Geothermal Energy
Maura Eveld and Emily Shira
What is geothermal energy?
● geo + thermal = heat from the earth
● geothermal
reservoirs
● hot springs
● renewable
resource
Background
● Geothermal fluids were exploited for their
energy long before the science was understood
● Geothermal steam used for mechanical
processes
○ gas lifts, reciprocating and centrifugal pumps and
winches
● Ring of Fire: Geographical area where most
geothermal activity occurs
Ring of Fire
Timeline
60 AD--Romans used geothermal water in
Pompeii to heat buildings
500-1500 AD--Wars over land with hot
springs
1820 AD--Boric fluid industry developed
1904 AD--First attempt to generate
electricity from geothermal steam
● Continued attempts at increasing
geothermoelectric capacity
How does it work?
Flash
Power
Plant
How does it work?
Direct
Steam
Power
Plant
How does it work?
secondary
fluid
Binary
Power
Plant
(lower temperature)
How do we use it?
Electricity (>150℃)
How much do we use it?
● 3,386 MW of installed
geothermal capacity
○ U.S. 2013, more
than any other
country
● 0.33% of total installed
operating capacity
● 1% of new renewable
energy projects in 2012
Resources
http://www.bgs.ac.uk/research/energy/geothermal/
http://geo-energy.org/Basics.aspx
http://www.geothermal-energy.org/what_is_geothermal_energy.html#c324
http://www.need.org/files/curriculum/infobook/geothermals.pdf
http://www.epa.gov/climatestudents/solutions/technologies/geothermal.htm
https://commons.wikimedia.org/wiki/File:Earth_layers_model.pngl
http://geo-energy.org/currentUse.aspx
http://www.greenfacts.org/en/geothermal-energy/index.htm
http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch04.pdf
http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decayaccounts-for-half-of-earths-heat
http://www.ucsusa.org/clean_energy/our-energy-choices/renewableenergy/environmental-impacts-geothermal-energy.html#references
Geothermal Energy: Week 2
Maura Eveld and Emily Shira
Background: Earth
Review
Heat flow: 1. Magma (upper mantle/lower crust) →
2. Permeable rock →
3. Through faults →
Earth surface
● Heat Source:
○ Radioactive Decay
○ Primordial Heat
Radioactive Decay of Isotopes
● Unstable nuclei
(radioactive isotopes)
spontaneously split up
(radioactive decay),
releasing energy as
heat
(radioactive radiation)
● uranium-238, thorium-232, potassium-40
Renewable Resource
● Not all of the water removed from a reservoir
can be reinjected because of losses to steam
● Other water sources, including non-potable
water, are used to replenish reservoirs
○ Clean water is not a necessity
Environmental Impact
● Water
○ Water consumption for re-injection
● Air
○ No impact from closed-loop systems
○ Hydrogen sulfide, carbon dioxide, ammonia, me
and boron can be emitted from open-loop systems
■ SO2 emissions 30x lower/MWh than from coal plants
● Land
○ Land subsidence is avoided by water reinjection
Carnot Cycle
Working
Fluid
Cold Sink
(Atmosphere)
High Temp. Reservoir
(From Earth)
Output Work
(Electrical
Energy)
Efficiency
TH-TC
η=
TH
● Larger temperature difference → more efficient
● Heat pump COP=3.0-4.5
○ 48% more efficient than gas furnaces
● Free hot water/gas from the earth
○ Efficiency of this system is arguably irrelevant
Scaling
● The Geysers (Calpine
Corporation)
○ largest complex of geothermal
power plants (14) in the world
○ net generating capacity 725 MW
○ 29,000 acres, 80 miles steam
pipelines, 68 miles injection water
lines, 70 miles 21 kV power lines,
8500 feet average well depth
Scaling
● Eburru Wellhead
Geothermal Power
Plant (Kenya
Electricity Generating
Co.)
○ small-scale: <5 MW
○ 2.52 MW
○ single power plant
Machinery
● Geothermal Power Plants
○
○
○
○
turbine
generator
cooling tower
injection well
● Geothermal Heat Pumps
○ ground heat exchanger
○ heat pump unit
○ air delivery system (ducts)
Resources
http://www.bgs.ac.uk/research/energy/geothermal/
http://geo-energy.org/Basics.aspx
http://www.geothermal-energy.org/what_is_geothermal_energy.html#c324
http://www.need.org/files/curriculum/infobook/geothermals.pdf
http://www.epa.gov/climatestudents/solutions/technologies/geothermal.htm
https://commons.wikimedia.org/wiki/File:Earth_layers_model.pngl
http://geo-energy.org/currentUse.aspx
http://www.greenfacts.org/en/geothermal-energy/index.htm
http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch04.pdf
http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decayaccounts-for-half-of-earths-heat
http://www.ucsusa.org/clean_energy/our-energy-choices/renewableenergy/environmental-impacts-geothermal-energy.html#references
http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec005.html
http://www.energyhomes.org/renewable%20technology/geoefficiency.html
Geothermal Energy: Week 3
Maura Eveld and Emily Shira
Roman Baths
● Hot spring located under Bath
○ Water rises at 46℃
● Roman engineers designed
reservoir to store water,
heated to the point of boiling
○ Warm water distributed to other
baths
● All natural; no pumping must
be done
What is a geothermal heat pump?
● Geothermal heat pump=ground source heat
pump (GSHP)
● The sun keeps the temperature of the
ground at a constant 45-55༠ F
○ warmer than typical winter air temperatures, cooler
than typical summer air temperatures
○ can take advantage of this constant temperature to
heat in the winter and cool in the summer
How does a standard heat pump work?
How do geothermal heat pumps work?
● Water-antifreeze solution is warmed by the
ground in pipes and pumped to the evaporator
○ Replaces outside air as source of heat to boil refrigerant
● Same concept as air-source heat pump
○ evaporator → compressor → heat exchanger →
expansion valve
How geothermal heat pump work?
Types of Heat Pumps
● Closed Loop
Types of Heat Pumps
● Open Loop
Why is it relevant?
● Much more efficient than air source heat pumps
○ Carnot cycle
○ 4 kW output for every 1 kW input
● Can be used anywhere, not just in the ring of fire
● Since the heat for the system comes from the
sun, the process is renewable
● Closed loops limit environmental impact
Cost
● £9,000-£17,000 to install
○ Save on running costs
○ Compare to gas boiler, average cost £2,300 without
radiators
● Save ~£500 a year if switching from electric
heating
○ Less saving if switching from gas
○ Very low maintenance, rarely must pay for repair
Resources
http://www.uswitch.com/energy-saving/guides/ground-source-heat-pumps/
http://www.icax.co.uk/Heat_Pumps.html
http://www.energysavingtrust.org.uk/domestic/electric-heating-systems
http://energy.gov/energysaver/articles/geothermal-heat-pumps
https://www.youtube.com/watch?v=KE3SvNRmwcQ
http://www.climatemaster.com/residential/how-geothermal-works/
http://deebrun.com/air-source-heat-pump-diagram-decorating-ideas.html
https://en.wikipedia.org/wiki/Geothermal_heat_pump#Standing_column_well
Geothermal Energy: Week 4
Maura Eveld and Emily Shira
In the News: The Geysers
● Valley fires in Sonoma County, Northern
California has affected 5 of Calpine’s 14
power plants (15 September 2015)
○ Unaffected plants are still transmitting energy to the
grid
○ Some third-party transmission lines also damaged,
cutting off power transmission to the grid
In the News: The Geysers
In the News: Kenya
Overview
The Future of Geothermal Energy
● Technology improvements
should advance the ability to
access new, deeper areas with
supposed higher heat content
● Cost of energy will decrease
with increased efficiency
○ More efficient → Decreased price → More practical
energy source
Drilling Technology
● Adapted from oil & gas drilling processes
● Improvements on existing technology
○ more robust drill bits
○ better casing methods and cementing
techniques
○ sensors that can withstand high temperatures
● New technology
○ method of rock penetration, such as projectile
drilling
Power Conversion Technology
● Goal 1: Improve heat-transfer performance
for lower-temperature fluids
● Goal 2: Develop plant designs for getting the
higher temperatures to the critical equipment
for efficiently
● Anticipated result: Improve reservoir
performance and heat-to-power conversion
efficiency by an order of magnitude
Reservoir Technology
● Energy extracted dependent on flow rate,
temperature, and pressure drop
● Long path length=longer reservoir life
○ But also causes higher pressure drop
● Solution: Many fluid paths
○
○
○
○
High flow rates
High fracture surface area
Low pressure drop
High heat exchange
Anticipated Result of New Technology
Questions?
Resources
https://mitei.mit.edu/system/files/geothermal-energy-full.pdf
http://sanfrancisco.cbslocal.com/2015/09/15/valley-fire-devastates-facilities-at-the-geysersgeothermal-power-plant/
https://commons.wikimedia.org/wiki/File:Geothermal_drilling_at_Te_Mihi_NZ.jpg
http://cleantechnica.com/2015/08/13/revolutionizing-geothermal-well-drilling-shooting-projectilesearth/