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Non-nuclear energy

Introduction to Geothermal energy

Fission and radiation protection

What is geothermal energy?

Geothermal energy embraces a variety of different technologies aimed at the use of heat from the earth. This resource is so large that it can be regarded for all practical purposes as renewable. Geothermal energy is able to provide a firm, dependable supply of electric power and heat energy, available to the consumer at any time during the day or the year, regardless of weather and climate.

What are the main concepts for using geothermal energy?

Geothermal utilisation is divided into two categories: electricity generation and direct use.

  • Conventional electricity production, in which turbines are driven by steam, is limited to fluid temperatures above 150°. At lower fluid temperatures, electricity generation requires the use of binary cycles, in which a working fluid, (usually an organic fluid) is heated and vaporised in a closed circuit. The vapour drives a turbine, before being cooled and condensed, and the cycle begins again. The low boiling point of the working fluid allows electricity production from geothermal fluids with temperatures as low as 85°C.
  • Direct use of heat is one of the oldest, most versatile and also the most common form of utilisation of geothermal energy. Space and district heating, agriculture, aquaculture and industrial uses are the best known and most widespread applications.
  • Geothermal heat pumps represent a relatively recent but fast-growing development. This technology has the advantage of being applicable at the scale of an individual dwelling as well as in group- or district-heating systems. This feature, combined with the ability to offer cooling as well as heating, has resulted in rapid growth in the US and Europe, and can be expected to account for much of the growth in total direct heat applications over the next decade or so.
  • Drillbit
     In Enhanced Geothermal Systems, a well is drilled into high-temperature (typically >180°C) fractured basement rock and stimulated to enhance the natural permeability of the fracture network to create a reservoir or heat exchanger into which additional wells are drilled. Water circulated through the fracture network in the hot rock via the wells gathers heat, which can be extracted at the surface to generate electricity or for direct use. The main components are thus the underground heat exchanger and the surface heat exchanger and power cycle.

What are the current uses of geothermal energy?

The best geothermal resources reside in those countries possessing deposits of steam and natural hot water (>160°C). Electricity generation from such reservoirs has been a commercial reality since the 1920s. Currently, 21 countries generate power from geothermal fluids. Recent inventories show that in 2000, the installed capacity world-wide reached 7,974 Mwe, which is a 16.7% increase since 1995; the total energy generated is at least 49,261 GWh annually.

There are far fewer geological restrictions on the occurrence of low temperature (<100°C) fluids, and some 58 countries now exploit such resources in direct heating applications. The major uses are space heating and bathing. The total energy supplied during 2000 has been estimated at 190,699 TJ/y world-wide. There is, however, much greater potential for growth in these lower temperature developments. A recent study by the International Geothermal Association suggested that the long-term potential could reach 1,400 million TJ/y.

Several Central European countries - notably East Germany, Poland, Romania, Hungary and Slovenia, possess good low-enthalpy aquifers. With increasing pressure to minimise the environmental effects of their outdated solid fuel fired heating systems, many have begun to develop district heating schemes along the lines of those in Paris.