More than a quarter of the world's coal reserves are located in the United States.

More than a quarter of the world's coal reserves are located in the United States.

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 2005, a million Btu of energy from coal cost approximately $2, versus $5 for natural gas and $10 for oil. However, prices can fluctuate due to changes in the economy and new government policies.

In 2005, a million Btu of energy from coal cost approximately $2, versus $5 for natural gas and $10 for oil. However, prices can fluctuate due to changes in the economy and new government policies.

90% of the coal mined in the United States was used to generate electricity in 2006.

90% of the coal mined in the United States was used to generate electricity in 2006.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

In 2008, the U.S. imported about 66% of its oil supply. This percentage is expected to grow even higher over the next two decades.

In 2008, the U.S. imported about 66% of its oil supply. This percentage is expected to grow even higher over the next two decades.

The ampere, or amp, is the most commonly used measurement for electric current.

The ampere, or amp, is the most commonly used measurement for electric current.

The ampere, or amp, is the most commonly used measurement for electric current.

In 2008, wind accounted for 0.5% of America's energy portfolio.

In 2008, wind accounted for 0.5% of America's energy portfolio.

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.