Units of Measurement

Energy is measured in Joules (J)
  • 1 BTU= 1,055 Joules
  • 1 Calorie= 4.187 Joules
Power is measured in Watts (W)
  • 1 Watt= 1 Joule/second
  • 746 Watts= 1 Horsepower
  • 1000 Watts= 1 Kilowatt

Source: Wisconsin K-12 Energy Education Program (KEEP)

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1 kilowatt-hour (kWh) = 1,000 watt-hours

1 megawatt-hour (MWh) = 1,000 kWh or 1,000,000 watt-hours

1 gigawatt-hour (GWh) = 1,000 MWh or 1,000,000,000 watt-hours

Source: Wisconsin K-12 Energy Education Program (KEEP)

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Kinetic energy is motion energy.

Potential energy is energy stored in matter.

Source: Wisconsin K-12 Energy Education Program (KEEP)

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Just as there are many forms of energy, there are different ways to measure these forms. In science, work and energy are commonly measured in joules. One joule is the amount of energy it takes to lift an object that weighs one Newton a one meter distance. A Newton is the metric unit for weight and is comparable to the weight of a stick of butter. (1 Newton = 0.445 lbs.)

Power: 1. The rate at which energy is transferred or converted per unit of time. 2. The rate in which work is done. Units of power include Horsepower, Kilowatt, Megawatt, and Watt.

Horsepower (abbrev. hp): A unit of power. One horsepower equals 550 foot-pounds per second or 746 watts.

Kilowatt (abbrev. kW; pl. Kilowatts): A unit of power equal to 1,000 watts.

Watt (abbrev. W; pl. Watts): A unit of power. One watt equals the production or use of one joule of energy per second.

Source: Wisconsin K-12 Energy Education Program (KEEP)

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Energy can neither be created nor destroyed, it can only be converted from one form to another. This is the first law of thermodynamics.

Source: Wisconsin K-12 Energy Education Program (KEEP)

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A single 20-watt compact fluorescent bulb, compared to a 75-watt incandescent light bulb, saves about 550kWh of electricity over its lifetime. If the electricity is produced from a coal-fired power plant, that savings represents about 500 pounds of coal. If every household in Wisconsin replaced one 75-watt incandescent light bulb with a 20-watt compact fluorescent bulb, enough electricity would be saved that a 500-megawatt coal-fired plant could be retired.

Source: Wisconsin K-12 Energy Education Program (KEEP)

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Physical units reflect measures of distances, areas, volumes, heights, weights, mass, force, and energy. Different types of energy are measured by different physical units:

  • Barrels or gallons for petroleum
  • Cubic feet for natural gas
  • Tons for coal
  • Kilowatthours for electricity

Source: US Energy Information Administration

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How Efficient Is Your Home?

To find out, visit: Home Energy Saver™ (HES)

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Btu Content of Common Energy Units

  • 1 barrel (42 gallons) of crude oil = 5,800,000 Btu
  • 1 gallon of gasoline = 124,238 Btu (based on U.S. consumption, 2008)
  • 1 gallon of diesel fuel = 138,690 Btu
  • 1 gallon of heating oil = 138,690 Btu
  • 1 barrel of residual fuel oil = 6,287,000 Btu
  • 1 cubic foot of natural gas = 1,027 Btu (based on U.S. consumption, 2008)
  • 1 gallon of propane = 91,033 Btu
  • 1 short ton of coal = 19,977,000 Btu (based on U.S. consumption, 2008)
  • 1 kilowatthour of electricity = 3,412 Btu

Source: US Energy Information Administration

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Examples of Converting Different Energy Sources to Btu

Example 1:
You have a natural gas furnace in your home that used 81,300 cubic feet of natural gas for heating last winter. Your neighbor has an oil furnace that used 584 gallons of heating oil last winter. To determine which home used more energy for heating, you can convert the natural gas and heating oil consumption figures into Btu, as follows:

Natural Gas: 81,300 cubic feet (your house) x 1,027 Btu per cubic foot = 83,495,100 Btu
Heating Oil: 584 gallons (neighbor’s house) x 139,000 Btu per gallon = 80,999,960 Btu

Answer: You used more energy to heat your house!

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Example 2:
You work for an electric power company. Your company’s power generators can run on one of two fuels: natural gas or residual fuel oil. Your job is to switch fuels when the cost of the fuel you are currently using becomes more expensive than the other fuel. This will keep costs down for you and your electricity customers. Your company’s generators are currently using residual fuel oil, but fuel oil prices have been going up much faster than natural gas prices. Based on the fuel costs below, you need to decide if it is time to switch to natural gas:

Natural Gas: $7.30 per thousand cubic feet ÷ 1.027 million Btu per thousand cubic feet = $7.11 per million Btu
Residual fuel oil: $57.75 per barrel ÷ 6.287 million Btu per barrel = $9.19 per million Btu

Answer: When you convert the fuels into the same units, you see that residual fuel oil now costs more than natural gas. You decide to switch to natural gas to save money.

Source: US Energy Information Administration

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