Power and energy are not the same thing. Power is the rate at which energy is used or work is done. For example, we burn fossil fuels, such as natural gas to generate steam (an example kinetic energy source shown below) that is responsible for turning a turbine and as a result, powering an electricity generator.1U.S. energy Information administration (EIA) independent statistics and analysis. How electricity is generated. U.S. Energy Information Administration (EIA). (n.d.). https://www.eia.gov/tools/faqs/faq.php?id=427&t=3/ The electricity from the generator is then delivered to consumer’s homes through high-voltage transmission lines.
Units of Power
There are many different units of power. In this list, notice how many of the units for describing power involve a unit of time in the denominator, which implies a rate of energy delivery. In some of these units, the time element is embedded in the unit itself (e.g., horsepower).
- Joule per second
- BTU per second
- Ft lb(f) per second
- W = kg m2/s3
- Horsepower (hp)
- kW = 1000 W
- lb(m) ft2/s3
We use various primary energy sources to generate electricity that is then transmitted to our homes, offices, and other destinations. According to the United States Energy Information Administration, “the three major categories of energy for electricity generation are fossil fuels (coal, natural gas, and petroleum), nuclear energy, and renewable energy sources.”2U.S. Energy Information Administration (EIA) independent statistics and analysis. (n.d.) Electricity in the U.S. U.S. Energy Information Administration (EIA). https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php#:~:text=The%20three%20major%20categories%20of,geothermal%2C%20and%20solar%20thermal%20energy. Most power plants use steam turbines to generate electricity. However, electricity can also be generated by means of hydroelectric-powered turbines, wind turbines, and solar photovoltaic panels.3U.S. Energy Information Administration (EIA) independent statistics and analysis. (n.d.) Electricity in the U.S. U.S. Energy Information Administration (EIA). https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php#:~:text=The%20three%20major%20categories%20of,geothermal%2C%20and%20solar%20thermal%20energy. While renewable energy sources for electricity generation have increased, fossil fuels still remain the largest source, specifically natural gas and coal (40% and 19% of electricity generation, respectively). Nuclear-power plants also make a significant contribution by supplying 20% of the country’s annual electricity generation.
Energy Conversion Always Results In a Loss of Power
When energy undergoes conversions, such as to produce electricity, some of the energy input is lost in the process. According to a study published by the University of Calgary, “some examples of these losses include heat energy, possibly as a result of air drag or friction. Heat energy is the most easily dissipated form of energy.”4The University of Calgary. (2020, April 28). Energy loss. Energy loss – Energy Education. https://energyeducation.ca/encyclopedia/Energy_loss. Losses of energy also occur when converting to light energy and sound energy.
The electricity we use to turn the lights on and heat our homes has already gone through many conversions from the primary energy source, such as petroleum extracted from beneath the Earth’s surface, to the point it reaches our home as a secondary energy source. Loss of energy along the way occurs when the fuel is initially burned to generate steam (converted to kinetic energy) that turns a turbine that produces mechanical energy to power a generator, finally resulting in electricity generation.5The University of Calgary. (2020, April 28). Energy loss. Energy loss – Energy Education. https://energyeducation.ca/encyclopedia/Energy_loss. This loss may be around 65%. Energy is also lost (~2%) throughout the process of transmission. If you’ve ever seen sagging metal transmission lines, that is a result of energy lost in the form of heat. Distribution of electricity to our neighborhoods and homes involves reducing the voltage. This safety measure of lowering the voltage also creates more energy loss (~4%).6Inside Energy. (2015, November 6). Lost In Transmission: How Much Electricity Disappears Between A Power Plant And Your Plug? http://insideenergy.org/2015/11/06/lost-in-transmission-how-much-electricity-disappears-between-a-power-plant-and-your-plug/
Energy loss is not just evident with regard to electricity generation. For example, we lose a significant amount of the energy that is stored in the gasoline or diesel we use to fuel our automobiles. When we fuel up our cars at the gas pump, that gasoline is first converted into heat energy that then produces kinetic energy responsible for turning the wheels. According to one study, “some of this kinetic energy is lost to the sound of the engine, light from combustion, and to heat energy from the friction between the road and the tires.”7The University of Calgary. (2020, April 28). Energy loss. Energy loss – Energy Education. https://energyeducation.ca/encyclopedia/Energy_loss. These losses are rather exorbitant, as it is currently projected that up to 80% of the stored energy in the gas tank is lost by the various processes we mentioned here.
While we can work to become more energy efficient, such as reducing the losses that occur at the power plant or when driving our vehicles, we will never reach the point where we do not encounter any type of energy loss. This is due to the nature of energy loss as a result of the various conversions that must take place to generate usable electricity or kinetic energy.
History of Electricity Generation in the United States
Throughout the United States’ history, different primary energy sources have been used to create the important secondary form of energy that we use every day – electricity. Let’s take a closer look at how energy sources for electricity generation have changed throughout the last seventy years. Use the interactive graph below to answer the following questions.