Geothermal energy

Next to hydropower and biomass, geothermal energy is the largest renewable energy resource in the U.S.  Harvesting geothermal energy distinguishes between energy gained from two or three km deep under the ground and from energy gained from approximately 100 m under the ground. The deeper the exploration the higher the temperature required. The United States have the most geothermal power of the world. Texas has the potential to contribute 10% to the United States’ geothermal energy potential. Currently, geothermal energy production in Texas is less than 1%.

Potential for geothermal energy in deeper earth finds itself in various ways. There is space for hydrothermal resources, as indicated by the orange areas in the adjacent figure. These are found in fractured and porous rocks in form of hot water or steam. Geo-pressured resources are represented by the green spots on the map below. They consist of hot brine with methane and are found in deep aquifers where water is trapped under high pressure due to burial processes. Also, the heated geological formation of hot dry rock is present in the East of Texas, providing possibilities for heating and electricity. In addition to that, the areas designated by the lines in the map show large geothermal potential, for the existence of oil and gas wells proved to hold temperatures above 212 degree Fahrenheit (100 degree Celsius) in these regions, some above 300 degree Fahrenheit (150 degree Celsius).

Since Texas has the experience of locating oil and gas resources and thus the skills for subsurface analyses of heat-resources, reservoirs and deep-water availability, they have an advantage in locating and drilling for geothermal resources as well. Costs of drilling wells have reduced, which is attributed to the improvements in drilling technology and horizontal drilling, which also allows for more efficient drilling in different directions. Next to that, hydraulic fracturing increased the permeability of the shale formations. Technology advancements in binary cycle heat exchange systems allow for efficient economic power creation with lower boiling points.

One big potential for geothermal energy production in Texas lies in the co-production with oil and gas wells, which produce hot fluids as a waste product representing a cost reduction for oil and gas producers in disposing of this co-product.

The Geothermal Laboratory of the Southern Methodist University and the University of Texas at Austin are research institutes assessing this potential. To obtain more knowledge about available resources, the National Geothermal Data System was developed, a website providing data for all states about criteria for geothermal development. The company Thermal Energy Partners, located in Austin, plans and implements geothermal power plant projects on a worldwide scale and are open to partner up with international research institutes and companies.

Another application of geothermal energy is geothermal heat pumps or heat exchange systems which employ geothermal energy from shallower grounds with temperatures of 10-30 Celsius. These technologies make use of a loop system in 60-80m deep ground where temperatures remain constant. Warmer water underground is pumped to heat houses and buildings during winter time under higher compression of the pump. During summer time underground temperatures are colder than the air above. Therefore, the fluid from underground is now transported to the pump and circulated to supply the building with cooler air. There is economic efficiency involved, as one unit of electricity is needed by the heat pump to generate four to five units of heat. A gas furnace can only produce one unit of heat for one unit of electricity. The U.S Department of Energy emphasizes that every state in the U.S. has the potential to deploy geothermal heat pumps as the ground has the same shallow ground temperature. In 2015 there has been an initiative by Whisper Valley in Texas to help the City of Austin reach its CO2 reduction goals by introducing 7500 net-zero solar and geothermal power equipped homes. The technology for this makes use of a heat pump geo-exchange system. In addition to this initiative ensured by international companies, there are several other private businesses from San Antonio until Dallas. Originally providing air-conditioning, they also discovered the potential of environmental friendly geothermal heating for houses and buildings.

There is clearly an established market for geothermal heat exchange systems. The great potential for deeper geothermal energy exploration has still to be taken up. With studies showing that geothermal energy from oil and gas wells could only cost $0.10 per kWh and the increasing demand for efficient energy, geothermal energy could just fulfill what we are looking for.

Posted by Saskia Pardaans May 12, 2017