With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

A gallon of gasoline contains about the same energy as 1 kg of hydrogen. Although fuel cells are expected to be twice as efficient as gasoline vehicles, hydrogen is very diffuse and storing an ample supply on board represents an engineering challenge.

A gallon of gasoline contains about the same energy as 1 kg of hydrogen. Although fuel cells are expected to be twice as efficient as gasoline vehicles, hydrogen is very diffuse and storing an ample supply on board represents an engineering challenge.

Nearly 80% of France's electricity is produced by nuclear power plants.

Nearly 80% of France's electricity is produced by nuclear power plants.

The average U.S. household consumes an average of 10,000 kilowatt-hours each year.

The average U.S. household consumes an average of 10,000 kilowatt-hours each year.

Almost 1% of U.S. electricity was generated by wind in 2008.

Almost 1% of U.S. electricity was generated by wind in 2008.

Less than 2% of the U.S. supply of natural gas is imported from outside North America.

Less than 2% of the U.S. supply of natural gas is imported from outside North America.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

All of the above are emitted from coal-fired power plants and can be harmful to our health and the environment.

All of the above are emitted from coal-fired power plants and can be harmful to our health and the environment.

All of the above are emitted from coal-fired power plants and can be harmful to our health and the environment.

All of the above are emitted from coal-fired power plants and can be harmful to our health and the environment.

In 2008, industry used 31% of the total energy used; next was transportation at 28%, then residential at 22%, and commercial at 19%.

In 2008, industry used 31% of the total energy used; next was transportation at 28%, then residential at 22%, and commercial at 19%.

In 2008, industry used 31% of the total energy used; next was transportation at 28%, then residential at 22%, and commercial at 19%.

The energy we capture for use on Earth comes largely from the sun or from nuclear forces local to our own planet.

The energy we capture for use on Earth comes largely from the sun or from nuclear forces local to our own planet.