Sources of Electricity

Electricity in the United States is generated using coal, natural gas, nuclear reactors, hydroelectric dams, renewable sources, and petroleum, but 90% of power comes from the first three categories. California has very little coal generation and a higher proportion of renewable energy than the national average, but still produces about half of its power from natural gas. Electricity must be generated at the time that it's needed, so different technologies have the ability to fill different needs.

Power Generation

Electricity is produced in generators, which contain coils of wire that spin between banks of magnets. The spinning coil induces an electric current, which is then carried out of the generator and transmitted into the electric grid. The more energy is put into the spinning coil, the more electricity is produced.

Most generators use steam to turn the coil inside the generator. Some, such as hydroelectric plants and wind turbines, use mechanical force (from water and wind, respectively) to spin the coil. Solar panels are unique in that they use silicon wafers to generate electric current instead of a generator.

Coal Power
Coal is the most common fuel for power plants in the United States. Coal power plants burn coal in order to generate the steam that powers the turbines. Coal is the least expensive way to produce electricity and has been used since the industrial revolution; however, it is arguably the most environmentally destructive method, as it releases large amounts of greenhouse gasses into the air. Because coal is so inexpensive, and because electric utilities will purchase inexpensive power whenever they can, most coal power plants run constantly.

Natural Gas
Natural gas is a combustible fuel which, like coal, is used to create steam and run a generator. Natural gas is more expensive and only produces half as much carbon dioxide as does coal. Natural gas generators are easy to start and stop, so they tend to be used during periods of peak demand.

Nuclear Power
Nuclear generators use radioactive metals to produce heat, which in turn creates steam to power a generator. Nuclear power is relatively inexpensive per unit of energy, but it takes an enormous investment in order to build a new plant. Political issues have also made it difficult for new nuclear power plants to be built. A nuclear reactor is difficult to turn on and off, so nuclear plants tend to run constantly.

Hydroelectric plants store energy by damming a river; the body of water that collects behind the dam can be released in a controlled way, and the force of the water spilling through the dam turns a turbine in a generator. Small hydroelectric plants are considered renewable energy resources, although large plants, due to the environmental impact they make on the stream and surrounding land, are not considered renewable. (The cutoff is defined state-by-state.) The hydroelectric plant operator can choose when to release the flow of water, so hydroelectric power is typically generated at peak times.

Renewable Energy
The most common sources of renewable energy are wind, solar, biomass, and geothermal. Wind Power is produced by windmills, whereby the wind spins the turbine directly. Solar energy is generally produced in one of two ways: either through photovoltaics such as rooftop solar panels, which turn sunlight directly into electricity, or through solar thermal plants. Solar thermal methods concentrate the light of the sun in order to boil water and create steam. Biomass generation turns biological material (woodchips, animal manure, etc.) into fuel, which is then burned to generate electricity. Geothermal plants will use the Earth’s internal heat – accessed through hot spots like those found under hot springs – to create steam and power a generator.

In the United States, very little power generation is fueled with petroleum products. Petroleum plants, typically diesel, are most frequently found in remote areas such as islands. Diesel power plants tend to be heavy polluters.

CO2 Reduction from Solar                                                                                                                                          Solar panels are one of the cleanest ways to generate electricity, and every watt generated with solar is one watt that is not generated with dirtier technology.

A variety of emissions come from almost every form of electrical energy production – of course, some emit more and others less. People mostly speak of carbon emissions, which is more specifically carbon dioxide. Carbon is easy to think about, but emissions we call greenhouse gases include much more: SOX, NOX, CO2, Mercury, and so on. Environmental policy does specifically account for these other emissions, but for ease of manageability, we use a “carbon equivalents measurement.”

According to the EPA, one 5-kilowatt DC solar system offsets carbon equivalents equal to:

  • 605 gallons of gasoline
  • 11,354 miles driven
  • 12.4 barrels of oil
  • 222 propane cylinders
  • 1.8 tons of recycled waste
  • 1.2 acres of pine forests