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.

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.

Energy intensity is a measure of a nation's energy efficiency represented through energy use per unit of GDP (Gross Domestic Product).

Energy intensity is a measure of a nation's energy efficiency represented through energy use per unit of GDP (Gross Domestic Product).

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.

As of 2014, total world consumption was approximately 92 million barrels per day, about 19 million or 21% of which were used by the United States.

As of 2014, total world consumption was approximately 92 million barrels per day, about 19 million or 21% of which were used by the United States.

As of 2014, total world consumption was approximately 92 million barrels per day, about 19 million or 21% of which were used by the United States.

Fuel cells are an efficient way to convert hydrogen to electricity, but the energy is stored in the hydrogen.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

Fossil fuels represent the largest source of stored solar energy, resulting from the transformation of biomass over millions of years into oil, natural gas and coal. 

Fossil fuels represent the largest source of stored solar energy, resulting from the transformation of biomass over millions of years into oil, natural gas and coal. 

The national average is around 1.5 million gallons per well , according to the EPA.

The national average is around 1.5 million gallons per well , according to the EPA.

The national average is around 1.5 million gallons per well , according to the EPA.

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.