By Mathew Prang

Geothermal and Ocean Thermal Energy Not known by many people as a source of energy is Geo and Ocean thermal energy. If you don’t know what these energies are I will tell you. Geothermal comes from the Greek language, Geo meaning earth and thermal meaning heat, so Geothermal is heat energy from the earth. Ocean thermal is even more unknown than Geothermal because it’s still in its testing stages. Ocean thermal is heat energy from waves and tides in the ocean. In an oil induced world were oil is thinning out people look toward other energy sources but it you look at energy comparison you can see that Geo and Ocean thermal energy have no green house gases and almost no depletion rate. In the next few pages you will see why Geo and ocean thermal energy is the way to go. The basics behind geothermal energy is that like the sun the earth gives off heat. The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises, moving slowly up toward the earth's crust, carrying the heat from below. (http://www.geo-energy.org/aboutGE/basics.asp) Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth) sometimes as hot as 700 degrees F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground,

By Mathew Prang trapped in cracks and porous rock. This collection of hot water is called geothermal reservoirs. (geothermal.marin.org) In past many cultures found ways to use geothermal energy. The Romans used hot spring water to heat buildings and to cure eye and skin diseases. Half around the world American Indians used the spring water to cook food and making medicine. Also France is the 1960s used geothermal energy to heat over 200,000 homes. These are just a few ways people have found uses for geothermal energy. In today’s world we drill wells into geothermal to bring hot water to the surface. These wells are called production wells. Production wells can be used to provide electricity to geothermal power or for energy saving non-electrical reasons. There are three types of geothermal plants. These plants depend on the reservoir’s temperature and pressure. The first power plant is called a dry steam power plant. These power plants are made when the geothermal reservoir produces steam but very little water. . The largest dry steam field in the world is The Geysers, about 90 miles north of San Francisco. Production of electricity started at The Geysers in 1960, at what has become the most successful alternative energy project in history. Hot water reservoirs produce large amount of water and to harness this water energy flash power plants are built water that is brought to the surface in the production well has a temperature ranging from 300-700 degrees F. Upon being released from the pressure of the deep reservoir, some of the water flashes into steam in a 'separator.' The steam then powers the turbines. The third power plant is called a binary power plant. A binary power plant is built when reservoirs range from 250-360 degrees F. This water is not hot enough to flash into steam but can still be used to create energy in the binary power plant. In a binary system the

By Mathew Prang geothermal water is passed through a heat exchanger, where its heat is transferred into a second (binary) liquid, such as isopentane, that boils at a lower temperature than water. When heated, the binary liquid flashes to vapor, which, like steam, expands across and spins the turbine blades. The vapor recondenses to a liquid and is reused repeatedly. In this closed loop cycle, there are no emissions to the air. (geothermal.marin.org) Unlike a lot of modern energy sources like oil, nuclear power, a fusion geothermal energy has very little negative side effects. One major positive of using geothermal energy is its very clean. The turbines in the power plants are spun by the steam and hot water from the earth not hazardous fuel. Also geothermal energy is easy on the land and does not arm the economy and its very reliable geothermal plants can run 24 hours a day 365 days a year. The biggest advantage to using geothermal energy is that it is cheap for the users and consumers. The United States alone produces 2700 megawatts of electricity from geothermal energy, electricity comparable to burning sixty million barrels of oil each year. (http://www.darvill.clara.net/altenerg/geothermal.htm)

Another unknown source of energy is ocean thermal energy. Ocean thermal energy conversion (OTEC) uses the heat energy stored in the Earth's oceans to generate electricity. Still under research many scientist believe that ocean thermal energy could be the most cost competitive energy source, ocean thermal energy could produce billions of watts of electrical power. In the past Cuba and France have toyed with this technology but the generators were destroyed before they could become major. The United States started researching OTEC in 1974. The US established a Natural Energy Laboratory also in 1974. The laboratory has become the leading test facility for OTEC research in the world. OTEC is said to work best when the oceans warm upper layer and the lower cold layer meet. It is said that the best spot is in the tropical ocean area between the Tropic of Capricorn and Tropic of Cancer.

By Mathew Prang The technologies involved with OTEC are closed-cycles, open-cycles, and hybrid. A closed-cycle use fluid with a low-boiling point, such as ammonia, to rotate a turbine to generate electricity. Warm surface seawater is pumped through a heat exchanger where the low-boiling-point fluid is vaporized. The expanding vapor turns the turbo-generator. Cold deep-seawater, pumped through a second heat exchanger, condenses the vapor back into a liquid, which is then recycled through the system. The open-cycle uses the tropical oceans' warm surface water to make electricity. When warm seawater is placed in a lowpressure container, it boils. The expanding steam drives a low-pressure turbine attached to an electrical generator. The steam, which has left its salt behind in the low-pressure container, is almost pure fresh water. It is condensed back into a liquid by exposure to cold temperatures from deep-ocean water. Lastly, the hybrid combines the features of both the closed-cycle and open-cycle systems. In a hybrid system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, similar to the open-cycle evaporation process. The steam vaporizes a low-boiling-point fluid (in a closed-cycle loop) that drives a turbine to produce electricity. (www.eere.energy.gov) Another technology in ocean thermal energy is ocean tidal power. Some of the oldest ocean energy technologies use tidal power. All coastal areas consistently experience two high and two low tides over a period of slightly greater than 24 hours. For those tidal differences to be harnessed into electricity, the difference between high and low tides must be at least five meters, or more than 16 feet. There are only about 40 sites on the Earth with tidal ranges of this magnitude. (www.eere.energy.gov) The downside of OTEC is In general, careful site selection is the key to keeping the environmental impacts of OTEC to a minimum. OTEC experts believe that

By Mathew Prang appropriate spacing of plants throughout the tropical oceans can nearly eradicate any potential negative impacts of OTEC processes on ocean temperatures and on marine life. But marine life may still be at risk. OTEC power plants require substantial capital investment upfront. Another factor of OTEC is that there are only a few hundred landbased sites in the tropics where deep-ocean water is close enough to shore to make OTEC plants feasible. Between geothermal energy and ocean thermal energy the choice can be very hard to make but looking at charts and research geothermal energy appears to be a little bit safer to the environment. In a energy source chart both geothermal and ocean thermal energy scored 5 out of 5 in low green house gases, 4 out of 5 low future cost, and 4 out of 5 on low depletion rate. Geothermal energy and ocean thermal energy is the way to go.

By Mathew Prang Geothermal Energy www.eere.energy.gov http://geothermal.marin.org/ http://www.darvill.clara.net/altenerg/geothermal.htm http://solstice.crest.org/renewables/re-kiosk/geothermal/index.shtml http://en.wikipedia.org/wiki/Geothermal

Ocean Thermal http://www.nrel.gov/otec/ http://www.energyquest.ca.gov/story/chapter14.html http://www.eere.energy.gov/RE/ocean_thermal.html http://www.pichtr.org/Ocean_Thermal_Energy_Conversion.htm http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion