ArticlePDF Available

Geothermal Energy: A Review

Authors:
Chijindu Ikechukwu Igwe at Simon Fraser University
Chijindu Ikechukwu Igwe
Download full-text PDF
Read full-text
Download citation

Abstract

Geothermal energy is energy created by the heat of the Earth. To extract energy from the underground, water is most times used as the heat carrier. As the crust is highly fractured and thus permeable to fluids, surface water, in most cases rainwater, penetrates at depth and exchanges heat with the rocks. Two main forms of heat transfer occur within the crust: conduction and convection. Where rocks are much fractured and circulating fluids are abundant, the resulting convective heat transfer is very efficient and can be easily exploited by drilling wells and discharge the hot fluids to the surface. The Earth’s geothermal resources are theoretically more than adequate to supply humanity’s energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, plate boundary movement and interest rates. Geothermal energy is a well-established and relatively mature form of commercial renewable energy characterized by a high load factor, which means that its installed capacity produces significantly more electricity during a year than other sources like wind and solar power plants. Geothermal power plants provide stable production output, unaffected by weather or climate, resulting in high capacity factors ranging from 60% to 90% which is ideal for making the technology suitable for base load electricity production.
Content uploaded by Chijindu Ikechukwu Igwe
Author content
All content in this area was uploaded by Chijindu Ikechukwu Igwe on Jul 19, 2021
Content may be subject to copyright.
Geothermal Energy: A Review
Chijindu Ikechukwu Igwe
Nnamdi Azikiwe University Awka,
Nigeria.
Abstract:- Geothermal energy is energy created by the heat of the Earth. To extract energy from the underground, water is most times
used as the heat carrier. As the crust is highly fractured and thus permeable to fluids, surface water, in most cases rainwater,
penetrates at depth and exchanges heat with the rocks. Two main forms of heat transfer occur within the crust: conduction and
convection. Where rocks are much fractured and circulating fluids are abundant, the resulting convective heat transfer is very
efficient and can be easily exploited by drilling wells and discharge the hot fluids to the surface. The Earth’s geothermal resources are
theoretically more than adequate to supply humanity’s energy needs, but only a very small fraction may be profitably exploited.
Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions
about technology, energy prices, subsidies, plate boundary movement and interest rates. Geothermal energy is a well-established and
relatively mature form of commercial renewable energy characterized by a high load factor, which means that its installed capacity
produces significantly more electricity during a year than other sources like wind and solar power plants. Geothermal power plants
provide stable production output, unaffected by weather or climate, resulting in high capacity factors ranging from 60% to 90%
which is ideal for making the technology suitable for base load electricity production.
1.1 INTRODUCTION
Geothermal energy is energy created by the heat of the Earth. Under the Earth’s crust lies a layer of thick, hot rock with most
times, pockets of water, which sometimes seeps up to the surface in the form of hot springs. When the water does not travel
naturally to the Earth’s surface, it is sometimes possible to reach it by drilling (Geothermal Energy, 2019). This hot water can be
used as a virtually free source of energy, either directly as hot water, steam or heat, or as a means of generating power.
This energy source, geothermal is nonpolluting, inexpensive and in most cases, renewable, which makes it a promising source
of power for the future (Geothermal Energy, 2019).
The word “geothermal originates from the Greek words geo, which means earth, and thermos, which means heat.”
The geothermal energy of the Earth’s crust originates from the original formation of the planet and from radioactive decay of
materials (Dye, 2012; Gando et al, 2011).
The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a
continuous conduction of thermal energy in the form of heat from the core to the surface. Earth’s internal heat is thermal energy
generated from radioactive decay and continual heat loss from Earth’s formation (Turcotte D. L. & Schubert G., 2002).
Temperatures at the core-mantle boundary may reach over 4000oC (7,200oF) (Lay et al, 2008).
The high temperature and pressure in Earth’s interior cause some rock to melt and solid mantle to behave plastically, resulting
in portions of the mantle convecting upward since it is lighter than the surrounding rock. Rock and water is heated in the crust,
sometimes up to 370oC (700oF). With water from hot springs, geothermal energy has been used for bathing since Paleolithic
times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, 11,700
megawatts of geothermal power is available in 2013. An additional 28 gigawatts of direct geothermal heating capacity is
installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications as of 2010
(Fridleifsson et al, 2008).
Geothermal power is cost effective, reliable, sustainable, and environmentally friendly (Glassley, 2010), but has historically
been limited to areas near tectonic plate boundaries. Recent technological advancements have dramatically expanded the range
and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation.
Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit
than those of fossil fuels.
The Earth’s geothermal resources are theoretically more than adequate to supply humanity’s energy needs, but only a very small
fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of
geothermal power depend on assumptions about technology, energy prices, subsidies, plate boundary movement and interest
rates.
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
655
1.2 GEOTHERMAL ENERGY EXTRACTION
According to Manzella (2017), to extract energy from the underground, water is most times used as the heat carrier. As the crust
is highly fractured and thus permeable to fluids, surface water, in most cases rainwater, penetrates at depth and exchanges heat
with the rocks. Two main forms of heat transfer occur within the crust: conduction and convection. Where rocks are much
fractured and circulating fluids are abundant, the resulting convective heat transfer is very efficient and can be easily exploited
by drilling wells and discharge the hot fluids to the surface. In these convective systems, named hydrothermal resources, the
aquifers represent the geothermal reservoir. Occasionally, in areas of very high heat flow, the fluid has high temperature (up to
above 300oC) and, depending on the pressure, can be vapor (steam) or water. Warm and hot fluids can be extracted from the
underground in a wide range of temperature and discharge rate, and used directly for their heat content or to produce electric
power. Even the modest temperatures found at shallower depths can be used to extract or store heat by means of ground source
heat pumps, which are nowadays a widespread application for geothermal energy.
Heat can be extracted at different rates. To guarantee a sustainable use of geothermal energy, the rate of consumption should not
exceed the rate of generation, so that the heat removed from the resource is replaced on a similar time scale. Geothermal plants
typically develop below a certain level of energy production. Geothermal typically provides base-load generation, since it is
generally immune from weather and seasonal variation, therefore producing almost constantly and distinguishing it from several
other renewable technologies that produce variable power or heat with time (Manzella, 2017).
Fig 1: Working Processes of A Geothermal Power Plant
Fig 2: Geothermal Power Plant
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
656
Geothermal energy extraction processes can be summarized thus:
• Hot high-pressure water is pumped from deep underground through a well.
• When the water reaches the surface, the pressure drops, causing the water to turn into steam.
• The steam spins a turbine, which is connected to a generator that produces electricity.
• The steam cools off in a cooling tower and condenses back to water.
• The cooled water is pumped back into the Earth to begin the process again.
1.3 TYPES OF GEOTHERMAL POWER PLANT
According to Renewable Energy World (2019), the three types of geothermal power plants are dry steam, flash steam and
binary cycle.
DRY STEAM power plants draw from underground resources of steam. The steam piped directly from underground wells to the
power plant, where it is directed into a turbine/generator unit. Here, the condensate is usually re-injected into the reservoir or
used for cooling. There are only two known underground resources of steam in the United States: The Geysers in northern
California and Yellowstone National Park in Wyoming, where there is a well-known geyser called Old Faithful. Since
Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers.
Fig 3: Operating Processes of A Geothermal Power Plant
Fig 4: Schematic of A Dry Steam Power Plant (Geo-Heat Centre and U.S. Energy Department)
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
657
FLASH STEAM power plants are the most common. They use geothermal reservoirs of water with temperatures greater than
182oC. This very hot water flows through wells in the ground under its own pressure. As it flows upward, the pressure decreases
and some of the hot water boils or “flashes” into steam. The steam is then separated from the water and used to power a turbine.
Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource. The remaining
hot water may be flashed again twice (double flash plant) or three times (triple flash) at progressively lower pressures and
temperatures to obtain more steam.
BINARY CYCLE power plants operate on water at lower temperatures of about 107oC to 182oC. These plants use the heat from
the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vapourized in
a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the
working fluid are kept separated during the whole process, so there are little or no air emissions.
Geothermal energy comes in either Vapour-dominated or Liquid-dominated forms.
Vapour-dominated sites offer temperatures from 240oC to 300oC that produce superheated steam.
Liquid-Dominated Plants: These plants are more common with temperatures greater than 200oC and are found near young
volcanoes surrounding the Pacific Ocean and in rift zones and hot spots. Flash plants are the common means to generate
electricity from these sources. Pumps are generally not required; they are instead powered when the water turns to steam.
However, lower temperature liquid-dominated reservoirs (120oC to 200oC) require pumping. They are common in extensional
terrains, where heating takes place via deep circulation along faults, such as in the Western US and Turkey. Water passes
through a heat exchanger in a Rankine cycle binary plant. The water vaporizes an organic working fluid that drives a turbine.
Fig 5: Schematic of A Flash Steam Power Plant (Geo-Heat Centre and U.S. Energy Department)
Fig 6: Schematic of A Binary Cycle Steam Power Plant (Geo-Heat Centre and U.S.
Energy Department)
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
658
1.4 ENHANCED GEOTHERMAL SYSTEM
Enhanced geothermal systems basically operate on the principle of injecting water into wells to be heated and pumped back out.
The water is injected under high pressure to expand existing rock fissures to enable the water to freely flow in and out.
The technique was adopted from oil and gas extraction techniques. However, the geologic formations are deeper and no toxic
chemicals are used, reducing the possibility of environmental damage.
1.5 GEOTHERMAL HEAT PUMPS
Geothermal heat pumps can be used almost everywhere in the world, as they not share requirements of fractured rock and water
as are needed for a conventional geothermal reservoir.
According to Oil & gas portal (2017), geothermal heat pump systems consist of basically three parts:
• The ground heat exchanger
• The heat pump unit
• The air delivery system (ductwork)
The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid
(usually water or a mixture of water and anti-freeze) circulates through the pipes to absorb heat within the ground.
In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the
summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger.
The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water.
Geothermal heat pumps come in four types of loop systems that loop the heat to or from the ground and the house. Three of
these, horizontal, vertical and pond/lake are closed-loop systems. The fourth type of system is the open-loop option. The choice
Fig 7: Enhanced Geothermal System
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
659
for the best option for a particular site is dependent on the climate, soil conditions, available land and local installation costs at
the site.
1.6 GEOTHERMAL ENERGY PROS AND CONS
According to Energy Informative (2020), some of the advantages of geothermal energy can be summarized as follows:
• Environmentally Friendly: Geothermal energy is generally considered environmentally friendly. There are a few polluting
aspects of harnessing geothermal energy, but they are minor compared to the pollution associated with conventional fuel
sources.
The carbon footprint of a geothermal power plant is minimal.
An average geothermal power plant releases the equivalent of 122Kg CO2 every megawatt-hour (MWh) of electricity it
generates – one eight of the carbon emissions associated with a typical coal power plant.
• Renewable: Geothermal reservoirs come from natural resources and are naturally replenished. Geothermal energy is
therefore a renewable energy source.
Sustainable is another label used for renewable sources of energy. In other words, geothermal energy is a resource that can
sustain its own consumption rate, unlike conventional energy sources such as coal and fossil fuels. According to scientists,
the energy in our geothermal reservoirs will literally last billions of years.
• Massive Potential: Worldwide energy consumption – about 15 terawatts (TW) – is not anywhere near the amount of energy
stored in earth. However, most geothermal reservoirs are not profitable and we can only utilize a small portion of the total
potential. Realistic estimates for the potential of geothermal power plants vary between 0.035 to 2 TW.
Geothermal power plants across the world currently deliver about 10,715 megawatts (MW) of electricity, far less than
installed geothermal heating capacity of about 28,000 MW.
Fig 8: Schematics of Open and Closed-Loop Systems of Geothermal Heat Pumps
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
660
• Stable: Geothermal energy is a reliable source of energy. We can predict the power output of a geothermal power plant with
remarkable accuracy. This is not the case with solar and wind, where weather plays a huge part in power production.
Geothermal power plants are therefore excellent for meeting the base load energy demand.
Geothermal power plants have a high capacity factor; actual power output is close to total installed capacity.
The global average power output was 73% (capacity factor) of total installed capacity in 2005, but as much as 96% has
been demonstrated.
• Great for Heating and Cooling: Water temperature of more than 150oC or greater is needed in order to effectively turn
turbines and generate electricity with geothermal energy. Another approach is to use the (relatively small) temperature
difference between the surface and ground source.
The earth is generally more resistant to seasonal temperature changes than air. Consequently, the ground only a couple of
meters below the surface can act as a heat sink/source with a geothermal heat pump, much in the same way an electric heat
pump works.
Disadvantages of geothermal energy, according to Energy Informative (2020):
• Environmental Issues: There is an abundance of greenhouse gases below the surface of the earth, some of which mitigates
towards the surface and into the atmosphere. These emissions tend to be higher near geothermal power plants.
Geothermal power plants are associated with sulfur dioxide and silica emissions, and the reservoir can contain traces of
toxic heavy metals including mercury, arsenic and boron.
However, it is needful to note that regardless of how it is being considered; the pollution associated with geothermal power
is nowhere near that of coal power and fossil fuels.
• Surface Instability (Earthquakes): Construction of geothermal power plants can affect the stability of land. In fact,
geothermal power plants have lead to subsidence (motion of the earth’s surface) in both Germany and New Zealand.
Earthquakes can be triggered due to hydraulic fracturing, which is an intrinsic part of developing enhanced geothermal
system (EGS) power plants.
In January 1997, the construction of a geothermal power plant in Switzerland triggered an earthquake with a magnitude of
3.4 on the Richter scale.
• Expensive: Commercial geothermal power projects are expensive. The exploration and drilling of new reservoirs come with
a step price tag (typically half the costs). Total costs usually end up somewhere between 2 – 7 million dollars for a
geothermal plant with a capacity of 1 megawatt (MW).
Most geothermal resources cannot be utilized in a cost effective manner, at least not with current technology, level of
subsidies and energy prices.
• Location Specific: Good geothermal reservoirs are hard to come by. Some countries have great reserves, Iceland and
Philippines meet nearly one third of their electricity demand with geothermal energy. However, some parts of the crust
have significantly high heat flow rates and these can provide heat energy at depths that can be economically exploited using
several existing technologies.
• Sustainability Issues: Rainwater seeps through the earth’s surface and into the geothermal reservoirs over thousands of
years. Studies show that the reservoirs can be depleted if the fluid is removed faster than replaced. Efforts can be made to
inject fluid back into the geothermal reservoir after the thermal energy has been utilized (the turbine has generated
electricity).
Geothermal power is sustainable if reservoirs are properly managed.
In summary, geothermal energy is generally regarded as environmentally friendly, sustainable and reliable. This makes
geothermal energy a no-brainer in some places, but heavy upfront costs stops us from realizing the full potential.
The level of influence geothermal power will have on the energy system in the future will be dependent on technological
advancements, energy prices and politics (subsidies).
REFERENCES
[1] Dye S. T. (2012). Geoneutrinos and the radioactive power of the Earth. Reviews of Geophysics. 50(3): RG3007
[2] Energy Informative (2020). Geothermal energy pros and cons. Retrieved from https://energyinformative.org/geothermal-energy-pros-and-cons/ on
January 02, 2020
[3] Fridleifsson Ingvar B., Bertani Ruggero, Huenges Ernst, Lund John W., Ragnarsson Arni, Rybach Ladislaus (2008). Hohmeyer O., and Trittin T.
The possible role and contribution of geothermal energy to the mitigation of climate change. Page 59-80
[4] Gando A., Dwyer D. A., McKeown R. D., Zhang C. (2011). Partial radiogenic heat model for Earth revealed by geoneutrino measurements. Nature
Geoscience. 4(9): 647
[5] Geothermal Energy. December 14, 2019. Retrieved from https://www.encyclopedia.com/science-and-technology/technology/technology-terms-and-
concepts/geothermal-energy on December 20, 2019.
[6] Glassley William E. (2010). Geothermal Energy: Renewable Energy and the Environment
[7] Lay Thorne, Hernlund John, Buffett Bruce A. (2008). Core-mantle boundary heat flow. Nature Geoscience, 1: 25-32.
[8] Manzella A. (2017). Geothermal Energy. Institute of Geosciences and Earth Resources - Pisa, Italy. EPJ Web of Conferences 148, 00012.
[9] Oil & Gas Portal (2017). Geothermal exploration process and production technologies. Retrieved from www.oil-gasportal.com/geothermal-
exploration-process-and-production-plants/
[10] Renewable Energy World (2019). Geothermal Electricity Production. Retrieved from https://www.renewableenergyworld.com/types-of-renewable-
energy/tech-3/geoelectricity/#gref on December 29, 2019.
[11] Turcotte D. L., Schubert G. (2002). Geodynamics, second edition. Cambridge, England, UK: Cambridge University Press, pp. 136-137.
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
IJERTV10IS030164 (This work is licensed under a Creative Commons Attribution 4.0 International License.)
Published by :
www.ijert.org
Vol. 10 Issue 03, March-2021
661
... When not naturally accessible, this heated water can be extracted through drilling. It serves as a virtually cost-free energy source, whether used directly as hot water, steam, or heat, or to generate electricity [5]. ...
... During this phase, the solenoid valve (13) connects the steam space in the work transfer cylinder (1) with the condenser (4) at a pressure pcond. The condensate in the condenser (4) is pumped to the evaporator (3) by pump (6), which is driven by the steam turbine (5). The steam turbine (5) is supplied from the superheater (2) through the extraction valve (14). ...
... The mathematical equations employed for the thermodynamic analysis of the ORPILI cycle, as detailed in Subsection 2.3, together with the thermal and second law efficiencies, are presented in Table 1. The work performed by the 3) and (4), allows for the calculation of the steam extraction ratio, as shown in Eq. (5). The specific expansion work is defined by Eq. (6), whereas the net specific work of the cycle is determined by Eq. (7). ...
Comprehensive optimization of a novel thermo-hydraulic machine for mechanical power generation
Article
Full-text available
  • Apr 2025
This paper is dedicated to the multi-aspect optimization of a novel thermo-hydraulic machine with liquid piston operating according to organic Rankine cycle, designed for mechanical power generation from low temperature reservoirs. This involves the implementation of thermodynamic and hydraulic analyses. Several issues have been identified in thermo-hydraulic machines built to date, particularly the limitation imposed by the location of the expansion phase under the equilibrium dome, which constrains maximum output work. This issue is addressed through the application of steam su-perheating followed by the organic Rankine cycle. The thermodynamic analysis showed that the R1233zd is the most suitable working fluid for the suggested novel machine within the temperature range of 65−130°C. The selection of the best working fluid was followed by the dimensioning of the hydraulic part of the machine under optimal operating condi-tions. A new parameter was introduced to link the gas and hydraulic sides of the machine. It is about the time scale of the cycle which influences significantly the mechanical output power. Furthermore, mathematical modelling of the hydraulic part of the machine concludes that high mechanical power output can only be achieved only in modes of operation with high thermal efficiencies. Conversely, operational modes with high second law efficiencies fail to deliver high mechanical power levels. These two conclusions can be regarded as equivalent to the various postulates of the second law of thermo-dynamics.
View
... However, geothermal energy ideal for base-load generation. The procedures used to harvest geothermal energy may be summed up as follows [88]. ...
... In this case, condensation is employed for cooling or reinjected into the reservoir [117,118]. The advantage of these power plant types is that they emit only steam and small quantities of gases, so they are less harmful to the surrounding environment [28,88]. ...
... A portion of the heated water boils into steam as it moves upward due to a drop-in pressure after being separated from the water, the steam powers the turbine. This is a sustainable resource, as any residual water and condensation vapour to returned to the storage reservoir [88,119]. ...
View
... The thermal energy found within the earth is referred to as geothermal energy which can be utilized for various human use and applications. This heat comes majorly from three sources; First is the radiogenic heat which is a result of the radioactive decay of long-living isotopes found within the crustal rocks in the earth, second is the heat from recent magmatic activities and third is the primordial heat coming deep from the earth crust resulting from the slow cooling of the crust since the formation of the earth [10]. ...
... Generally, GEPs consist of three main parts. The primary unit, secondary unit and the ground source heat pump [8,10]. Figure 1 shows the three components of a GEP. ...
... In the context of geothermal piles and soil, radiation is not a significant contributor to the heat flow mechanism. The temperature gradient between the piles and the ground is usually small, and the radiative heat transfer is generally negligible compared to conduction and convection [10]. Also, radiation contributes less than 1% of the overall heat flow in smaller grain soils. ...
Challenges of Geothermal Energy Pile Application for Tropical Climates
Article
  • Jan 2025
There has been a growing global interest in geothermal energy piles as a promising technology for sustainable heating and cooling of buildings in various climates. However, there seems to be limited adoption of this technology in tropical climates. Geothermal energy piles, through the utilization of piles as ground heat exchangers, provide a reliable and efficient geothermal energy extraction for the purpose of heating as well as cooling. However, in climates where cooling dominates, there is an imbalance in heat extraction and injection, with heat injection into the ground prevailing throughout the year. This imbalance results in a rise in soil temperature over time, which must be considered during the design phase. This paper seeks to highlight the obstacles associated with implementing geothermal energy piles in nations with tropical climates, such as Malaysia. Decrease in system efficiency over time arising from unbalanced energy demand, long payback period and lack of adequate incentives etc. have been identified as some of the leading obstacles among others.
View
... The term "geothermal" is derived from the Greek words "geo," meaning earth, and "thermos," meaning heat (Igwe, 2021). Geothermal energy is sourced from various outlets, including the Earth's crust, radioactive decay, volcanic activity, and solar energy absorption at the Earth's surface (Aliyu &. ...
... The geothermal energy sector exhibits a high load factor due to its well-established and mature nature. According to Igwe (2021), the installed capacity of this energy source results in an annual electricity generation that surpasses that of wind and solar power. Ziagos et al. (2013) identified several crucial criteria for optimizing and commercializing EGS. ...
View
... Extensive research has been conducted over the past years to develop sustainable and renewable energy such as solar energy (Maka and Alabid, 2022), tidal energy (Masood Ahmad, Kumar and Ranjan, 2022), geothermal (Igwe, 2021), biofuels (Ali Abbas and M. Flayeh, 2019;Abd and Al-Yaqoobi, 2023;Abd, Alyaqoobi and Abdul-Majeed, 2024), etc. Biodiesel is widely used as an alternative to fossil fuels to enhance combustion efficiency and reduce the release of automobile oxides and sulphur. Biodiesel is extracted from renewable sources and is directly biodegradable (Sahu et al., 2023). ...
Production of biodiesel by using CaO nano-catalyst synthesis from mango leaves extraction
Article
Full-text available
  • Sep 2024
Development and population expansion have the lion's share of driving up the fuel cost. Biodiesel has considerable attention as a renewable, ecologically friendly and alternative fuel source. In this study, CaO nanocatalyst is produced from mango leaves as a catalysis for the transesterification of waste cooking oil (WCO) to biodiesel. The mango tree is a perennial plant, and its fruit holds significant economic worth due to its abundance of vitamins and minerals. This plant has a wide geographical range and its leaves can be utilized without any negative impact on its growth and yield. An analysis was conducted to determine the calcium content in the fallen leaves, revealing a significant quantity of calcium that holds potential for utilization. The catalyst was characterized by different analytic techniques such as XRD, SEM-EDS, FT-IR, and BET analyses. Several parameters impacted on the transesterification process were exploited by conventional transesterification (batch). The result revealed that the optimum reaction was reached at a methanol to oil ratio of 50% w/w, catalyst loading of 3%, temperature of 65℃ and reaction time of 1.5 h with a yield of 93.21%, and the activation energy of the transesterification reaction was found to be 38.906 KJ mol-1. The reaction was verified to be irreversible pseudo-first order based on a linear Arrhenius plot and a high R2 value. The catalyst shows good stability and catalytic activity when it is reused and the yield was found to be 80.293% in the 5th cycle.
View
... They entail the creation of engineered geothermal systems (EGS) by drilling into hot rock formations and stimulating the rock to develop a network of linked cracks. This system operates by pumping fluids into a reservoir, where they are heated by the adjacent rocks, and then removing the fluids at the surface to harness energy or get direct heat (Fleckenstein et al., 2022;Fleckenstein et al., 2021;Igwe, 2021;Xia et al., 2017). ...
Unraveling Damage Variables in Hot Dry Rocks: An Optical Investigation of Geothermal Rocks from UTAH FORGE
Conference Paper
Full-text available
  • Sep 2024
Geothermal resources are worldwide renowned for their sustainable and clean attributes. The US Department of Energy (DOE) estimates that harnessing only 0.1% of Earth's geothermal energy could support mankind for two million years. Enhanced geothermal systems (EGS) are highly acclaimed for their ability to extract heat from hot, dry rock. However, issues remain in assuring safe drilling and proper fracturing owing to a lack of knowledge of damage factors and fracture sequences, both of which are crucial for regulating crack propagation. Conventional laboratory approaches often fail to capture the nuanced variation seen in HDR. To address this, the present work uses a three-dimensional optical approach called digital image correlation (3D-DIC) to investigate damage factors in HDR. HDR samples from the DOE UTAH FORGE project's Well 16B (78)-32 are subjected to uniaxial (D 1.5", L 2") and diametrical (D 1.5", L 1") compression using a 100kN precision electro-mechanical load Instron frame at a constant displacement rate of 0.05mm/min. During the uniaxial and diametrical compression studies, a Trilion 3D-DIC image capturing system was used to monitor the samples at a rate of 10 frames per second in a non-contact manner. To monitor deformation during loading, a black-in-white speckle pattern is placed on the specimen. The GOM 3D-DIC system is used to process images, visualize data, and analyze HDR damage variables under various load circumstances. The findings showed that DIC-generated quantitative full-field strain preliminary maps (tension, compression, and shear) include all sequences involved in the damage process as well as discrete strain localization zones (SLZ). Damage factors are quantified using DIC maps to assess sample damage; the tension-compression ratio ranges between 2% and 8%. The damage evolution process of HDR specimens is divided into four phases that are assessed using damage variables: initial damage stage, linear elastic, elastic-plastic, and plastic damage stage. The damage variable regulates the deterioration of the material's stiffness, resulting in a nonlinear relationship between stress and strain. The damage to the SLZ demonstrates that it is bigger than the entire. The damage was at 65% in the yield stage and 35% in the first two stages. The 3D-DIC findings showed that the sample failed when the overall damage variable reached 0.25-0.35, and the damage in the SLZ region reached 0.8-near unity. The damage variable in HDR, which indicates fracture progression, is a unique characteristic in geothermal systems. These results have a substantial impact on our capacity to forecast the damage process in EGS. DIC outperforms CT, SEM, and AE methods in test range, cost-effectiveness, accuracy, and full-field monitoring. It improves our knowledge of damage factors in anisotropic and heterogeneous HDR, increases fracturing efficiency, and improves heat extraction from EGS.
View
... The geothermal fluid used for power generation has a temperature of more than 225˚C [13]. The properties of geothermal fluids are influenced by their natural characteristics, such as the presence of non-condensation gases, which cause scale formation and corrosion in pipes. ...
View
Renewable Energy, Alternative Fuels, and Technological Innovations for Sustainable Development
Chapter
  • Feb 2025
The conventional sources of energy are depleting continuously with increasing the world population. Industrialization during the modern times results in an increment in energy demand. By substituting fossil fuels with green fuels, we can preserve more energy and improve the environment. There are various replacements for fossil fuels in order to fulfill energy requirements without harming nature: Biodiesel, Biobutanol, Bioethanol, Biohydrogen, Biogas, and Biochar. The employing of renewable energy technology is very suitable and sustainable. Various renewable substrates such as industrial waste, agricultural residue, municipal waste, dairy waste, etc. are present in abounded, and there is a requirement for waste management. Hence these waste streams could be utilized for energy production. Depending on substrate availability and the type of fuel, it is needed for different conversion technologies for biofuel production. Major techniques that are being used nowadays for the purpose of obtaining biofuels include hydrolysis, fermentation, saccharification, pyrolysis, gasification, torrefaction, transesterification, anaerobic digestion, etc. With the goal of handling global energy issues, scientific research and development have recently concentrated on developing new technologies. Hence, this chapter addresses the requirement of biofuels, renewable resource, technologies involved, and sustainable development of on green and circular economy.
View
Bifurcations and Stability of Phase Transition Fronts in Geothermal Reservoirs
Article
  • Nov 2024
The stability of a layer of water above a layer of vapor, separated by a boiling or condensation surface, in a geothermal reservoir is considered. In an unperturbed state in low-permeability rocks, there is one interface, which can be either a water boiling surface or a vapor condensation surface. At relatively large permeability values, two new solutions can be formed, corresponding to other positions of the interface. The conditions for the existence and merging of stationary solutions depending on the parameters of the physical system are studied numerically. The stability of stationary positions of interfaces was studied using the normal mode method. It was found that the transition to instability precedes bifurcations of solutions and can occur both at finite and infinite wave numbers.
View
Power supply characterization of baseload and flexible enhanced geothermal systems
Article
Full-text available
  • Jul 2024
We investigated the techno-economic feasibility and power supply potential of enhanced geothermal systems (EGS) across the contiguous United States using a new subsurface temperature model and detailed simulations of EGS project life cycle. Under business-as-usual scenarios and across depths of 1–7 kilometers, we estimated 82,945 GW and 0.65 GW of EGS supply capacity with lower levelized cost of electricity than conventional hydrothermal and solar photovoltaic projects, respectively. Considering the scenario of flexible geothermal dispatch via wellhead throttling and power plant bypass, these estimates climbed up to 184,112 GW and 44.66 GW, respectively. The majority of EGS supply potential was found in the Western and Southwestern regions of the United States, where California, Oregon, Nevada, Montana, and Texas had the greatest EGS capacity potential. With advanced drilling rates based on state-of-the-art implementations of recent EGS projects, we estimated an average improvement of 25.1% in the levelized cost of electricity. These findings underscored the pivotal role of flexible operations in enhancing the competitiveness and scalability of EGS as a dispatchable renewable energy source.
View
The possible role and contribution of geothermal energy to the mitigation of climate change
Article
Full-text available
  • Jan 2008
Electricity is produced by geothermal in 24 countries, five of which obtain 15-22% of their national electricity production from geothermal energy. Direct application of geothermal energy (for heating, bathing etc.) has been reported by 72 countries. By the end of 2004, the worldwide use of geothermal energy was 57 TWh/yr of electricity and 76 TWh/yr for direct use. Ten developing countries are among the top fifteen countries in geothermal electricity production. Six developing countries are among the top fifteen countries reporting direct use. China is at the top of the latter list. It is considered possible to increase the installed world geothermal electricity capacity from the current 10 GW to 70 GW with present technology, and to 140 GW with enhanced technology. Enhanced Geothermal Systems, which are still at the experimental level, have enormous potential for primary energy recovery using new heat- exploitation technology to extract and utilise the Earth's stored thermal energy. Present investment cost in geothermal power stations is 2-4.5 million euro/MWe, and the generation cost 40-100 euro/MWh. Direct use of geothermal energy for heating is also commercially competitive with conventional energy sources. Scenarios for future development show only a moderate increase in traditional direct use applications of geothermal resources, but an exponential increase is foreseen in the heat pump sector, as geothermal heat pumps can be used for heating and/or cooling in most parts of the world. CO2 emission from geothermal power plants in high-temperature fields is about 120 g/kWh (weighted average of 85% of the world power plant capacity). Geothermal heat pumps driven by fossil fuelled electricity reduce the CO2 emission by at least 50% compared with fossil fuel fired boilers. If the electricity that drives the geothermal heat pump is produced from a renewable energy source like hydropower or geothermal energy the emission savings are up to 100%. The total CO2 emission reduction potential of geothermal heat pumps has been estimated to be 1.2 billion tonnes per year or about 6% of the global emission. The CO2 emission from low-temperature geothermal water is negligible or in the order of 0-1 g CO2/kWh depending on the carbonate content of the water. Geothermal energy is available day and night every day of the year and can thus serve as a supplement to energy sources which are only available intermittently. Renewable energy sources can contribute significantly more to the mitigation of climate change by cooperating than by competing. Likely case scenarios are presented in the paper for electricity production and direct use of geothermal energy, as well as the mitigation potential of geothermal resources 2005-2050. These forecasts need to be elaborated on further during the preparation of the IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation.
View
Partial radiogenic heat model for Earth revealed by geoneutrino measurements
Article
Full-text available
The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet’s interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2±1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute TW to Earth’s heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth’s total heat flux. We therefore conclude that Earth’s primordial heat supply has not yet been exhausted.
View
Core–mantle boundary heat flow
Article
Full-text available
  • Jan 2008
The Earth can be viewed as a massive heat engine, with various energy sources and sinks. Insights into its evolution can be obtained by quantifying the various energy contributions in the context of the overall energy budget. Over the past decade, estimates of the heat flow across the core-mantle boundary, or across a chemical boundary layer above it, have generally increased by a factor of 2 to 3. The current total heat flow at the Earth's surface - 46 +/- 3 terawatts (1012 J s-1) - involves contributions from heat entering the mantle from the core, as well as mantle cooling, radiogenic heating of the mantle from the decay of radioactive elements, and various minor processes such as tidal deformation, chemical segregation and thermal contraction gravitational heating. The increased estimates of deep-mantle heat flow indicate a more prominent role for thermal plumes in mantle dynamics, more extensive partial melting of the lowermost mantle in the past, and a more rapidly growing and younger inner core and/or presence of significant radiogenic material in the outer core or lowermost mantle as compared with previous estimates.
View
Geoneutrinos and the radioactive power of the Earth
Article
  • Sep 2012
Chemical and physical Earth models agree little as to the radioactive power of the planet. Each predicts a range of radioactive powers, overlapping slightly with the other at about 24 TW, and together spanning 14-46 TW. Approximately 20% of this radioactive power (3-8 TW) escapes to space in the form of geoneutrinos. The remaining 11-38 TW heats the planet with significant geodynamical consequences, appearing as the radiogenic component of the 43-49 TW surface heat flow. The nonradiogenic component of the surface heat flow (5-38 TW) is presumably primordial, a legacy of the formation and early evolution of the planet. A constraining measurement of radiogenic heating provides insights to the thermal history of the Earth and potentially discriminates chemical and physical Earth models. Radiogenic heating in the planet primarily springs from unstable nuclides of uranium, thorium, and potassium. The paths to their stable daughter nuclides include nuclear beta decays, producing geoneutrinos. Large subsurface detectors efficiently record the energy but not the direction of the infrequent interactions of the highest-energy geoneutrinos, originating only from uranium and thorium. The measured energy spectrum of the interactions estimates the relative amounts of these heat-producing elements, while the intensity estimates planetary radiogenic power. Recent geoneutrino observations in Japan and Italy find consistent values of radiogenic heating. The combined result mildly excludes the lowest model values of radiogenic heating and, assuming whole mantle convection, identifies primordial heat loss. Future observations have the potential to measure radiogenic heating with better precision, further constraining geological models and the thermal evolution of the Earth. This review presents the science and status of geoneutrino observations and the prospects for measuring the radioactive power of the planet.
View
View
Geothermal Energy. Institute of Geosciences and Earth Resources -Pisa, Italy. EPJ Web of Conferences 148
  • Jan 2017
  • 12
  • A Manzella
Manzella A. (2017). Geothermal Energy. Institute of Geosciences and Earth Resources -Pisa, Italy. EPJ Web of Conferences 148, 00012.