What Is Geothermal Energy? | Alternative Energy Sources | Which Are Main Techniques Used to Exploit Geothermal Energy?

What Is Geothermal Energy?

Geothermal energy is thermal energy generated & stored inside the Earth’s crusts. The center of Earths remains at the same temperatures as the Sun, which remains almost constants due to the continuous process of nuclear fusions.

Such high temperatures and pressures cause some rocks to melt, resulting in an upward movement of the mantle as they become lighter with heat. These molten rocks formed in the Earth’s crusts are pushed upwards where they become trapped in certain areas called ‘hot spots.

When underground waters come in contact with hot spots, steams are generated. Sometimes this hot water area finds an outlet on the surface. When this hot water emerges from one of these outlets, it is called a hot spring.

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Alternative Energy Sources:

Alternatives energy sources include those that do not consumes fossil fuels. These are widely available & do not cause any undesirable consequences for the environment. Here is a list of major alternative energy sources.

#1. Hydroelectric Energy

The potential energy stored in the water is used to drive a water turbine that produces electricity. This type of energy generation is known as hydroelectric power. It is the most widely adopted alternative energy source at present.

#2. Solar Energy

These are the energy that is received from the Sun. It is the most promising alternatives energy source and is bound to remain available to mankind for centuries.

#3. Wind Energy

Wind power are controlled by pushing the blades of a wind turbine connected to an electric generator to produce wind power. It is an effective alternative source in areas where wind velocity is high.

#4. Biomass Energy

This energy is developed from animal and human waste which includes agricultural produce, municipal solid waste, and by-products from the lumber industry.

#5. Geothermal Energy

It is the energy these are generated from the heat within the Earth. Hot rocks in the center of the Earth emit steam and pressure to the Earth’s surface. This steam is used to drive turbines & generate electricity.

#6. Tidal Power

71% of the Earth’s surface is covered by water bodies which are mainly oceans. Due to the gravity of the Moons & the Sun, the tides in the water body rise and fall.

#7. Geothermal Gradient

The geothermal gradient is defined as the difference in temperature between the planet’s core and crust. The geothermal gradients are the driving force for the continuous conduction of thermal energy in the form of heat from the cores to the surfaces. The temperature gradient can sometimes reach more than 4000 °C.

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Geothermal Energy:

To harness geothermal energy, hydrothermal convection systems are used. In this process, holes are drilled deep under the Earth, through which a pipe is inserted. Steams trapped in the rocks are carried through this pipe to the surface of the Earth.

This steam is then used to turn the blades of the turbine of an electric generator. In another method, steam is used to heat water from an external source which is then used to spin a turbine.

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What Is Exactly Geothermal Energy?

Geothermal energy comes from the Earth’s natural heat, mainly due to the decay of natural radioactive isotopes of uranium, thorium, and potassium. Due to internal heat, the Earth’s surface heat flux averages 82 mW/m2, which is equivalent to a total heat transfer of about 42 million MW.

On average, Earth’s temperature increases with depth, about 25–30˚C/km above the ambient surface temperature, and at 10 km, the Earth’s temperature will exceed 300˚C. Depending on the continental crust, the temperature is thought to be between 200 and 1000 °C, and the heat is mostly transferred towards the surface by conduction.

In some areas, heat flows more readily to the surface, among others, due to the intrusion of deeply molten magma, in higher surface heat fluxes due to thin crust, or the ascent of groundwater that has warmed. Earth’s thermal energy is immense, but only a fraction of it can be harnessed in regions where geological conditions allow a carrier such as water to ‘transfer’ heat from deep warm regions to or near the surface, thus Create geothermal resources.

Geothermal production wells are usually deeper than 2 km, but rarely more than 3 km, and most geothermal exploration and use occur where temperatures exceed an average of 300 °C, where drilling is shallow and Is less expensive. Geothermal resources are usually classified into different categories based on the average annual ambient temperature it can provide.

These can be dry vapor or warm water, such as for a storm, an up-flow zone at the center, an outflow zone or plume of warm water moving laterally away from the center of the system, & a downflow zone where recharges is taking place.

Warm water actually has a lower density than the surrounding cold groundwater and therefore flows toward the surface and appears as hot springs, fumaroles, geysers, or travertine deposits on the Earth’s surface with fractures and other permeable structures.

For hot, dry rock resources, new experimental techniques are being tested, including shale gas extraction, hydraulic fracturing under pressure, followed by a flow of cold water into one well and producing hot water from another well in a closed system.

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How Much Represent This Potential Geothermal Energy?

In generals, resources above 150˚C are used for power generation, and resources below 150˚C are usually used for direct heating and cooling. Ambients temperatures in the 5-30˚C ranges can be used with heat pumps, which provide both heating and cooling.

The amount of low-temperature geothermal resources in the world is about 140 EJ/yr of heat, or a third of the current world energy consumption. The expected geothermal power potential ranges from 35 to a maximum of 140 GWe.

The potential is 5–10 times higher, based on advanced geothermal systems (EGS) technology, and the most likely value for the technical potentials of geothermal resources suitable for power generation is 210 GWe. With geothermal resources, it is considered possible to produce up to 8.3% of the total world electricity, which supplies 17% of the world’s population.

Twenty-nine countries (mostly located in Africa, Central/South America, and the Pacific) can potentially produce 100% of their electricity using geothermal resources. The main advantage of geothermal heating & power generation systems is that they are available 24 hours per day, 365 days a year, & are closed only for maintenance.

Power generation systems typically have a 95% capacity factor, i.e., they operate at nearly full capacity year-round, while direct-use systems have an efficiency factor of about 25 to 30%, as heating is not required throughout the year.

Heat pump systems have an operating efficiency of about 10-20% in the heating mode, and they double this if the cooling modes are also included.

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Where Are Exploitable Geothermal Systems Situated?

Exploitable geothermal systems can be found in many geological environments. They can be roughly divided into two groups, depending on whether they belong to young volcanoes and to magmatic activity. High-temperature regions (>180 °C) are regions where volcanic activity occurs mainly along the boundaries of tectonic plates and are used for conventional power generation because the crust is highly fractured and thus can be used for water and heat.

Permeable to other sources. Most plate boundaries are below sea level, but there are cases where volcanic activity has been intense enough to form islands or where active plate boundaries cross continents with high-temperature geothermal regions, such as ‘rings.’ Off ‘fire’ that surrounds the Pacific Ocean, Iceland, and ‘hot spots such as Hawaii and Yellowstone.

Low-temperature regions (<180°C) are geothermal resources that, with a few exceptions, can also be linked to volcanic activity. Hot springs can occur in most rock types of all ages but are most frequent in mountainous areas, where hot springs appear along faults in the valleys.

Zones of youth tectonic activity are usually thus enriched. The most important types of geothermal resources not associated with young volcanic activity are characterized by deep basins filled with a sedimentary rock of high porosity & permeability.

If these are properly separated from surface groundwater by impermeable strata, the water in the sediment is heated by regional heat flow. Thermal water temperature depends on the depth of the individual aquifer and the geothermal gradient in the area concerned but is usually in the range of 50–100 °C (in wells less than 3 km) that have been exploited.

These types of geothermal resources are rarely seen on the surface but are commonly found during deep drilling for oil and gas.

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How Much Is Energy Produced Via Geothermal Sources?

As of the end of 2008, installed geothermal power generation capacity produced over 63 000 GWh/yr, and direct heat use was approximately 120 000 GWh. The annual increase in energy production between 2008 and 2013 has been 3.8% for electricity generation and about 10% for direct use, including geothermal heat pumps.

The energy produced by ground-source heat pumps alone has increased by 20% per year over the same period. The low growth rate for electricity generation was mainly due to the low price of the main competitor, natural gas.

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Is Geothermal Energy Economically Competitive?

Financing is an important factor in the economics of any project and, thus, the potential for market penetration and growth. For many new projects, the highest annual operating cost is the amortization cost of capital, which can be as high as 75% of the annual operating expenses for new geothermal district energy projects.

With rising fossil fuel prices and limits on emissions of greenhouse gases, the development of geothermal energy has to become more competitive as a renewable & ‘green’ energy resource. However, market development is highly dependent on competition from other sources of electricity or direct use product supply fish, vegetables, flowers, minerals, etc.

Remote areas, often off-grid, are excellent candidates for electrical energy. The availability of transmission lines can be critical, & they are often lacking and costly to build over large distances.

Direct-use projects must have a market and a transportation system for consumers to get the product economically. Unfortunately, the geothermal resources that can be used are often remote, which can limit their development for commercial operation.

Development risks are high, and predicting resource quality requires capital investment in drilling and testing wells.

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Which Are Main Techniques Used to Exploit Geothermal Energy?

#1. Electric Power Generation

Electric Power Generation A Vapor-Predominant (Dry Steam) The resource can be used directly to power a turbine-generator set to produce electricity while reducing the pressure to produce steam is needed to flash the hot water resource, typically 15–20 in the % range.

Low-temperature resources usually require the use of a secondary low boiling point liquid hydrocarbon to generate vapor. Binary plant technology using wastewater from the main plant is playing a very important role in the modern geothermal power market.

The economics of power generation is influenced by drilling costs and resource development; a typical capital expenditure quota is 30% for a heat reservoir and 70% for a plant.

The higher the energy contents of the reservoir fluid, the smaller the number of wells required. Single geothermal wells can produce from 1-5 MW, and some can produce up to 30 MW.

#2. Direct Utilisation Geothermal

Direct Utilisation Geothermal energy resources for direct use projects in low to intermediate temperatures are more widespread & exist in at least 80 countries at economical drilling depths.

In addition, there is no conversion efficiency loss, and projects can use conventional water-well drilling and off-the-shelf heating and cooling equipment. Geothermal energy can typically meet 80–90% of annual heating or cooling demand yet can only be sized for 50% of peak loads.

Projects can be small-scale, such as for an individual home, greenhouse, or aquaculture pond, but can also be large-scale commercial operations, such as district heating/cooling or food and wood drying.

#3. Geothermal Heat Pumps

Geothermal Heats Pumps Ground-sources heat pumps (GHPs) use the Earth’s relatively constant temperature close to the surface to provide heating, cooling, & domestic hot water for homes, schools, government, and commercial buildings.

GHPs come in two basic configurations: ground-coupled (closed-loop), which are installed horizontally or vertically, & groundwater (open-loop) systems, which are installed in wells & lakes. A small amount of power input is required to run a compressor, although the energy output is on the order of four times this input.

Europe began using this technique around 1970, and it is now popular in the United States and Canada as well. The growing awareness & popularity of geothermal ground-source heat pumps had the most significant impacts on the growth in geothermal energy uses. Annual energy use for these has grown at a compounded rate of 24.9% compared to the year 2000.

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How to Enhance the Efficacy of Geothermal Systems?

Principles are simple: in the deep subsurface, where temperatures are high enough for power generation (150–200 °C), an extended fracture network is created, & water from deep wells and/or surface cold water is pumped through this deep reservoir.

Using injection and production wells and then recovering as steam/hot water. The heat extracted can be used for district heating and/or electricity generation. Techniques for fabrication, profiling, and operation of deep fracture systems need to be developed, and some environmental issues, such as the possibility of triggering seismicity and surface water availability, also require detailed investigation. Several pilot projects are underway.

Other developments include the Internationals Iceland Deep Drilling Project (IDDP) to improves the efficiency & economics of geothermal energy by using deep unconventional geothermal resources. Recent advances in binary cycle technology now allow the use of low-temperature liquids at around 100 °C, thus increasing the number of possible locations.

The use of combined heat & power plants has made low-temperature processing and deep drilling more economical. Geothermal fluid is used at progressively lower temperatures, thus maximizing the energy extracted. District heating using spent water from a binary power plant can make such a marginal project economical.

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Is Geothermal Energy Production Sustainable?

Geothermal energy is generally classified as a renewable resource because the energy extracted from the resource is continuously replaced by more energy in the same amount of time required to remove the energy.

The production system is able to maintain production levels over a long period of time by using moderates productions rates that take into account local resource characteristics, field size, natural recharge rates, etc. The production of geothermal fluid/heats continuously creates a hydraulic/heat sink in the reservoir, & regenerations of the geothermal resources process that occurs on various time scales depending on the type and size of the production system, the rates of extraction.

And on the characteristics of the resource. The extent of CO2 emissions from high-temperature geothermal fields used for electricity generation is variable but much lower than from fossil fuel plants. With regard to their environmental impact, depending on the geological conditions of the different regions, geothermal fluids contain a variable amount of gases, mainly nitrogen and carbon dioxide, some hydrogen sulfide and ammonia, mercury, radon, and boron with small proportions.

Most of these chemicals are concentrated in disposal water, which is routinely re-injected into drill holes and thus not released into the environment.

Geothermal schemes are relatively benign, but they typically produce highly corrosive brine, which may require special treatment and discharge consent. Removal of hydrogen sulfide from geothermal power plants is mandatory in the United States and Italy. The concentrations of other gases are usually not harmful and can be released into the atmosphere.

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Applications:

Generation of electricity: Geothermal power plant is usually installed within a two-mile radius of the geothermal reserve. Steam from these stores is either used directly to drive the turbines of an electric generator or to heat water which then produces steam for the process.

#1. Farming

In cold countries, geothermal energies are used to heat greenhouses or to heat water used for irrigation.

#2. Industry

Geothermal energy is used in industries for purposes of food dehydration, milk pasteurization, gold mining, etc.

#3. Heating

Geothermal energy is used to heat building through district heating systems in which hot water through springs are delivered directly to buildings via pipelines.

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Advantages:

Renewable Resources: Geothermal energy is free and abundant. The constant flow of heat from Earth makes this resource inexhaustible and limitless for an estimated period of 4 billion years.

#1. Green Energy

Geothermal energy is non-polluting and eco-friendly as no harmful gases are evolved from the use of geothermal energy, unlike the use of fossil fuels. In addition, no residue or by-product is generated.

#2. Employment Generation

Geothermal power plants are highly sophisticated & involve extensive research prior to installation. It creates a very large scale of employment for skilled and unskilled workers at each stage of production and management.

#3. It Can Be Used Directly

In cold countries, geothermal energy is used directly to melt snow on roads, heat homes in winter, greenhouses, public bathrooms, etc. Although the initial cost of installations is very high, the costs of maintenance and repair are negligible.

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Disadvantages:

#1. Transport and Transmission

Unlike fossil fuels, geothermal energy cannot be easily transported. Once the tapped energy is used up, it can only be used efficiently in the surrounding areas. Apart from this, along with the transmission, there is also a possibility of the emission of toxic gases into the atmosphere.

#2. High Installation Cost

Setting up geothermal power plants to obtain steam from deep below the Earth requires huge investments in terms of material & human resources.

#3. Intensive Research Required

Before a plant can be installed, extensive research is required, as the site can run out of steam over time due to temperature drops resulting from the excessive or erratic supply of inlet water.

#4. Limited to Particular Regions

Sources of geothermal energy are available in limited areas, some of which are extremely inaccessible, such as high mountains and rocky terrain, which in many cases makes the process economically unfeasible.

#5. Impact on the Environment

Geothermal sites are located deep beneath the Earth, so the drilling process can result in the release of highly toxic gases into the atmosphere near these sites, which sometimes prove fatal to the workers involved in the process.

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Frequently Asked Questions (FAQ)

What Does Geothermal Cost to Install?

On average, a homeowner can expect total expenses to reach between $18,000 to $30,000 on geothermal heating and cooling cost. This cost would cover a complete geothermal installation. The price can range from $30,000 to $45,000 with high-end ground-source heat pump systems for large homes.

What Is the Most Efficient Geothermal System?

WaterFurnace systems are rated number one in energy efficiency because they can deliver more than five units of energy for every one unit of electrical energy used.

What Is Enhanced Geothermal Systems?

The EGS concept is to extract heat by creating a subsurface fracture system to which water can be added through injection wells. Creating an enhanced or engineered geothermal system requires improving the natural permeability of the rock.

What Causes Geothermal Energy?

Magma heats nearby rocks and underground aquifers. Hot water can be released through geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots. These are all sources of geothermal energy. Their heat can be captured and used directly for heat, or their steam can be used to generate electricity.

What Are the Advantages of Geothermal Energy?

All the advantages of geothermal energy

• Always available.
• Doesn’t require large spaces.
• Silent energy.
• It creates record numbers of jobs.
• Provides more energy for the same nominal power.
• Allows double recycling.
• The plants are long-lasting, safe, and reliable.
• Requires very little maintenance.

What Is the Cost of Geothermal Energy?

On average, a homeowner can expect to invest about $12,000 to $30,000 in geothermal heating and cooling cost. This cost would cover a complete geothermal installation. For large homes, the cost can range from $30,000 to $45,000 for high-end ground source heat pump systems.

What Is the Meaning of Geothermal Energy?

Geothermal energy is heat that is generated within the Earth. (Geo means “earth,” and thermal means “heat” in Greek.) It is a renewable resource that can be harvested for human use.

Deep Geothermal Energy

Geothermal energy utilizes the accessible thermal energy from the earth’s crust. Heat is extracted from geothermal reservoirs using wells (‘deep geothermal’) or other means, including pipes that are deposited close to the surface and heat pumps (‘shallow geothermal’).

Geothermal Energy Plant

Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or from hot water wells.

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