Out of all the renewable energy sources, biomass contributed the most to U.S. energy consumption in 2008.

Out of all the renewable energy sources, biomass contributed the most to U.S. energy consumption in 2008.

Out of all the renewable energy sources, biomass contributed the most to U.S. energy consumption in 2008.

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.

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

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

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.

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.

Renewable energy accounted for 7% of the total U.S. energy supply in 2008, less than any other type of energy source.

Renewable energy accounted for 7% of the total U.S. energy supply in 2008, less than any other type of 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.

All of the reasons mentioned are considered obstacles to producing cars that run on hydrogen fuel cells.

All of the reasons mentioned are considered obstacles to producing cars that run on hydrogen fuel cells.

All of the reasons mentioned are considered obstacles to producing cars that run on hydrogen fuel cells.

U.S. domestic production of crude oil peaked around 1970 at about 9.5 million barrels per day (MBD) and declined to about 5.1 MBD by 2006.