During the twentieth century, energy has become much more easily available. Most energy comes from burning fossil fuels (oil, gas, and coal). These resources are only found in certain geologic formations. Fossil fuels were formed millions of years ago from vegetative matter and animal remains (fossils) that collected and decayed in swamp-like conditions. Over the eons of time, this material was compacted, overlaid with sedimentary rock, and put under great pressure from the geologic processes of the Earth. This is where the term fossil fuels came from—they are the fuels from the fossils of dead plants and animals.
Subsequently, only specific areas of the world have deposits of petroleum (oil). These deposits were formed only under specific geologic conditions in specific locations on Earth. According to the U.S. Department of Energy, the world’s top five crude-oil-producing countries are:
• Saudi Arabia
• Russia
• United States
• Iran
• China
Wind energy is one way of producing clean, renewable electricity. Wind power plants, or wind farms as they are sometimes called, are clusters of wind machines used to produce electricity. Wind power plants need to be built in areas where there is a consistent wind source. Because wind speed increases with altitude and over open areas with no windbreaks, good sites for wind plants are the tops of smooth, rounded hills; open plains; shorelines; and mountain gaps that funnel wind. In some geographic areas, the wind blows more on a seasonal basis, which is another factor to consider when deciding on the location to construct a wind tower.
Hydropower is also limited in terms of where it can be produced. Because the source of hydropower is water, hydroelectric power plants must be located on a water source. Therefore, it wasn’t until the technology to transmit electricity over long distances was developed that hydropower became widely used.
Geothermal energy is energy from the Earth’s core. In a few places, heat from the Earth can be collected. Usually, engineers try to collect this heat from these rare places where the Earth’s crust has trapped steam and hot water by drilling into the crust and allowing the heat to escape, either as steam or as very hot water. Pipes carry the hot water to a plant where some of the steam is allowed to “flash,” or separate, from the water. That steam then turns a turbine generator to make electricity. Energy generation from geothermal sources is “site specific,” meaning it is only possible in a few places under unique geologic conditions. There are several geothermal areas in the United States. Some European countries also use geothermal energy. The capital of Iceland—Reykjavik—is heated mostly by geothermal energy.
