Geothermal Energy; Types and Processes

Geothermal Energy

What is Geothermal Energy?

If you dig a hole down into the earth, the temperature would get warmer as we go deeper. This happens because the earth’s core is extremely hot (10,800 F). This heat radiates out of the core in all directions and raises the temperatures of other layers of the Earth. 

The heat (thermal) energy generated from the core and stored in Earth’s layers is known as geothermal energy. 

The temperatures below the surface (8ft for Horizontal piping and 250ft for vertical) are used for heating and cooling above the surface. 

What makes Geothermal Energy Renewable?

Geothermal energy is a form of renewable energy since the Earth’s core will always be radiating heat! And this heat will spread out into the Earth’s layers. 

The Core temperature is around 5000K currently, with a reduction of 250K since the Solar system was established 4.5 Billion years ago. So if the temperature reduces at the current rate of 55 degrees every billion years; it will take more than 90 billion years for the Earth’s core to cool down to 0 K where no life can exist.

Benefits of Geothermal energy

One of the major benefits of geothermal energy is that it has a very low carbon impact because it uses the heat from natural sources. This makes the process environmentally friendly, but there is a catch to it

Although geothermal power plant plants do not require electricity, geothermal heat-source pumps installed in homes and commercial spaces do require a bit of electricity to run heat pumps. If that electricity is sourced from non-renewable sources then the process would have a small carbon footprint. 

Along with being Eco-friendly, Heat-source pumps have very little noise because they don’t use an internal combustion motor like a generator. This is a good way to prevent and reduce noise pollution.

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Geothermal helps to save money as it reduces your heating and cooling bills up to 70%. You can also save your money in many countries when you get tax credits for installing and using geothermal energy.

Other than these benefits, geothermal energy is much cheaper than other renewable sources of energy in the long run. 

Heat Source-pumps based on geothermal energy last as long as 20 years whereas geothermal power plants go on for 30 years with optimum efficiencies. F

Geothermal Power Plants

Geothermal power plants don’t require burning fossil fuels in order to work. They use natural hot water stream beds which are renewable resources. There are three types of geothermal power plants. All of them generate power but in slightly different ways.

Dry-Steam Power Plant

These are the most common ones, more than half of the geothermal plants installed in the world are dry steam power plants. The heat reservoirs underground help the plant to pump hot steam into turbines which spins them; this process then powers the generator to provide electricity.

The steam condenses into water after powering the turbines. The water is piped back into the ground by injection well so it can warm up again.

Flash-Steam Power Plant:

This type of plant’s process is somewhat similar to dry steam power plants. Instead of pumping hot steam, these plants pump hot water. These plants pump hot water with high pressure from the ground and bring that water into a flash tank above the ground. The flash tank is set at a much lower temperature which quickly causes the hot water to turn or ‘flash’ into steam. 

The turbines are powered by steam produced after. The steam later cools down and condenses into water which is then pumped back into the ground by the injection well. 

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Binary Cycle Power Plant:

The main difference between binary cycle power plants and other power plants is that in a binary cycle power plant the water or steam which is pumped from underneath the ground does not come in direct contact with the turbines. 

The water pumped from geothermal reservoirs is channeled through a heat exchanger which heats a second liquid. The second liquid gets heated and produces steam for the turbines to rotate and power the generator.

The water is recycled back into the ground by the injection well, whereas, the second liquid is pumped into the turbine and sent back to the heat exchanger where it can be heated again to continue the process.

Geothermal heat pumps

Geothermal heat pumps are usually installed in homes. By powering your house with a geothermal heat pump you can make use of ground temperatures to either cool (in summers) or heat your house (in winters). The temperatures vary above the earth in different seasons but stays the same below the ground at 50F- 60F throughout the year. This makes sure the heating pumps can efficiently run throughout the year without any interruptions.

Types of Geothermal Heat pumps

There are in-total four types of heat-source pumps, 1 open-looped system and 3 closed-loop systems. They are all slightly different and installed according to different factors including climate conditions, type of soil and the size of land available.

Closed loop systems

There are three types of closed loop systems; horizontal, vertical and pond/lake systems. All of these work in the same way. 

The horizontal systems are most commonly used because they are very cost-effective for setting up in residential areas. If you want to set up a system for larger commercial buildings, then you can go for a closed-loop vertical system which can go as deep as 400 feet below the round. The closed loop systems constructed under a lake or a pond are the most cheap.

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In closed-loop systems, a mixture (ethylene glycol/water) runs through a loop of pipes underground which come up to connect with the heat-exchanger in the building. The mixture pumped from underground is warm in winters and cool in summers. The heat-exchanger makes the exchange of heat energy between the water and the ventilation air which will be used to cool or heat the building. 

In winters, the electric compressors use the heat derived from the mixture to heat air and send it through ducts into the building.

In summers, the process is reversed as the heat-exchangers draw heat from the air in the building and transfer it to the earth or the water which absorbs the heat and goes underground to dissipate the heat. 

This maintains the indoor temperature at a mild level so you’re covered in all seasons!

Open-loop systems

In this system, the water is directly taken in from an open water source to the heating pump. Once the water reaches there it has two choices; Either it can be recycled back or it can be pumped into another water body without causing pollution. There is only a slight difference in temperature of the water, so you need more volume for efficient transfer of heat.

These can be very cheap but the only problem is that they require a flow of water which is steady and in good volume. 

Open-loop systems can be used all over the world because of the temperature remaining constant underground. However, they all vary in costs and efficiency. 

The geothermal energy has the potential to last as long as the earth would. Therefore, consider it as a gift and encourage use of geothermal energy.

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