Geothermal Energy – How It Works

Nesjavellir Geothermal Power Plant Iceland

Geothermal energy is somewhat of an unknown entity in the average person’s knowledge of alternative power sources, even though it has been used for heating, cooking and bathing, in some countries, for hundreds of years.

For a brief language lesson, geothermal comes from the Greek word’s “geo” and “therme” which translates into earth’s heat or the natural heat of the earth.

The interior of the Earth is made up of molten rock, called magma. What geothermal energy does is capture the heat under the Earth’s crust to create a power source.

Is Geothermal Energy Renewable

Energy 101: Geothermal Energy

Picture the centre of the Earth. It is so hot that it can melt rock quite easily. Well, as you go down into the Earth’s crust, the temperatures get higher and higher. It is estimated that for approximately every forty yards (not quite half the length of a football field), the temperature rises about thirty-four degrees Fahrenheit.

What happens is that the heated rocks below the Earth’s surface heat up water to create steam. Holes are then drilled into these specific geothermal regions so that the steam can escape.

During the process, the geothermal power station drills the holes mentioned above and creates an injection well where cold water is pumped down the well.

This cold-water filters through the hot rocks, and then pressure is used to bring the water back up. Once the hot water reaches the surface, it turns into steam, which is then harnessed for power. That steam is cleaned and filtered and then used to power turbines, which in turn provide an electric power source.

How is Geothermal Energy Generated

There are currently three types of technology used in geothermal power plants.

These are –

  • Dry Steam
  • Flash
  • Binary Cycle

Dependent upon the characteristics of the geothermal resources at any one location dictates which technology is used.

Dry steam and Flash power plants use higher temperature resources, while Binary Cycle plants operate with lower temperature resources.

Dry Steam Geothermal Power Plant

Dry Steam Geothermal Power Plant Diagram

This is the oldest and most efficient technology, where high temperature steam is taken directly from the ground to drive turbines. The steam is then cooled, turned back to water and is pumped back into the deep well. The first dry steam power plant was built in Larderello, Italy in 1904, and they are still in use today at the world’s largest geothermal energy power source at the Geysers in California.

Flash Geothermal Power Plant

Flash Steam Geothermal Power Plant Diagram

Flash geothermal power plants are the most common currently in use. They use high-pressure, high temperature geothermic fluid pulled from deep underground reservoirs into cooler, low-pressure water. The resulting steam from this process is used to drive the turbine. Any remaining geothermal fluid is either flashed again in a second tank or returned to the underground reservoir.

Binary Cycle Geothermal Power Plant

Binary Cycle Geothermal Power Plant Diagram

Binary cycle technology uses the geothermal water to boil a second fluid (Isobutane), the vapour of which is used to drive the turbine, which in turn generates electricity. Unlike dry steam and flash systems, the geothermal fluid never comes into contact with the turbines and because it is a closed loop system, and aside from water vapour, there is nothing emitted into the atmosphere. Leftover water from the process is returned to the subsurface.

Because lower temperature geothermal energy resources are the most common, Binary cycle power plants are likely to become the main generators of geothermal electricity in the future.

Advantages of Geothermal Energy

  • Non-polluting – When a power station harnesses geothermal energy in the correct manner, there are no by-products, which are harmful to the environment
  • Renewable and sustainable energy – Heat from the earth is limitless. If managed correctly, the underground water and steam will never diminish
  • Reliable source of energy – The earths heat is available 24/7 365 days a year
  • No wastage – Spent water is re-injected into the underground reservoir
  • Low emissions – Geothermal power production does not output any type of greenhouse effect
  • Minimal environmental impact – Geothermal power plants have a small footprint when compared with coal, wind and solar power generation plants
  • Self-sufficient – In terms of energy consumption, the power plants are self-sufficient and do not use any type of fossil fuels
  • Low maintenance – After the construction of a geothermal energy power plant, there is little maintenance to contend with
  • Can be used to recycle wastewater
  • Power generation is weather independent

Disadvantages of Geothermal Energy

  • First, you cannot just build a geothermal power plant in some vacant land plot somewhere. The area where a power plant would be built should consist of those suitable hot rocks at just the right depth for drilling. In addition, the type of rock must be easy to drill into.
  • It is important to take care of a geothermal site because if the holes were drilled improperly, then potentially harmful minerals and gas could escape from underground. These hazardous materials are nearly impossible to get rid of properly. Pollution may occur due to improper drilling at geothermal stations.
  • It is also possible for a specific geothermal area to run dry or lose steam.

Alternative Uses

Besides power resources, geothermal energy can be harnessed for other means as well.

  • Thanks to geothermal water, there are natural hot springs all over the world and many people enjoy the warm waters and its restorative effects.
  • Geothermal water can also be beneficial for growing agricultural products in a greenhouse within a cold or icy climate.
  • Geothermal waters can be harnessed to create space heating in buildings, or even to keep streets and side walks warm enough to prevent icing over. Several cities have actually used it in this unique manner.

Future of Geothermal Energy

Because geothermal energy is reliable and renewable, this alternative power source will start to enjoy more growth.

It is present everywhere beneath the earth’s surface, although the more desirable, high temperature resources are located in the so-called “ring of fire” areas of active or geological young volcanoes.

Areas such as California, Iceland, Hawaii and Japan are just a few places where it is being used, mainly due to underground volcanic activity.

Statistics from Our World in Data show a global increase in geothermal power capacity of 41% to 14,075 Megawatts in the 10 years from 2010 to 2020.

The U.S. remains the top producer with 2,587 MW in 2020, followed by Indonesia at 2,131 MW, the Philippines at 1,928 MW, Turkey at 1,613 MW and New Zealand at 984 MW.

This Overlooked Energy Source Could Supply 50% Of Electricity