RENEWABLE ENERGY SOURCES: AN OVERVIEW
INTRODUCTION TO GEOTHERMAL ENERGY:
--Geothermal energy is heat energy that comes from the crust of the earth. In some parts of the world, particularly in locations near the boundaries of tectonic plates, the molten rock of the earth’s core creates high subterranean temperatures close to the surface. In areas where there are no heated reservoirs, the natural insulating properties of the earth can also be used for heating.
--Geothermal energy is used to make electricity in power plants, to heat homes and office buildings with heat pumps, and to heat directly with hot water reserves beneath the ground
Geothermal Energy: Power Plants
Geothermal power plants are prevalent in the western United States where there are reservoirs of hot geothermal steam or fluid close enough to the earth’s surface that they are economical to use. There are three types of power plant systems: dry steam, flash, and binary cycle. The type that is used at a given site depends on the temperature of the reservoir.
The dry steam system uses the hottest reservoirs where steam comes directly from the ground and drives turbines with in turn generate electricity.
The flash system, utilized at sites with lower temperatures, usespressurized geothermal fluids which are ‘flashed,’ or un-pressurized, into the steam that drives the turbines.
The binary cycle system is used at the coolest geothermal reservoirs that produce electricity. Hot fluid is pumped up to the plant and is used to heat a secondary fluid with a lower boiling point to create steam.
Two 36-ton geothermal heat pumps used at the College of Southern Idaho.
Heat pumps are more widely used and rely on the temperature differences between the air and the ground. A heat pump has two basic components: a system of pipes buried in the ground that exchange energy and a heat pump that concentrates the energy and exchanges it with the area that is being conditioned. In the summer, the heat pump takes heat from the building and transfers it to the system of pipes where it is dissipated. In the winter, the heat pump takes heat energy from the system of pipes, concentrates this heat energy, and releases it into the building.
Direct use of geothermal energy is the use of geothermal reservoirs of low-to-moderate temperature for direct heating applications in municipal districts, agriculture and industry. The basic direct use system involves running heated geothermal fluids through pipes to areas that need heating. Cities can heat buildings and keep roads clear of snow. In agriculture, the ponds of fish farms and plants of greenhouses can be kept heated. Industrial applications include drying fruit and running naturally heated spas.
POSITIVES OF GEOTHERMAL ENERGY:
-its use helps decrease the United States’ dependence on foreign oil. This in itself would be an economical advantage for the United States
-emissions of geothermal power plants are also very low when compared to those of coal an oil power plants
-Heat pumps themselves have essentially zero emissions and the use of heat pumps and direct use applications also help home owners and other users cut back on the use of electricity
-one major advantage to geothermal energy is that it has a lot of room for development
- As technology progresses, the practically unlimited energy in the earth’s molten core could be used to meet energy needs.
NEGATIVES OF GEOTHERMAL ENERGY:
-The largest disadvantages with geothermal energy come from the generation of electricity in power plants
-Power plants require very hot geothermal reserves to operate, their locations are limited to certain sites in the west where reserves are close to the ground
-Electricity produced by geothermal energy also costs twice as much as that produced by coal
-According to the Geothermal Technologies website, www.nrel.gov/geothermal, geothermal electricity costs between 4 and 8 cents per kilowatt hour
-The Energy Information Administration website, http://www.eia.doe.gov/, states that electricity produced from the burning of coal costs between 2 and 3 cents per kilowatt hour.
Innovations in Geothermal Energy
There is a considerable amount of research being done today to decrease the cost of geothermal electricity. Researchers are working to make it cheaper to tap heated geothermal reservoirs and to operate power plants. A recent innovation has been the development an acoustic telemetry device for geothermal well drilling by the U. S. Department of Energy’s Sandia National Laboratories. The device improves drilling and lowers geothermal well costs.