Tidal energy is gravitational in origin. Solar energy comes from nuclear reactions in the sun.

Tidal energy is gravitational in origin. Geothermal energy comes from radioactive decay inside the earth.

Tidal energy is gravitational in origin. Solar energy comes from nuclear reactions in the sun, and geothermal energy comes from radioactive decay inside the earth.

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.

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.

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.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

Biofuels contain carbon and although they may burn “cleaner” than oil-derived fuels, they do not avoid generating carbon dioxide emissions.

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.

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.

In 2009, there were no commercial coal-fired plants utilizing carbon capture and sequestration.

In 2009, there were no commercial coal-fired plants utilizing carbon capture and sequestration.