This is how the heat that comes from inside the Earth works

Under the earth we walk on beats an energy that is born from internal heat, silent, so constant that neither the night nor the clouds can interrupt it. We don’t see it, we don’t hear it, but it is there: an engine running since the planet was formed. In recent decades, as we looked to the sun and wind to fuel our modern lives, that subterranean heat remained almost forgotten. It is an energy that has always been there, waiting to be understood. Here we are going to tell what it is about.

What is geothermal energy?

The geothermal energy It is basically take advantage of the heat that the Earth keeps inside or underground. This renewable energy is used to produce electricity or to heat and air condition buildings. That heat is trapped in rocks, soils and groundwater at different depths and temperatures.

The Energy Information Agency mention a fact that is striking: the core of the Earth is at 5,982 ºCalmost the same as the surface of the sun. However, that heat does not stay down there, but rises slowly and warms the mantle and crust. As it rises, it becomes accessible, and with today’s technologies, we can capture it and transform it into useful energy.

How is geothermal energy generated?

The process itself is no mystery: the heat coming from the Earth’s interior heats the water under the ground. Sometimes that water is so hot that it exceeds the 150ºC and, in those cases, it can be used to produce electricity, as explained by the Institute for Energy Diversification and Saving (IDAE). When the temperature is lower—between 30 ºC and 100 ºC— that heat is used for district heating or for certain industrial processes.

When the subsoil heat is not so high, what is known as surface geothermal. The idea it’s simple: the terrain maintains a fairly stable temperature, between 10 and 15 ºCand geothermal heat pumps take advantage of that stability. In winter they extract heat from the ground and in summer they do just the opposite, sending it downwards. This natural balance allows these systems consume much less energyin some cases between a 70 and 80% less than traditional solutions.

In recent years, a technology that can revolutionize the sector has also begun to expand: Enhanced Geothermal Systems (EGS), that artificially create permeability into deep hot rocks to generate resources where none existed before.

How does a geothermal power plant work?

A geothermal power plant works in a similar way to a thermal power plant: a turbine that moves thanks to steam that drives a generator. The difference is in the origin of the steam, in the case of geothermal energy the heat comes from the subsoil.

There are three main technologies:

• dry steam: uses steam directly from the reservoir.
• Flash: evaporates very hot water by decreasing its pressure.
• Binary cycle: transfers heat to a secondary fluid that vaporizes at a low temperature.

After moving the turbine, the fluid is reinjected into the subsoil to maintain the reservoir and close the cycle. The advantage of these plants is decisive, since they generate electricity 24 hours a day, seven days a week. The International Renewable Energy Agency (IRENA) emphasizes that its ability firm helps stabilize electrical grids and mitigate the variability of other renewables.

What is geothermal energy used for?

To begin with, it is used to generate electricity. In countries like Iceland, it is an important piece of your electrical system. In Europe the use is less, but even so the European Commission estimates that it is already there is about 1 gigawatt installed.

The greatest growth does not come from electricity, but from something much more domestic: heating. In several European cities, the heat that comes from kilometers underground travels through pipes to the radiators of thousands of homes. In the EU they already have with almost 400 of these networks functioning totally or partially with energy from the subsoil.

In addition, geothermal energy has a lot of direct uses in very different sectors. It is used to heat greenhouses, feed spas, dry industrial products, maintain stable temperatures in fish farms or air-condition large buildings, like university campuses.

Pros and cons of geothermal energy

We start with the advantages:

• Constant and manageable energy: It does not depend on the weather.
• Low emissions and minimal visual impact: It does not need towers, panels or large surfaces.
• Extreme efficiency in homes: Consumption can be reduced by up to 80%.
• Very long useful life: Between 25 and 50 years, with little maintenance.
• Possible extraction of lithium as a by-product: The European Commission highlights it as a key benefit for the continental industry.

Now comes the not-so-good part:

• High initial investment: Drilling is expensive and risky.
• Need for complex geological studies: the systems may require complex technical interventions, especially in wells and underground circuits.
• Not all places have suitable deposits: either due to heat, permeability or access.
• Lack of specialized labor: A detected problem through Brussels.
• Insufficient regulatory framework: compared to other types of renewables.

Are there geothermal power plants in Spain?

Spain does not yet have any geothermal power plants, as detailed by the IDAE. However, there is clear growth in surface geothermal energy, which is used for heating and cooling. Thousands of homes, hospitals, universities and public buildings already operate with geothermal heat pumps.

Although the big leap can arrive from the Canary Islands. Due to their volcanic origin, the islands concentrate the most promising medium and high temperature resources in the country. Added to all this is that the State is beginning to invest decisively. The program Deep Geothermalfinanced with NextGenerationEU funds, covers up to 50% of the cost of the surveys, which can reach 3,000 meters. It is an unprecedented bet in Spain

In summary, Spanish geothermal energy is taking off, but it is doing so from an initial phase of deep exploration. The difference is that, for the first time in decades, there is funding, political interest and real projects underway. The future of this energy in Spain has literally just begun to be excavated.

A source without limits

Geothermal energy is the only renewable energy that does not depend on the sun or the wind, that can operate without interruption and that can power homes, industries or entire cities. A decisive part of the Spanish ecological transition may be under our feet. What remains to be known is whether the country will be able to take advantage of this dormant heat to transform it into energy independence, industrial innovation and a realistic path towards decarbonization.

Image | Gretar Ivarsson

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