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

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.

Refrigerators are not likely to be used more or less hours in the day, but people are more likely to have more of them if they cost less to operate.

Refrigerators are not likely to be used more or less hours in the day, but people are more likely to have more of them if they cost less to operate.

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

On average, even after passing through hundreds of kilometers of air on a clear day, solar radiation reaches Earth with enough energy in a single square meter to run a mid-size desktop computer-if all the sunlight could be captured and converted to electricity.

On average, even after passing through hundreds of kilometers of air on a clear day, solar radiation reaches Earth with enough energy in a single square meter to run a mid-size desktop computer-if all the sunlight could be captured and converted to electricity.

Extraction of "tight" oil—light crude oil contained in geological formations of shale or sandstone—accounted for only 12% of total U.S. oil production in 2008. By 2012, it made up 35%, and is predicted to rise to 50% in the near term.

All of the above are emitted by vehicles running on gasoline and diesel fuel.

All of the above are emitted by vehicles running on gasoline and diesel fuel.

All of the above are emitted by vehicles running on gasoline and diesel fuel.

All of the above are emitted by vehicles running on gasoline and diesel fuel.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

In the United States, the amount of electricity generated from wind doubled between 2009 and 2014, and now makes up 18% of all renewable energy consumed and almost 2% of total U.S. energy use.