People have three main uses for energy: transportation, electricity, and heating/ cooling. The three main fossil fuels used to create this energy are coal, oil, and natural gas; but scientists estimate that the earth will run out of fossil fuels in forty to seventy years. Green energy is the alternative and includes renewable natural resources such as wind, water, and sunlight. Solar cells made of silicon harness the energy of the sun and convert it into electricity which can be used to power street lights, homes, and factories. While the sun is a free source of energy, the cost of converting from regular electricity to solar energy can be expensive. Wind turbines generate electricity from winds that blow at seven and a half miles per hour or more and require wind to generate any energy; but do not store energy as easily as other forms of green energy. Tapping into the natural water reservoirs that are heated beneath the earth and using the water or the steam generated produces geothermal energy. Using water in its natural environment either in the ocean or rivers, called hydropower, is already the leading source of renewable energy being used today.

Biomass energy is produced when natural sources are used to create biofuels instead of being thrown away. After explaining the main types of green energy, Rau's final chapter gives readers useful pointers on how to conserve energy in their homes and community and how to help spread the word about conserving energy. Throughout the book, Rau includes quotes from notable people in history, fun facts and data for all chapters, relevant photographs, a glossary and index, and additional resources. This book from the "Green Generation" series is an invaluable resource on a relevant and critical topic.