Geothermal Energy - Its Types and How It Works
Geothermal energy is energy created by the heat of the Earth. Under the Earth’s crust lies a layer of thick, hot rock with occasional pockets of water. This water sometimes seeps up to the surface in the form of hot springs. Even where the water does not travel naturally to the Earth’s surface, it is sometimes possible to reach it by drilling. This hot water can be used as a virtually free source of energy, either directly as hot water, steam, or heat or as a means of generating power. Geothermal energy is nonpolluting, inexpensive, and in most cases the sources is renewable. This make geothermal renewable energy a promising source of power for the future. The word geothermal comes from two Latin words, geo, meaning ‘‘earth,’’ and thermal, meaning ‘‘heat.’’ So the word geothermal means ‘‘heat from the earth.’’ In most cases, the geothermal resource that people want is water that has been trapped within the Earth, where it becomes very hot.
Types of geothermal energy
There are two main types of geothermal energy. The energy can be used directly, as heat or hot water, or it can be a means of generating electricity. Naturally hot water has been recognized as a resource for thousands of years. People have used hot springs for bathing, for medical treatments, and as heating for their buildings. The hot water can also be used in agriculture, aquaculture, industry, and other applications. Geothermal power can also generate electricity. Geothermal electricity is becoming increasingly important. In 1999 over 8,000 megawatts of electricity were produced by about 250 geothermal power plants around the world, located in twenty-two different countries. Most of these geothermal plants are located in developing nations. However, that same year the United States produced nearly 3,000 megawatts of geothermal electricity, more than twice the amount of power generated by wind and solar power. Ten percent of the electricity in Nevada and 6 percent of the electricity in Utah came from geothermal power plants.
How geothermal energy works
Geothermal power uses the geothermal heat of the Earth to produce electricity and heat. This form of power works because the inside of the Earth is much hotter than the surface.
The structure of the Earth The Earth consists of several layers of matter. The outer layer, called the crust, is the surface where people live and plants grow. It is composed of aluminum, silicon, oxygen, iron, and other minerals. Below the crust is a layer called the mantle, a thick layer of rock and oxides that comprises about 82 percent of the Earth’s total volume. It is made up mostly of peridotite, a kind of rock containing iron, magnesium, oxygen, and silicon. The mantle is mostly solid but can also flow like a liquid when it is under pressure. The top layer of the mantle consists of hot liquid rock called magma. The crust floats on top of this liquid rock. At the center of the Earth is the core, a chunk of extremely hot iron and nickel. The core itself consists of two layers, the outer core, which is liquid, and the inner core, which is solid because of the tremendous pressure it experiences. The center of the core is about 4,000 miles (6,400 kilometers) from the surface of the Earth.
Water heated underground The Earth’s temperature increases about 41.7 F (5.4 C) for every 328 feet (about 100 meters) traveling from the surface to the core. About 10,000 feet (3,048 meters) below the surface, temperatures are hot enough to boil water. The inner core may be over 9,000 F (4,982 C). This heat constantly travels upward toward the surface, heating the mantle, which carries heat toward the crust. Similar to the curved pieces of peeled skin from an orange, Earth’s outermost layers are cut and fractured into pieces or sections called plates. Like the inner and outer sides of an orange peel, these plates have distinct sections, an inner side and an outer crust. Each plate (also called a lithospheric plate) moves over a hotter, denser—but in many ways more fluid-like (molten)—region of Earth’s interior termed the asthenosphere (a portion of Earth’s mantle). The visible continents such as North and South America are actually an outer crust of the lithospheric plates upon which they ride, shifting slowly over time as a result of forces, including differences in temperature, which help move or drive the plates. The theory that describes this motion is perhaps the most important in all of geology (the study of Earth’s structure) and is called plate tectonics (the theory of plate structure and movements). Although plates move very slowly (in many cases, just inches per year) they are, of course, very heavy and so their rubbing, sliding, slipping, collisions, and bending causes earthquakes.
Where the edges of plates overlap, volcanoes may form. Depending on the materials that compose them, one plate may drive under another (subduction) or both plates may drive sky- ward to form mountain chains. Hot magma from Earth’s molten inner layers (or from pieces of plate being destroyed during subduction) can carve tunnels, chambers, and channels in the plate and crust and so allow hot magma to reach the surface of the plate (even if it is under the ocean). When magma reaches the surface and flows from a volcano it becomes known as lava. Volcanoes can also form over areas in plates away from the edges (especially thinner areas of plates under the oceans) called ‘‘hot spots’’ where molten material from Earth’s mantle pushes upward.
The rock underground is full of cracks and small pockets, and these can fill with water. Water that gets trapped in underground caves will get very hot, even hotter than boiling temperature, but it cannot boil because there is no place for steam to escape into the air. This water sometimes finds its way to the surface in the form of hot springs. Most of the hot water stays underground in pockets called geothermal reservoirs.
Making use of geothermal energy
There are several ways to make use of geothermal energy. The most basic is simply to use the water as hot water when it comes out of the ground. The water can be channeled to different places as heat, for heating homes, or for cooking. This will be easier if the process are using geothermal heat pump.
In most of geothermal plants, engineers can drill down into the ground to reach geothermal reservoirs and then use the hot water, steam, or geothermal heating system to power generators to make electricity. Scientists have developed techniques to find geothermal water. When they find reservoirs, they drill production wells down into them. The hot water or steam travels up the well to the surface, where it can be collected and harnessed for various uses.
The Ring of Fire and other hot spots The Pacific Ocean is one of the most geologically active areas in the world. The land that borders the Pacific is sometimes known as the Ring of Fire because of the volcanic activity that occurs there. New Zealand, Japan, the Philippines, Hawaii, Alaska, California, and other places in the area experience a great deal of tectonic shifting, as pieces of the Earth’s crust move around and crash into one another. All of these areas also have active volcanoes.
There are active volcanoes in many other places. Iceland has so much volcanic activity that it derives much of its power from geothermal sources. Kenya, Turkey, Italy, and Zambia all have enough geothermal energy to make profitable use of it. Because of the nature of current geothermal technology, these geologically active areas are also the main sites of geothermal power. Current and future technology Geothermal technology are used in the generation of electricity and in direct uses of the hot water. There is room for development of new technologies in both categories.