Geothermal and other non-traditional energy sources

Lecture index: Geothermal, hydroelectric, tidal and wave energy, geologic components of biofuels, other energy sources.

Geothermal

Yellowstone is one of the better known geyser fields, fueled by the earth's internal energy. This image of an eruption where groundwater has been transformed into steam, a striking demonstration of the amount of energy locally available.

Heat capacity of rocks - Heat capacity is a basic descriptor of the energy content of a given material. For granite it is estimated at .19 calories/gram C° (https://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html). 1 kg = 1000 grams, which with a density of 2.5 gm/cc would be a cube of rock roughly 7.36 cm on a side, or 2.89 inches on a side the energy associated with a 1° C temperature change would be 190 calories. Since water is the transporting medium its heat capacity is important also, and is aout 1 calory/gram C°. Remember that water is less dense than rock, but even per unit volume there is a greater calory change associated with a 1° change in T. With this information you could estimate how much energy is a cubic kilometer of rock.

• geothermal gradient is the increase of T with depth in the earth's crust.
• range of values: 10-70 Centigrade/kilometer.
• as expect, higher in volcanic regions.

A suite of geothermal maps - http://smu.edu/geothermal/heatflow/heatflow.htm

Types of Geothermal energy:

• existing developed hydrothermal systems: Iceland, New Zealand, Nothern California
• evolving natural plumbing and mineralization can be a challenge.
• reducing pressure and temperature by extracting the heat can change these dynamics.
• why not Yellowstone?
• hot-dry rock program
• recovery of energy from deep oil brines (in theory at this point), a form of waste-heat recovery.
• shallow geothermal and heat pumps (ground as a balancing reservoir)

Northern California geothermal power plant at The Geysers. Image source: http://pubs.usgs.gov/gip/dynamic/geothermal.html

What is controlling the pattern here? Source: http://pubs.usgs.gov/ha/ha730/ch_h/jpeg/H096.jpeg

Video of hot well out of control in Yellowstone: http://pubs.usgs.gov/of/2008/1014/

USGS Fact Sheet on U.S. geothermal power: http://pubs.usgs.gov/fs/2008/3082/

Hydroelectric

This is a traditional approach. Remember previous discussion on effects of dams on river systems. Mountainous countries such as Norway have abundant hydroelectric resources. Pump storage, where another energy source is used to pump water up to a reservoir which can then be released later to produce electricity when it is needed, is also a possibility.

Glen Canyon Dam - Image source: http://walrus.wr.usgs.gov/grandcan/dam.html

Diagram of typical arrangement for hydroelectric power. Image source: http://ga.water.usgs.gov/edu/hyhowworks.html

Tidal and wave energy

This is more non-traditional, and a related question is as to why? Below are some considerations

Large sand waves (mega-ripples) caused by tidal currents in and out of San Francisco Bay. Image source: http://pubs.usgs.gov/sim/2006/2944/

Geologic components of biofuels

We don't have time to address in detail, but there is a geologic element here in that soil, water and fertilizers are involved in the production of many biofuels.

• ethanol from corn ( very important to Nebraska's economy).
• algal vats - still largely in research phase.

What is the relative efficiency of solar panels versus photosynthesis and plants?

Other energy sources

We won't discuss in detail in this particular class, but can be quite important, especially locally.

• Wind
• Solar
• Hydrogen
• Efficiency!!

The significance of energy storage:

• traditionally batteries, where there are significant geologic considerations:
• rare metals required for more powerful batteries (e.g. lithium).
• carbonatites and pegmatitites, rare sorts of igneous intrusions, are two potential sources.
• geopolitical distribution - China a major supplier.
• USGS report - https://pubs.usgs.gov/fs/2002/fs087-02/fs087-02.pdf.
• Elk Horn Creek carbonatite deposit in SE Nebraska may soon be mined.
• Graph from above USGS report showing mining production of rare earths. Accessed 11/27/2017/
• disposal/recycling concerns.
• pump and store systems discussed above.
• hydrogen?

There is a significant array of energy possibilities in the future, but many have specific site requirements and environmental considerations. Linked energy systems and smart grids are research focal points.