### Journal ofEngineering and Technology Research

• Abbreviation: J. Eng. Technol. Res.
• Language: English
• ISSN: 2006-9790
• DOI: 10.5897/JETR
• Start Year: 2009
• Published Articles: 184

Review

## Geothermal Energy

1Department of Physics, Payame Noor University, PO Box 19395-3697 Tehran, Iran 2Faculty of Physics, Shahid Bahonar University, P.O. Box 76175, Kerman, Iran
Email: [email protected]

•  Accepted: 24 November 2014
•  Published: 28 December 2014

ABSTRACT

INTRODUCTION

History says that the first use of geothermal energy occurred more than 10,000 years ago in North America by American Paleo-Indians. People used water from hot springs for cooking, bathing and cleaning. The first industrial use of geothermal energy began near Pisa, Italy in late 18th century. Steam coming from natural vents (and from drilled holes) was used to extract boric acid from the hot pools that are now known as the Larderello fields.  In  1904,  Italian  scientist  Piero  Ginori Conti invented the first geothermal electric power plant in which steam was used to generate the power. With the above experiment, the first geothermal plant in USA started in 1922 with a capacity of 250 kilowatts. It produced little output and due to technical glitch had to be shut down. However, in 1946 first ground-source geothermal heat pump installed at Commonwealth Building in Portland, Oregon During the 1960’s, pacific gas  and  electric  began  operation  of  first   large   scale geothermal power plant in San Francisco, producing 11 megawatts. Today there are more than 60 geothermal power plants operating in USA at 18 sites across the country. In 1973, when oil crisis began many countries began looking for renewable energy sources and by 1980’s geothermal heat pumps (GHP) started gaining popularity in order to reduce heating and cooling costs. As effect of climate change started showing results, governments of various countries joined hands to fight against it, for which Kyoto Protocol was signed in Japan in 1997, laid out emission targets for rich countries and required that they transfer funds and technology to developing countries, 184 countries have ratified it. Geothermal power today supplies less than 1% of the world’s energy in 2009 needs but it is expected to supply 10 to 20% of world’s energy requirement by 2050. Geothermal power plants today are operating in about 20 countries which are actively visited by earthquakes and volcanoes.

Geothermal energy is the energy stored in the form of heat below the earth’s surface. Its potential is limitless in human terms and its energy is comparable to the sun. Geothermal heat and water have been used for thousands of years. The Romans, Chinese and Native Americans used hot mineral springs for bathing, cooking and for therapeutic purposes.Today geothermal water is used in many applications such as district heating, systems which provide steam or hot water to multiple units, as well as for heating and cooling of individual buildings, including offices, shops and residential houses, by using geothermal heat pumps. Moreover, it has industrial potential for raising plants in greenhouses, drying crops, heating water at fish farms and other industrial processes.For close to 100 years geothermal energy has also been used for electricity generation. Today, so called Enhanced Geothermal Systems (EGS, also known as Hot Dry Rock), enable the exploitation of the Earth’s heat for producing electricity without having natural water resources. To extract energy from hot impermeable rock, water is injected from the surface into boreholes in order to widen them and create some fractures in the hot rock. Flowing through these holes, the water heats up and, when it returns to the surface, it is used for generating electricity. Clean, renewable, constant and available worldwide, geothermal energy is already being used in a large number of thermal and electric power plants
(http://ec.europa.eu/research/energy/eu/index_en.cfm?pg=research-geothermal).

The International Geothermal Association (IGA) has reported that 10,715 megawatts (MW) of geothermal power in 24 countries is online, which was expected to generate 67,246 GWh of electricity in 2010 (Erkan et al., 2008). This represents a 20% increase in online capacity since 2005. IGA projects growth to 18,500 MW by 2015, due to the projects presently under consideration, often in areas    previously   assumed   to   have  little  exploitable resource (Erkan et al., 2008).

In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants (Lay et al., 2008). The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California (Khan and Ali, 2007). The Philippines is the second highest producer, with 1,904 MW of capacity online. Geothermal power makes up approximately 27% of Philippine electricity generation (Lay et al., 2008) (Table 1).

Geothermal electric plants were traditionally built exclusively on the edges of tectonic plates where high temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology enable enhanced geothermal systems over a much greater geographical range (Holm, 2010). Demonstration projects are operational in Landau-Pfalz, Germany, and Soultz-sous-Forêts, France, while an earlier effort in Basel, Switzerland was shut down after it triggered earthquakes. Other demonstration projects are under construction in Australia, the United Kingdom, and the United States of America (Tester et al., 2006)

The thermal efficiency of geothermal electric plants is low, around 10 to 23%, because geothermal fluids do not reach the high temperatures of steam from boilers. The laws of thermodynamics limits the efficiency of heat engines in extracting useful energy. Exhaust heat is wasted, unless it can be used directly and locally, for example in greenhouses, timber mills, and district heating. System efficiency does not materially affect operational costs as it would for plants that use fuel, but it does affect return on the capital used to build the plant. In order to produce more energy than the pumps consume, electricity generation requires relatively hot fields and specialized heat cycles. Because geothermal power does not rely on variable sources of energy, unlike, for example, wind or solar, its capacity factor can be quite large, up to 96% has been demonstrated (Lund, 2003). The global average was 73% in 2005.

GEOTHERMAL SUSTAINABILITY GOALS

If possible, sustainable production should be the goal during geothermal utilization. However, in cases where excessive production is necessary (e.g. for electricity generation), a geothermal reservoir must be afforded a recovery period. Such recovery periods should be on a timescale acceptable to society and the use of other geothermal reservoirs should be possible in the meantime. Resource management strategies should therefore consider a number of geothermal systems based around a central volcanic system.

Water usage for the power plant is compatible with other water usage needs in the hydrological catchment area of the geothermal resource.

Efficiency

The geothermal resource is managed in such a way as to obtain the maximum use of all heat and energy produced and to minimise the waste of energy, by adequate forward planning and design of plants, the use of efficient technologies, reinjection where appropriate and cascaded energy uses.

Research and innovation

New technologies for the exploitation of previously untapped geothermal, or other energy resources, are actively researched or supported either directly or through links with university programmers or other research and development groups.

Environmental impacts

The geothermal resource is managed so as to minimize local and global environmental impacts through thorough resource and environmental impact assessment before development, appropriate reinjection management, usage of mitigation technologies and environmental management strategies during all phases of development.

Social aspects

The use of the geothermal resource generates net positive social impacts.

Energy security, accessibility, availability and diversity

The energy supplied by the geothermal resource is readily available, accessible and affordable.

The geothermal energy source is reliable and contributes to energy security for a nation or region.

Economic and financial viability

The geothermal energy project is cost-effective, financially viable and minimizes risk. The project should carry positive net national economic benefits.

The enterprise managing the geothermal resource practices corporate social responsibility.

Overarching issues: Information sharing/transparency

Knowledge and experience gained during the development of geothermal utilization projects should be accessible and transparent to the public and other interested groups.

1. Geothermal energy is relatively environmentally friendly. Pollution in the form of fumes are not produced although usually drilling of the earths surface takes place. The surrounding environment is not harmed with the exception of the land required for the power plant and transport links.
2. Unlike wind power, geothermal power can be relied on as it provides constant power.
3. The use of conventional polluting fuels such as oil and coal can be reduced if geothermal and other alternative energy forms are used (reducing pollution).
4. Geothermal power can take different forms. For instance, it can be used to produce electricity or the hot water can be used directly to heat homes and businesses.

Even though there is quite a number of arguments going on with regards to geothermal energy, but this one is still considered to be the most inexpensive and very affordable green energy solution that is very much available out there. Nevertheless, geothermal energy is truly effective all through any season and it can greatly help a lot when it comes to saving loads on energy costs. Aside from being less expensive compared to solar panel technology, it is also sustainable and completely clean.

First on the advantage list is with the fact that geothermal energy is surely environmental friendly. Since geothermal energy emerges from the natural that is being produced by the earth underground, so there are really no burned fossil fuels that were used along with the corresponding release of harmful and dreadful gases.

Another advantage is that the supply of this renewable energy is constant, as well as without limits. Put in mind that the earth is never going to stop producing heat energy and in theory, energy is abundant enough to supply all the needs of all mankind.

Third advantage is that when generating heat for a home system, it ensures you that it is really condensed. A standard geothermal heat pump is not larger compared to a small fridge.

The next advantage is that geothermal energy is considered low maintenance. It seems though these energy source do not really require regular servicing unlike many other standard heating systems out there. However, this just simply means that it can cost less, as well as hassle.

For the disadvantage, one would include the space that is needed for the piping system. For big scale operations, it would definitely require a massive amount of space in order to be able accommodate the maze of huge pipes.

Speaking of pipes, the repair, as well as the maintenance can also bring forth a big disadvantage since the maze of pipes located deep underground, maintenance work is definitely not an easy task to do.

This energy cannot be transferred over long distances. Unlike fuels such as coal, natural gas and petroleum, they can easily be hauled from the source to the user, even if it’s miles away.

Lastly, the hazard of geothermal gases can produce. Tapping onto this energy may bring forth release of potentially harmful and hazardous chemicals, as well as gases such as hydrogen sulfide. (http://topdiysolarpanels.net/advantages-and-disadvantages-of-geothermal-energy/)

1. It is a renewable source of energy.
2. By far, it is non-polluting and environment friendly.
3. There is no wastage or generation of by-products.
4. Geothermal energy can be used directly. In ancient times, people used this source of energy for heating homes, cooking, etc.
5. Maintenance cost of geothermal power plants is very less.
6. Geothermal power plants don't occupy too much space and thus help in protecting natural environment.
7. Unlike solar energy, it is not dependent on the weather conditions.

1. Only few sites have the potential of Geothermal Energy.
2. Most of the sites, where geothermal energy is produced, are far from markets or cities, where it needs to be consumed.
3. Total generation potential of this source is too small.
4. There is always a danger of eruption of volcano.
5. Installation cost of steam power plant is very high.
6. There is no guarantee that the amount of energy which is produced will justify the capital expenditure and operations costs.
7. It may release some harmful, poisonous gases that can escape through the holes drilled during construction.

HOW IS GEOTHERMAL ENERGY HARNESSED?

There are several different ways of harnessing the heat of the Earth for energy. We have outlined a few, below. Direct geothermal energy can be accessed in areas where hot springs/geothermal reservoirs are near the surface of the Earth. In these areas, hot water (pumped through a heat exchanger) can be directly piped in to heat homes or buildings. The “used” water is then returned to the reservoir for re-heating.

Geothermal heat pumps are another method for harnessing geothermal energy. These systems utilize a series of underground pipes, an electric compressor and a heat exchanger to absorb and transfer heat.

In the summer, the system removes heat from the house/building and returns it to the Earth. In the winter, the geothermal pump absorbs heat from the ground and transfers it into the house/building.

Geothermal power plants also harness the heat of the Earth through hot water and steam. In these plants, heat is used to generate electricity. There are three main types of geothermal power plants, including dry steam plants, flash steam plants, and binary cycle plants (http://www.justenergy.com/blog/beneath-our-feet-an-introduction-to-geothermal-energy/).

CONCLUDING REMARKS

Geothermal power requires no fuel (except for pumps), and is therefore immune to fuel cost fluctuations. However, capital costs are significant. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. A typical well doublet (extraction and injection wells) in Nevada can support 4.5 megawatts (MW) and costs about $10 million to drill, with a 20% failure rate (Geothermal Economics 101, 2009). In total, electrical plant construction and well drilling cost about €2 to 5 million per MW of electrical capacity, while the break–even price is 0.04 to 0.10 € per kWh. Enhanced geothermal systems tend to be on the high side of these ranges, with capital costs above$4 million per MW and break–even above $0.054 per kWh in 2007 (Sanyal et al., 2007). Direct heating applications can use much shallower wells with lower temperatures, so smaller systems with lower costs and risks are feasible. Residential geothermal heat pumps with a capacity of 10 kilowatt (kW) are routinely installed for around$1 to 3,000 per kilowatt. Geothermal resource extraction is independent of seasonal, diurnal and meteorological factors. It is essentially a base load electricity supply. There are no fuel costs other than the cost of identifying and maintaining the resource. Geothermal resource developments are well suited to development of complimentary applications such as space and process heating assuming that the resource is reasonably convenient to a market for the heat. Development of a geothermal   resource    is   entirely   dependent   upon  a successful exploration program which could take years depending upon factors such as funding, the level of effort and compliance with regulatory provisions. Actual plant construction, however, is straightforward and, depending on the size of the plant, construction may be expected to take two to three years once the resource has been quantified. Geothermal plants are being constructed and operated throughout the world. The technology, while innovative in some respects, is not radical. Accordingly, the completion risk is expected to be on par with that for any other energy project. Geothermal energy is very “green”, that is, no or minimal emissions, no combustion, small pant footprint. Insome areas, however, extraction of water from geothermal reservoirs have been linked to seismicity. This has been an issue in densely populated regions such as in Europe. Geothermal electricity would be expected to qualify for carbon credits.

CONFLICT OF INTEREST

The authors have not declared any conflict of interest.

REFERENCES

 Bertani R (2009). Geothermal Energy: An Overview on Resources and Potential. Proceedings of the International Conference on National Development of Geothermal Energy Use, Slovakia. Erkan K, Holdmann G, Benoit W, Blackwell D (2008). Understanding the Chena Hot flopë Springs, Alaska, geothermal system using temperature and pressure data. Geothermics 37(6):565-585. CrossRef Geothermal Economics 101, Economics of a 35 MW Binary Cycle Geothermal Plant, New York: Glacier Partners, October 2009. Retrieved 2009-10-17. Holm A (2010). Geothermal Energy: International Market Update, Geothermal Energy Association, p. 7, Retrieved 2010-05-24 Lay T, Hernlund J, Buffett BA (2008). Core–mantle boundary heat flow. Nat. Geosci. 1:25. Bibcode:2008NatGe...1...25L. CrossRef Lund JW (2003). The USA Geothermal Country Update. Geothermics 32(4–6):409-418. CrossRef Sanyal SK, Morrow JW, Butler SJ, Robertson TA (2007). "Cost of Electricity from Enhanced Geothermal Systems", Proc. Thirty-Second Workshop on Geothermal Reservoir Engineering, Stanford, California.    Tester JW, Margolis G, Reid RC, Botsaris G (2006). The Future of Geothermal Energy, Impact of Enhanced Geothermal Systems (Egs) on the United States in the 21st Century: An Assessment, Idaho Falls: Idaho National Laboratory, Massachusetts Institute of Technology, pp. 1-33. ISBN 0 615-13438-6, retrieved 2007-02-07.