Geothermal energy is thermal energy generated and stored in the Earth. Geothermal electricity is electricity generated from geothermal energy. Geothermal Electricity power plant technologies in use are dry steam power plants, flash steam power plants and binary cycle power plants. Geothermal electricity generation and geothermal heat pump technologies are currently in use and development. Geothermal electricity generation has many advantages and disadvantages (pros and cons) compared other conventional power generation technologies.

Geothermal Electricity Generation

Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW. Geothermal power is considered to be sustainable because the heat extraction is small compared with the Earth’s heat content. The emission intensity of existing geothermal electric plants is on average 122 kg of CO2 per megawatt-hour (MW·h) of electricity, a small fraction of that of conventional fossil fuel plants.

Electricity generation requires high temperature resources that can only come from deep underground. The heat must be carried to the surface by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation, oil wells, drilled water wells, or a combination of these.

The geothermal gradient is 25-30°C per kilometre (km) of depth in most of the world, and wells would have to be several kilometres deep to permit electricity generation. At present, geothermal wells are rarely more than 3 kilometres (2 miles) deep. Upper estimates of geothermal resources assume wells as deep as 10 kilometres (6 miles). Drilling at this depth is now possible in the petroleum industry, although it is an expensive process. The deepest research well in the world, the Kola superdeep borehole, is 12 kilometres (7 miles) deep.

Geothermal Heating and Heat Pumps

Geothermal heating is the direct use of geothermal power for heating applications. A geothermal heat pump, ground source heat pump (GSHP), or ground heat pump is a central heating and/or cooling system that pumps heat to or from the ground. It uses the earth as a heat source (in the winter) or a heat sink (in the summer). Geothermal heat exchangers are underground heat exchangers to capture or dissipate heat to or from the ground.

Geothermal heating systems have applications including geothermal HVAC system, geothermal home heating/cooling system, geothermal air heating, geothermal water furnace and pool heater, geothermal heat pumps and heat exchangers for geothermal electricity generation plant, etc.

Geothermal Energy Advantages (Pros)

  • Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth’s heat content.
  • Geothermal sites are capable of providing heat for many decades.
  • Geothermal Electricity generation allows direct use of geothermal energy without the need of energy converters.
  • Geothermal Electricity generation produces low carbon (CO2) emissions, a small fraction of that of conventional fossil fuel plants.
  • Geothermal energy is renewable.

Geothermal Energy Disadvantages (Cons)

  • Electricity generation requires high temperature resources that can only come from deep underground.
  • For installation, wide spaces and long pipes are needed. As a result, areas of dense population will have a tougher time getting the energy into homes.
  • More importantly, there is no guarantee that the site being drilled will facilitate access to steam or hot water forever, or that the site in which one has invested will continue to provide steam or water in desired amounts.

Enhanced Geothermal Systems (EGS) are a new type of geothermal power technologies that do not require natural convective hydrothermal resources. Enhanced Geothermal Systems (EGS) technologies “enhance” and/or create geothermal resources in the hot dry rock (HDR) through hydraulic stimulation.