Nuclear power accounted for 9% of the U.S. energy supply in 2008.

Nuclear power accounted for 9% of the U.S. energy supply in 2008.

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.

Roughly 21% of the electricity used in residential and commercial buildings goes to lighting.

Roughly 21% of the electricity used in residential and commercial buildings goes to lighting.

Roughly 21% of the electricity used in residential and commercial buildings goes to lighting.

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

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

Gasoline, diesel fuel, and natural gas all release CO2 when burned.

Gasoline, diesel fuel, and natural gas all release CO2 when burned.

Gasoline, diesel fuel, and natural gas all release CO2 when burned.

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.

Lighting accounts for 18% of the electricity used in the United States. A 12% decrease in overall electricity use in buildings could be realized if incandescent bulbs were replaced with CFL or LED bulbs.

In 2008, 37% of the United States' total energy consumption came from oil, more than any other energy source.

In 2008, 37% of the United States' total energy consumption came from oil, more than any other energy source.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.