Geothermal is a term for a form of sustainable energy which utilizes the warmth of the Earth itself as a resource.
Rather than requiring the burning of fuels, geothermal energy captures the heat emanating from within Earth itself in several possible ways, bringing that energy to the surface to turn a turbine and create electricity or alternatively to provide temperature control directly, without the generation of electricity.
What is geothermal?
Geothermal energy is thermal energy present within the planet itself. There are several layers to the Earth, generally the crust, mantle, and core. Temperatures developed from radioactive decay and latent heat from Earth’s formation creates high temperatures, with the core-mantle boundary reaching over 4000 degrees celsius. The crust, the upper and most accessible layer, is capable of temperatures exceeding 370 degrees celsius.
The heat from hot springs have been used to warm humanity since before civilization, but today, geothermal is as much about electricity as it is about heat.
The Earth’s naturally occurring geothermal energy is theoretically more than adequate to supply humanity’s energy needs for millenia if it is able to be effectively exploited.
In order to generate geothermal electricity, you must have access to a geothermal resource – currently, all geothermal electrical plants exploit underground water temperatures above 100°C, with the most efficient implementations requiring temperatures over 360°C.
Though many nations do have extant geothermal resources which require relatively little investment to access, many other nations do not. The proximity to a geological fault line such as a subduction zone result in decreased distance separating the surface from the hot magma, allowing for extraordinary temperatures at relatively shallow distances.
How Does Geothermal Create Electricity?
Geothermal power is much like most forms of power generation in that it ultimately produces electricity by spinning a turbine. Electricity is produced by moving that thermal energy from deep within the Earth to the surface in a variety of ways.
The three main designs for geothermal power plants are “dry steam”, “flash steam”, and “binary cycle”. Each uses hot water or steam to turn a turbine in one way or another.
Dry Steam
“Dry steam” plants use existing underground resources of steam. The steam is tapped directly from underground pipes or wells which capture and direct it to turn a turbine. Dry steam requires not only geothermal accessibility, but also that an underground aquifer exists simultaneously, because of this, they are rare. “Dry steam” is preferable for a number of reasons from cost to environmental impact.
The U.S. only has two sites where the conditions for a “dry steam” plant exist – Yellowstone National Park and The Geysers of Northern California.
Flash Steam
“Flash Steam” geothermal power plants are the most common means by which geothermal energy is converted to electricity. Water is introduced into a geothermal resource through an “injection well” and it is then heated and brought to the surface through a “production well”. Super-heated water from deep underground is depressurized and “flash” vaporized to steam. This steam creates pressure and drives a turbine. Once the steam has condensed, it is returned to the geothermal resource by the injection well.
Binary Cycle
“Binary Cycle” geothermal power plants operate at the lowest temperatures of any of the existing large-scale geothermal generators. Using underground water temperatures between 220-360°F (105-180°C), binary cycle geothermal uses hot water to heat a secondary fluid, or working fluid, using a heat exchanger. The working fluid and water never come into contact with one another. The “working fluid” is typically a low-boiling organic compound. After hot water is used to heat the working fluid, the working fluid boils and spins a turbine, then condenses and begins the cycle again just as the water returns and is recycled.
In addition to producing electricity, geothermal resources can be used to heat any space utilizing steam or hot water after it has been used to generate electricity but before being returned to the Earth.
Further, “geothermal heat pumps”, where the consistent temperature (around 60°F) realized about 6 feet under ground can be used to exchange heat – which can cool a home or office in the summer and heat it in the winter with virtually no energy consumption.
Simple heat exchangers can be made with a little land, basic construction skills, and a lot of labor. They have the potential of greatly reducing heating and cooling costs – which represents half of the energy consumed by homes. Geothermal, just like solar and even wind, can be utilized at a microscale to reduce costs and the individual environmental burden of a family or individual and their home. In fact, ideally, an individual would use many of these approaches to achieve the greatest results – for example, using solar, wind, a battery system, and a geothermal heat pump could very possibly result in a net-zero household energy consumption with relatively little financial investment.
Iceland: The Land Of Geothermal
Iceland is a nation that has completely embraced geothermal.
For good reason – they are a very northern, island nation sitting atop an active subduction zone. They have access to hot, underground resources very near the surface across much of the nation. Though few nations have the geothermal resources Iceland does, there are many regions which could easily expand geothermal energy production.
In Iceland, five major geothermal power plants produce approximately 26.2% (2010) of the nation’s electricity. In addition, geothermal heating meets the heating and hot water requirements of approximately 87% of all buildings in Iceland, furthering the value of this resource.
As of 2004, around 54% of primary energy in Iceland was produced by geothermal, with hydro power producing over 17%, coal 3% and petros around 26% – with much of the burning of fossil fuels being related to transportation. Plans are underway to turn Iceland into a 100% fossil-fuel-free nation in the near future. Iceland’s existing and abundant geothermal infrastructure and energy has enabled renewable energy initiatives, including several which take advantage of existing infrastructure to sequester carbon – even manufacturing methanol from carbon dioxide.
In addition to meeting energy demands, the geothermal energy Iceland utilizes has made the nation considerably more prosperous. Reducing reliance on imported fuels, maintaining impeccable air quality, and enjoying plentiful energy resources at a low cost promotes growth of industry without taxing the planet.
It is important to understand, however, that Iceland didn’t just wake up overnight with over over half of its energy needs met by geothermal. Their primary power source wasn’t always so – it has been the product of intentional design beginning with government’s investment in infrastructure.
The most important take-away from the success of Iceland’s geothermal programs are the relationship between political will and the agenda of those in office and the reality they manifest.
Only with a government ambitious and eager to tackle climate and environmental challenges can such large-scale success be realized. The U.S. government’s open antagonism for logic and rational energy production has continued to cost the planet and all it’s denizens for decades. The vanity of the few that prosper off of the inefficient and ruinous fuels of yesterday have disproportionate influence over legislation. This sad state has evolved a form of quasi-capitalism that spews up money for the corporations in the dirtiest industries while simultaneously claiming proposals such as the Green New Deal “too costly”. These people must be ousted – we must find a way to replace our current congressional population with benevolent, capable leadership otherwise we will be stricken by a world plagued with disaster.
Geothermal In The United States
The United States has ample untapped geothermal resources. The Western U.S. sits on geological features which make geothermal power production highly feasible. The states of Hawaii, Alaska, and California and several others are capable of enormous electricity production in a predictable, consistent, and renewable way with very little emissions or environmental impact.
Despite the fact that the United States leads the world in total electricity production through geothermal, with seven states producing 16B kW/h, investment in geothermal infrastructure has remained essentially flat since the 1970s and 80s.
The United States has been the defining pioneer into geothermal, yet, as interest in “renewables” has increased, interest geothermal has been outpaced by solar and wind, for example.
Over a decade ago, MIT commissioned and published this report, which clearly describes the opportunities geothermal offers the United States and the world, weighed against costs and risks and other technologies; this detailed resource goes far into the data regarding geothermal energy production – indeed, virtually all energy production – in the United States past, present, and future.
The Future Of Geothermal
The future of geothermal really requires little in the form of technological advancement – the technologies are largely extant and in practice,. The real challenge geothermal energy faces is in marketing, investment and application.
Geothermal really needs to be included in the conversation – opportunities in geothermal are often far more prolific as compared to the same investment in solar or wind, despite the fact that the total installed resources are far greater for wind and solar at this point.
What are the environmental impacts of geothermal energy?
Water returning to the surface to generate electricity often contains dissolved gases, most notably carbon dioxide, hydrogen sulfide, methane, and ammonia. These gases do contribute to global warming and impact the planet in other ways as well, though it is important to point out the concentrations of these gases is generally minute, though it varies by location.
Currently, geothermal produces average CO2 emissions equal to 122 kg carbon dioxide per megawatt hour, dramatically less than traditional plant emissions, which hover around 2,100 kg carbon dioxide per megawatt hour.
Another factor to be considered with geothermal is the possibility of the relationship between geothermal power generation and seismic events. Though these factors would depend on the technology and the location, it is important to include in the conversation. Serious failures of implementation – that like what we saw with Fukushima with nuclear or 3 gorges with hydro – are possible with geothermal as well; Pohang is an example of the risks associated with geothermal when implemented irresponsibly.
Another aspect of geothermal is the potential use and contamination of water resources – depending on the implementation, often, water is driven down into geothermal resources to be exploited as steam to drive a turbine once the water is superheated within the Earth. When the water returns to the surface, it has dissolved compounds from deep within the ground. Many of these are innocuous minerals, but the water requirements, and the reality that water used will almost certainly dissolve mineral constituents of the rock below is something that must be taken into account.
In Conclusion
It is important that we examine all of the available solutions to our need for electricity and energy while also meeting the challenge of reversing our prolific emissions of greenhouse gases and their corresponding impact on our climate and weather events. Just like all available sustainable energy technologies, geothermal has a place in our planet’s future power grid.
With wise utilization, geothermal can help the United States and the world realize a society in harmony with the planet.
