What is Geothermal Energy?


Geothermal energy is literally the heat contained within the earth that generates geological phenomena on a planetary scale. Geothermal resources have three main components: 1. Heat source, 2. Fluid carrying heat from the earth’s crust to the surface, 3. Sufficient rock permeability to circulate thermal water. In geothermal areas, hot rocks and high temperature groundwater are at shallow depths. The main reasons are:

  • The rise of molten rocks (magma) through the crust, which transports heat,
  • Heat flow resulting from high temperature gradient where the crust is thin,
  • Return of geothermal water to the earth’s surface after circulating down and absorbing some of the heat.

The simple representation of an ideal geothermal system is shown in Figure 1. 


Fig.1 Schematic representation of an ideal geothermal system.

To distinguish between geothermal area, system, and reservoir following definitions can be made;

Geothermal Area: It is a geographical term which indicates a geothermal activity. It is used to define the area above the geothermal reservoir if there is no hot spring or steam vent.

Geothermal System: It expresses the hydraulic system underground with its all components.

Geothermal Reservoir: It expresses the part of geothermal system which is hot and permeable.

Geothermal systems and reservoirs are classified according to reservoir temperature, enthalpy of the fluid, its physical state, untuvatakkinature and geological location etc. For example, geothermal reservoir may be classified into two groups according to temperatures at 1km depth.

1.Low temperature systems, reservoir temperature of which is lower than150 ºC: In such systems, generally hot springs can be seen.

2.High temperature systems, reservoir temperature of which is higher than

200 ºC: In such systems, generally steam vents (fumaroles) and boiling mud lakes can be seen.

According to physical state of geothermal system, reservoirs can be classified into 3 groups.

a. Geothermal reservoirs in which liquid phase is dominant: It is used to express the reservoirs in which water temperature is lower than the dunjakker moncler vaporization temperature under reservoir conditions. Reservoir pressure is controlled by the liquid phase of water.

b. Two phase geothermal reservoirs: Both liquid and gas phases of water exist in reservoir. Reservoir pressure and temperature follow the steam pressure curve.

c. Geothermal reservoirs in which vapour phase is dominant: Water temperature is higher than the vaporization temperature in such reservoirs. Reservoir pressure is controlled by the vapour phase.

Physical and chemical properties of geothermal reservoir may change depending on time. In addition, the properties may change depending on the position in the same reservoir. For instance, a liquid phase dominant reservoir may become two phase reservoir because of pressure drop resulting from production.

Geothermal energy is an energy source, which does not contribute to air pollution and reduce environmental problems when used properly. It should be aimed to use geothermal energy source in sustainable projects. Geothermal systems and reservoirs should be understood clearly to provide sustainability of the project.

IGA, http://www.geothermal-energy.org/geothermal_energy/what_is_geothermal_energy.html#c255