**1. Introduction**

Electrical power generation using innovative renewable and alternative geothermal energy technologies have shown merits and received renewed interest in recent years due to an in‐ creasing concern of greenhouse gas (GHG) emissions, being responsible for global warming & climate change, environmental pollution, and the limitations and conservation of natural energy resources. Organic Rankine Cycle (ORC) power generation using low-temperature geothermal resources is one of these innovative geothermal power generation technologies. The vast low-temperature geothermal resources found widely in most continental regions have not received much attention for electricity generation. Continuous development of ORC power generation and state-of-the-art drilling technologies and other factors make this renewable and nonconventional energy source one of the best future viable, alternate and available source to meet the required future electricity demand worldwide, significantly re‐ ducing GHG emissions and mitigating global warming effect. The first part of this chapter will introduce the ORC-based geothermal power generation technology. It will also present its fundamental concept for power generation and discusses its limitations, environmental & economic considerations, and energy conversion performance concept. Another novel "dou‐ ble-benefit" technology is enhanced (engineered) geothermal systems (EGS) using CO2 as the working fluid for combined renewable power generation and CO2 sequestration. CO2 is of interest as a geothermal working fluid mainly because it transfers geothermal heat more efficiently than water. While power can be produced more efficiently using this technology, there is an additional benefit for carbon capture and sequestration (CCS) for reducing GHG emissions. Using CO2 as the working fluid in geothermal power systems may permit utiliza‐ tion of lower-temperature geologic formations than those that are currently deemed eco‐

© 2013 Ismail; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Ismail; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

nomically viable,leading to more widespread utilization of geothermal energy. The second part of this chapter will present and discuss the merits, limitations, environmental, econom‐ ic and fundamental aspects of CO2-based EGS technology.

value) due to geothermal structure and composition of these areas (Dickson& Fanelli, 2005). The type of geothermal resource determines the type of system and method of its harvesting and utilization for electrical power generation. For example, high-temperature geothermal resources (vapour- and liquid-dominated) can be harvested and utilized to generate electric‐ ity using one of the following methods depending on the compositional and thermal charac‐ teristics of the resource: (1) single-flash steam power systems, (2) double-flash steam power systems, and (3) dry-steam power systems. Generating electricity from medium- and lowtemperature geothermal resources (i.e. water-dominated resources) can be efficiently accom‐ plished using a Binary-cycle technique, such as, ORC (Ismail, 2011a; Chandrasekharam&

ORC-Based Geothermal Power Generation and CO2-Based EGS for Combined Green Power Generation and CO2

Sequestration

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http://dx.doi.org/10.5772/52063

Generating electricity from geothermal steam resources using an experimental 10 kW-elec‐ trical generator was made at Larderello of Italy in 1904 (Dickson& Fanelli, 2005; Panea et al., 2010). The commercial success of this attempt indicated the industrial value of geothermal energy and marked the beginning of a form of exploitation that was to develop significantly from the on. By 1942, the installed geothermal-electric capacity had reached approximately 128 MWe (Dickson& Fanelli, 2005). In the early 1950's, many countries were attracted by ge‐ othermal energy, considering it to be economically competitive with other forms of energy. It was estimated (Dickson& Fanelli, 2005; Ruggero, 2007) that the worldwide installed geo‐ thermal-electric capacity reached 1.300 GWe (in 1975), 4.764 GWe (in 1985), 6.833 GWe (in 1995), 7.974 GWe (in 2000), 8.806 GWe (in 2004), 8.933 GWe (in 2005), 9.732 GWe (in 2007). In 2010, it was reported (Holm et al., 2010) that 10.715 GWe is online generating 67,246 GWh which represents a 20% increase in geothermal power online between 2005 and 2010. While power on-line grew 20% between 2005 and 2010, countries with projects under development grew at a much faster pace. In 2007, Geothermal Energy Association (GEA) reported that there were 46 countries considering geothermal power development. In 2010, this report identified 70 countries with projects under development or active consideration, a 52% in‐ crease since 2007. It should be noted that projects under development grew the most in‐ tensely in two regions of the world; namely, Europe and Africa (Holm et al., 2010).Very recently, it was reported (GEA, 2012) that as of May 2012, approximately 11.224 GWe of in‐ stalled geothermal-electric power capacity was online globally, and is increasingly contribu‐ ting to the electric power supply worldwide. It was estimated (Ruggero Bertani, 2007) that geothermal energy provides approximately 0.4% of the world global power generation, with a stable long term growth rate of 5%; the largest markets being in USA, Mexico, Indonesia, Philippines, Iceland, and Italy. Security for long-term electricity supply and GHG emission from fossil fuelled power plants is becoming a cause of concern for the entire world today. It was estimated (Chandrasekharam& Bundschuh, 2008) that the world net electricity demand is going to increase by approximately 85% from 2004 to 2030, rising from 16,424 TWh (in 2004) to 30,364 TWh in the year 2030. It was also reported (Chandrasekharam& Bundschuh, 2008; Dickson & Fanelli, 2005) that the emissions of GHG from geothermal power plants constitute less than 2% of the emission of these gases by fossil-fuelled power plants. To meet future energy demands renewable energy sources should meet the following criteria (Chan‐ drasekharam& Bundschuh, 2008): (1) the sources should be large enough to sustain a longlasting energy supply to generate the required electricity for the country, (2) the sources

Bundschuh, 2008; Dickson & Fanelli, 2005; DiPippo, 2008).
