What is geothermal energy production?


Geothermal energy takes advantage of the heat under your feet to charge your devices and keep your home warm during the colder months. But given the relative lack of attention that the power source receives compared to other production resources, let’s take a look at the basics.

Geothermal power generation is a method of generating electricity. By tapping into Inner Earth, we can harness the thermal energy of the planet to run a turbine generator with steam.

The interior of the Earth is made up of several layers, including an inner core of solid iron, an outer core of magma, a mantle of magma and rock, and the solid rocky crust on which you currently live. Energy developers dug several miles into the ground and constructed wells to allow steam to rise from a potential geothermal reservoir.

Depending on the type of power plant, the process and the necessary infrastructure change. The National Renewable Energy Laboratory, or NREL, says there are three types of geothermal power plants.

With a dry steam power plant, “the steam is routed directly from underground wells to the power plant,” essentially taking advantage of where the steam naturally springs from the earth without much intervention, according to the lab. This style of geothermal power plant is rare, explained Maurice Dusseault, geothermal expert and professor at the University of Waterloo. The largest of this type of production facility is also the largest geothermal power plant in the world: the Geysers Geothermal Complex north of San Francisco.

Then there are flash steam power plants, a process NREL calls the “most common” form of geothermal power generation. Geothermal fluids are pumped from a pressurized well to an aboveground chamber, where the fluids vaporize into vapor.

Another form is binary cycle geothermal generation. This process uses multiple chambers that separate geothermal fluids from a secondary fluid. A heat exchanger is then used to raise the temperature of the secondary fluid with the heat of the geothermal fluid, turning the liquid into vapor to turn a turbine.

One type of binary cycle generation is known as an improved geothermal system.

“We are using [EGS] refer to trying to extract thermal energy from deep, low permeability, low porosity rocks that do not contain fluids in significant amounts, such as in New Hampshire, Maine and Massachusetts, ”said Dusseault.

Geothermal energy isn’t just used for power generation – it can also be used to heat your home instead of home heating fuels thanks to an on-site pump. Some cities, like the Icelandic capital Reykjavík, heat all their buildings with geothermal energy. And, of course, geothermal reservoirs can heat pools of water and create relaxing hot springs and forming geysers that spew extremely hot water into the air.

What makes a site suitable for geothermal energy?

To run a turbogenerator, sufficient steam and hot water – a mixture called geothermal fluids – must be present in a geothermal reservoir and capable of being siphoned off in order to transform that thermal energy into electricity.

A reservoir should also be hot enough that it is worth the effort, and any rock should be permeable enough to allow geothermal fluids to move, according to the US Department of Energy’s Office of Energy Efficiency & Renewable Energy. . The deeper you go into the earth, the higher the temperature.

“But in a place like Maine… there are no hot spots and there is very little sediment,” Dusseault explained. “If you want to try to access high temperatures, now you have to drill five, six, or seven kilometers through hard rock. And it is expensive. “

But what is a hotspot? Dusseault says it will depend on who you ask and what your goal is. If you are looking to generate electricity at economically realistic prices, the temperatures you envision for such a project will be extremely high and easily accessible. But if you are looking to use geothermal energy for heating in an area of ​​the country less close to a high temperature fluid, a developer may consider areas with relatively lower temperatures in rock types that are more difficult to penetrate. .

Where can we find geothermal power plants?

In the United States, there are few hot spots outside of the west coast states, with the easternmost geothermal hot spot located in Yellowstone National Park in Wyoming, according to Dusseault. This means that the bulk of America’s geothermal power plants are in California, Nevada, Utah, and Hawaii.

Yet the United States leads the world in the production of geothermal energy, even though data from the US Energy Information Administration shows that such production represents only 0.4% of total electricity production at the scale of American utilities. Other federal estimates suggest that geothermal energy could grow at a rate of 2% per year in the future; Geothermal electricity production is expected to increase from 16 billion kWh in 2019 to 52.2 billion kWh by 2050, an increase of 226.25% over 31 years.

In 2019, 72% of the installed geothermal electric capacity across the planet came from six countries: the United States, Indonesia, the Philippines, Turkey, Mexico and New Zealand, according to agency data. Renewable Energy International cited by the University of Michigan.

But looking ahead to 2022, only four countries – Indonesia, Kenya, Turkey and the Philippines – will account for around two-thirds of this new capacity. The international energy agency Renewable Energy Report 2020 predicts that global cumulative geothermal capacity will increase by 7% to 16.5 GW by that year.

Further, the IEA report notes that while Indonesia in particular can overcome many national energy and environmental concerns, such as low energy prices and lack of investment, the country “could have accumulated as much installed capacity as the [U.S.] by 2025.

Even without human development, geothermal energy rises to the earth’s surface through volcanoes, hot springs and geysers. In the Pacific Ocean, for example, the seismically active Ring of Fire is a well-known geothermal hotspot that follows the boundary of several tectonic plates. Subsequently, the region has the most volcanoes and earthquakes on Earth, according to National geography.

Comparisons with hydraulic fracturing

There are few reported drawbacks to geothermal power generation, making it one of the safest sources of energy for workers and the environment. Siphoning electricity and heat from virtually unlimited thermal energy from the earth’s core comes with low emissions, low costs and long term stability.

However, most geothermal reservoirs are not easily accessible, increasing the engineering challenges involved and requiring the use of techniques such as the improved geothermal systems approach. This approach is similar to the methods used in hydraulic fracturing, the controversial process of extracting oil and gas.

There are several differences, including the way fractures are made, according to Dusseault, who believes that “the dangers of hydraulic fracturing have been massively, massively exaggerated.”

With EGS, the fractures are made to create a single path between wells, whereas with natural gas fracturing, a developer creates many fractures from that single well. Regardless, this fracking process has raised concerns among some experts about the potential increase in seismic activity.

Improved geothermal systems have already been blamed for devastating earthquakes in some countries. In 2019, the South Korean government recognized that a 5.4 magnitude earthquake that injured dozens of people and caused $ 290 million in damage in the city of Pohang was the results an operational EGS power station nearby.

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