T. Ferguson, University ofMinnesota, Duluth. 2008.

Session 13 – Geothermal Energy

The Nesjavellir Geothermal Power Plant in Iceland, Gretar Ívarsson. Wikipedia

T. Ferguson, University ofMinnesota, Duluth. 2008.

Session 13 Outline

• Definitions

• Renewable Status, Sustainability

• Geothermal Resource Types

• Utilization

• Advantages/Disadvantages

• General Status; Potential in Minnesota

• R&D

T. Ferguson, University ofMinnesota, Duluth. 2008.

Geothermal Definitions

• Geothermal Energy

• Crustal Heat Flow

• Core, Mantel, Crust of the Earth

• Geothermal Gradient

• Types: Spontaneous Hot Fluid Production & Non-spontaneous

Source: EIA

T. Ferguson, University ofMinnesota, Duluth. 2008.

Sustainable/Renewable Status

• 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 ofMinnesota, Duluth. 2008.

Geothermal Resource Types

• Four Types– Natural Hydrothermal – Iceland– Geopressurized – sedimentary rocks– Hot Dry Rock (HDR) – Drill and circulate– Magma - Yellowstone

T. Ferguson, University ofMinnesota, Duluth. 2008.

Utilization Modes

• Electrical Generation– For electrical delivery– For hydrogen production

• Process Heat

• Space Heating

Source: EIA

T. Ferguson, University ofMinnesota, Duluth. 2008.

Hydrothermal Process(from Chevron)

http://www.chevron.com/stories/#/stories/re_geo/geo_hiw/

T. Ferguson, University ofMinnesota, Duluth. 2008.

Pros and Cons of Geothermal Energy Conversion

Advantages– 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 ofMinnesota, Duluth. 2008.

Status

Source: EIA

5% of 7%

T. Ferguson, University ofMinnesota, Duluth. 2008.

The GeysersNorthern 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

Sources: The Geysers; Geysers Geothermal Association

T. Ferguson, University ofMinnesota, Duluth. 2008.

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

Sources: Text; Canadian Geothermal Energy Association; Chevron

T. Ferguson, University ofMinnesota, Duluth. 2008.

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.”

EERE: Energy Efficiency and Renewable Energy Office