We are in a continual search for sustainable and clean energy to secure our future, looking across oceans, within fields of specialized grass, and even towards the ethereal skies that harbors today’s supply of solar energy. But how often have we looked way below, beyond the depths of oil and pockets of natural gas, instead towards depths nearing the Earth’s core? The solar system’s largest fusion reactor, a bright yellow ball of energy that lights up our skies is incidentally not the only spherical source of radiance within the vicinity of our planet. In fact, within our own planet, at its center lies a glowing mass of superheated iron, nickel, and possibly silicon, which forms what is known as the Earth’s core.1 Most planets and stars in our solar system have a superheated core that is rotating along with these bodies, maybe even faster than the planets’ rotation speed.
Heat and Energy
Most importantly, however, is the aspect of heat that is intrinsically tied to a layered and glowing mass of superheated metals at the Earth’s core. By definition, heat is referred to as a transfer of thermal energy, and this transfer occurs between an area of relatively high temperature and low temperature.2 As one can imagine, the Earth’s core is many times hotter than the surface, and therefore a heat transfer should theoretically yield a high transfer of thermal energy between areas beneath the Earth’s surface towards its core and the Earth’s surface, which has proven to be far from warm in places such as the Antarctic. Technologically, however, heat transferring is an almost prehistoric means of harnessing energy. Most coal burning plants today generate energy through a steam driven turbine, in which the energy for creating steam comes from coal. The first steam engine created by Thomas Newcomen in the year 1712 also used the same principle of creating steam and condensing the vapor to create a temperature and pressure differential that was capable of doing work.3
While using heat as a means of creating energy falls short of being a new idea, a more thorough and revised understanding of the Earth and its subterranean environment has elucidated a source of heat independent of traditional fossil fuels. Researchers alike have wondered whether the Earth’s naturally hot core could be a source of heat to generate power and this is the basis of geothermal energy—from the Greek words geo, or “earth,” and therme, meaning “heat.”5 Intuitively, it would seem nearly impossible to access the Earth’s core, which is nearly 4000 miles underground.6 Thankfully, there is still much thermal energy near the Earth’s surface in the form of magma, or molten rock, due to the uneven nature of the Earth’s crust that makes different parts of the planet closer to the core than others. The general idea is that the deeper we venture towards the Earth’s center, the greater the temperatures.
If, however, we are interested in harnessing heat from the depths of the underground, more practical and shallow pockets of heat must be found. This is particularly why geothermal power stations cannot be built just anywhere. Many of us have seen magma as lava flows during volcanic eruptions, and likewise there are sources of heat that often come in contact with water to create hot springs that gush to everyone’s amazement at some of North Americas most prominent natural parks. While the beauty is captivating, these natural formations illustrate the presence of accessible, subterranean heat for geothermal power.
Direct Geothermal Energy
There are several ways to harness geothermal energy, and one very common method may not even involve producing electricity for the grid. Using direct geothermal energy, many cities around the world pipe heated water from nearby hot springs into homes instead of using natural gas as it is conventionally done.7 Heated water can also act as a vehicle for heat exchange, so it possible to use the heat from geothermal water to heat an entire building. Those who have seen the old radiator heaters are familiar with this principle, and it is essentially the same scientific principle used for decades. There has been general widespread success using this simple technique in cities or even countries rich in natural spring activity, and a great example would be Iceland, in which the abundance of natural springs coupled with environmental proactivity has managed to take care of 87% of Iceland’s heating demands.8
The global utility of geothermal energy, however, is measured by its ability to contribute to electricity on the grid such that the energy demands of households and businesses can be met. Therefore, much of the focus for geothermal energy has been centered on the creation of geothermal power plants that can contribute to electrical power instead of heat alone.
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Geothermal Power Plants
The United States currently leads the world in total power output from geothermal power plants at over 3000 Megawatts combined.10 California alone makes up a huge portion of the total output, with 2565.5 Megawatts of installed capacity according to data gathered in 2007, as well as a commendable 5% of its energy being derived from geothermal power.11 The general concept is actually rather simple and follows the standard recipe for power generation. Just as there are turbines that spin in hydroelectric dams and conventional coal fired power plants, the geothermal power plant also has turbines whose blades are spun with the help of steam created by heat channeled from underground sources of thermal energy. Three general categories of geothermal plants help elucidate the conceptual framework for energy generation through geothermal power.
- 13Direct Steam (Dry Steam) Plants: these are perhaps the oldest kind of geothermal plant dating all the way back to 1904 in Italy,12 making use of the basic concept described above to generate energy. Water is pumped underground into a reservoir that is exposed to the exceedingly high temperatures of subterranean Earth. Under high temperature and pressure, the water is converted to steam and essentially shoots back up to the surface while turning a turbine generator in its path. In this type of set up, water is continuously being fed into the geothermal reservoir while simultaneously being expelled as steam. While the concept may seem scientifically sound, one of the issues with such a method has been excessive corrosion due to underground minerals being pushed up with the steam to the surface. There have also been concerns regarding pollution, as quite a bit of sulfur may be released to the surface while being dragged up by steam. The largest direct steam plant in the world is at The Geysers in Northern California, and is the world’s largest single source of geothermal power.14
- 16Flash Steam Plant: As one of the most common forms of geothermal plants seen today, flash steam plants use a temperature and pressure gradient in a unique fashion to create steam for turbine spinning.15 Heated geothermal fluid at temperatures exceeding 360 degrees Fahrenheit and at high pressure is pumped from underground into a surface tank that is at a much lower pressure. The sudden change in pressure combined with the already high temperatures of the fluid causes the fluid to instantly vaporize into steam, which can be used to drive a turbine. This scientific phenomenon is comparable to an observation of how boiling points tend to decrease with higher elevation at camping sites or even cities. With less pressure to stop the fluid from boiling, there is a greater tendency for the fluid to boil and undergo a phase transition into gaseous form. Engineers have become creative with this mechanism, and have even managed to couple the process with a second flashing step to maximize the steam output from high pressure geothermal fluids pumped from subterranean Earth.
- 17Binary Power Plant: The newest kind of geothermal power plant design comes in the form of a dual fluid system in which thermal energy is transferred from geothermal fluid to another working fluid via a heat exchanger. The working fluid vaporizes and creates enough pressure to drive a turbine and then re-condense back into a fluid form for heat exchange once again. The working fluid has a lower boiling point than water, and therefore a higher vapor pressure than water that contributes to more turbine spins for energy generation. Therefore, the binary design incorporates two closed systems that avoid the need for emitting excess steam that could contain unwanted environmental pollutants and improve efficiency.
Advantages of Geothermal Energy
As a form of alternative energy that is conceptually simple and high yielding, there are several notable advantages to using geothermal energy.18 First and foremost, geothermal energy produces almost nuclear power plants. Not only does a geothermal plant take up much less space and remain self-sufficient for its energy needs, but it may be eligible for tax cuts that further reduce the operating cost of the plant.
The news is also good for consumers seeking cheaper energy as the typical cost of geothermal energy from California’s largest plant amounts to $0.03 as compared to $0.05 per kWh19 for coal derived electricity. Although this may seem like pennies on the dollar, the macroscopic effect is huge given that the average household uses 940 kWh of energy per month.20 Another legislative hurdle passed by geothermal energy is the lack of serious environmental pollution and significant risk of failure. The lack of environmental pollution frees the plant operator from implementing control measures that could cost the company a fortune to maintain, and the State a fortune to regulate. Additionally, the plant is failsafe in comparison to nuclear power plants that may pose a great risk to the community and beyond.
Disadvantages of Geothermal Energy
Although the prospects of geothermal energy seem almost ideal, there are a few drawbacks that prevent this form of power generation from being as popular as conventional coal.21 A geothermal station is fairly location specific to areas of the Earth close to a heat source from magma flows. The drilling infrastructure needed in less ideal locations would build the cost of the plant beyond sustainability. Additionally, this location specific constraint limits the areas in which geothermal energy can be utilized since long range electric transmission suffers from energy loss across distances. As a result, only a few areas with high thermal activity can benefit from geothermal energy and most of these areas tend to be towns or small cities rather than major metropolitan areas in the United States. There is also the more fundamental and bizarre problem of geothermal sites losing their thermal energy over time. Many geothermal ventures have failed due to heat losses that render power plants inoperable.
The Future of Geothermal Energy
A powerful and mysterious resource under our feet has the theoretical potential of becoming an abundant and clean source of energy, and yet the natural order of our planet prevents us from tapping a great deal of this energy. At the moment, it is hardly expected that geothermal power plants will be the silver bullet to the growing problem of nonrenewable energy demands but the concept does provide some hope for light at the end of a tunnel that has been quite dark for commercial energy. wind power have, so far, been unable to provide the energy yields required for the global replacement of fossil fuels, but perhaps greater explorations into geothermal accessibility and technologies may provide a powerful avenue for phasing out a fossil fueled energy sector. Rather than the technology itself, the main hurdle for geothermal energy seems to be in finding the proper locations that would make the technology practical on a national level. Given the growing improvements in energy transmission technology and seismic underground detection, geothermal energy could very well be a serious contender as a sustainable energy source of the future.
