Geothermal energy is the natural heat of the Earth. It is derived from the decay of the radioactive elements in the Earth’s crust and transferred to the subsurface by conduction and convection.
The word geothermal comes from the Greek words geo (earth) and therme (heat).
The exploitable geothermal resources are found throughout the world and are utilized nowadays in more than 80 countries.
It is reliable — Geothermal power plants produce electricity consistently, running 24 hours per day / 7 days per week, regardless of weather conditions. It also has the ability to produce more electricity over the same time period than coal, natural gas, nuclear or large hydro stations.
Historians believe that human civilizations have been using geothermal energy for centuries. For example, the Romans are known to have used hot springs for bathing more than 1000 years ago! They would also run the hot water through underground channels to heat the floor of a house during winters.
Yet, in the 16th century Georgius Agricola observed that temperature in mines generally increased with their depth. Later on, Alexander Von Humboldt calculates an approximation of 3.8 deg Celsius increase for every 100 meters of depth, and so we have our first study of the Earth’s thermal gradient.
First modern measurements were performed in 1740, in a mine near Belfort, France. Since the 1950’s, worldwide geothermal heat research have been conducted.
By the end of the 19th Century, Prince Piero Conti proposed an idea to harness natural steam from the Larderello geothermal field in Italy to produce electric power. He started by conducting technical experiments in 1903, and a year later, the first geothermal power experiment produced enough energy to illuminate five incandescent light bulbs.
By 1913, Conti had completed the construction of a 250 kW commercial power plant fed by pure steam, and in 1916, two more power units of 3.5 MW each. And this is how geothermal power production was born.
- Through Geothermal power plants, which use heat from deep inside the Earth to generate steam to make electricity.
At a geothermal power plant, wells are drilled 2 or 3 km deep into the Earth to pump steam or hot water to the surface. You’re most likely to find one of these power plants in an area that has a lot of hot springs, geysers, or volcanic activity, because these are places where the Earth is particularly hot just below the surface.
- Hot water is pumped from deep underground through a well under high pressure.
- When the water reaches the surface, the pressure is dropped, which causes the water to turn into steam.
- The steam spins a turbine, which is connected to a generator that produces electricity.
- The steam cools off in a cooling tower and condenses back to water.
- The cooled water is pumped back into the Earth to begin the process again.
- Through Geothermal heat pumps, which tap into heat close to the Earth’s surface to heat water or provide heat for buildings.
Not all geothermal energy comes from power plants. Geothermal heat pumps can do all sorts of things—from heating and cooling homes to warming swimming pools. These systems transfer heat by pumping water or a refrigerant (a special type of fluid) through pipes just below the Earth’s surface, where the temperature is a constant 10 to 15°C.
During the winter, the water or refrigerant absorbs warmth from the Earth, and the pump brings this heat to the building above. In the summer, some heat pumps can run in reverse and help cool buildings.
- Water or a refrigerant moves through a loop of pipes.
- When the weather is cold, the water or refrigerant heats up as it travels through the part of the loop that’s buried underground.
- Once it gets back above ground, the warmed water or refrigerant transfers heat into the building.
- The water or refrigerant cools down after its heat is transferred. It is pumped back underground where it heats up once more, starting the process again.
- On a hot day, the system can run in reverse. The water or refrigerant cools the building and then is pumped underground where extra heat is transferred to the ground around the pipes.