Overview6 copies each of all three reading levels, 18 books total. Energy use is one of the key issues of our time. People have traditionally relied on fossil fuels, including oil, coal, and natural gas. There are growing concerns, though, about the pollution caused by these energy resources. In addition, these sources of energy are nonrenewable. That is, they can be used up. Countries around the world are exploring ways to use renewable sources of energy, such as solar power. Energy Resources examines the role of traditional sources of energy and the development of alternative energy resources.