During the past few years, great attention has been paid to the use of waste heat and renewable energy due to their contribution towards reducing the reliance on fossil fuels. Moreover, there is a great demand for energy worldwide (Sheng et al. 2013). Renewable energy is becoming an important source of energy for the industry. The use of renewable energy does not contribute to gas emissions that harm the environment at the same level as emissions from fossil fuels. One of the most readily available renewable energy sources is geothermal energy which is stored within the Earth all over the globe at varying depths according to location.
This new source of available energy is environmentally safe as it has fewer harmful effects than traditional energy sources that rely on fossil fuels (Lurque et al. 2008; McKendry 2002). The depletion of the fossil fuel reserves calls for more sources of sustainable energies such as geothermal, wind, solar, and tidal energy. As a result of this need, a new device for tidal energy conversion was tested (El Haj Assad et al. 2016).
The conversion of geothermal energy into electrical energy is neither a cheap nor a simple process so there is a real need to use the available energy in an efficient way. As of today, there are three different types of geothermal power plants which are (1) the flash steam, (2) the dry steam, and (3) the binary ORC (Organic Rankine Cycle) geothermal power plant (DiPippo 2007). Building these power plants depends on the geothermal resources which are classified accordingly as having low enthalpy, medium enthalpy, or high enthalpy (Dickson and Fanelli 2003).
In dry steam reservoirs, the dry steam is obtained by digging wells that are 7000–10,000 feet deep, after which the steam is transported through pipe from the well to the turbine generator in order to generate electricity. Moreover, the condensed water from the turbine can be used to cool the power plants. Using dry steam reservoirs is an efficient and successful way of generating electricity, but it is rarely used. As for hot water reservoirs, the hot water from the wells is connected to one, two, or more separators to convert the water into steam. This steam then flows through pipes towards the turbine to produce electricity, after which the steam is condensed and used to cool the power plant system. This type is more common than the previously described dry steam reservoirs.
In a single flash steam power plant, the geothermal fluid is in liquid state (Ameri et al. 2006) which is expanded through an expansion valve resulting in two-phase flow. This mixture of liquid and vapor is directed to a separator kept at a constant temperature and pressure, so that the liquid and the vapor are separated from each other. The produced vapor is directed to the steam turbine to generate electricity while the remaining liquid is re-injected to a re-injection well.
The double flash steam power plant has the same working principles as the single flash power plant except that in the former, two separators are used which result in both high- and low-pressure steam flows that run the steam turbine. Double flash geothermal power plants produce a higher power output than single flash geothermal power plants but at a higher cost. The cost of the dual flash is higher than the single flash due to the use of more piping, a second separator, and low- and high-pressure steam turbines. To compensate for the high cost of a double flash power plant, an exergy analysis has been used as an effective tool to maximize the power output and hence improve the efficiency of the double flash power plant (Ameri et al. 2011; Pambudi et al. 2013).
In a binary geothermal power plant (ORC), the hot geothermal fluid is directed to a heat exchanger (vaporizer) where a secondary fluid of low boiling point and high vapor pressure circulates. The heat exchange process between the geothermal fluid and the secondary fluid causes the secondary fluid to vaporize and this generated vapor is then used to run the turbine in order to produce electricity. A flash steam power plant produces about 27 kg/MWh CO2 emissions while the ORC power plant produces zero CO2 emissions (Kagel et al. 2007). The beauty of the geothermal power plant is that it requires about 160 m2/GWh land usage which is a very small area when compared to other conventional and renewable power plants (Tester 2006).
Due to the importance of ORC, recently many investigations have been conducted to evaluate the performance of the ORC power plant by using different mixtures of the secondary fluid in the Rankine cycle part of the geothermal power plant (Bao and Zhao 2013; Garg et al. 2013; Yang et al. 2013).
Recently, second law analysis has been applied to evaluate the thermal performance of a suggested ORC-OFC combined geothermal power plant (Jianyong et al. 2015), which showed that the performance of the ORC-OFC combined power plant is much higher than the performance of ORC and OFC power plants operated separately. A second law analysis of combined Flash-ORC power plant has been applied to determine the power output and the efficiency of the power plant (Gong et al. 2010).
Negawo (2016) reviewed some geomaterial aspects of geothermal energy to show and discuss the role of geomaterials on the utilization of geothermal energy. This research focuses on analyzing the geothermal energy power plants to improve their performance and increase the dependency on renewable energy sources where geothermal energy represents 2% of the total renewable energy resources (Pazheri et al. 2014). Modeling of these systems helps in anticipating the amount of power generated and the cost as a function of geothermal system parameters such as temperature, depth, and pressure along with many other parameters. In this study, the so-called System Advisor Model (SAM) software was used.
This study was carried out based on the built-in location parameters for Geneva in Switzerland (Vuataz 2008) at a time when countries such as Pakistan (Younas et al. 2016) and Ethiopia (Teklemariam et al. 2000) have started relying on geothermal energy. The geothermal source available under the ground of Geneva is hydrothermal resource. Hydrothermal resources mean that the fluid can be in vapor form as found in steam reservoirs or it can be at a high temperature as found in deep underground hot water which keeps the surface that comes in contact with it constantly hot. There are different ways to use hydrothermal resources depending on the temperature of the fluid and its depth. If the temperature of the hydrothermal resource is low, it can be used directly to heat buildings or warm swimming pools in addition to other similar uses. Such use of hydrothermal resources is referred to as direct use. On the other hand, if the temperature of the hydrothermal resource is high, it may be used to produce electricity (Yari 2010). Two types of hydrothermal resources that can be used to produce electricity are (1) a vapor form source (known as dry steam reservoirs), and (2) a liquid form source (known as hot water reservoirs).