Energy for concerned consumers

Geothermal Energy

As demonstrated by volcanoes, hot springs and measurements from drilling, the interior of the earth is very hot, and the temperature at its core is more than 5000 °C. This heat in the earth’s interior is geothermal energy and it is so huge that it can be considered to be a practically inexhaustible source of energy.

Going from the surface of the earth towards the core, we observe that the temperature increases according to the depth. This is called the geothermal gradient. Near the surface of the earth, the geothermal gradient has an average value of about 30 °C/km. In some areas, either due to volcanic activity during a recent geological age, or due to the rise of hot water from very deep levels through fissures, the geothermal gradient is significantly greater than the average.

The result is that aquifers can be found at relatively shallow depths which contain hot water or high temperature steam. These areas are called geothermal fields and exploiting their geothermal energy is very cost effective.

Such areas in Greece are the volcanic islands of the Aegean (Milos, Nisyros, Santorini, Lesvos, Samothraki, etc.), many areas in Macedonia and Thrace (Nigrita, Siderokastro, Neo Erasmio, Nea Kessani, Tychero Evrou, etc.) as well as the environs of all of the 56 hot springs in Greece.

The applications of geothermal energy vary according to their temperature and include:

Power generation(θ>90 °C)

Space heating (with radiators, θ>60 °C, fan-coils, θ>40 °C, floor heating systems, θ>25 °C)

Refrigeration and air conditioning (using absorption heat pumps, θ>60 °C, or with water cooled heat pumps, θ<30 °C)

Heating greenhouses and soil because plants grow more quickly and become bigger with heat (θ>25 °C), and also for protection from frost.

Aquaculture (θ>15 °C) because fish require a specific temperature togrow.

Industrial applications such as desalination of seawater (θ>60 °C), drying agricultural products, etc.

Thermal spas (θ = 25-40 °C)

Besides geothermal fields, with today’s technology, heat from rock at a shallow depth, as well as low temperature underground or surface water can be used for heating and air conditioning. This technology involves the use of a very long pipe with a small diameter buried in the ground, or in wells, where it acts as an underground heat exchanger, coupled with a water cooled heat pump which provides heating or cooling to a building. Geothermal heat pumps consume one quarter of the electricity consumed by an electrical resistor and 1/2 that of an air conditioner. If the cost of energy is calculated over the life cycle of the system, geothermal heat pumps cost less than a system which consumes oil or natural gas.

In the future, geothermal energy will be exploited using hot dry rock, which is found everywhere at depths between 3 and 5 kilometers, by artificial water circulation through it at a temperature of up to 150 °C.