What is Geothermal Energy

Geothermal
Geo = Earth; Thermal = Heat

Geothermal energy is the heat contained within the Earth which can be recovered and exploited for heating and other direct uses (residential, industrial), or generation of electricity. Geothermal system is a transfer of heat energy from the inner part of the Earth to the surface.

Geothermal power is sustainable, cost effective, and environmentally friendly. Recent technology advances have expanded the range and size of viable resources, especially for direct uses such as home heating. Geothermal power plants release greenhouse gases, but the emissions are much lower per energy unit than fossil fuels. As a result, geothermal power has potential to mitigate global warming, if it is deployed in place of fossil fuels.

Geothermal Reservoir
Requirements for a Geothermal Reservoir to Exist:

• Heat source (Magma)
• Permeability (flow capacity)
• Porosity (storage capacity)
• Recharge – natural or artificial (injection)
• Discharge – required to allow circulation to occur

Resource types:

1. single phase; water dominated; T = 100°C - 300°C (212°F - 570°F)
2. two-phase; steam and water; T = >230°C (>450°F)
3. single phase; steam dominated; T = >240°C (>465°F)
4. special conditions:

• critical fluid conditions T>374.15°C (>705.44°F)
• high salinity brines (up to 30 wt-% solids)
• high gas contents (up to 10 wt-%)

Geothermal Resources –
Located by:

1. surface geology and tectonic setting
2. surface manifestations – Geochemistry
3. geophysical techniques – to find anomalies: resistivity surveys, gravity, magnetic, etc.

Extracted by:

1. Drilling wells – wells may self flow or require pump
2. Pipes
3. Surface facilities (HE, separators, turbine, cooling towers, fluid treatment)

Energy utilization:

1. Direct Use (snow melting, heating, drying/dehydration, agriculture - greenhouse, etc.)
2. Power Generation (Steam turbine generator; Binary plant)
3. Hot Dry Rock (Enhanced Geothermal Systems)