WHERE IS GEOTHERMAL ENERGY FOUND?
Most geothermal reservoirs are deep underground with no visible clues showing above the ground. Geothermal energy can sometimes find its way to the surface in the form of: volcanoes and fumaroles (holes where volcanic gases are released), hot springs and geysers.
The most active geothermal resources are usually found along major plate boundaries where earthquakes and volcanoes are concentrated. Most of the geothermal activity in the world occurs in an area called the Ring of Fire. This area rims the Pacific Ocean.
When magma comes close to the surface it heats ground water found trapped in porous rock or water running along fractured rock surfaces and faults. Such hydrothermal resources have two common ingredients: water(hydro) and heat(thermal). Naturally occurring large areas of hydrothermal resources are called geothermal reservoirs. Geologists use different methods to look for geothermal reservoirs. Drilling a well and testing the temperature deep underground is the only way to be sure a geothermal reservoir really exists.
Most of the geothermal reservoirs in the United States are located in the western states, Alaska, and Hawaii. California is the state that generates the most electricity from geothermal energy. The geysers dry steam reservoir in northern California is the largest known dry steam field in the world. The field has been producing electricity since 1960.
USES OF GEOTHERMAL ENERGY
Some applications of geothermal energy use the earth's temperatures near the surface, while others require drilling miles into the earth. The three main uses of geothermal energy are:
- Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface.
- Electricity Generation in a power plant requires water or steam at very high temperature (300 to 700 degrees Farenheit). Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface.
- Geothermal Heat Pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.
DIRECT USE OF GEOTHERMAL ENERGY
The direct use of hot water as an energy source has been happening since ancient times. The Romans, Chinese, and Native Americans used hot mineral springs for bathing, cooking and heating. Today, many hot springs are still used for bathing and many believe the hot, mineral rich waters have natural healing powers.
After bathing, the most common direct use of geothermal energy is for heating buildings through district heating systems. Hot water near the earth's surface can be piped directly into buildings and industries for heat. Other examples of direct uses include growing crops and drying lumber, fruits and vegetables.
GEOTHERMAL HEAT PUMPS
While temperatures above ground change a lot from day to day and season to season, temperatures in the upper ten feet of the Earth's surface hold nearly constant between 50 and 60 degrees Farenheit. For most areas, this means that soil temperatures are usually warmer than the air in winter and cooler than the air in summer. Geothermal heat pumps use the Earth's constant temperaures to heat and cool buildings. They transfer heat from the ground (or water) into buildings in winter and reverse the process in the summer.
According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps ar the most energy efficient, environmentally clean and cost effective systems for temperature control. Although, most homes stilll use traditional furnaces and air conditioners, geothermal heat pumps are becoming more popular. In recent years, the U.S. Department of Energy along with the EPA have partnered with industry to promote the use of geothermal heat pumps.
GEOTHERMAL ENERGY AND THE ENVIRONMENT
The environmental impact of geothermal energy depends on how it is being used.
- Direct use and heating applications have almost no negative impact on the environment.
- Geothermal power plants do not burn fuel to generate electrticity, so their emission levels are very low. They release less than 1 percent of the carbon dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. Geothermal plants emity 97% less acid rain - causing sulfur compounds that are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth.
- Geothermal features in national parks, such as geysers and fumaroles in Yellowstone National Park, are protected by law, to prevent the land from being disturbed.