Geothermal Energy

What is Geothermal Energy?

Geothermal energy is heat energy originating deep in the earth’s molten interior. It is this heat energy that is responsible for tectonic plates, volcanoes and earthquakes. The origin of this heat is from primordial heat (heat generated during the Earth's formation) and heat generated from the decay of radioactive isotopes. The temperature in the earth’s interior is as high as 7000°C, decreasing to 650 - 1200°C at depths of 80 km -100 km (Wright, 1998). Through the deep circulation of groundwater and the intrusion of molten magma into the earth’s crust, to depths of only 1 km-5 km, heat is brought closer to the earth’s surface. The hot molten rock heats the surrounding groundwater, which is forced to the surface in certain areas in the form of hot steam or water (e.g. hot springs and geysers). The heat energy close to, or at the earth’s surface can be utilised as a source of energy, namely geothermal energy.

Figure 1 A lava fountain is an example of the amount of heat stored in the Earth

The total geothermal resource is vast. An estimated 100 PWh (1 x 10¹⁷ W) of heat energy is brought to the earth’s surface each year (World Energy Council 1994). However, geothermal energy can only be utilised in regions where it is suitably concentrated. These regions correspond to areas of earthquake and volcanic activity, which occur at the junctions of the tectonic plates that make up the earth’s crust. It is at these junctions that heat energy is conducted most rapidly from the earth’s interior to the surface, often manifesting itself as hot springs or geysers.

Low-grade geothermal resources are more abundant and widespread. They are located in deep sedimentary basins around the world (e.g. along the Gulf Coast of the United States and in Central and Southern Europe), as well as on the edges of tectonic plates. Western Australia’s Coral Bay sits on top of a very low-grade source, which is nonetheless used (among other things) as a source of water for bathing in tourist centres.

The Need for Geothermal Power in a Sustainable Energy system

With the concern over anthropogenic climate change (i.e. man-made climate change), there is a growing awareness that we must utilise energy resources that are sustainable. Geothermal power is one such sustainable resource that has the potential to supplement our energy systems and to displace many conventional fuels such as coal. This is due to the inherent stability of the resource. In contrast to many renewable technologies, such as wind or solar, the geothermal resource can be used 24 hours a day, 7 days a week.

Geothermal Resources

There is currently an estimated 15,000 MW of direct use and over 8,000 MW of generating capacity in geothermal resources worldwide. To put geothermal generation into perspective, this generating capacity is about 0.4% of the world total installed generating capacity. In 2003 there was 8,402 MW of installed geothermal electricity generation capacity worldwide. This total is stabilising after a growth period due to the over exploitation of the Californian fields in the United States which is decreasing output, with investments from other countries making up for this deficit. The US is the largest producer of geothermal electricity, followed by the Philippines, Mexico, Indonesia, Italy, Japan and New Zealand (International Geothermal Association, 2007).

Based on data from over 3,500 boreholes, conservative estimates of the Australian geothermal resource suggest the energy available for electricity generation is 23 million petajoules, or 7,500 years of Australian energy consumption at the current level. Over 80% of this resource is located in the Eromanga (Great Artesian) Basin. About 11% of this energy resource (2.5 million petajoules), or more than 800 times the current annual demand for electricity in Australia, is thought to be in granite rock, which is the most favoured host rock for heat extraction in what is known as Hot Dry Rock (HDR) (Australian National University, 2003).

There are four types of geothermal resources: hydrothermal, geopressured, hot dry rock and magma. Of the four types, only hydrothermal resources are currently commercially exploited.

Hydrothermal
Hydrothermal (or hot water) resources arise when hot water and/or steam is formed in fractured or porous rock at shallow to moderate depths (100 m to 4.5 km) as a result of either the intrusion in the earth’s crust of molten magma from the earth’s interior, or the deep circulation of water through a fault or fracture (World Energy Council 1994) (see Figure 2). High temperature hydrothermal resources (with temperatures from 180°C to over 350°C) are usually heated by hot molten rock. Low temperature resources (with temperatures from 100°C to 180°C) can be produced by either process (Wright, 1998).

Figure 2 Hydrothermal plant in New Zealand.

Hydrothermal resources come in the form of either steam or hot water depending on the temperatures and pressures involved. High-grade resources are usually used for electricity generation, while low grade resources are used in direct heating applications.

Figure 3 Simplified cross section of the essential characteristics of a geothermal site (Image adapted from Boyle, 1998).

Hydrothermal resources require three basic components (see Figure 3) a heat source (e.g. crystallised magma), an aquifer containing accessible water, and an impermeable cap rock to seal the aquifer. The geothermal energy is usually tapped by drilling into the aquifer, and extracting the hot water or steam.

In Australia there is a large hydrothermal potential in the Great Artesian Basin from central South Australia through most of western Queensland to the Gulf of Carpentaria (see Figure 4).

Figure 4 Hydrothermal resources in Australia (courtesy of the SA Dept. of Transport, Energy and Infrastructure).

Geopressured
Geopressured geothermal resources consist of a hot brine, saturated with methane, found in large, deep aquifers under high pressure. The water and methane is trapped in sedimentary formations at a depth of about 3 km - 6 km (World Energy Council 1994). The temperature of the water is in the range of 90°C - 200°C. Three forms of energy can be obtained from geopressured resources: thermal energy, hydraulic energy from the high pressure, and chemical energy from burning the dissolved methane gas. The major region of geopressured reservoirs discovered to date is in the northern Gulf of Mexico.

Hot Fractured Rock

Hot dry rock (HFR, or sometimes called Hot Dry Rock -HDR) is a heated geological formation formed in the same way as hydrothermal resources, but containing no water, as the aquifers or fractures required to conduct water to the surface are not present (see Figure 5). This resource is virtually limitless and is more widely accessible than hydrothermal resources.

Figure 5 Hot Fractured Rock Technology (Image courtesy of the Hot Rock Energy program, Australian National University).

The geological profile of Australia is such that there is a large potential for HFR technologies to be used for energy production in the eastern states of Australia. Figure 6 is a false colour map of Australia, showing the temperature of Earth's crust at a depth of 5 km.

Figure 6 The potential for HFR technologies in Australia are closely related to the temperature of Earth (courtesy of the Hot Rock Energy program, Australian National University

There may be locations in the northern Perth Basin that might have a high enough temperature gradient for HFR applications. The potential resource of the region is estimated to be 49 EJ, which may be sufficient to supply the electricity requirements of the South West Integrated System (SWIS) for in excess of 100 years. The estimated break-even price for electricity from an HFR project proposed by Geodynamics Limited for the Cooper Basin was 6.2 c/kWh initially, at demonstration plant stage, falling to around 4.0 c/kWh at full-scale production. These figures are yet to be demonstrated, but there seems to be increasing reasons to consider further investment in HFR opportunities within Western Australia. (ERDC, 1994).

Magma
Magma, the largest geothermal resource, is molten rock found at depths of 3km -10km and deeper, and therefore not easily accessible. It has a temperature that ranges from 700°C - 1,200°C. The magma resource has not been well explored to date.

The Future for Geothermal Energy

In the short term, it is likely that hydrothermal resources will remain the only geothermal resource that is commercially viable. However this resource alone represents an immense source of energy. It is estimated that 80 GW of geothermal electricity could be generated in the short to medium term from known hydrothermal resources worldwide (Wright, 1998).

In the medium to longer term, technological developments will see the utilisation of the geothermal energy in hot dry rocks and geopressured reservoirs. Usable geothermal resources will no longer be limited to the shallow hydrothermal reservoirs. These resources represent a virtually limitless source of energy, and are the future of sustainable geothermal energy.

Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Demonstration & System Design - Renewable energy applications, systems designs and case studies.

Geothermal Technology - RISE Information Portal

Geothermal Education Office

US DOE Office of Geothermal Technologies

CADDET Geothermal Register

Chevron Thermal Energy

Hot Dry Rock research at UNSW (pdf)

Hot Dry Rock research at ANU

International Geothermal Association

References

Australian National University, 2003. “Hot Rock Energy Website” (Online) http://hotrock.anu.edu.au/resource.htm (Accessed 16 February 2007).

Burns, K.L., Weber, C., Perry, J. and H. J Harrington, (2000). “Status of the Geothermal Industry in Australia.” (Online), http://iga.igg.cnr.it/pdf/WGC/2000/R0559.PDF (Accessed 21 July 2008).

Energy Research and Development Corporation (ERDC), 1994."Hot Rock Feasibility Study, Report 243", The Australian Commonwealth Government, Canberra.

International Geothermal Association, 2007. Website (Online) http://iga.igg.cnr.it/index.php (Accessed 21 July 2008).

World Energy Council, 1994. New renewable energy resources, Kogan Page, London.

Wright, P.M., 1998. "The earth gives up its heat", Renewable Energy World, vol.1, no.3, pp.21-25.

Geothermal Energy in Afghanistan:
Prospects and Potential

SABA et al 1feb04

Saba, D. S.¹, Najaf, M. E.², Musazai, A. M.2, and Taraki, S. A.³

1 Consultant, 12201 Mara Lynn Road, #8307, LR, AR 72211, USA. daudsaba@yahoo.com
2 Department of Geology and Exploration of Mineral Resources Faculty of Geology and Mines, Kabul Polytechnic Institute, Afghanistan.
3 Faculty of Economics, Herat University, Herat, Afghanistan.

Prepared For:
Center on International Cooperation, New York University, New York, USA. &
Afghanistan Center for Policy and Development Studies, Kabul, Afghanistan.

February 2004

ABSTRACT

Historically, geothermal energy in Afghanistan has been only used for medical bathing. This application is still one of important utilization of geothermal energy in Afghanistan. Initial exploration efforts for mineral and thermal water resources of Afghanistan began in 1969. However, geological studies, geophysical exploration and drilling programs have not been carried out for characterization of reservoirs and capacity of the country's geothermal prospects. This study is a framework to facilitate such studies.

The structure of Afghanistan is created by the collision of the Indian and Eurasian plates along the Herat-Panjshir E-W striking geosuture, resulting in the uplifting of the Hindu Kush on this axis since the end of the Cretaceous, some 65 million years ago. Neotectonic movements in Afghanistan generated by these collisional events are characterized by seismic and geothermal activities all over the country. Upon this geological condition, many geothermally active areas are currently known with surface manifestations in the form of hot springs, which demonstrate the wide perspective of development and utilization of geothermal prospects in this country.

Further geological, geochemical, and geophysical exploration is required to characterize the reservoirs of numerous geothermal prospects in Afghanistan for possible electric power generation and other technologically advanced uses of this renewable energy resource. Use of geothermal energy in Afghanistan is realistic. However, it is suggested that at this stage, direct use of geothermal energy is the most feasible way to put this abundant renewable energy resource into use. In this framework, there is tremendous potential for applications such as in the food processing, fruit drying, carpet and wool processing, chemical industry, greenhouse industry, fish hatchery and farming, refrigeration, and many other small-scale local industries.

Foreword

Afghanistan is an energy-deprived country. Anecdotal evidence suggests that per capita energy use in this country is substantially lower by international standards. As the reconstruction process advances further, the demand for energy will increase. As the World Energy Commission puts it, energy affects all aspects of modern life and human development (WEC, 1993). For Afghans to successfully rebuild their country, new initiatives has to be undertaken to satisfy the increasing energy needs of the country. In this circumstance, there is urgent need to deploy sustainable and environmentally clean energy sources, such as geothermal energy, which is abundantly available in Afghanistan.

On a worldwide scale, geothermal energy already makes an important contribution. More than 50% of installed electric power capacity from "new" renewables such as geothermal, wind, tidal, and solar is realized in geothermal power plants. In recent years, significant advances have been achieved with engineered geothermal systems. Innovative power plants permit the production of electricity using low thermal water temperatures of the order of 100 °C. A major advantage of geothermal energy among other renewables is the availability of the resource all day, all year round.

Today, many countries stand out as having made utilization of geothermal resources a national priority. For example, in Tibet, which is very similar in its culture, geography and geological structure to Afghanistan, until 1997, the annual power generation only from Yangbajing power plant was at 110 GWh/yr, which accounts for 41% of total power in the Lhasa in the summers, and up to 52% during the winter times. The development of other potential reservoirs in Tibet is growing at a very fast pace (Du Shaoping, 2000). Approximately 26 percent of electrical power generation in the Philippines, which is another developing country, though very different from Afghanistan, comes from geothermal steam. Afghanistan like many other countries possesses underutilized geothermal resources. The examples of developed geothermal resources in different industrial and developing countries could be replicated, as the World Geothermal Congress declared, if there was the will to do so (WGC, 2000).

1. Introduction

As Afghanistan continues the process of reconstruction, the national demand for commercial energy services is expected to grow, especially with respect to the majority of population of the country without access to modern energy services. The current electric power capacity in Afghanistan based on available data could be estimated to be somewhere in the range of 400 MW (megawatt of energy). Hydroelectric dams, most notably at Kajaki, accounts for 260 megawatts, which represents only about 5 percent of the total hydroelectric potential of the country. Thermal plants, fired by oil and coal, provide another 134 megawatts of this capacity (Nyrop and Seekins, 1986). By completion of the Turkmenistan and Iranian transmission lines to western Afghanistan during the 2004, another 80 MW of electrical power would be added to the present capacity. At the same time, anecdotal evidence suggests serious power shortages all over the country. In Kabul, for example, there are frequent blackouts, and in the city's poorer neighborhoods, homes averaged to have only fifteen to twenty hours of power per week. This is at a time that few industries are functioning.

But the status quo is changing. We know that in the United States, a megawatt of electrical power provides 700 typical Americans with their power needs. Of course, this is not a realistic and appropriate level to be adopted as a target for Afghanistan, but, if we assume the level of power consumption by developing countries such as Turkey, Mexico, or Egypt, which is ten times lower than that of the United States (IEA, 1998), as an optimal hypothetical target for Afghanistan, then the country requires at least 3.5 GW (gigawatt of energy) of electrical power, based on the number of the population that has been estimated to be [24,377,530] persons (CSO, 2003). It is obvious that the power capacity and demand gap in Afghanistan is a very wide one. Meeting this growing demand for energy, while at the same time, addressing the adverse environmental effects of using non-renewable fossil fuels, will necessitates an increase in the use of reliable and diversified renewable energy sources, preferably indigenous, be it hydroelectric, geothermal, biomass, solar or wind.

There is a tremendous amount of heat energy locked inside the planet earth in magma, and dry hot rocks, sometimes, as shallow as a mile or two below the surface. In a sense, the earth's interior can be thought of as a natural nuclear power reactor, because, the heat is mainly derived by the decay of radioactive elements. Under normal conditions, the earth's natural heat increases by as much as (10-38º C) with every mile of depth. This heat flow towards the earth's surface is an indication of the colossal amounts of heat energy at the earth's interior. There are times when some of this comes to the surface in the form of lava, steam, or hot water. This is geothermal energy — "geo" meaning earth, and "thermal" meaning heat. Thus, the earth is a reliable source of energy with its potential available at any time.

Presently some sixty countries around the world are either plugging into the earth, tapping its heat, and drawing some of it off in the forms of steam and hot water to run geothermal power plants and produce electricity, or are in the process of developing their geothermal resources. Other countries use this source for residential and district heating systems, heating greenhouses for growing vegetables, fruits, and flowers, or simply use it for balneological applications. It is suggested that wherever geothermal energy is used, in the long run, it turns out to be cheaper than oil or coal, natural gas or nuclear power (Goldin, 1981; WEA, 2000).

For today's energy starved Afghanistan, there is plenty of this renewable energy resource available to be exploited. Geothermal energy is the earth's interior heat made available to man by extracting it from natural hot water or underground rocks by appropriate technology, which is readily accessible. High-temperature geothermal resources suitable for power generation are generally located in areas subjected to volcanic or seismic activity. Afghanistan is located in such an area, where geothermal resources can make a worthwhile contribution to providing a reliable, renewable energy service for the country.

In Afghanistan, active geothermal systems are generally located in the main axis areas of the Hindu Kush, which runs along the Herat fault system, all the way from Herat in the westernmost part of the country, up to the Wakhan corridor in the Afghan Pamirs. This structure marks the compressed boundary of the Eurasian plate and the Gondwanan fragments that have collided onto this boundary in the territory of Afghanistan prior to the final collision of the Indian plate onto Asia. Geothermal systems of Afghanistan are mainly associated with the fault and fracture networks, seismic activity and young magmatism encountered at this boundary and its associated branching fault systems.

Prospects of low to medium temperature geothermal resources are widespread all over Afghanistan. There is tremendous potential for direct-use applications of these resources, such as in the food processing, fruit drying, refrigeration, fish hatchery and farming, carpet and wool processing, recreation and tourism, and many other possible small-scale local industries. Directly using geothermal energy in district heating and commercial operations is much less expensive than using traditional fuels. From the environmental perspectives, geothermal energy is also very clean, producing only a small percentage of the air pollutants emitted by burning fossil fuels.

In the light of such an understanding, geothermal energy is a highly valuable, clean and reliable heat and power source in Afghanistan, still untapped. Through this study, an effort has been made to assess and evaluate the potential of this resource for the development of Afghanistan's energy sector, as well as tourist and food processing industries. Though many indications of geothermal energy in the form of visible heat leakage in Afghanistan are known, but their significance in the energy policy of Afghanistan is never been appreciated, and to date totally ignored. The authors of this study hope to shed light on this forgotten resource of the country and facilitate the development of geothermal resources of Afghanistan.

2. Historical Background

Worldwide, geothermal energy for electricity generation and direct use has been commercially utilized since 1913. Globally, use of geothermal energy amounts to 49 TWh/y (terawatt hour per year of energy) of electricity and 53 TWh/y for direct use. Electricity is produced with geothermal steam in 21 countries. Of these, five countries obtain 10-22% of their electricity from geothermal energy (Fridleifsson, 2000). However, so far, only a small fraction of the global geothermal potential is developed.

The use of geothermal resources in Afghanistan might have begun with the settlement of the first people in the vicinity of the many hot springs in the valleys of Hindu Kush, where these springs, served as a source of warmth, and cleansing, and their mineral water as a source of healing. In this way, probably, long time ago, these people learned to use the healing properties of the hot water that came naturally out of the ground to make their life easier. Through experience, they might have discovered that a good soak in those hot springs cured certain ailments, e.g., stiff muscles and sore backs became limbed, skin diseases cleared up, and wounds healed. For this particular reason, many of these hot springs in Afghanistan are called "chashma-e shafa", meaning the healing spring, a property that deemed them sacred. Thus, the communities all over the country rightfully consider the protection of these springs as their duty (Figure 1).

Figure 1. A satisfied young Afghan enjoys the traditional use of this known "shefa" hot spring that healed his skin condition (Aabe-Garm, Ghorband valley, province of Parwan, Afghanistan).

It is found that traditionally people are knowledgeable that drinking the water which comes from springs with carbonic acid are good for stomach troubles, bathing in sulfur-bearing springs improves their blood circulation, alum springs are helping in healing their skin problems, springs with rare earth elements (REE) contents relieve or even cure certain forms of arthritis, and strong acid springs are good for venereal diseases. During fieldwork in Obe hot springs, the authors met a family from Badghis province, who have traveled hundreds of kilometers along the torturous dirt roads of northwestern Afghanistan to come to this remote valley, just to tap into the healing properties of their known healing hot spring.

Modern use of mineral thermal springs in Afghanistan goes back to 1940s, when few thermal springs in Herat (Obe and Safed Koh), Balkh (Aabe Garm), and Orezgan were developed for therapeutic purposes. However, soon these developments were abandoned. In 1974, the Obe springs in Herat were renovated for bathhouse usage (Akhi, 2001). Probably, at the same times, single bathrooms were built on hot springs along the Kabul-Mazare Sharif highway in Pole-khumri and Hairatan towns. The rest of the hot springs of Afghanistan are left undeveloped to date, but the people continue to use them in their traditional ways (Figure 1).

The potential of modern exploitation of geothermal resources of Afghanistan has not been studied. In 1964, an attempt has been made by Soviet geologists working with the Geological Survey of Afghanistan (GSA) to conduct systematic studies on thermal waters of the country for their potential mineral contents to be used as exploration tools in search of minerals. In this way, the carbonated hot springs in the valleys of Kalu, Ghorband, Shina, Dara-e Soof, and Istalef were explored.

These exploratory studies had culminated with a survey of mineral and thermal waters of Afghanistan during 1969-1970 (Belianin, et al., 1970). However, these works were mainly focused on mineral contents and geological conditions of the mineral water systems. No attempts have been made to characterize the dynamics of geothermal systems of the Hindu Kush, or assess their energy reserves. Thus, the potential of geothermal energy associated with these springs were totally ignored and not been included in the exploration activities of GSA or any other institution. This work is an attempt to kick-start efforts to fill this gap and provide a framework for development of a geothermal databank for Afghanistan.

3. Geothermal Potential in the Structural Domain of the Hindu Kush in Afghanistan

3.1. Geological Structure:

In the earth, a certain amount of heat is generated by friction, as well as by other sources, at the boundaries of the crustal plates. The structure of Afghanistan is the result of accretion of such colliding Gondwanan microplates or fragments onto the margins of Eurasia (Tapponnier, et al., 1981) along the Herat-Panjshir E-W striking geosuture, which is a deep seated strike-slip fault, dipping as deep as up to 700 kilometer into the mantle. This major structural fault and fracture system in Afghanistan facilitates the percolation of water into the superheated zones in the crust to produce geothermal fluids.

Similar structures along the Chaman-Moqor NE-SW striking fault system, the Sarobi-Altimore NE-SW arcuate fault system, and other secondary faults throughout Afghanistan cover most of the regions of this country (Figure 2), where hot springs are the surface indication of geothermal energy resources associated with them.

Neotectonic movements in Afghanistan generated by collisional events since the end of the Cretaceous some 65 million years ago, resulted in the uplifting of the Hindu Kush mountain ranges that extend from the north-easternmost corner of the country in Badakhshan province in a NE-SW-W direction up to the westernmost border of the country in Herat province, dividing the whole structure of Afghanistan into northern and southern structural components (Saba and Avasia, 1995a). Recent tectonic movements are characterized by seismic and geothermal activities all over the country. The dynamic characters of the resulting structures indicate north-south compression and east-west extension. In addition, neotectonic movements show strong vertical uplifting, total rising and differential tilting. Seismic activities in Afghanistan show a decreasing tendency from east to west, with the strongest seismic activity occurring in the northeaster Badakhshan province, where the most active structures of the country are located (Figure 2).

Although the collision processes in the territory of Afghanistan have been ended at the beginning of Palaeogene, approximately some 50 MY ago, based on scenario of the Indian plate's final closure to Eurasia (Beck, et al., 1995), but the geo-structural components of Afghanistan are still under enormous stress from the south, exerted upon them by the ongoing movement of the Indian plate northwards (Saba and Avasia, 1995b). This process produces enormous frictional seismic and heat energy in the crust of this region, particularly along the geosutures, faults and fracture zones.

Figure 2. Surface Indications of Geothermal Prospects of Afghanistan. (Map shows thermal waters with a surface T of more than 20ºC)

Geothermal activities are closely associated with active terrains, and therefore, the activity strength of a given hydrothermal system is directly proportional to the activity strength of its associated active terrain. Due to the collision of many Gondwanan microplates moving northwards onto the southern margin of Eurasian plate, the strongest Neotectonic movements and intensive associated hydrothermal activities are evidenced south of the Hindu Kush main axis or the Herat-Panjshir geosuture. Thus, major geothermal manifestations are located along the Herat-Panjshir geosuture and the Chaman-Moqor fault systems in central Afghanistan active terrain (Figure 3).

Geothermal manifestations in these areas are mostly marked in the fracture systems of active faults, within graben or halfgraben basins and linear faulted valleys or wide valleys of the southern structural component of Afghanistan.

Figure 3. Neotectonic activity in the Hindu Kush resulting in dramatic uplift and displacement of the crust, as viewed in this photo of the Bande-Azhdar, Bamiyan, in central Afghanistan.

3.2. Active Magmatism and Volcanic Terrains:

Almost, all geological formations, i.e., from Precambrian to Quaternary systems are contributing to the geological structure of Afghanistan. Generally, these formations are of marine sediments with carbonaceous and continental characters. Lesser amounts of submarine volcanic formations are also present. Continental volcanism of Palaeogene, Neogene and Quaternary periods are widespread in central, and southwestern Afghanistan (Shareq, et al., 1980), where more than 50 dormant volcanic cones together form a volcanic zone with two distinct belts, occupying a vast surface area in the deserts of these regions.

Geothermal fields of Afghanistan are basically associated with magmatic activity and collisional tectonic structures. A diverse array of magmatic intrusive formations occupy approximately 8 percent of the total surface area of the country (Musazai, 1994), which includes a variety of rocks with wide range of temporal affinities, from the Precambrian era to Quaternary period.

Among these, geothermal indicators are found to be only associated with the Palaeogene-Neogene magmatic formations that resulted from continental collisional processes of Gondwanan fragments and the Eurasian plate margin in the territory of Afghanistan. These are mainly distributed in the form of linear magmatic structures in northeastern, central, southwestern and western Afghanistan. In these geothermal fields, the energy source of geothermal activity is controlled by magma chambers, which are located in shallow and intermediate depths with various intrusion periods, depths and volumes.

An interesting observation in the field reveals that almost all thermal indicators in Afghanistan are located in close contacts with young granitic massifs, which are void of pegmatitic or aplitic vein formations. Thus, we could not find surface manifestation of thermal waters in eastern Afghanistan, despite extensive exposures of magmatic formations in this region. This implies that the permeability in these rocks is controlled by fractures, which are already sealed by pegmatite-aplite bearing mineralisations and the successive hydrothermal alteration minerals, reducing the overall permeability of reservoir rocks.

Laterally continuous permeability forming domes or ridges that is difficult to unequivocally relate to faults has also been reported in a number of geothermal fields that are related to intrusive margins, which are usually very permeable and form large and more easily predicted continuous targets (Bogie and Lawless, 2000). The prospect of geothermal energy is much higher in association with intrusive contacts of such magmatic terrains, which occupy the core of the Hindu Kush mountain system, extending from northeastern extensions of the ranges towards central, southern, and southwestern Afghanistan.

These include magmatic complexes such as the Wakhan with a surface area of 300 km², Baghe Aareq with a surface area of 2500 km², and Shiva, with multiple sub-complexes of up to 300 km² each, in the northeast; the Baraky, with multiple sub-complexes of up to 35 km² each, the Helmand, which has not been fully exposed on the surface, but exhibit multiple sub-complexes of up to 50 km², and the Arghandab complex with a surface exposure area of 15000 km² in central Afghanistan. Without exception, all of these complexes are of Palaeogene-Neogene ages, forming granitoid plutons in multiple temporal phases, exhibiting linear and extended structures with northeast-southwest strikes (Musazai, 1994).

The volcanic-subvolcanic complexes of the Nawor desert to the west of the city of Ghazni have dacite-andesitic compositions, forming volcanic cones with basal diameters of 100-500m, and sometimes up to 1.5 km. The conical subvolcanic carbonatite complex in Khan-Nashin to the left flank of the Helmand River, which is the most recent volcanic activity in Afghanistan (Quaternary), has a diameter of 7 km with a very shallow carbonatitic cover. Similarly, the Malek-Dukan carbonatite conical volcanic complex, located in the Rigestan desert on the foothills of the Chagai-e mountain range in the southwestern corner of Afghanistan, has a basal diameter of 3.6 km, with the carbonatitic cover thickness reaching 500-800m. All volcanic-subvolcanic complexes of Afghanistan, including those in the upstream of the Farahrud in the province of Farah, have young ages that extend from Late Neogene into the Quaternary period (Shareq, et al., 1980).

Some of these geothermal prospect fields may be void of adequate groundwater resources as a heat transport medium, but dry hot rock is also a source of geothermal energy. By definition, dry hot rocks are naturally heated unmelted crustal rocks, which lie beneath the surface in areas where the geothermal gradients are two to three times greater than normal. Dry hot rocks are absolutely certainly present in volcanic and active magmatic regions in shallow depths. The temperature in dry hot rocks hovers around 177ºC in shallower depths, while at a depth of many kilometers, the heat may increase to up to 760ºC (Tester, and Smith (1978/79). Since the rocks are bone dry, there is no medium to transport the heat energy to the surface. The process of artificially making a geothermal reservoir within hot buried rocks is difficult and expensive, but if successful, the potential is enormous. The technology to tap this resource is already in existence in developed countries, but it is yet to be developed into commercially viable means for tapping this resource.

In the view of the authors of this report, considering the recent volcanic activities in south-southwestern structural blocks in Afghanistan, the prospect of these volcanic regions for geothermal energy is very promising. Other prospects associated with the young magmatic complexes of Afghanistan, particularly in the vicinity of fault and fracture systems are as promising and interesting in regards to their potential geothermal energy reserves.

3.3. Geopressured Prospects in Northern Afghanistan:

These very high-pressured geothermal energy prospects are associated with the hydrocarbon-bearing strata of northern Afghanistan. Geopressured thermal zones are deposits of water trapped and buried under thousands of feet of rocks and clay. This kind of water is very old, perhaps a million year or more, which is under abnormally high pressure, and is hot, with temperatures at times as high as 296º C. In these zones, which generally lay some 3-8km below the surface, the heat is trapped and insulated by encircling layers of sand, clay, and shale. The Geopressured zones are a dual source of heat and methane at the same time (Holt, 1977). Indications of this type of prospects are recorded in the oil and gas fields of the Jozjan and Balkh provinces of northern Afghanistan (Kurenoe and Belianin, 1969)

4. Hydrogeochemistry of Thermal Waters in Afghanistan

4.1. Hydrogeochemical Characteristics:

By definition, geothermal reservoirs are naturally occurring hydrothermal convection systems. Natural fluids are usually complex chemical mixtures, thus, hydrothermal waters in Afghanistan, exhibit a wide range of compositions and concentrations of solutes that generally increases with the temperature of the associated geothermal systems.

There are a diversity of thermal water types in Afghanistan, i.e., bicarbonate, chloride, sulphate, and sodium-chloride, all produced by complex geological structures and the development of various metamorphic and metasomatic processes in different geological environments, resulting in a variety of geochemical and hydrogeological conditions. Many categories of thermal waters are distinguished in Afghanistan, such as carbon dioxide rich, which in some instances having viable amounts of REE contents, nitrogen-bearing, hydrogen sulfide-bearing, Fe-Al-bearing, and brine. All these categories of thermal waters are originating from three major hydro-geochemical environments: metamorphic, reducing, and oxidizing (Kurenoe and Belianin, 1969).

In the main geothermal axis of the Hindu Kush, CO₂ is the dominant gas phase constituent. Carbon dioxide and CO₂-nitrogen-bearing waters are mostly originating from metamorphic environments associated with granitoid complexes. In this case, they are mainly characterized with high surface temperatures (>37ºC), high pH levels (>7.5), and low solid mineral contents in the solution (1-2.5 gm/lit). Such geothermal systems are located in the areas of higher CO₂ flux, resulting from their peculiar geological structures that give origin to the geothermal reservoirs of these systems. As a matter of fact, a larger amount of natural CO₂ is produced at depth, mainly by thermo-metamorphism of marine carbonate rocks. This CO₂ is usually trapped in deep structures, saturates the deep aquifers and is discharged with hydrothermal activities at the surface in the form of carbonated thermal waters.

In 1968-69, a number of thermal springs with high CO₂ reactivity in the Kalu, Ghorband, Dara-e-Soof, and Istalif valleys have been surveyed by the GSA, and it was found that many of these are comparable with some therapeutically famous thermal waters of Russia, with many of them exhibiting high to moderate concentrations of REE elements (Kurenoe and Belianin, 1969), which are of extreme value in balneological applications.

Spatially, in some instances, nitrogen-bearing hydrothermal activities are also associated with the same structures that exhibit carbonated hydrothermal activities. Most of the times, these two types of waters coexist in single systems, thus creating a spatial transition in between their typology. Carbonated waters are a characteristic of the central portions of the main geothermal axis, and are closely related with deep-seated faults. As the distance from the main axis increases towards the peripheries, the nitrogen-bearing waters are becoming more typical of the hydrothermal activities, to the extent that at the peripheries of the main axis, the nitrogen gas becomes the dominant gas species.

Nitrogen-bearing waters that originate from reducing geochemical environments are basically associated with the contact zones of granitoid batholiths, having high surface temperatures (>37ºC), considerable water discharges (1-10 lit/sec), and high pH levels (>7.5). These kind of hydrothermal activities are normally rich in silicic acid (1-100 mg/liter). Their geochemistry is reflective of their host rocks, mainly those of granitoid affinity. They include chemical elements such as Mo, W, Sn, Be, Li, Ge, etc., in the solution as reported by GSA (Kurenoe and Belianin, 1969). Though having higher surface temperatures, nitrogen-bearing thermal waters are generally poor in their geochemical contents comparing to carbon dioxide-rich thermal waters, which are normally having higher amounts of Li, Rb, Cs, Ge, B, and Sr in their solutions.

The hydrogen-sulfide-bearing thermal waters are basically associated with reducing hydro-geochemical environments. These are mainly observed in association with hydrocarbon-bearing structures of northern Afghanistan, and probably would be found in similar strata in southeastern Afghanistan. Example of this type could be the "Chahe Gandzh" geopressured system in Sheberghan province, in which the surface temperature is recorded to be 51ºC.

Hydrogen-sulfide-bearing category of thermal water is also found in the areas of contacts with granitoid batholiths in central as well as northwestern Afghanistan, associated with oxidizing environments in the vicinity of the main geothermal axis of the Hindu Kush. Emission of hydrogen sulfide is a characteristic of such springs, which are also sometimes rich in silica, nitrogen and CO₂. In the Arghandab district of southwestern Afghanistan, thermal water springs in oxidation environments are characterized by their high discharge volumes, low pH levels, and richness in sulfides. Chemical elements such as Li, Ga, Ti, Cr, Se, Be, Ba, Pb, Zn, Ag, and As, are the defining geochemical elements in these waters, where sometimes they reach industrial proportions, e.g., the amount of Li up to 10 mg/liter in some of these springs is not unusual (Kurenoe and Belianin, 1969).

Oxidizing hydro-geochemical environment in Afghanistan also produces brine waters associated with Mesozoic and Cenozoic evaporites (a mixture of salt and anhydrate) strata of the country. Low temperature, iron-aluminum-bearing acidic springs are also produced in this environment. In this case, they are associated with the oxidation zones of the sulfide deposits, such as in the Aynak area, which exhibit a surface temperature of 18ºC.

4.2. Dynamics of Hydrothermal Activities in Afghanistan:

With respect to geothermal resources, energy transport within the earth's crust takes place by advection of magma, advection of geothermal fluids, and thermal conduction. Heat transport associated with the advection of magma and geothermal fluids is a relatively fast process, with time constants in the range of days or months. These are the processes that drive the high-temperature geothermal systems encountered in young volcanic and in seismic areas at the boundaries of tectonic plates, such as in the Hindu Kush. On the other hand, thermal conduction in a geological setting is a relatively slow process, where a time constant of the order of hundreds of years is needed to characterize the system. In this process, heat is transferred from the earth's interior towards the surface mostly by the conduction process, causing the temperatures to rise with increasing depth by an average of 25-30ºC per kilometer of depth. Dry hot rock geothermal systems are associated with such thermal conductions.

The water that comes from the rain and snow seeps into the ground. It will reach impermeable rock layers. There it will spread along the lines of least resistance until it comes to a system of fault and fractures in the surrounding structure. Down the cracks of this system, it will flow to the aquifer or the porous rocks that permits water to flow though it. If the aquifer is deep enough, it may rest on the impermeable rock layer that is in contact with superhot magma. Such an aquifer will be very hot, soaking up heat and circulating it through its structural components.

The heat from the superhot magma moves up through the impermeable rock layers into the aquifers and heats the water. If the heated water encounters some fracture leading upward, it expands, becomes less dense and more buoyant, and consequently rises to the surface as hot water or steam. The rising water is then replaced with denser cold water seeping into the aquifer. Hot-water deposits though abundant, but do not always announce their location in the form of hot springs or geysers. They are often hidden in volcanic and earthquake regions, and in some sedimentary areas. Thus, knowing the geology and the structure of the geothermal fields will facilitate the delineation of favorable prospects.

In Afghanistan, it is suggested that one of the main controlling factors in the formation of thermal water systems is continuous Neotectonic activity that facilitate the creation of passageways through fault and fracture zones in the lithosphere of this region. A structural analysis indicates that hydrothermal activities in Afghanistan are closely associated with major faults that divide the country into smaller structural blocks (see figure 1).

Comparatively, plentiful reserves of thermal waters are associated with the structures located in the junction areas of fault systems, e.g., where the Herat-Panjshir deep-seated fault system intersects with the Moqor and the Panjao fault systems, respectively. Such intersections form fracture networks that cover vast areas in central Afghanistan, controlling the permeability of the reservoirs of geothermal systems in these fields. It is along these networks that the geothermal fluids move to the surface and forms the geothermal prospects of the country. A second and determining factor in hydrothermal activity is young magmatism of the Hindu Kush, which provides the thermal energy for percolating underground reservoirs in the vicinity of granitic intrusive complexes throughout the country.

Infiltration dynamics, particularly the altitude of the watershed, also play a determining role, as most of the hydrothermal activity depends on the amount of atmospheric water that could feed the hydrothermal systems. At higher altitude and latitude the atmospheric precipitation contains lighter isotopes than in the lowlands. The isotopic analyses of water samples from springs and wells gives information about the origin of the field discharges, their age and possible underground mixing processes between different waters, about water-rock interaction and about steam separation processes (Nuti, 1991). Oxygen isotope analysis of five representative samples from thermal waters in Afghanistan reveals a value of δO18 (a deviation in parts per thousand of the sample from standards mean ocean water) in the range of -10.5 to -11.7 (Belianin, et al., 1970). This implies that the major volumes of thermal waters in Afghanistan are of meteoric origin, derived mainly from recharged water, rather than juvenile.

All the aforementioned factors contribute to the formation of a single hydrothermal system in Afghanistan, in which the high hydrostatic pressure forces the cold meteoric waters downward towards hot magmatic chambers that define the basic hydro-geochemical composition of the thermal fluids in the source region. The heated water, which is rich in dissolved gases, particularly CO₂, is much lighter than colder incoming water, thus moving upward through fractures and pores in different strata, picking many other elements into the solution en route to the surface.

Considering the complex geotectonic structure and endogenic processes in Afghanistan, the most potential prospects of geothermal reserves are suggested to be associated with the junctions of major fault systems, as well as the currently dormant volcanoes. A general trend in hydro-geochemical categories of thermal waters could be established, such as the changes in the category and types of water. For example, as the system gets closer to the main geothermal axis, it becomes richer in its CO₂ and total dissolved solid (TDS) mineral contents. In the contrary, as the system gets farther away from the main geothermal axis, the surface temperature of water increases and the water becomes richer in its nitrogen and silica contents, with an overall lower TDS contents of less than 1gram/liter.

The authors are in the view that geothermal fields in Afghanistan are mainly water-dominated systems, where liquid water at high temperature and under high hydrostatic pressure is the pressure-controlling medium, filling the fractured and porous rocks. Thus, major faults and fracture zones provide the initial structural components of these hydrothermal systems, based on which the following interconnected geothermal fields could be distinguished in the country: the Harirud-Badakhshan, the Helmand-Arghandab, the Farahrud, and the Baluchistan geothermal fields.

4.2.1. The Harirud-Badakhshan Geothermal Field:

This geothermal field forms the main and axial component of the geothermal activity in the country, extending throughout the length of the geosuture structural zone of central Afghanistan. This system includes structures such as the Harirud deep-seated fault system, Gharghanow fault system, and the central Badakhshan fault and fracture system. It extends eastward, beginning from Herat in western Afghanistan, to Panjao, Ghorband, Panjshir, Badakhshan, and up to the Pamirs to the most northeasterly corner of the country.

Of major hydrothermal indications in the western extensions of this field are the nitrogen-bearing siliceous hot springs in the Obe district of Herat province, 120 km to the east of Herat city, and 8km to northwest of the Obe township, as well as the Safed-Koh hot spring with surface temperatures of 48-52ºC as measured in September 2003 (Figure 4). In Panjao-Bande Amir region of central Afghanistan, many CO₂-bearing thermal springs with carbonate-chloride-calcium-sodium salts are recorded to have surface temperatures of 24-35ºC and a TDS of up to 3 gra,m/liter. The pH in these waters is controlled by the amount of CO₂ (up to 4 gram/liter), which ranges from 6.1-6.5. Geochemical elements in these waters include Be, Ge, Ba, Sr, Ti, V, As, Ga, Ni, Co, Fe, and traces of Rb, Cs, Cu, Pb, P. (Belianin, et al., 1970).

Figure 4. The Obe Shefa (healing) hot spring, Obe Township, 120 km to the east of Herat city, with a surface temperature of 52ºC and a very hot ground in a granitic contact zone.

The hot springs in the Kalu and Ghorband valleys, as well as Khwaja Qeech, and Ghorghuri hot springs in central Afghanistan are examples from the central portions of the Harirud-Badakhshan geothermal field. Generally, these waters with chloride-bicarbonate-sodium or chloride-sodium compositions are having high concentrations of elements such as Ge, Be, B, Fe, Ag, Zn, Pb, Ba, Li, Rb, Sr, and Sc (Kurenoe and Belianin, 1969).

High mineralisations in these thermal waters could be attributed to the higher amounts of CO₂ in the metamorphic hydro-geochemical environment, which facilitates the release of geochemical elements from the surrounding country rocks into the solution. Of these springs, those in the Kalu Valley (Figure 5), which is located 20 km to the east of the Bamiyan township, have promising potentials for balneological applications and tourist attraction, as well as the development of a small scale geothermal power plant, probably in the range of up to 10MW, in the immediate future.

In the eastern extensions of this field, in the Andarab-Panjshir region, as well as in the Badakhshan and the Pamirs, fewer hydrothermal manifestations are exposed on the surface. These are mainly of the nitrogen-bearing category, e.g., the Qala-e Saraab hot springs in Andarab, and Bobe-Tangi and Sarghaliyan hot springs in the Wakhan and Badakhshan regions, respectively. Compared to their more westerly counterparts, these having lower concentrations of geochemical elements. The Bobe-Tangi and Sarghaliyan also contains some amounts of hydrogen sulfide in their solutions.

Figure 5. Southerly view of the Kalu Valley, 20 km to the east of Bamiyan Township, with may hot spring manifestations, seen here to the left of the Kalu River.

4.2.2. The Helmand-Arghandab Geothermal Field:

With mainly CO₂ and nitrogen-bearing waters, hydrothermal activities in this geothermal field are associated with the Helmand-Arghandab granitoid massifs, connecting to the main geothermal axis through southern extensions of the fault and fracture systems of central Afghanistan. The deep-seated Chaman-Moqor fault system, and other groups of secondary faults are the main structural factors in the formation of this geothermal field, which covers regions such as Helmand, Moqor, and Tirin-Azhdar in south-central Afghanistan. The latter having thermal springs with the highest water discharges in the country. Hydrothermal activity here is mostly characterized by categories of CO₂ and nitrogen-bearing springs, which are normally rich in silicic acid and many solid minerals as micro-components in the solution.

The main areas of activity in this field are those in the vicinities of the Chaman-Moqor fault system, which is characterized with many CO₂-bearing thermal springs, rich in alkali and rare earth elements. In the Helmand fault and fractures system, thermal springs are more similar in their hydrogeochemical composition to those of the Panjao-Bande Amir hot springs. Geothermal activity in the vicinity of Helmand-Arghandab granitoid complex in the Tirin-Aajar area is very typical, in the sense that in southeasterly direction from the main Helmand fault system, the content of CO₂ decreases as the amount of nitrogen and nitric acid increases.

4.2.3. The Farahrud Geothermal Field:

This field is located in the Farahrud structural depression to the southwest of the main geothermal axis in southwestern Afghanistan. Geothermal activity in the form of hydrothermal springs in this field is associated with Pasaband deep-seated fault and fracture system. In its southwestern extension, it joins the nitrogen-bearing hydrothermal system of the Helmand-Arghandab geothermal field. Bicarbonate-calcium nitrogen-bearing thermal waters rich in silica and void of CO₂ are the norm in this geothermal field.

4.2.4. The Baluchistan Geothermal Field:

To the extreme southwestern corner of Afghanistan lies the volcanic terrain of Chagai-e in Baluchistan, with lots of hydrothermal activity, mainly of brine nature, rich in CO₂ and calcium. Two types of brine waters are typical for this field: thermal chloride-sodium rich pressured waters with a pH level of 6-6.6 that release high amounts of gases from the solution at the surface, leaving behind travertine and halite deposits; and chloride thermal waters with little or no gas in the solution, having a pH level of 7.8-8. These hydrothermal activities are suggested to be associated with carbonatitic post-volcanic processes in this region, resulting in the deposits of beautiful onyx marbles.

5. Economics and the Applications of Geothermal Energy

5.1. Geothermal Energy is a Viable Option:

Presently, Afghanistan is very dependent on foreign energy sources, importing most of its energy needs from Iran or Turkmenistan in the forms of electricity, natural gas, and petroleum products. The most important economic aspect of geothermal energy use is that it's homegrown. Utilization of indigenous resources reduces the dependency of the country on foreign energy sources, which in turn will decrease the annual trade deficit that translates into more jobs and a fairly healthy economy. At the same time, a vital measure of national security is gained when the country control its own energy supplies.

Although fossil fuels are draining the foreign exchange reserves of the country and are very costly for Afghanistan, their consumption is growing and will continue to grow in the foreseeable future by necessity, causing further stress to the overall economy and to the very fragile environment of the country. On the other hand, geothermal energy is a clean, renewable and sustainable energy source, available for Afghanistan to exploit on its own turf, either directly as a heat source or to generate electric power.

Currently, over 60 countries around the world use the geothermal energy as a source for power generation or in direct use applications (Table 1).

Table 1: Regional geothermal power plants in operation in 2000 (IGA, 2001)

Region  Electric Power   Direct Use .
  MWe GWh/y MWt GWh/y
Africa  53.5 396 121 492
Americas 3,390 23,342 5,954 7,266
Asia  3,095 17,509 5,150 22,532
Europe  998 5,745 5,630 19,090
Oceania  437 2,269 318 2,049
Total  7,974 49,261 17,174 51,428

Geothermal energy is independent of weather, contrary to solar, wind, or hydro applications, with an inherent storage capability. The relatively high share of geothermal energy as a source for electricity production, compared to solar or wind, reflects the reliability of geothermal plants, which commonly have a capacity factor of 70-90% (IGA, 2001), i.e., the average geothermal power plant is available 90% of the time.

Of the total electricity production of 2826 TWh in 1998 from renewable energy sources in the world, 92% came from hydropower, 5.5% from biomass, 1.6% from geothermal and 0.6% from wind. Solar electricity contributed only 0.05% and tidal 0.02% of the total (WEA, 2000). Comparison of the four "new" renewable energy sources (Table 2) shows that 70% of the electricity generated by these four comes from geothermal, while it holds only 42% of the total installed capacity. Among these, wind energy contributes 27% of the electricity, whole having 52% of the installed capacity.

Table 2. Electricity from four renewable energy resources in 1998 (WEA, 2000)

  Operating Production
  capacity     per year    .
  GWe % TWh/y %
Geothermal 8 41.4 46 69.6
Wind  10 52.1 18 27.2
Solar  0.9 4.7 1.5 2.3
Tidal  0.3 1.5 0.6 0.9
Total  19.2 100 66.1 100

Heat production from renewable energy sources deemed to be commercially competitive with conventional energy sources. Of these, biomass constitutes 93% of the total direct heat production from renewable energy sources, geothermal 5%, and solar heating 2%.

5.2. Geothermal Energy is Efficient and Cost Effective:

Research sponsored by governments and companies continues to improve geothermal technology. Despite higher initial cost, the life-cycle cost of geothermal energy utilization is reasonably low. When the environmental benefits are factored in, the case for increased geothermal use among other renewables is compelling (IGA, 2001).

Current geothermal power plant installation costs are in the range 1000-3000 USD/kW, which is equivalent to the production cost of 2.2 to 5.4 US cents/kWh. The investment cost of a conventional direct heat district heating system is in the range 400-1400 USD/kW. This corresponds to a production cost of some 0.8-3 US cents/kWh (IGA, 2001). A comparison of the renewable energy sources by UN World Energy Assessment Report (WEA, 2000) shows that the current electrical energy cost is 2-10 US cents/kWh for geothermal and hydro, 5-13 US cents/kWh for wind, 5-15 US cents/kWh for biomass, 25-125 US cents/kWh for solar photovoltaic and 12-18 US cents/kWh for solar thermal electricity.

The current cost of direct heat from biomass is 1-5 US cents/kWh, geothermal 0.5-5 US cents/kWh, and solar heating 3-20 US cents/kWh (Fridleifsson, 2000). These figures indicate that currently electricity produced by geothermal power plants is becoming cost-competitive with other forms of energy

It is apparent that the cost of geothermal electrical energy is compatible with the costs that Afghanistan is paying for electricity purchased for a period of ten years from Iran (2.8 US cents/kWh) and Turkmenistan (2.0 US cents/kWh). These prices are on top of the installation expenses of 16 million USD for 132km of high voltage lines and a transfer substation with a capacity of 50MWe from Iran; and 6.3 million USD for 120 km transfer lines and 2.3 million USD transfer substation with a capacity of 30MWe from Turkmenistan, respectively (DEPCH, 2003). At this point, though these projects seem to be great deals, and the immediate cost to Afghanistan is much lower than if it had developed a hydroelectric power station with the same capacity, or few small-scale geothermal power plants. But, if we factor in the price that would be paid out of the country's reserves for the consumption of the power supply, continuously for the lifetime of these projects, the lost of job opportunities for Afghans, the underdeveloped renewable energy potentials of the country, environmental, strategic, as well as national security issues, then, they are not such sweet deals at all.

Though, such cross-border projects may be viable options for certain regions of Afghanistan, they may not be feasible options for supplying energy to remote communities, such as the ones in central and northeastern Afghanistan. In the view of the authors, having numerous small scale multipurpose hydroelectric and geothermal power plants in the range of 5-20 MWe (megawatt of electric energy) can be extremely useful for Afghanistan. Such plants could potentially provide significant power for isolated populations, mining operations, and other local small industries, while creating thousands of permanent jobs for people who are in dire need of it.

5.3. Geothermal Energy For Electricity Production:

Electricity is in serious shortage all over Afghanistan, in particular in the remote rural areas. This is severely affecting the overall reconstruction efforts and economic development of the country. Reconstruction of industry, agriculture and food processing is not possible without a sustainable supply of electricity. Moreover, increasing forest cutting and use of animal waste is progressively damaging the severely degraded natural environment of the count

Potential geothermal energy reserves in Afghanistan could provide part of the electricity needs required to satisfy the demand. Electrical power production is the most profitable use of geothermal energy, and worldwide has grown the most, comparing to other geothermal applications. Electricity is produced with geothermal steam in 21 countries, with the USA being the top producer in 1999, producing 2228 MWe. In the Philippines, about 22% of the electricity is generated with geothermal steam. Other countries presently generating 10-20% of their electricity with geothermal energy are Costa Rica, El Salvador, Iceland and Nicaragua (Huttrer, 2001). Currently many developing countries such as Turkey, Kenya, Taiwan, Chile, and Tibet in China are also developing their geothermal fields.

To generate electricity from geothermal hot water, two prerequisites are required to be fulfilled: adequate technology, and an abundant high-temperature water or steam. At present, efficient and durable technology is readily available to Afghanistan to produce low-cost electricity from its geothermal resources. At the meantime, the tectonic structure of Afghanistan suggests the presence of vast hot water circulation systems underground. But only under certain conditions of depth, temperature, and chemistry does it pay to drill into these systems, conditions that require further explorations to be undertaken.

In planning for a geothermal electrical plant, the following questions has to be answered: how much steam can be exploited form the field, how long will the steam last, and where should the drilling take place? When the hot-water wells are of low temperature, either a flash steam or a binary cycle system would be installed. These systems are used where the geothermal fluids are just barely mineralized. Additionally, the costs of these systems are higher than the simple steam cyclone and turbine system. However, low temperature water can be used very economically for non-electrical purposes.

In water-dominated geothermal systems, such as the one in Afghanistan, water comes into the wells from the reservoir, and the pressure decreases as the water moves toward the surface, allowing the water to boil. Only part of the water boils to steam, and a separator is installed between the wells and the power plant to separate the steam and water. The steam goes into the turbine, and the low temperature water is then circulated through heat exchangers to heat a secondary liquid, usually an organic compound such as isobutene, with a low temperature of boiling. The resulting organic vapor then drives another type of turbine, called a binary power system. The cooler water then could be used for direct applications and at the end reinjected back into the reservoir to sustain the geothermal hydraulic system.

In a flash system, where the steam is the dominant phase, the hot geothermal fluid is piped up to a separator. As soon as the pressure is released, some of this fluid flashes into steam that rushes off to turn a turbine that spins a generator. The spent steam is then chilled in a condenser and changed to water to be pumped back into the ground. However, in a binary system, a heat exchange method is used. In this system, heat from the geothermal fluid is transferred to another liquid, a refrigerant such as freon or isobutane that vaporizes and turns into a highly pressurized gas that flows up a pipe leading to the turbine. The vaporized refrigerant is then recycled back into the system to continue its work.

5.4. Geothermal Energy For Direct Uses:

Direct-use geothermal technologies use naturally hot geothermal water for commercial applications. Afghans know the medicinal and healing properties of hot water springs, especially its therapeutic power for skin conditions and rheumatic arthritis. Medicinal bathing or balneology is an important sector to be considered for modern developments of some of the well-know healing hot springs of the country. This has the potential to contribute to the improvement of life standard and the overall well being of the people of Afghanistan, while creating hundreds of new and permanent jobs.

Afghanistan needs to preserve some of its current available geothermal resources in their natural state and use them only for recreation and tourism industry. Thus, not all of the resources currently known may be made available for development. However, shallow resources suitable for heat pumps are available and accessible anywhere in the country. Geothermal heat pumps (GHP), which can be used almost anywhere, use the constant temperature of the top 15-18 meters of Earth's surface to heat buildings in the winter and cool them in the summer. This mode of using geothermal energy has enjoyed the largest growth rate in recent years all over the world (IGA, 2001).

Geothermal heat pumps can contribute significantly to improving energy utilization efficiency and are developing considerable momentum. If installation of GHPs is combined with the construction of the foundations of new buildings, its initial capital cost significantly decreases, as successfully demonstrated in the construction of GHP loops that have been incorporated in the foundation piles of the new International Airport Building in Zurich (IGA, 2001). In GHP applications, USA leads the way with approximately 400,000 GHP units (about 4800 MW of heat energy) and energy production of 3300 GWh/y in 1999 (Lund and Boyd, 2000) followed by Switzerland, which is traditionally not known for hot springs or geysers. The energy extracted out of the ground with heat pumps in Switzerland amounts to 434 GWh/y, with an annual growth rate of 12% (Rybach, et al., 2000). It is suggested that any major construction project in Afghanistan, particularly the new international airport south of the Kabul City, should consider incorporating this option in the design of the project.

Other non-electrical applications of geothermal energy can involve a wide variety of end uses, such as chemical industry, greenhouse industry, food processing, and fish farming, etc. The technology, reliability, economics, and environmental acceptability of direct use of geothermal energy have been demonstrated throughout the world. Currently the main types of direct uses are bathing/swimming/balneology (42%), space heating (35% including 12% with geothermal heat pumps (GHPs), greenhouse (9%), fish farming (6%), and industry (6%) (Lund and Freeston, 2001).

Some economically feasible and useful applications of low-temperature waters in Afghanistan are suggested to be: hatching and fish farming, greenhouse by combined space and hotbed heating, mining of placer deposits (with high feasibility in Badakhshan and Ghazni placer gold deposits), fruit drying and processing, food processing, fur and intestine processing (a traditional industry in Afghanistan), refrigeration by ammonia absorption, wool processing, carpet cleaning, tourist and balneological facilities, district heating, drying and curing of light aggregate cement slabs, extraction of industrial chemical salts by evaporation and crystallization, biodegradation, fermentation, mushroom farming, and other small-scale local industries.

Direct application uses, however, are more site specific for the market, as steam and hot water is rarely transported long distances from the geothermal site. The production cost/kWh for direct utilization is highly variable, but commonly under 2 US cents/kWh, proven so economic for Chinese, that their direct utilization is expanding at a rate of about 10% per year, mainly in the space heating, bathing, and fish farming sectors. Other examples of a high growth rate in the direct use of geothermal are found in developing countries such as Turkey and Tunisia. In the latter, for example, geothermally heated greenhouses have expanded from 10,000 m2 in 1990 to 955,000 m2 in 1999, with the main products in the greenhouses being tomatoes and melons for export to Europe, creating thousands of new jobs in this oasis (Fridleifsson, 2000). Turkey, while developing its geothermal resources for electricity production, is very focused on the recreational and other direct applications of this natural resource.

6. Environmental Impacts of Geothermal Energy:

Increasing interest in controlling atmospheric pollution and the spreading concern about global warming provide a framework for a continuing strong market for geothermal electrical generation and heat energy extraction. Geothermal development will serve the growing need for energy sources with low atmospheric emissions and proven environmental safety. Among all renewables, the geothermal energy currently produces the third most energy, after hydroelectricity and biomass. This source of energy does not require fuel-burning to produce heat or electricity, thus, with its proven technology and abundant resources, can make a significant contribution towards reducing the emission of greenhouse gases.

Geothermal fluids contain minerals leached from the reservoir structure, as well as a variable quantity of gases, mainly nitrogen, carbon dioxide and small amounts of hydrogen sulphide, and ammonia. The amounts depend on the geological conditions encountered in the different fields. Virtually the entire minerals content of the fluid and some of the gases are reinjected back into the reservoir. Only an inconsiderable amount of noncondensable gas is released into the environment.

The industrial exploitation of a geothermal system is based on the heat mining from the rocks by using the geothermal fluids as vectors, without any specific process of CO₂ generation. Geothermal power plants emit little carbon dioxide (fossil-fuel power plants produce 1000 to 2000 times as much), no nitrogen oxides, no particulate matter, and very low amounts of sulfur dioxide. Steam and flash plants emit mostly water vapor. Binary power plants run on a closed-loop system, so no gases are emitted as shown in the following chart (Figure 6). In this chart, the amount of sulfur dioxide and carbon dioxide emissions between two fossil-fueled power plants (coal, and oil) and a geothermal power plant with and without waste gas reinjection into the ground has been compared.

Figure 6. Comparison of sulfur dioxide and carbon dioxide emissions between two fossil-fueled power plants, and a geothermal power plant (after Goddard & Goddard, 1990).

At the same time, land use for geothermal developments is small compared to land use for other extractive energy sources such as oil, gas, and coal. Low-temperature geothermal applications are usually no more disturbing of the environment than regular water wells. Geothermal development projects often coexist with agricultural land uses, including crop production or grazing.

The Clean Development Mechanism (CDM), promoted by the Kyoto Protocol, encourages countries such as Afghanistan to invest in their renewable energy sources, and thus receive credit for the carbon dioxide emissions saved by these projects to offset the greenhouse gas emission charges in developed countries. This in turn, fosters financial partnerships that provide access to affordable, low greenhouse gas emitting commercial energy technologies. By developing its geothermal resources, Afghanistan will immensely benefits from these international provisions.

7. Conclusion and Proposals

With the presence of many young magmatic, metamorphic, volcanic, and collisional tectonic processes in Afghanistan, the potential of geothermal energy in this country is enormous. Geothermal systems in Afghanistan are not limited to those with hot springs indicators at the surface. Many systems are hidden and do not reach the surface. The authors of this report believe that the most promising prospects for geothermal exploration and characterization of known and hidden reservoirs are in regions along the Herat-Panjshir and Chaman-Moqor fault systems.

To develop the potential geothermal prospects for industrial exploitation, systematic geological, geochemical and geophysical techniques, including fluid inclusion geothermometry, stable isotope analysis, electrical resistivity surveys, self-potential (SP) surveys (Ross, et al., 1995), and micro-seismic analysis are required to locate and delineate shallow producing geothermal fields. Such a work will pinpoint with much accuracy the particular depths of hot water reservoirs in particular prospects and set the stage for drilling exploratory investigations, which would be the final arbitrator for the evaluation of the reservoirs of these resources. Thus, a major exploration effort is needed to characterize geothermal reservoirs and build the inventory of prospect geothermal areas for further development.

Benefits of Geothermal Energy Development to Afghanistan could be summarized as the following:

• Geothermal resources provide the country with a homegrown source of energy that can be extracted without burning fossil fuels. Once it is developed, the country's dependence on foreign energy sources decreases proportionately.
• Use of geothermal energy create the needed permanent full-time jobs for Afghans, decreases trade deficits, and saves valuable foreign reserves of the country.
• With very low or no pollutant byproducts, this is one of the most environmentally clean and friendly sustainable renewable energy source to be exploited in Afghanistan.
• Afghanistan has the leverage to get financing under the "Clean Development Mechanism" (CDM), promoted by the "Kyoto Protocol", which encourages developed countries to invest in renewable energy projects in developing countries.
• Under the (CDM) provisions, the greenhouse gas credits created by geothermal power plants could be sold on global markets to bring extra cash revenues.
• Afghanistan has very limited acreage of usable land for industrial development. The average geothermal power plant requires a total of only 400 square meters of land to produce a gigawatt of power over a period of 30 years, which is incomparable to the huge acreages needed for other power plant developments.
• Development of geothermal resources in Afghanistan strengthens the technological, scientific and research capacity of the country through improved international cooperation.

Considering that geothermal energy is a clean, proven and reliable resource for supplying the needs of a sustainable society and helping to improve the environment, and also that the life-cycle costs of geothermal technologies are competitive with the costs of other forms of energy, especially when environmental externalities are considered, the authors of this report believe that strong commitments in research, development, and market deployment are needed by government of Afghanistan to promote increased utilization of this natural resource.

It is upon the government of Afghanistan to make strong commitments to promote the developing of the geothermal resources of the country for the benefit of its own citizens, humanity and the global environment. A thorough assessment of the country's geothermal resource potential for use in electrical power generation, district heating, cooling of homes and buildings, food processing, green house industry, fish farming and hatchery, refrigeration, recreation and tourism, and a myriad of other industries has to be undertaken. To facilitate the accomplishment of these goals, policies and regulations that promote investment in development of geothermal resources has to be worked out.

It is suggested that the United Nations, World Bank, Asian Developing Bank, and other interested global institutions should include strong geothermal energy components in their developing programs in Afghanistan, and encourage geothermal industries and agencies worldwide to help in the development of geothermal resources of this country as a component of the international cooperation in the rebuilding of Afghanistan.

There is no reason that at the beginning of the 21st century, the development of geothermal energy that will last a long time and is clean, abundant, and economically feasible, is not pursued in Afghanistan. The country has the potential of rapidly developing its geothermal resources for direct uses such as geothermal tourist and balneological networks, greenhouse industry, food processing, fruits drying and processing, wool processing, carpet cleaning, and chemical applications. Though, development of geothermal resources for electric generation may not be a priority at this point, nonetheless, a large electric power generation potential from geothermal resources is readily available for Afghanistan. Use of geothermal energy in Afghanistan for electric and non-electric applications is feasible and realistic.

Acknowledgements:

The fund for this work is provided by the Center on International Cooperation, New York University, by a grant from the Open Society Institute. The Afghanistan Center for Policy and Development Studies has facilitated and supported this research project in Afghanistan. The Kabul Polytechnic Institute and the Herat University in Afghanistan have provided local support and research facilities. The Department of Geological Survey of the Ministry of Mines and Industry of Afghanistan has kindly provided permission to access the pertaining archive information on the previous work. We are grateful to the AIMS office of the UNDP Kabul, for generously providing the topographical maps of Central and Western Afghanistan to this project.

This work would have not been possible without the support of Dr. Barnett Rubin, Director of CIC, New York University, USA. We would like to express our gratitude for efficient help and kindness of Dr. Omar Zakhilwal, senior advisor to the Ministry of Rural Rehabilitation and Development of Afghanistan. We are indebted to Prof. Edward Friedman of the St. Stevens Institute of Technology, New Jersey, USA, for his review of the draft of this report and very useful comments. We are grateful to Prof. Najibullah Safdari for his kindly review of the draft of this report and comments. We are also indebted to many colleagues and locals in Kabul, Bamiyan, Parwan, and Herat provinces, who have generously provided us with guidance, logistical support and encouragement throughout this work.

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Appendix 1.

Glossary:

Advection: Transport or transfer of heat, by means of the movement of a media such as water in the system.

Andesite: A volcanic rock composed essentially of the mineral andesine and one or more mafic mineral constituents, such as pyroxene, hornblende, or biotite, or all three in various proportions.

Aquifer: Water-bearing stratum of permeable sand, rock, or gravel.

Batholith: The largest and massive body of intrusive rocks, solidified as coarse crystalline rock in the deep horizons of the crust.

Binary-cycle plant: A geothermal electricity generating plant employing a closed-loop heat exchange system in which the heat of the geothermal fluid (the "primary fluid") is transferred to a lower-boiling-point fluid (the "secondary" or "working" fluid), which is thereby vaporized and used to drive a turbine/generator set.

Biomass: Plant material, vegetation, or agricultural wastes used as an energy source.

Brine: A geothermal solution containing appreciable amounts of sodium chloride or other salts.

Carbonated: Water containing carbon dioxide gas in solution, common in volcanic and tectonically active zones. Sometime contain so much gas that if a little sugar thrown into water, it effervesces like soda water.

Carbonatitic: Pertaining to carbonatite, an igneous carbonate rock, which is associated with alkaline igneous intrusive activity in many localities, produced by a phase of magmatism that is rich both in soda and lime.

Cenozoic: The latest of the four geological eras, extending from the close of the Mesozoic era to and including the present, including the periods called Tertiary and Quaternary in accordance to the US geological nomenclature.

Condenser: Equipment that condenses turbine exhaust steam into condensate.

Cretaceous: The third and latest of the periods of geological time included in the Mesozoic era.

Crust: The hard outer covering, or the exterior portion of the earth that lies above the Mohorovicic discontinuity.

Dacite: An extrusive igneous rock, in which the principal minerals are plagioclase, quartz, pyroxene or hornblende or both with minor amounts of biotite and sanidine.

Direct use: Use of geothermal heat without first converting it to electricity, such as for space heating and cooling, food preparation, industrial processes, etc.

District heating: A type of direct use in which a utility system supplies multiple users with hot water or steam from a central plant or well field.

Drilling: Boring into the earth to access geothermal resources, usually with oil and gas drilling equipment that has been modified to meet geothermal requirements.

Dry hot rock: Dry hot rock. Subsurface geologic formations of abnormally high heat content that contain little or no water.

Dry steam: Very hot steam that doesn't occur with liquid.

Efficiency: The ratio of the useful energy output of a machine or other energy-converting plant to the energy input.

Endogenic: Pertaining to processes that originate within the earth, and to rocks, ore deposits, and landforms, which owe their origin to such processes.

Eurasia: The landmass and a major tectonic plate of the earth, comprising the continents of Europe and Asia.

Fault: A fracture or fracture zone in the Earth's crust along which slippage of adjacent earth material has occurred at some time.

Flash steam: Steam produced when the pressure on a geothermal liquid is reduced. Also called flashing.

Fracture: Breaks in rocks due to intense folding or faulting.

Geology: Study of the planet earth, its composition, structure, natural processes, and history.

Geochemical: Pertaining to the distribution and circulation of chemical elements in the earth’s crust, soil, water and atmosphere.

Geosuture: Large mobile zones between two rigid plates of the earth crust, normally joining two plates together such as a suture.

Geothermal: The generation of hot water or steam by hot rocks in the earth’s interior. Of or relating to the earth's interior heat.

Geothermal energy: The earth's interior heat made available to man by extracting it from hot water or rocks.

Geothermal gradient: The rate of temperature increase in the earth as a function of depth. Temperature increases an average of 1° Fahrenheit for every 75 feet in descent.

Geothermal heat pumps (GHP): Devices that take advantage of the relatively constant temperature of the earth's interior, using it as a source and sink of heat for both heating and cooling. When cooling, heat is extracted from the space and dissipated into the earth; when heating, heat is extracted from the earth and pumped into the space.

Geyser: A spring that shoots jets of hot water and steam into the air.

Gondwana: The supercontinent of the southern hemisphere of the earth, which broke up into India, Australia, Antarctica, Africa, and South America during the Paleozoic Era.

Granitoid: Pertaining to coarse-grained igneous or metasomatic rocks, including granite, diorite, syenite, granite porphyry, diorite porphyry, massive gneiss, migmatite, gabbro, peridotite, hornblendeite, pyroxenite, and amphibolites.

Greenhouse gases: gases, principally water vapor and carbon dioxide that trap surface heat, thereby warming the earth’s atmosphere.

GWh/y: Gigawatt-hour per year of energy. A gigawatt is one thousand megawatts or a billion watts.

Heat exchanger: A device for transferring thermal energy from one fluid to another.

Heat flow: Movement of heat from within the earth to the surface, where it is dissipated into the atmosphere, surface water, and space by radiation.

Hydrothermal: Underground systems of hot water and/or steam.

Injection: The process of returning spent geothermal fluids to the subsurface. Sometimes referred to as reinjection.

Intrusive: any igneous body that solidifies in place below the surface of the earth.

Juvenile water: Water that is derived from the interior of the earth and has not previously existed as atmospheric or surface water.

Kilowatt (kW): A kilowatt or kW is one thousand watts of energy.

Kilowatt-hour (kWh): The energy represented by 1 kilowatt of power consumed for a period of 1 hour.

Magma: A molten rock material generated within the earth, from which, igneous rocks are being formed by cooling.

Magma chamber: A large reservoir in the earth’s crust occupied by a body of magma.

Mantle: The earth's inner layer of molten rock, lying beneath the earth's crust and above the earth's core, composed of dense iron-magnesium-rich rocks.

Megawatt-hour (MWh): A megawatt-hour is one thousand kilowatts or a million watts-hour of energy.

MWe: Megawatt of electric energy.

MWt: Megawatt of thermal power.

Mesozoic: One of the grand divisions or eras of geologic time, following the Paleozoic and succeeded by the Cenozoic era, comprising the Triassic, Jurassic, an Cretaceous periods.

Metamorphic: Pertaining to rocks, which have formed in the solid state in response to pronounced metamorphism.

Metamorphism: Changes of temperature, pressure, and chemical environment, below the shells of weathering and cementation.

Meteoric water: Water that occurs in or is derived from the atmosphere.

Neogene: The later of the two periods into which the Cenozoic era is divided according to the European nomenclature of geologic time.

Neotectonic: Pertaining to the tectonic activities that occurred between the end of the Miocene and the present.

Onyx marble: Translucent layered variety of calcite somewhat resembling true onyx in appearance, usually formed as vein filling or spring and cave deposits.

Palaeogene: The earlier of the two periods comprised in the Cenozoic era according to European nomenclature of geologic time.

Period: A division of geologic time longer than an epoch and included in an era.

Permeability: The capacity of a substance, such as rock, to transmit a fluid. The degree of permeability depends on the number, size, and shape of the pores and/or fractures in the rock and their interconnections. It is measured by the time it takes a fluid of standard viscosity to move a given distance. The unit of permeability is the Darcy.

Plate: In the theory of plate tectonics, one of the sections of the earth’s lithosphere, constantly moving in relation to the other sections.

Plate tectonics: A theory of global-scale dynamics involving the movement of many rigid plates of the earth's crust. Tectonic activity is evident along the margins of the plates where buckling, grinding, faulting, and volcanism occur as the plates are propelled by the forces of deep-seated mantle convection currents. Geothermal resources are often associated with tectonic activity, since it allows groundwater to come in contact with deep subsurface heat sources.

Pluton: A body of igneous rock formed beneath the surface of the earth by consolidation of magma.

Precambrian: Of or belonging to the period of geological time from approx. 3.8 billion years ago to approx. 570 million years ago, often subdivided into the Archean and Proterozoic eons.

Quaternary: Of or belonging to the geologic time of the second and last period of the Cenozoic Era, characterized by the appearance of humans.

Reducing: A system devoid of free oxygen in the solution or geochemical environment.

Renewable energy source: Renewable describes a property of the energy resource, which are in one way or another linked to some continuous energy process in nature. The conditions must be such that the action of extracting energy from the natural process will not influence the process or energy circulating in nature.

Reservoir: A natural underground container of liquids, such as water or steam, or in the petroleum context, oil or gas.

Salinity: A measure of the quantity or concentration of dissolved salts in water.

Strata: Layered rock formations, also called beds.

Strike-slip fault: Transcurrent fault. A fault in which the net slip is practically in the direction of the fault’s strike.

Strike: The course or bearing of the outcrop of an inclined bed or structure on a level surface.

Sustainable energy source: Sustainable describes how the energy resource is utilized. Sustainable operation of the resource is achieved by matching the heat extraction rate with the natural recharge rate.

TDS: Total dissolved solids. Used to describe the amount of solid materials in water.

Tectonics: Pertaining to building or construction of the structure of the earth’s crust due to the forces or conditions within that cause movements of the crust of the earth.

Terrain: A region of the earth’s surface that is treated as a physical feature or as a type of environment.

Thermal gradient: The rate of increase or decrease in the Earth's temperature relative to depth.

Transmission line: Structures and conductors that carry bulk supplies of electrical energy from power-generating units.

Turbine: A bladed, rotating engine activated by the reaction or impulse, or both, of a directed current of fluid. In electric power applications, such as geothermal plants, the turbine is attached to and spins a generator to produce electricity.

TWh/y: Terrawatt-hours per year of energy. A terawatt is one thousand gigawatts or a trillion watts.

Uplift: Elevation of any extensive part of the earth’s surface relatively to some other parts.

Volcanism: Pertaining to the phenomena of volcanic eruption, the explosive or quiet emission of lave, pyroclastic ejecta or volcanic gases at the earth’s surface, usually from a volcano.

Watt (W): One watt is a rate for the production or use of energy, which equals to 1 joule of energy per second. A 100 watt light bulb uses 100 joules of energy every second.

Water-dominated: A geothermal reservoir system in which subsurface pressures are controlled by liquid water rather than by vapor.