geothermal energy

1. Session 13 – Geothermal Energy
T. Ferguson,
University of
The Nesjavellir Geothermal Power Plant in Iceland, Gretar Ívarsson. Wikipedia

2. Session 13 Outline
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Definitions
Renewable Status, Sustainability
Geothermal Resource Types
Utilization
Advantages/Disadvantages
General Status; Potential in Minnesota
R&D
T. Ferguson,
University of

3. Geothermal Definitions
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Geothermal Energy
Crustal Heat Flow
Core, Mantel, Crust of the Earth
Geothermal Gradient
Types: Spontaneous Hot Fluid Production
& Non-spontaneous
T. Ferguson,
University of
Source: EIA

4. Sustainable/Renewable Status
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Large and well-distributed resource base
Crust heat conduction rate: 10 yr recharge
Local depletion occurs
Replenishment
– Conduction from adjacent crust
– Decay of radioactive isotopes
– Fluid-base convective heat transfer
T. Ferguson,
University of

5. Geothermal Resource Types
• Four Types
– Natural Hydrothermal – Iceland
– Geopressurized – sedimentary rocks
– Hot Dry Rock (HDR) – Drill and circulate
– Magma - Yellowstone
T. Ferguson,
University of

6. Utilization Modes
• Electrical Generation
– For electrical delivery
– For hydrogen production
• Process Heat
• Space Heating
T. Ferguson,
University of
Source: EIA

7. Hydrothermal Process
(from Chevron)
http://www.chevron.com/stories/#/stories/re_geo/geo_hiw/
T. Ferguson,
University of

8. Pros and Cons of Geothermal
Energy Conversion
Advantages
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Enormous Stored Energy
Dispatchable
Multiple “products”
Access uses proven oil/gas technology
Simple and safe operationally; quick startup
Disadvantages
– 9 of 10 largest US Cities: >800km from hi-temp sources; only
electrical gen possible
– Only high-grade, hydrothermal reservoirs are economic
– 5-20% Carnot cycle efficiencies
– Treatment of dissolved gases
– Geothermal wells are 2-4 times oil/gas well costs
T. Ferguson,
University of

9. Status
5% of 7%
T. Ferguson,
University of
Source: EIA

10. The Geysers
Northern California
• Calpine owns 19 of 22 Geysers power
plants
• 850 MW
• Largest geothermal electrical gen in world
• Energy output declining ~7-8%/yr
• About 7% of California’s electrical energy
is geothermal
T. Ferguson,
University of
Sources: The Geysers; Geysers Geothermal Association

11. Status of Geothermal Energy
• US Geothermal Output: ~17 million MWh
in 2004; 69% capacity factor
• About 10,000 MW capacity worldwide
(2000); ~8 % annual growth
• Chevron claims top spot with 1273 MWe
• Competitiveness with other sources:
– Low grade geothermal (20-40°C): 8-200 c/kWh busbar price
– High grade (80 °deg +): 4-9 c/kWh
T. Ferguson,
University of
Sources: Text; Canadian Geothermal Energy Association; Chevron

12. Minnesota’s Geothermal Potential
From DOE’s EERE:
“Minnesota has vast low-temperature
resources suitable for geothermal heat
pumps. However, Minnesota does not
have sufficient resources to use the other
geothermal technologies.”
T. Ferguson,
University of
EERE: Energy Efficiency and Renewable Energy Office