GEOTHERMAL ENERGY -Energy from the earth
AUTHORS:
V M Satyajith Mahesh
B.Tech III-II Year B.Tech III-II Year
E-Mail: 1681satya@gmail.com E-Mail:sci_mahesh@yahoo.co.in
Ph:9492211985 ph:9030253736 MAHAVEER INST. OF SCIENCE AND TECH. AFFILIATED TO JNTU
ABSTRACT:

Geothermal Energy is the energy from the Earth. What could be more natural or plentiful? The source of geothermal power is the heat contained inside the Earth; heat so intense that it creates molten magma. There are a few different types of geothermal energy that can be tapped. "Some geothermal systems are formed when hot magma nears the surface (1,500 to 10,000 meters deep) directly heats groundwater." The heat generated from these hot spots flows outward toward the surface, manifesting as volcanoes, geysers, and hot springs. Naturally-occurring hot water and steam can be tapped by energy conversion technology to generate electricity or to produce hot water for direct use. "Other geothermal systems are formed even when no magma is nearby as magma heats rocks which in turn heat deeply-circulating groundwater." In order to maximize the energy gleaned from these so-called "hot dry rocks," geothermal facilities will often fracture the hot rocks and pump water into and from them in order to use the heated water to generate electricity.

INTRODUCTION:

Geothermal energy was first discovered in the seventh century, when mines dug were found to be actually hotter than the surface. This was assumed to be resulting from a heat source located inside the earth, termed Geothermal Energy. Both Romans and Chinese used geothermal springs to heat buildings and gather warm water. The Maoris in New Zealand used geysers to cook their food. Currently, it is also in use in Japan, Iceland, New Zealand, and California as a commonly seen source of energy. All these locations use the energy to heat homes, power electricity, and other such uses.

The concentration of geothermal energy at any given location must be quite high in order to make heat extraction feasible, and not all geothermal sites are created equally. Regions that have well-developed geothermal systems are located in geologically active areas. These regions have continuous, concentrated heat flow to the surface. The western United States has the best geothermal regions in the country, while Iceland, New Zealand, the Philippines, and South America are some of the more prominent global "hot spots." In Iceland, geothermal energy, caused by the constant movement of geologic plates coupled with the volcanic nature of the island, is used to heat 95% of all homes.

PRESENT SITUATION

Unfortunately even good geothermal areas are a non-renewable renewable. "The Geysers," the world's largest geothermal facility, is a working model on how not to approach a so-called "renewable" geothermal resource. Built in the 1950s on a steam field in Northern California, the facility was established on the apparent assumption that geothermal resources were infinite at that location. However, by the late 1980s, steam decline became noticeable and sustained. Depletion occurred because steam was being extracted faster than it could be naturally replaced. According to a report by Pacific Gas and Electric, "because of declining geothermal steam supplies, the Company's geothermal units at The Geysers Power Plant are forecast to operate at reduced capacities." In response, "plant operators and steam suppliers continually seek new operating strategies to maximize future power generation coupled with daily injection of millions of gallons of reclaimed municipal wastewater." Even though improvements in efficiency and conservation are being implemented and in 1996 The Geysers was still producing enough electricity to supply the power demand of a city like San Francisco, it is projected that the steam field will be defunct in 50 years or so. To prevent this sort of thing from happening elsewhere, geothermal facilities can use a closed-loop system at all times, or the re-injection of water back into the system for constant steam generation, as PG&E is now implementing at The Geysers.

Despite the fact that geothermal energy is abundant renewable, and able to reduce our dependence on imported fuels, the fact remains that fields of sufficient quality to produce economic electricity are rare. In addition, many of those that are known are located in protected wilderness areas that environmentalists want to preserve. Unless research and technology join forces to "harvest" geothermal power through non-traditional means, such as deep-crustal drilling or the acquisition of heat from magma, the tapping of geothermal energy is limited to a handful of locations.

Another type of geothermal energy being used commercially is Earth energy, extracted through heat pumps. Heat contained in shallow ground is used to directly heat or cool houses since the temperature inside the ground tends to stay at the yearly average. Therefore, in the winter the ground is warmer than the air and can be used to heat a building, and in the summer the ground is cooler than the air and can act as an air conditioner. Researchers know that "no active technology for home cooling is more efficient than the geothermal heat pump." This technique reduces the reliance on other resources and can be utilized anywhere, resulting in significant environmental benefits and reduced energy costs.

There are also other problems that prevent us from taking full advantage of this form of energy. Even though there are geothermal resources throughout the world, our current technology is not sufficient or economical enough to warrant its widespread use. Funding for energy extraction that involves the penetration of magma is not available because we do not yet know how to prevent a high-temperature, high-pressure blowout. When heat pumps are considered, which tap local sources of heat and can help to reduce a family's electricity bill by about $1 per day, the system is not economically viable. It "may have a payback period in excess of 5 years," which will increase with decreased electricity rates "unless equipment and installation costs drop dramatically." In addition, Earth energy is not "intense" enough to produce power for the electrical distribution grid; it is only sufficient to reduce the draw from the grid.

There are definite obstacles to be overcome before geothermal energy can be easily and economically harnessed for everyday, worldwide use. Case in point: "Construction of new domestic electricity-producing geothermal facilities in the Western United States during 1996 was limited to one site, due to the availability of cheap, plentiful natural-gas-fired electricity in the West."

Approximately 70 countries made direct use of a total of 270 pet joules (PJ) of geothermal heating in 2004. More than half of this energy was used for space heating, and another third for heated pools. The remainder supported industrial and agricultural applications. The global installed capacity was 28 GW, but capacity factors tend to be low (30% on average) since heat is mostly needed in the winter. The above figures are dominated by 88 PJ of space heating extracted by an estimated 1.3 million geothermal heat pumps with a total capacity of 15 GW. Heat pumps are the fastest-growing means of exploiting geothermal energy, with a global annual growth rate of 30% in energy production. Most of these new heat pumps are being installed for home heating.

Direct heating in all its forms is far more efficient than electricity generation and places less demanding temperature requirements on the heat resource. Heat may come from co-generation with a geothermal electrical plant or from smaller wells or heat exchangers buried in shallow ground. As a result, geothermal heating is economic over a much greater geographical range than geothermal electricity. Where natural hot springs are available, the heated water can be piped directly into radiators. If the ground is hot but dry, earth tubes or downhole heat exchangers can collect the heat. But even in areas where the ground is colder than room temperature, heat can still be extracted with a geothermal heat pump more cost-effectively and cleanly than it can be produced by conventional furnaces. These devices draw on much shallower and colder resources than traditional geothermal techniques, and they frequently combine a variety of other functions, including air conditioning, seasonal energy storage, solar energy collection, and electric heating. Geothermal heat pumps can be used for space heating essentially anywhere in the world.

Geothermal heat supports many applications. District heating applications use networks of piped hot water to heat buildings in whole communities. In Reykjavík, Iceland, spent water from the district heating system is piped below the pavement and sidewalks to melt snow. Geothermal desalination has been demonstrated.

Environmental Aspects

Environmental concerns also taint the issue of geothermal energy. Although no combustion occurs, some applications produce carbon dioxide and hydrogen sulphide emissions, require the cooling of as much as 100,000 gallons of water per megawatt per day, and dispose of toxic waste and dissolved solids.

SOURCES OF ENERGY:

The Earth's internal heat naturally flows to the surface by conduction at a rate of 44.2 terawatts, (TW,) and is replenished by radioactive decay of minerals at a rate of 30 TW. These power rates are more than double humanity’s current energy consumption from all primary sources, but most of it is not recoverable. In addition to heat emanating from deep within the Earth, the top ten metres of the ground accumulates solar energy (warms up) during the summer, and releases that energy (cools down) during the winter.

Beneath the seasonal variations, the geothermal gradient of temperatures through the crust is 25–30 °C per kilometre (km) of depth in most of the world. The conductive heat flux is approximately 0.1 MW/km2 on average. These values are much higher near tectonic plate boundaries where the crust is thinner. They may be further augmented by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation or a combination of these.

A geothermal heat pump can extract enough heat from shallow ground anywhere in the world to provide home heating, but industrial applications need the higher temperatures of deep resources. The thermal efficiency and profitability of electricity generation is particularly sensitive to temperature. The more demanding applications receive the greatest benefit from a high natural heat flux, ideally from using a hot spring. If no hot spring is available, the next best option is to drill a well into a hot aquifer. If no adequate aquifer is available, an artificial one may be built by injecting water to hydraulically fracture the bedrock. This last approach is called hot dry rock geothermal energy in Europe, or enhanced geothermal systems in North America. Much greater potential may be available from this approach than from conventional tapping of natural aquifers.

Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW depending on the scale of investments. Upper estimates of geothermal resources assume enhanced geothermal wells as deep as 10 kilometres (6 mi), whereas existing geothermal wells are rarely more than 3 kilometres (2 mi) deep. Drilling at this depth is now possible in the petroleum industry, although it is an expensive process. The deepest research well in the world, the Kola superdeep borehole, is 12 kilometres (7 mi) deep. This record has recently been imitated by commercial oil wells, such as Exxon's Z-12 well in the Chayvo field, Sakhalin.

Advantages:

We can generate geothermal energy by drilling deep holes into the earths crust pumping cold water through one end and then by the time it rises back to the surface the water can be hundreds of degrees Celsius which we then use as steam to drive a turbine which drives a generator creating power. Geothermal energy is one of the best natural energies around.

So the first advantage of using geothermal heat to power a power station is that, unlike most power stations, a geothermal system does not create any pollution. It may once in a while release some gases from deep down inside the earth, that may be slightly harmful, but these can be contained quite easily.

The cost of the land to build a geothermal power plant on, is usually less expensive than if you were planning to construct an; oil, gas, coal, or nuclear power plant. The main reason for this is land space, as geothermal plants take up very little room, so you don't need to purchase a larger area of land. Another factor that comes into this is that because geothermal energy is very clean, you may receive tax cuts, and/or no environmental bills or quotas to comply with the countries carbon emission scheme (if they have one).

No fuel is used to generate the power, which in return, means the running costs for the plants are very low as there are no costs for purchasing, transporting, or cleaning up of fuels you may consider purchasing to generate the power.

The overall financial aspect of these plants is outstanding, you only need to provide power to the water pumps, which can be generated by the power plant itself anyway.

So if geothermal power stations are able to provide an excellent source of clean, cheap, simple, renewable power

Disadvantages

There are some other deciding factors that may convince a constructor to build a different type of renewable energy power plant in a different location, such as a wind turbine.

So, we have established the main disadvantages of building a geothermal energy plant mainly lie in the exploration stage. During exploration, researchers will do a land survey (which may take several years to complete) and then post their findings to the company that contracted the survey.

Many companies who order surveys are often disappointed, as quite often the land they were interested in cannot support a geothermal energy plant. To extract the heat we have to find certain hot spots within the earths crust, these are very common around volcanos and fault lines, but who wants to build their geothermal energy plant next to a volcano?

Some areas of land may have the sufficient hot rocks to supply hot water to a power station, but what if these areas are contained in harsh areas of the world (near the poles) or high up in mountains. Some very good proven spots have been found in New Zealand, Iceland, Norway and Sweden.

The questions that are usually asked during a survey are; is the rock soft enough to drill through, do the rocks deep down contain sufficient heat, will this heat be sustainable for a significant amount of time, is the environment fit for a power plant. If the answer to these basic questions is yes, a more in depth survey should go ahead.

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Another big disadvantage of geothermal energy extraction, is that in many cases, a site that has happily been extracting steam and turning it into power for many years, may suddenly stop producing steam. This can happen and last for around 10 years in some cases.

Developers of such sites must be careful and aware that in some cases, harmful gases can escape from deep within the earth, through the holes drilled by the constructors. The plant must be able to contain any leaked gases, but disposing of the gas can be very tricky to do safely.

Conclusion:

Thus, here by we can conclude that the geo thermal energy is a very good renewable resource that can be used for any amount of time with just making very little care like pumping water into the crust.

REFERENCES:

• www.mit.edu

• www.wikipedia.org.html

• www.termpaperwarehouse.com/html

• www.geothermalenergy.com/html

• Science for u magazine

• www.Chevron.com

• www.renewableenergyworld.com/rea/tech/geothermal

• www.indiaenergyportal.org/subthemes_link.php?...geothermal