While the weather in Iceland is often cold, wet and windy, an almost endless supply of heat bubbles beneath the surface.
In fact, nearly every building in the country is heated with geothermal energy, producing virtually no carbon emissions in the process.
So how does this renewable energy work?
Between the Earth's core and its crust is a mixed layer of solid and partially molten rock called the mantle. The temperature here ranges from 1,000 to 3,500 degrees Celsius.
Some of this heat comes from the radioactive decay of metals. But most of it comes from Earth's core, which has been radiating energy since the planet formed four billion years ago.
While the mantle moves slowly,
circulating about 40 km below the Earth's crust, there are places where it approaches the surface.
Here, magma forms pockets and veins in the ground, heating underground rivers and pools to temperatures of up to 300 degrees.
Controlling hot water is central to harnessing geothermal energy, and there are two basic models for how to do it. A geothermal power plant is to be built that uses these hot, deep pools to generate electricity.
First, engineers drill a well several kilometers into permeable rock such as sandstone or basalt. As hot, highly pressurized groundwater flows into the well, rapid changes in pressure and temperature produce large amounts of steam.
This steam then turns turbine blades to generate electricity.
Finally, the remaining cooled water and condensed steam are pumped back into the ground to create an open loop that provides electricity without losing water.
However, we don't need to drill that deep to take advantage of the planet's heat. Thanks to solar radiation, only 1.5 meters deep dirt can reach temperatures above 20 degrees Celsius.
A geothermal heat pump pumps water or antifreeze liquid through this layer of the earth to siphon its energy. These fluids are then pumped through local infrastructure, dissipating their heat before returning through the ground to absorb more energy.
While external electricity is required to run the pump, the energy supplied far exceeds the energy used, meaning the process is also a sustainable loop. In fact, geothermal heat pumps are cheaper to operate and at least twice as energy efficient as fossil fuel equivalents.
geothermal energy is bubbling up just below our feet,
or heating water several kilometers deep, the planet is constantly radiating heat. In an average year, the Earth gives off about three times as much energy as humans use.
So why does geothermal only make up 0.2% of humanity's energy production?
The answer has to do with warmth, location and cost. Because geothermal heat pumps rely on the constant heat found in the shallow ground, they can be applied almost anywhere.
But geothermal power plants need to tap into high-temperature geothermal fields. Areas hotter than 180 degrees and usually several kilometers underground.
These high-temperature zones are difficult to find,
and it can cost a plant up to $20 million to drill just one of several wells at this depth. There are areas with shallow geothermal fields.
Iceland and Japan are active volcanoes and near tectonic plate boundaries, where magma rises above the crust.
But these same factors also make these regions prone to earthquakes, which can be triggered by intensive drilling.
Furthermore, while geothermal energy is clean and renewable, it is not completely harmless. Drilling can release vapors containing pollutants such as methane and hydrogen sulfide.
And drilling tools that use pressurized water can contaminate groundwater. Fortunately, new technologies are emerging to address these challenges
Emission control systems can capture pollutants,
and electromagnetic monitoring can help detect seismic hazards.
We're also uncovering entirely new sources of geothermal energy, such as pockets of magma in mid-ocean volcanoes.
So if we can safely and responsibly harness the heat that sustains our planet, we may be able to sustain humanity as well.
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