There’s Energy Under the Ground

Introduction

By looking at the history of energy we see that there has been many fuel sources become dominant over other ones, and then as it depletes or another fuel source seems better it eventually becomes comparatively obsolete.  These fuel sources are used to power everything from cars, lights in houses, and HVAC systems in buildings.  To look out for the future generations we need look into renewable sources which could either get us off of fossil fuels or decrease our dependence on fossil fuels; therefore enabling the use of fossil fuels for a longer period of time.  With all the hype over solar and wind energy most people do not give geothermal a second thought, but in the United States geothermal heat is the third largest source of renewable energy.  There are hundreds of thousands of megawatts of energy under the ground which scientists believe it to be relatively inexhaustible [6].

What exactly is geothermal energy and how can it be used? 

 First we need to know where the heat underground comes from.  Most of the heat underground is believed to come from a layer of magma deep under the earth’s surface caused by the decay of radioactive material [1]. Because of this extreme heat deep in the earth there are at depths of 10 to 100’s of feet a constant temperature ranging from 45-60 degrees fahrenheit all around the world.  This constant heat source is where scientists and engineers are getting geothermal energy from.

One of the most common ways to harvest geothermal energy is by tapping into naturally convecting water source in which water naturally goes down as cold water and come back as heated water, which can then be harvested as steam for steam turbine power plants.  Although this method is an efficient way to produce energy, it is limited by location because it has to be in a place where this natural convection is occurring.

Another way that geothermal energy is being used is through ground-source heat pumps for residential and commercial buildings.  The process begins with running water lines usually made of high density polyethylene pipe under the ground.  When there are not space constraints horizontal trenches are dug around 10 feet deep and the length depends on the size of the application, but typical lengths are 150 feet.  In situations where there are space constraints vertical holes are drilled to around 150 feet deep [3].  The geothermal units rely on the constant temperature of 45 to 60 degrees Fahrenheit.  In the winter months, the geothermal unit cycles the water underground through the pipes and takes the warm water and creates heat for the building using a similar method as the refrigeration cycle.  The cool water is then taken down through the pipes underground and reheated by the earth and the cycle repeats itself.  In the summer the same principle is applied except the system uses the cool 50 degrees underground to cool off the heat the system rejects in order to cool the building [5].

Where is it already being used?

The U.S. is the largest producer of geothermal energy in the world and the largest geothermal development is in California, near San Francisco.  The power plant is called Calpine and has a capacity of 725 MW which they claim is enough to roughly power 725,000 homes [2].  As of 2007 the United States was installing 58 new geothermal energy plants.  These 58 stations will provide 2,250 MW of energy or 18 billion kilowatt-hours of electricity annually when they are completed [1].  Below is a description of a map of the U.S. which describes what part of the country is better for what type of Geothermal use.  This was obtained from [6].

“The map below shows areas of geothermal resources in the United States. The white areas show low temperature areas good for geothermal heat pumps (geoexchange systems) that can work almost anywhere in the United States. The blue areas have hotter water for direct use projects, and the pink areas have the high temperatures required for most geothermal electrical power generation. Geothermal electrical power generation has traditionally been more restricted to the western states where high temperatures are closer to the surface of the Earth.” [6]

Conclusion

With the energy demand in the U.S. increasing annually and so many Americans wanting to get off of foreign oil for safety issues there is a need to produce energy in our own country.  Presidents of the past have sought to find an economical way to extract energy from our home soil and geothermal energy could be the answer.  Geothermal energy looks to be very promising and is a renewable source that we could tap into for years to come.

References

[1]  2012 Union of Concerned Scientists. (2012). Introduction. In How Geothermal Energy Works . Retrieved February 21, 2012, from http://www.ucsusa.org/‌clean_energy/‌technology_and_impacts/‌energy_technologies/‌how-geothermal-energy-works.html

[2] Calpine. (2012, January/‌February 21).The Geysers. Retrieved from http://www.geysers.com/

[3] Closed Loop Systems. (n.d.).Dragin geothermal well drilling . Retrieved February 21, 2012, from http://www.dragingeothermal.com/‌system_types.html

[4]Geothermal Energy: International Market Update. (n.d.). Retrieved May 23, 2012, from http://www.geo-energy.org/pdf/reports/GEA_International_Market_Report_Final_May_2010.pdf

[5] How Geothermal Works. (2012). Hydron Module. Retrieved February 21, 2012, from http://www.hydronmodule.com/‌about/‌geothermal-process

[6] State Government. (n.d.).Texas Geothermal Energy. Retrieved February 21, 2012, from http://www.seco.cpa.state.tx.us/‌re_geothermal.htm

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2 Comments

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2 responses to “There’s Energy Under the Ground

  1. sultan316

    Very informative blog. Gives a great outlook on geothermal energy and all the energy resources that we have that’s just right under our feet. I found it interesting how you mentioned the company Calpine. I had no idea how large they were on a geothermal energy basis. While previously working for Shell at their Deer Park refinery, the Calpine steam plant could be seen right next door from the parking lot. Calpine was the sole provider for all of the refinery’s steam necessities. The steam provided at 1250 psig is converted into typically three different pressures for use throughout the plant. Every now and then steam delivery problems occurred. [1]

    That was just my personal experience with the company. Building off what you said regarding its limitations based on location, there is actually another big disadvantage linked to that: the difficulty of transportation. In comparison with oil, transportation of geothermal energy is not exactly the easiest thing. The risk of energy loss can prove too much to handle during this process. This disadvantage along with the location constraints provides way too much restriction on delivering energy across the US. Even though geothermal energy does seem like it could be promising, it just doesn’t seem feasible enough.

    [1] http://www.roe.com/projects/power/calpinedeer.htm
    [2] http://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2011/mansure.pdf

  2. lauramtaylor

    This blog provides a good insight into how geothermal energy can be used and where it is feasible.

    One thing you do not mention is the possibility of emissions in drilling for geothermal energy sources. Geothermal power plants can emit nitrous oxide, sulfur dioxide, and carbon dioxide to name a few.

    I visited New Zealand two summers ago and focused a lot on the geothermal activity of the surrounding regions. The New Zealand Geothermal Association has estimated that, for equivalent sized power plants, emissions of geothermal plants equal that of about 10% fossil fuel [1].
    So while it is significantly lower than oil and coal, it is still a concern.

    One of the world’s oldest geothermal power plants, Wairakei Power Station, is located in New Zealand just north of Taupo and south of Rotorua. While visiting these regions, I noticed they had a rotten eggs smell, particularly in Rotorua. The city has a large amount of geothermal activity and is known as “Sulfur City” due to the hydrogen sulfide emissions.

    This is a potential drawback to geothermal energy but as a sustainable energy source, it is certainly an area for further exploration.

    [1] New zealand geothermal association: Emissions. (2009). http://www.nzgeothermal.org.nz/emissions.html

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