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

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

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

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

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

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

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

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

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

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.

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

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