Direct Use of Geothermal Energy

Direct-use of geothermal energy is one of the oldest, most versatile and also the most common form of utilization of geothermal energy [10]. The early history of geothermal direct-use has been well documented for over 25 countries in the Stories from a Heat Earth - Our Geothermal Heritage [11] that documents geothermal use for over 2,000 years [12].

As of 2009, direct utilization of geothermal energy worldwide is 50,583 MWt. The total annual energy use is 438,071 TJ (121,696 GWh). The five countries with the largest installed capacities are: USA, China, Sweden, Norway and Germany accounting for 60% of the world's capacity, and the five countries with the largest annual energy use are: China, USA, Sweden, Turkey, and Japan, accounting for 55% of the world use. However, an examination of the data in terms of land area or population shows that the smaller countries dominate, especially the Nordic ones. The largest increase in geothermal installed capacity (MWt) over the past 5 years are: United Kingdom, Korea, Ireland, Spain and Netherlands; and the largest increase in annual energy use (TJ/year) over the past 5 years are: United Kingdom, Netherlands, Korea, Norway and Ireland. All of these increases are due to geother-mal heat pump installations [12]. During the last decade, a number of countries have encouraged individual house owner to install ground source heat pumps to heat their houses in the winter and cool them in the summer.

Summary of various categories of direct use worldwide is given in Fig. 4.1. The result shows that geothermal heat pumps were increased exponentially during the last 10 years. Other uses also increased with a linear trend.

Geothermal fluids contain certain minerals leached from the reservoir rock and variable quantities of gas, mainly carbon dioxide and a smaller amount of

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♦ Geothermal Heat Pumps —■■ — Space Heating . .4. . Greenhouse Heating —x— Aquaculture Pond Heating

Geothermal Heat Pumps /

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/

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—#— Bathing and Swimming

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---Others

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Fig. 4.1 Summary of the various categories of direct use worldwide, referred to period 1995-2010 [12]

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Fig. 4.1 Summary of the various categories of direct use worldwide, referred to period 1995-2010 [12]

hydrogen sulphide. The gas composition and quantity depend on the geological conditions encountered in different fields. Virtually the entire mineral content of the fluid and some of the gases are reinjected back into the reservoir. Most non-condensable gases are released to the environment. Some plants remove H2S in a gas treatment process before releasing CO2 to the environment. At one plant in Kizildere, Turkey, the non-condensable gases are scrubbed of H2S, and CO2 are recovered to provide about 80% of CO2 used by the country's soft drinks industry [13].

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