work on your electrical wiring then hire a professional to do it.

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