By Randy Carroll-Bradd
Texas geothermal heat can provide a viable, cost-effective alternative to expanding current coal and nuclear power generation. Solar and wind generation are practical and get a lot of press, but they’re often dismissed as too intermittent for base load electric generation. Geothermal resources are not intermittent and currently provide more electricity, nationwide, than all solar and wind installations combined.
Southern Methodist University’s Geothermal Lab has studied the geology of Texas since the 1970s and identified the local potential lying between the coast and I-35, using binary technology, a workable, low-cost solution available today. Using binary systems, the geothermal resource does not need to be as hot as that around the Pacific Rim. Deep source hot water or low-temperature steam (190-300 degrees F) goes through a heat exchanger to vaporize a refrigerant, similar to that used in your air conditioner, which expands and drives a turbine. The working fluid is then radiator or water-cooled into a liquid again, while the cooled well water is re-injected into the geothermal reservoir. The two fluid streams are separate and never mingle.
Binary units take much less space than coal or nuclear plants, require no fuel to mine or buy, emit no toxic or greenhouse gases, consume no water, have no security issues, and no waste to dispose. They run outdoors, unattended, and are so reliable they have the best uptime percentage of any power source: at 98%, easily beating both coal and nuclear.
Geothermal equipment manufacturers have built power plants around the world, some for over 40 years. Binary generators are typically very similar to industrial AC chiller units, allowing economies of scale since chillers are mass-produced and readily available. ln fact, they are so similar, the number of parts required to convert a United Technologies (Carrier) chiller into a geothermal generator is extremely small- 13 geothermal parts replaced or added to 171 original chiller parts.
A single, binary geothermal unit fits easily on a truck trailer and generates about 250 kW so power plants consist of generator arrays, sized by the available heat source reservoir and desired electrical output. Because of these constraints, geothermal arrays vary in size and location, creating a distributed, decentralized supply. Unlike large centralized plants, they’re immune to the catastrophic breakdowns experienced last summer at CPS Energy coaland gas-fired units.
An equivalent-output geothermal array costs no more than a conventional coal plant and millions less than a nuclear plant. According to a Texas State Energy Conservation Office report, a 1 MW plant costs about $1.5 million, including the big expenses of well exploration, drilling and grid connection.
Fortunately, of Texas’ 600,000+ existing oil and gas wells - producing and not- over 100,000 wells have geothermal resources at depths and temperatures suitable for binary generation:
- All oil and gas wells depth and initial fluid temperature are recorded with the Railroad Commission, greatly reducing exploration costs.
- Since drilling is a large portion of the cost of geothermal generation, the ability to use existing even abandoned wells saves significant site development money.
- Roads and power lines remain in place at all but the oldest wells, so connection-to-grid costs can be mitigated even in relatively remote areas.
The hottest well recorded with the Railroad Commission is 5 10°F @ 23,800 ft., east of Victoria, Texas. In 2004 the U.S. produced over 5xl01° bbl (that's 2, l00,000,000,000,000,000,000 gallons !) of “waste” water along with the oil and gas production, primarily from the Gulf States with temperatures high enough to produce electricity. This hot water could be used to generate power directly, without impacting oil and gas production. Some estimates suggest up to 5000MW of additional power could be generated in Texas alone -- that's more than 10 times the amount of power used by the entire State of Alaska!
So, there’s no reason local geothermal power generation in South Texas couldn’t be developed at significantly reduced cost. All that’s needed is entrepreneurial vision and political will.
Some Geothermal Power Facts
- Direct (non-binary) geothermal energy currently provides more than 2700 megawatts (MW) of electric power to U.S. residents - comparable to 60 million barrels of oil per year, enough for 3.5 million homes. This is only a small fraction of the potential value of geothermal energy in the U.S.
- Geothermal electricity is clean - no fossil fuels are burned. Geothermal electricity produced in the U.S. displaces the emission of 22 million tons of carbon dioxide a year!
- Geothermal electricity is reliable - plants have average system availabilities of 95% or higher, compared to 60-70% for coal and nuclear plants.
- Geothermal electricity is cost-effective - today's cost of geothermal electricity ranges from $0.05 to $0.10 per kilowatt-hour, and technology improvements are steadily lowering that range.
- The average geothermal field uses 1-8 acres per megawatt (MW) versus 5-10 acres per MW for nuclear operations and 19 acres per MW for coal power plants.
- Geothermal electricity is homegrown - it reduces our need for coal and uranium, reduces the trade deficit, and adds jobs to the U.S. economy.
Resources and References
Southern Methodist University Geothermal Department
MIT Evaluation of U.S. Geothermal Potential
Texas State Energy Conservation Office
Pratt & Whitney (binary system manufacturer)
Ormat Technologies (binary system manufacturer)
Sologen (San Antonio geokinetic technology development company)
Greenfire Energy (Geothermal technology utilizing CO2 as well fluid in binary system)
Thanks to Randy Carroll-Bradd for permission to publish this article which was distributed to attendees at the October 27, 2010 meeting of the Texas Green Network. Randy is a sometimes attendee at San Antonio Sustainable Living meetings and an expert in the manufacture of SIPS panels with EH Systems LLC.