What is Geothermal?

Photo: Exergy International

The Heat Beneath Our Feet

  • Geothermal reservoirs are formed when hot brine (fluid) is trapped underground in permeable and porous rocks under a layer of impermeable rock

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  • Rain and groundwater can seep down faults and fractured rocks for kilometres and heat up at depth

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  • This hot or warm fluid can flow to the surface as steam or hot brine (fluid) through hydrostatic pressure

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  • Many geothermal areas have visible surface manifestations of the underground heat source, such as hot springs, fumaroles, and geysers

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  • The geothermal fluid can also be pumped to the surface with a geothermal well

Types of Geothermal Sources

Moderate-High Temperatures

P O W E R   G E N

  • High temperatures (over 150°C) are suitable for power generation

  • Includes plate subduction zones (“Ring of Fire”), rift zones (East African Rift), and extensional environments such as mid-oceanic ridges (Iceland)

  • Mature technology - over 100 years old

  • Considered conventional geothermal

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Low-Moderate Temperatures

D I R E C T   U S E

  • Moderate temperatures (90°C to 150°C) are suitable for power generation and/or direct heat use

  • Can be shallow or deep

  • Can be used for direct-use applications in a cascading system or stand-alone

  • Can produce power through Organic Rankine Cycle (ORC) technology

  • Considered conventional geothermal

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Low Temperatures

G E O E X C H A N G E

  • Low temperatures can be used for space conditioning (heating and cooling) and hot water

  • Shallow, low-temperature source (the ground, lakes, etc.)

  • Geoexchange systems relies on seasonal temperature differentials, treating the Earth as a thermal battery

  • Should not be confused with conventional geothermal

Types of Geothermal Power Generation

  • Dry Steam Power Plants: steam directly creates power

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  • Flash Steam Power Plants:  hot brine (fluid) flashes to steam as pressure decreases

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  • Binary Power Plants: transfers heat from geothermal fluid to a working fluid with lower boiling point to produce vapour

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Alberta No. 1 is a binary power plant.

How Geothermal Energy Works

Conventional Geothermal Energy Diagram -

Hot brine (fluid) can be pumped to the surface to create electricity and/or supply heat.

  • If the brine is hot enough for the intended purpose, large diameter production wells will be drilled, along with adjacent injection wells.

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  • After the wells and facility infrastructure are established, brine heated by the Earth's thermal energy is pumped to the surface

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  • Thermal energy is extracted from the brine for useful work through an Organic Rankine Cycle (ORC) system.