Advanced Electrical Power Generation Technology Using Renewable & Clean Low-Enthalpy Geothermal Energy Sources

Introductory Chapter: Power Generation Using Geothermal Low-Enthalpy Resources and ORC Technology

“…The geothermal resources of the Earth are vast. For instance, the amount of geothermal energy stored at a depth of approximately 3 km is estimated to be 1,194,444,444 TWh which is much larger compared to all fossil fuel resources combined, whose energy equivalent is estimated to be 1,010,361 TWh [1,2]. Unlike other renewable energy resources, geothermal energy has distinct characteristics; namely, it is available and stable at all times throughout the year, has an inherent storage capability, and is independent of weather conditions [1].…”

“…In general, the utilization of geothermal energy is divided into two parts: (a) electricity generation and (b) direct heating (non-electrical) applications. Recently, this form of renewable energy source has grown in 25 countries, with installed geothermal-electric capacity up to 11 GW e in 2010 [1,2], and is increasingly contributing to the electric power supply worldwide [1][2][3].…”

“…Geothermal energy resources typically differ in temperature from about 50 to 350°C. The high-temperature geothermal resources (with temperature >200°C) are typically found in volcanic regions and island chains, whereas the medium-temperature (150-200°C) and low-temperature geothermal resources (<150°C) are usually found widely in most continental regions and by far the most commonly available geothermal resource [2,3]. The increase in temperature with depth in the Earth's crust can be expressed in terms of what is known as the geothermal temperature gradient.…”

“…The increase in temperature with depth in the Earth's crust can be expressed in terms of what is known as the geothermal temperature gradient. Down to the depths accessible by drilling with state-of-the art technology (over 10 km), the average geothermal gradient is about 2.5-3.0°C/100 m [2]. For example, at depth around 3 km below ground surface, the estimated temperature is approximately 90°C.…”

“…There are, however, regions in which the geothermal temperature gradient is far from the average value. For instance, in some geothermal areas, the gradient is 10 times the average value due to composition of these areas and geothermal structure [2]. It was also reported that the emissions of GHG from geothermal power plants, in general, constitute less than 2% of the emission of these gases by fossil-fuelled power plants [2].…”