1. Geothermal Energy and
Geothermal Energy Technologies
Dr. Akepati S. Reddy
School of Energy and Environment
Thapar University
Patiala (PUNJAB), India - 147001
2. Geothermal Energy
• The Earth’s core is a heat source
– Radioactive decay of long half-life nuclei generates heat
• Heat from the core is continuously transferred outwards by
convection (in the mantle) and conduction (in the crust)
– Estimated heat transfer from the core is 42000 GW
• Heat is continuously lost from the earth surface
– Mean heat flux of the earth surface is 1/16 W/m2 (16 kW/km2!)
• Earth shows a temperature gradient from core to surface, and the
gradient is steeper for the earth crust (crust appears insulating us
from the earth’s interior heat)
– Temperature drops from 930°C to 15°C through the 30-70 km thick
continental crust (oceanic crust is 5 to 10 km thick)
– Temperature of the earth increases with depth in the crust at 17-
30°C/km (1°C per 36 m !)
– The gradient is higher along the tectonic plate boundaries and in the
zones of high volcanic activities
• Beyond certain depth (>10 – 100 feet) the earth’s temperature is
constant throughout the year
– At shallower depths it varies both diurnally and seasonally
3.
4. Geothermal Energy
• Geothermal energy is the heat energy stored beneath the earth
surface (heat generated by natural processes within the earth)
• Volcanic activity transports hot molten material (magma) closer to
the earth surface (5 to 20 km beneath the surface)
– Molten material flowing out from volcanic erruptions is lava
– Slow cooling of molten rock form very large crystals, and molten
magma heats up nearby rock (forms hot dry rock)
• In shallow depths (upto 500 to 3000 m), to which water can
penetrate, hydrological convection of heat occurs and geothermal
reservoirs are formed
• Geothermal reservoir: hot water or steam trapped in the
permeable porous rocks under a layer of impervious rock
• Geothermal field: thermal area of permeable rock formation
containing working fluid (water)
– Semi thermal fields: water with temp <100C can be obtained
– Wet hyper thermal field: product is pressurized water at >100C temp.
– Dry hyper thermal fields: product is dry saturated or slightly
superheated steam
5.
6. Geothermal Energy
• Geothermal energy system requires heat, permeability and water –
if any of these are lacking/limiting they are provided
– Drilling to reach the geothermal heat source
– If no water, water is used for hydrothermal convection of heat
• Geothermal reservoirs (of hot water and/or steam under pressure)
– Hot geothermal water of a reservoir can manifest itself as hot springs
(hot water), geysers (water and steam) and fumerols (only steam)
– Hot water or steam are extracted from the reservoir and used either
for power generation or directly used
– Dry steam, flashed steam, and binary cycle for power generation
– Direct use of geothermal heat, and Combined-Heat Power generators
• Hot dry rock technology (crystalline rock formation, at 3-6 km depth
– Cold water injection into engineered geothermal reservoir and (high
pressure) hot water pumping out for power generation – Enhanced
Geothermal Systems (EGS)
– Geopressed resources and Super critical cycles
• Constant year round temperature below the ground surface
– Ground source heat pumps (geothermal heat pumps)
• Geothermal water a byproduct of oil and gas wells
7. How much geothermal energy?
• Geothermal energy is a clean, renewable energy resource
(inexhaustible, essentially limitless and constantly available)
• Geothermal energy accounts for 3% of the total renewable
energy based electricity
• In 2012, 11.224 GW geothermal power generation capacity
was online around the world (in 24 countries)
– US, Philippines, Indonesia, Mexico, Italy, New Zealand, Iceland,
Japan, El Salvador, Kenya, Costa Rica, Nicaragua are important
• US amounts to 28% of the world geothermal energy production
• Indonesia has 27150 MW potential
• In 2011, Italy has 50% of the Europe installed capacity (1600 MW)
• Iceland derives 25% of its electricity and 90% of its heating from
geothermal sources
• El Savador and Costa Rica, geothermal produces 24% and 12% of
the electricity respectively
– India is not in the list
• In 2010, the geothermal direct use in 78 countries amounted
to 51 GWt (includes GHPs also)
8. How much geothermal energy?
• As on 2013, globally 11.7 GW geothermal electricity
generation capacity was in operation
• In 2015, world’s geothermal electricity generation capacity
was 12.676 GW and geothermal direct application was 18 GW
• World’s geothermal resources potential was estimated (by
Geothermal Energy Association in 1999) as 35,448 to 72392
Kw (95% and 5% probability respectiely)
– Potential of the East African Rift System (in 2012): 10,000 to
20,000 MW
– Potential of the Central America: 3000 to 13000 MW at 50
identified geothermal sites
• Geothermal heat pumps potential is available everywhere on
the earth surface
• EGS (enhanced geothermal systems) technology can
immensely increase the geothermal energy potential
9.
10.
11.
12.
13. Geothermal energy potential: India
• India has about 400 thermal springs distributed in 7
geothermal provinces
• These springs are perennial and their
surface temperature range from 37 to 90oC and their
cumulative surface discharge is over 1000 l/m.
• Temperature of the water at Tattapani is 90oC; at Puga
(Himalaya) it is 98oC and at Tuwa (Gujarat) it is 98oC
• Estimated reservoir temperature are 120oC (west coast), 150oC
(Tattapani) and 200oC (Cambay)
• The geothermal systems are mostly liquid dominated (steam
dominated systems are seen in Himalayan & Sonata provinces)
• Depth of the geothermal reservoir is about 1 to 2 km
• The power generating capacity of the thermal springs is
estimated at about 10,000 MW
– Binary cycle method can be utilized to generate power
– Puga valley (Ladakh) has the most promising geothermal field
14. Geothermal provinces
Himalaya (a & b !)
– Puga and Manikaran
Sohana
- Delhi
Combay
- Tuwa
Sonata
– Tattapani, Jalgaon, Bakreswar
West coast
– Unai, Bombay
Godavari
Mahanadi
Heat flow values (mW/m2)
Thermal gradients (°C/km)
15. Technologies
• Traditional/ conventional hydrothermal power production systems
(geothermal power plants) types
– Dry steam
– Flash steam (2 types: single flash and double flash power plants
– Binary cycle
– Combined cycle and Hybrid
• Coproduction, Enhanced Geothermal Systems (EGS), Geo-pressured
and Supercritical systems
• Direct use of geothermal heat (without involving a power plant or a
heat pump)
– Space heating and cooling, food preparation, hot spring bathing
and spas, agriculture, aquaculture, green houses, snow melting
and industrial uses
– These are applied at aquifer temperatures 90-200C.
– The geothermal water/steam is accessed and brought to a plate
heat exchanger
• Ground Source Heat Pumps (GSHP)/ Geothermal Heat Pumps
(GHPs) – Geothermal Heating and Cooling Systems
16. Condensate must be good quality water
Mostly lost to atmosphere as vapours at
cooling towers (60-80%)
Water from some other source (treated
wastewater) can be injected
Geothermalsourceswith>150°Ctemp.(180-225°C)and4-8
MPapressureareused
Undergroundsteamisdirectlyusedintheturbines(steam
movesat200m/Sec.speed)
Opensystems-associatedwithairpollutionbyH2Sand
pollutionbytracesofarsenicandminerals
17. Hot geothermic fluid and steam
condensate can be put to direct uses
Steam condensate is lost into
atmosphere at cooling towers
Highpressurehotgeothermicfluidistransportedintoalow
pressurechamberforflashing-Flashedsteamdrivesturbine
Lowpressurefluidfromtheflashingchamberisinjectedback
Saltbuildupinpipelinescanbeaproblem
19. Geothermal resource of <150C
temperature can be used
Working/motive fluids:
isobutane, pentafluoropropane
A closed loop system – no
emissions – everything brought
to surface is returned
underground
Typical efficiency: 7-12%
20. Combined cycle plants -
Hybrid power plants
Combined cycle power plant
• Steam from geothermal reservoir (after liquid separation) turns
level-1 turbine (dry steam or flashed steam power plant!)
• Exhaust steam is used in the working fluid vapourizer and vapours
of the working fluid turn level-2 turbine (binary cycle!)
• Exhaust of level-2 turbine is condensed and condensate of the
working fluid is preheated (prior to sending to the vapourizer) by
– separated geothermic liquid (brine)
– condensate of the vapourizer
• Efficiencies are significantly greater
Hybrid power plants
• Integration of numerous generating technologies
– Still water solar geothermal plant
– Geothermal pre-heated hybrid power plants
21.
22.
23. Hot dry rocks and EGS
• Deep Earth (3 to 6 km) geothermal resources (hot dry rocks)
– Lack of water and being at 3-6 km depth are the problems
– 1 km3 hot rock on cooling by 100C (70,000 ton coal equivalent
energy) will yield 30 MW years of power for 30 years
– Extraction of energy from deeper hot rock (about 20000 feet)
may prove uneconomical
• Enhanced geothermal systems (EGS) makes up for the deficiencies
of permiability and water
– Wells of 3 to 6 km depth drilled into the crust are used
– Fracture network in the rock is enhanced through introducing
working fluid (water) at higher pressure
– The geothermal system will have one injection well and two or
more production wells
– Pressurized cold water is injected into the fractured rock and
pressurized hot water is taken up for use
• EGS requires innovative methods to attain sustained, commercial
production rates while reducing the risk of seismic hazard
24.
25. Direct use technologies
• Geothermal heat (hot water of <150C, 30-90C) is used directly,
without a power plant or a heat pump
• Direct uses may include
– For cooking and medicinal purposes (traditional uses of hot springs)
– In Geothermal heated spas, resorts and pools
– For heating buildings
– For heating industrial processes
– Using in Green houses, Aquaculture systems and Drying
– Melting of snow
• Geothermic fluid often contain chemical contaminants
– Use heat exchangers to transfer heat to cleaner water/air and use
• Typical geothermal direct use system configuration includes
– accessing the fluid
– bringing to plate heat exchanger
– returning the used fluid through recharge well
– a second loop of clean water or air for energy use
• Applications are usually within 10 km distance from source
27. Air conditioning and heat pumps
• Heat pumps and their use for heating and cooling
– Heat pumps cause heat flow uphill against the temperature
gradient and bring about space heating and cooling
• Heat pumps (refrigeration cycles) two types
– vapour compression refrigeration cycle
– vapour absorption refrigeration cycle
• Heat pumps are two types: Air source heat pumps and water
source heat pumps
– Water source heat pumps are used in geothermal heat pumps
• Ground source heat pump systems includes 3 components
– Geothermal earth connection sub-system
– Geothermal heat pump sub-system
– Geothermal heat distribution subsystem
• Earth is a steady and incredibly large heat source (in winters)
and heat sink (in summers) of the geothermal heat pumps
– Beyond 6 feet depth earth temp. remains constant year round
32. Geothermal heat pumps (GHPs)
• Also referred to as GeoExchange, earth-coupled, ground-source, or
water-source heat pumps
• These are able to heat, cool, and, if so equipped, supply hot water
• Earth’s constant temp. is used as exchange medium (instead of
variable temp. of outside air) – through a ground heat exchanger
– A few feet below, earth's temp. is constant (vary with latitude: 7-21°C)
• System efficiencies are high (300 - 600%) on coldest winter nights
– Air-source heat pumps are 175% to 250% efficient
– Some models use two-speed compressors and variable fans for more
comfort and energy savings.
• Installation costs are several times higher (compare with air source
units), but are quieter, last longer, and need little maintenance
– The additional cost is returned in 5 to 10 years as energy savings
– System life expectancy is 25 years for inside components and 50+
years for the ground loop
• Dual-source heat pump (water source and air source heat pumps)
– Efficiency ratings are higher than those of air-source units, but lesser
than those of water source units
33.
34. Geothermal heat pumps (GHPs): Types
Closed loop systems
– Antifreeze solution circulates in a closed loop buried in the
ground or submerged in water
– heat transfer between the refrigerant in the heat pump and the
antifreeze solution in the closed loop occurs in a heat exchanger
– Direct exchange systems (a variant of closed loop system)
• Heat exchanger is not used – instead refrigerant is directly
pumped through copper tubing buried in ground of non-
corrosive soil
• Requires a larger compressor and works best in moist soils
• should avoid installing in soils corrosive to the copper tubing
– The loop can be in a horizontal, vertical, or pond/lake
configuration.
• Pond/lake
– Sites with a closeby water body (of minimum volume, depth and
quality) can go for this cheaper option
– Water supply pipeline is run underground from the building to
the water boy and coiled into circles at >8 feet depth
35. Geothermal heat pumps (GHPs): Types
• Horizontal
– Cost-effective for residential installations if sufficient land is
available
– Requires >4’ deep 2’ wide trenches, and two pipes burried in
the trench (one at 6’ and the other at 4’, or, both at 5’ side-by-
side) are used
– Use of more pipes can reduce the trench length required
• Vertical
– Large commercial buildings, schools, etc., the vertical systems
(avoids prohibitively large land area requirements of horizontal
loops)
– also used in places of too shallow soil for trenching
– ~4” holes are drilled 20’ apart upto 100 to 400 feet deep. – 2
pipes forming a loop by U-bend at the bottom are inserted into
the holes
– The loops are connected with a horizontal pipe or manifold
(placed in trenches) connected to heat pump at the other end
36. Geothermal heat pumps (GHPs): Types
• Open loop systems
– These use a well or surface body water as the heat exchange
fluid circulating directly through the GHP system
– The used water is either returned to back through a recharge
well, or discharged on the surface
– Practical only if adequate supply of clean water is there
• Hybrid systems
– A combination of one or more water source units and/or air
source units (i.e., a cooling tower) are used
– Effective if the cooling needs are larger than the heating needs
– standing column well system (variant of an open-loop system)
– one or more deep vertical wells are drilled
• Water is drawn from well bottom and returned to well top
• During periods of peak heating/cooling, part of the used water is
bleed out and not returned to the well
• Causes water inflow from aquifer and cools/heats well water
• Climate, soil conditions, available land, and local installation
costs will influence the selection of GHP type
37. Advances in geothermal technologies
• Expansion of usable resources, improvements to the economics of
generation, and new applications
• New and better working fluids for binary power systems to achieve
greater heat transfer efficiencies and produce power at lower temp.
– Kalina cycle and green machine: uses ammonia-water mixed working
fluid to produce upto 50% more power from the same heat source
• On-site small power generation (distributed generation facilities)
– Energy not being used could be sold back to the grid
• Use of hot water produced by oil wells
• Coproduction, enhanced geothermal systems (EGS), geopressured
and supercritical systems
– Coproduction of geothermal and oil/gas at oil and gas wells
– Geo-pressured resources (reservoirs of high-pressured hot water)
– Super critical cycles
• Pumping of supercritical fluid (CO2) into underground geological formation
(at 4-5 km depth and 400-600C temp.)
• Fluid is heated up and expanded, and fracture system is enhanced
• pumping out hot fluid to the surface power plant
38. Geothermal energy and Environment
• Geothermal wells
– Drilling of wells is noise polluting
– Land subsidence, land instability and induced seismicity
• Extraction of large quantities of geothermic fluid
• Greater concern specially for high temp. installations
• Induced seismicity - a potential problem for EGS technology
– Geothermal energy wells can blow up from the top
• Geothermal fluid can
– Be a brine solution and can be corrosive and scaling
– Trace amounts of toxic chemicals/ minerals (boron and arsenic)
– Have gases like H2S and CO2
• Solutions to problems
– Binary cycle or closed loop operation
– Chemical treatment or mineral recovery
• Zinc, lithium, manganese, strontium, rubidium, potassium,
manesium, lead, copper, boron, silver, tungston, gold, cecium,
barium, silica, and sulfur
– Monitoring and targeted injection can minimize the subsidence
39. Geothermal energy and Environment
• Geothermal energy is a renewable energy
• Geothermal power plants have capability to provide base load
power and there are no seasonal variations
– Immunity from weather effects and climate change impacts
– Unlike coal and nuclear plants geothermal plants can be online
for >90% time (75% for coal plants and 65% for nuclear plants)
• Geothermal power carbon generation is 13.38 g/kWh
– Natural gas plants produce 453 g/kWh, oil plants produce 906
g/kWh and coal plants produce 1042 g/kWh of CO2
• Land requirement is very less – 400 m2 per GW power
• Geothermal heat pumps produce 4 times the power they
consume
• Overall, geothermal energy is environmentally advantageous
– Environmental and social impacts of geothermal energy are site
and technology specific and largely manageable.
Editor's Notes
Geothermal power plants account for >25% of the electricity produced in Iceland and El Salvador
Exploration of geothermal reservoirs – drilling and testing for conditions of production (temperature and flow of the resource)
Geothermal energy accounts for 3% of the total renewable energy based electricity
6 most promising geothermal energy sites include
Tattapani in Chattishgarh
Puga in J&K (Geothermal gradient is 250C/1.2 km)
Cambay Graben in Gujrat
Manikaran in Himachal Pradesh
Surajkund in Jharkhand
Chhumanthang in J&K