Geothermal means heat from within the earth. It is a Greek word, with ‘geo’ meaning earth and ‘thermal’ meaning heat.
Geothermal energy is as old as the earth and therefore is one of the oldest forms of energy on the planet. It is also a renewable source of energy because the heat within the Earth never dies out. So geothermal energy can consistently be used to produce power.
The core within the earth, the innermost part of it is hotter than the surface of the sun. Radioactive particles follow a slow process of decay within the core and heat is released as a result of it.
Geothermal energy is used for both heating and cooling purposes. It can be used for heating water and oils, while at the same time stable temperatures within the earth can also help heat and cool buildings and houses.
Geothermal energy can be harnessed by digging deep wells because rocks and water within the earth, especially closer to the core are already heated by its heat. The water that is found is then pumped up to the surface.
Natural geothermal sites commonly where volcanoes, geysers and hot-springs are found. Volcanoes form when melted rock (magma) at the core of the earth melts from its heat and rises to the top.
Hot springs are groundwater outlets that release hot water more than 300 oF, that has been naturally heated by the Earth’s core, and therefore stays at a consistent temperature.
Geysers are explosions of hot water and steam that suddenly explode into the air. For a geyser to function there must be extreme amounts of heat, lots of water, a unique plumping system and finally they have to be in really remote places.
During the 16th and 17th centuries man realized the earth’s heat increased with its depth. The Romans used heat to treat illnesses and heating, while Icelanders and New Zealanders used it for cooking as did the North American tribes.
In the 1860s USA first started using hot springs for heating, and in 1904 Piero Conti an Italian scientist invented the dry steam geothermal electric power plant.
The 1980s saw the first commercial binary plant in the USA while the use of geothermal energy reached 1000 megawatts. By 1995 worldwide production had rapidly increased, while in America many states began using geothermal electricity.
Heating systems using geothermal technology act as heating systems during winter and as cooling systems during summer. The cooling system does not waste much energy because it absorbs the heat of the air within the building and transfers it back to the earth.
Building a geothermal heating system requires digging and placing pipes about four to five feet below the earth’s surface. At this point, the earth’s interior is said to have a relatively constant temperature according to geologists.
Geothermal energy can only be extracted from areas, which have large amounts of naturally occurring geothermal energy. These are called geothermal reservoirs.
The most famous geothermal energy site is the area around the Pacific Ocean called the Ring of Fire, named so because of the many volcanoes and earthquake regions surrounding it.
The unique quality of geothermal reservoirs is that on the surface there is no sign of their existence. It is only when geothermal energy rises to the surface of the earth like in the case of volcanoes, hot springs or geysers that there is an obvious indication of the geothermal energy below.
Geothermal energy plants use hydrothermal technology to make electricity through three types of power plants; dry steam, flash and binary. However, their production of electricity depends on certain environmental factors like the temperature, quality, and depth of the water and steam in the particular area.
Dry steam geothermal energy power plants use dry steam (gas) at about 455 oF that power turbines. It is the oldest type of geothermal energy generation, and one of the more economical ones. Important thing is that it can only be productive in its pure form, which means that it cannot be mixed with water.
They use hot water above 360 oF found in geothermal reservoirs, which are preserved in the liquid state because of the high pressure within the ground.
During the pumping of this water from underground to the surface there is a sudden drop in pressure which converts or ‘flash’ the water into steam, which then powers generators/turbines that create electricity.
Binary cycle power plants have temperatures ranging between 225 and 360 oF. The heat passes through a heat exchanger and is then sent through a separate pipe which has fluids (Iso-butane/Iso-pentane) boiling at much lower levels. It is these fluids that are vaporized to power the turbines/generators.
Binary cycle power plants are favoured over the flash and dry steam power plants. They are efficient, economical, do not release gasses, and can be operated on lower temperature reservoirs. Because of these factors, most geothermal power plants found today are binary cycle plants.
Geothermal energy use can either be direct heating systems, electricity plants or geothermal heat pumps. Direct heating use hot waters from nearby hot water springs.
Electricity generating power plants do so through water or steam, usually at temperatures as high as 300 oF to 700 oF.
Geothermal heat pumps on the other hand use ground or water temperatures which are comparatively stable and closer to the Earth’s surface to control building temperature above ground level for heating and cooling purposes.
Direct uses of geothermal energy are mostly for supplying power to buildings through district heating systems. Hot water is pumped directly through pipes into buildings and industrial complexes for heating purposes.
Hot-springs are also used as public bathing sites today, similar to those in the ancient Roman, Chinese and Native American civilizations.
Geothermal energy is also used for industrial purposes of gold mining, pasteurizing milk, and food dehydration. Food dehydration is the most common of them.
The advantages of geothermal energy, besides it being a renewable and clean energy source, its production does not cause any environmental pollution.
The overall cost of building a geothermal power plant is comparatively less than building a nuclear, coal, gas or oil plant because it uses less land area.
A major advantage is that no additional fuels are used to enhance the production of geothermal energy, and there are no emissions. This means that operating such a power plant is economical.
Some of the disadvantages of geothermal energy are finding suitable building locations, which are safe as the heat being generated from within the deep interiors of the earth, are most often in sites similar to those found in the Ring of Fire.
Another concern is that sites that have consistently been producing heat can suddenly stop producing for about 10 years, although they bounce back.
Sometimes through the holes drilled in the earth, harmful gasses can leak out and these can be somewhat difficult to manage.
The future of geothermal energy rests firmly in its advantages, which look increasingly attractive with the looming of worldwide oil shortage. America has many on-going geothermal projects that have a bright future.
Since it is renewable, and can be harnessed at relatively low costs, it has the potential of providing power for the entire planet. However, the cost of construction and the necessary technology is currently not within affordable range considering the world’s economy.