Uses of Geothermal Energy





Hot Springs

Grand prismatic hot spring in Yellowstone National Park. Image by US National Park Service.

Grand prismatic hot spring in Yellowstone National Park. Image by US National Park Service.

Earliest uses of geothermal energy involved hot springs for bathing and relaxing. Hot baths are a common luxury today but thousands of years ago hot springs were providing this same comfort to early humans. Early in the history of the United States at private hot springs entrepreneurs would allow you to “bath three times for one dollar.”[1] Beauty is often an admired feature of natural hot springs with some hot spring parks like Yellowstone attracting millions of tourists.[2] Grand Prismatic springs in Yellowstone has an interesting and captivating appearance due to pigmented bacteria that lives on the various minerals in the water. Other springs like geysers, mud pots, and fumaroles are fascinating natural wonders as well but this is about geothermal energy.

Direct Geothermal

Oldest known direct use geothermal pool built in the Qin dynasty, 3rd century BC. Image by Ytrottier.

Oldest known direct use geothermal pool built in the Qin dynasty, 3rd century BC. Image by Ytrottier. License: CC BY-SA 3.0

Taking things one step farther than using natural hot springs is direct use geothermal. There are many applications where geothermal heated water can be used directly. Heating homes and other buildings, aquaculture (fish farms), and greenhouses are all examples of direct geothermal. District heating is also possible where water is pumped through pipes traveling to many homes and businesses. District geothermal systems can save customers 30-50% on heating bills compared to similar natural gas systems.[3] Commerce and industry can also use direct geothermal energy for things like food dehydration, laundries, gold mining, milk pasteurizing, and spas.[3] One of the earliest known examples of direct use geothermal is a spa built in 3rd century, shown to the left.

Geothermal Heat Pumps (Geoexchange Ground Source Heat Pump)

Geothermal slinky loop weighing 3 tons. Image by Marktj.

Geothermal slinky loop weighing 3 tons. Image by Marktj. License: US PD

Geothermal heat pumps heat and cool buildings by exchanging thermal energy with the ground by way of a heat pump. This process is known as geoexchange as heat is either being taken from the ground or placed into it. Mechanically these systems are nearly identical to a refrigerator or air conditioner. Coils exist on both the heating and cooling side that allow for the flow of a refrigerant (usually water or antifreeze). There are two junctions for this flowing refrigerant. First is a compressor that increases the pressure on one side. Second is an expansion valve that reduces the pressure on the other. Increasing and decreasing the refrigerant pressure in either coil causes temperature differences. One coil (condenser) is at a higher temperature (than the heat sink, air, water, earth, etc) and releases heat and the other (evaporator) is at a lower temperature causing it to absorb heat. This allows heat to flow from one space to another. In a refrigerator the condenser is exposed to your house and the evaporator is inside the refrigerator. In ground source heat pumps the evaporator is in the ground and the condenser is in a building. By reversing the compressor and expansion valve this process can be reversed to allow for geothermal cooling instead of heating. Geoexchange systems can be either closed loop (as shown in the image) or connected to an underground source of water resulting in an open loop.

Below is a video on geothermal heat pumps that explains these concepts visually.

Geothermal Electricity

Geothermal energy is one of the cleanest and most reliable renewable energy sources available for producing electricity. Several geothermal power plant technologies exist that allow generation of electricity from geothermal energy.

  • Dry Steam Geothermal Plants

    Dry steam technology uses heated steam rising from vents at the Earth’s surface. This rising steam is piped into a turbine to generate electricity and then condensed. Resulting condensed steam and water is injected back into the Earth to prolong the life of the energy source.

    Diagram of a dry steam geothermal power plant.

    Diagram of a dry steam geothermal power plant.

  • Flash Steam Geothermal Plants

    Flash steam geothermal energy uses drilled heater water reservoirs. Water reaching the surface is under high pressure and some converts to steam in a flash tank. Generated steam travels through a turbine generating electricity before reentering the reservoir. Water that did not flash steam rejoins the outlet for condensed (used) steam and is injected back into the reservoir.

    Diagram of a flash steam geothermal power plant.

    Diagram of a flash steam geothermal power plant.

  • Binary Cycle Geothermal Plants

    Binary cycle geothermal technology operates the same as flash steam but the geothermal water passes through a heat exchanger next to a separate liquid. This allows the heat to exchange from the water to the binary liquid vaporizing it. Resulting vapor is used to drive turbines to generate electricity where it condenses and rejoins the binary cycle.

    Diagram of a binary cycle geothermal power plant.

    Diagram of a binary cycle geothermal power plant.

Sources:

1. Hot Springs, Arkansas
2. Yellowstone National Park
3. Direct Use of Geothermal Energy

Sponsors:

Leave a Comment

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>