Is Geothermal Energy Renewable?

Being produced by the inner core of our planet, geothermal energy is the heat that comes from underground reservoirs and is used for residential heating and cooling, and also to produce electricity.

The geothermal resource is produced when heat from the Earth’s crust warms water that has seeped into underground reservoirs, and when this warm water reaches a certain temperature, it can break through the Earth’s surface as hot steam and water. This is usually happening in areas of the planet where the Earth’s crust (plates) meet and shift.

In the past, the geothermal resource was harvested only in areas where the hot water reached the surface, limiting this way the true potential of this underground resource.

However, the technology used to harvest the geothermal resource has evolved, and today we can leverage much more of this clean energy resource.

To take advantage of the geothermal resource, nowadays we are using wells drilled into the underground to extract the warm water and hot steam even if they can’t reach the surface.

How Does Geothermal Energy Work?

To answer the question, we first need to look at the natural resource that is behind geothermal energy.

I already mentioned that the underground reservoirs of water are heated by the inner core of our planet, which is a solid ball with a radius of about 758 miles (1,220 kilometres), consisting of a molten iron–nickel alloy along with other elements.

The temperature of the inner core is estimated to be around 5,700 K (5,430°C), which is almost similar to the temperature at the surface of the Sun (5,778 K or 5,504°C).

The inner core of our planet has been warm since the formation of the planet, and will remain the same as long as the planet exists.

This means that as long that the planet exists, and we have water in the underground reservoirs, the geothermal resource will be produced continuously.

Being produced continuously, it means that geothermal energy is a renewable resource.

How is Electricity Generated from Geothermal Energy?

Today, our civilization uses several ways to produce electricity from geothermal wells drilled into the ground.

This way, there are several types of geothermal power plants used to produce electricity, relying only on the geothermal resource.

Types of Geothermal Power Plants

Dry Steam Geothermal Power Plant

This is the most common geothermal power plant used today, and uses the hot steam extracted from the underground that flows through a system of pipes directly to a turbine to drive a generator, which produces clean electricity.

This type of geothermal power plant, uses two wells: the production well and the injection well.

The hot steam (180°-350°C) is extracted from the underground reservoir using the vents of the production well.
The steam reaches the surface at high speed and is used to drive turbines and generate electricity.

Nowadays, the low pressure steam output from the turbine is no longer vented into the atmosphere, but is passed through a condenser to convert it back to water.

That water is injected back into the underground resource using the injection well to prolong the working life of the reservoir.

Dry steam geothermal power plants are built only in areas where the geothermal steam is not mixed with water.

Geothermal Flash Steam Power Plant

This type of geothermal power plant also uses two types of wells, one being the production well, while the other the injection well.

The production well must be sunk deep enough to reach the subterranean rocks that have a higher temperature than the boiling point of water. The hot water filters through the rocks becoming heated and rises to the surface using the nearby production well.

When reaching the surface, the hot water from the production well will enter a flash tank where the reduced pressure will cause the water to “flash” into vapor (boils extremely quickly).

Water that remained in liquid form in the flash tank, returns to the groundwater pump and is injected back into the underground reservoir using the injection well.

The vapor obtained in the flash tank is used to drive a steam turbine, which will produce electricity using a generator.

A small part of the condensed vapor can be used as drinking water and for irrigation because it is distilled water.

Geothermal Binary Cycle Power Plant

This type of geothermal power plants uses a two-step process in order to get a liquid that can produce steam to spin the turbine.

They can be found in areas where the underground reservoir contains warm water that is not hot enough to produce steam by itself (this water has a temperature of about 200 to 360°F or 93 to 182°C).

The binary cycle power plant uses the production well to extract the warm water from the underground reservoir, and the warm fluid is passed through a heat exchanger when reaching the surface.

Inside the heat exchanger, we have a second fluid such as butane or pentane that has a much lower boiling point than water, and when the warm water enters the exchanger, the second fluid will flash into vapor.

That vapor is the hot steam that will be used to spin the turbine and produce electricity by rotating the shaft of a large generator.

The cooled steam is injected back into the system to run again through the heat exchanger and produce additional vapor.

And this is the main reason why geothermal energy is considered renewable, because a properly managed geothermal reservoir can potentially produce energy indefinitely.

They Work All Year Long

A geothermal power plant can work 24/7 without requiring the presence of the Sun or wind.

This type of power plant, will generate clean energy with minimal impact on the environment such as: low emission, and small physical footprint.

Nowadays, the greenhouse gases that can reach the surface along with the hot steam and water, are often re-injected back into the underground reservoir along with the used water to keep the reservoir active for a longer period of time.

Geothermal Power Plants Help In Recycling Waste Water

Geothermal energy can also help in recycling waste water because as I already mentioned that waste water produced by a city located near a geothermal power plant (Santa Rosa in California) can be re-injected back into the underground reservoir to produce more geothermal power.

Some geothermal power plants produce solid waste containing minerals, and this waste can be removed or sold to others.

Estimates say that the untapped geothermal resource in the United States can cover about 10% of today’s energy needs of the country, which means that it can replace 10% of the energy produced from fossil fuels.

Final conclusion

Geothermal energy is a great source of renewable energy that could help mankind reduce its dependence on fossil fuels.

Being produced by the inner core of our planet, geothermal energy is here to stay, and will certainly be part of the green future that will follow after the fossil fuel era.