GEOTHERMAL ENERGY-CURRENT STATUS AND FUTURE POSSIBILITIES
fossil fuels remains consider- able. Foreign fossil fuels are in high demand and, because they are non-renewable, sources are finite and diminishing. Energy independence would free finan- cial resources for other, more socially beneficial uses and help foster better working relation- ships with foreign countries (IEA, 2007; Valentine, 2011).
Figure 2. Different Methods of Geothermal Energy.
Binary technology is when the geothermal water is kept at a constant pressure rather than being flashed to steam. This geothermal water then will heat another fluid, referred to as a “working fluid” which will have a lower boiling temperature than water and will vaporize. This vaporized working fluid is used to power the turbines. The binary method is considered a closed-loop system with no emissions and is isolated from surface resources such as ground water. Figure 2 illustrates the differences between each of the methods
Why Geothermal?
Geothermal energy is a renewable resource as it is con- stantly replenished by a virtually unlimited and reoccurring (geologic) heat production process. As such, geothermal energy can be an attractive solution to the current dilemma of finding natural non-polluting power. As geothermal energy systems are brought to larger scales, over 3500 megawatts of electricity have been generated, which makes it a close competitor to fossil fuel based generation. Figure 3 shows the trend of generation capacity for each type of geothermal energy system production.
Geothermal energy has neg- ligible environmental impacts. Water availability does not affect the use of geothermal energy. For example, several geothermal plants are in the western part of the United States and although that area is prone
to drought and low water supply, geothermal power plants are not significant competitors for water use (Matek and Schmidt, The Values of Geothermal Energy: A Discussion of the Benefits Geothermal Power Provides to the Future U.S. Power System). Geothermal liquids are primarily brines or salt saturated water solutions. Fresh water is not used and in many cases once the plant is done using the water, it can be reclaimed for either industrial or agricultural applications. Geothermal energy plants take up less land area than other types of power generation plants, including conventional sys- tems and other renewables.
Geothermal energy also has the potential to serve as excel- lent heat sources for thermal desalination processes (Davies & Orfi, 2014; Gude, 2016). The concern over the rising level of Greenhouse gases in the atmosphere is driving industrial development away from reliance on fossil fuels and is providing an incentive for the use of renewable energy (Osmani, et al., 2013; Mai et al., 2014; Tokimatsu et al., 2016). Geothermal processing has no combustion phase, which essentially eliminates the emissions of greenhouse gases; however, for both the dry and flash steam methods, the steam turbine condensers used to process the geothermal energy also can
release small quantities of CO2 from condensate and steam reprocessing (Duffield and Sass). These types of plants emit
about five percent of the CO2 that a coal-fired plant of equal size would emit.
In contrast, binary plants use a closed loop system which has a near zero emission rate because the gases are eventually returned to the reservoir. Table 1 compares the emission levels of a geothermal energy system to an
Figure 3. Generation Capacity for Different Geothermal Methods.
Geothermal energy has many advantages that make it a compelling choice for future power generation. Its widespread use would promote national security and help the United States and other countries to become less dependent on fuels including from often unreliable foreign markets. In 2014, the United States imported nearly half of the crude oil processed in its refineries. While these rates have gone down in the past few years, the reliance the United States has on imported
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equivalent coal burning power plant. While not CO2 free, emissions of Greenhouse gases related to energy production from geothermal sources are orders of magnitude lower when compared to those created by fossil fuels (Figure 4). Greenhouse gas emissions from geothermal energy plants also stack up favorably compared with other types of fossil fuels such as fuel oil and natural gas. While natural gas releases 300 kilograms of carbon dioxide per megawatt-hour, geothermal produces less than half that amount, 120 kilograms of carbon dioxide per megawatt-hour (Matek and Schmidt, The Values of Geothermal Energy: A Discussion of the Benefits Geothermal Power Provides to the Future U.S. Power System).
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