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Salt Water Energy Extracting Renewable Energy from Estuaries Milan Desai STREAM A Mrs. Wildfong February 18, 2010 Salt Water Energy Table of Contents Abstract……………………………….2 Introduction…………………………...3 Literature Review……………………..4 Research Plan……………………........16 Methodology………………………….17 Results/Data Analysis/Discussion........19 Conclusions…………………………...22 Limitations / Assumptions…................24 Applications / Future Experiments…...24 Literature Cited……………………….25 Acknowledgements…………………...26 1 Salt Water Energy Abstract The possibility of energy extraction from the mixing of saltwater (.6 molar NaCl) and freshwater (.022 molar NaCl) was explored and extended to investigate the feasibility of practical applications. The proposed method involves the assembly of an electric double layer (EDL) supercapacitor made from activated carbon electrodes and a saltwater dielectric. The capacitor is initially charged to approximately 300mV, and freshwater is flushed into the system. The reduced sodium and chloride ion concentrations result in a decrease in the capacitance and a consequential increase in the stored voltage, which can be discharged from the capacitor in the form of electricity. The source of energy for this process is the entropy increase from the amalgamation of saltwater and freshwater. The laboratory results are significant; however, the effects of water temperature and true ocean water were investigated to explore the practical viability of this method, which can be used to generate energy from estuaries. It was determined that the property differences between laboratory water and ocean/river waters are too minute to impact significantly the energy output of this method, contradicting the original hypothesis. This encourages future research and presents a clear possibility towards the generation of energy from the mixing of ocean and river water at estuaries. 2 Salt Water Energy Introduction It has long been known that separating salt from water is a process that requires energy from an outside source. It has also been known that the reverse process releases energy; the dissolving of salt in water releases energy. Throughout the world, thousands of rivers pour freshwater into the salty oceans. The amount of energy being released on a single day at a single estuary is incredible, let alone the amount of energy released each year. Capturing just part of this energy could theoretically provide power to the entire human population. With Doriano Brogioli’s new discovery, a small portion of this energy can be extracted and converted to electricity using a simple, cost-efficient method (Brogioli, 2009, p. 1). Brogioli’s method, however, is not perfect. His results were demonstrated in a laboratory environment using table salt to model ocean water. In reality, the ocean consists of countless other ions, minerals, and molecules that may have unpredictable effects on the system. Furthermore, the high salinity of the ocean causes extreme corrosion on materials (Lee, 2009, p. 1). Corrosion prevention mechanisms may come at a high cost. In addition, the effects of water temperature were not recorded; the ocean temperature varies significantly and higher or lower temperatures may have an important effect on the system. These are all important parameters that could greatly affect the design and location of large-scale generation systems. Before an industrial-scaled application can be sought, a thorough analysis of the methodology and results must be completed. The power output of the experimental model can be scaled to the power output of a theoretical power plant. The cost of the essential materials can be expanded to the preliminary cost of this hypothetical plant. The price of secondary materials for building and maintaining the plant must also be considered along with the probable energy consumption of the plant itself. Lastly, data must be analyzed to predict suitable locations for a large-scale plant. Clearly, an in-depth analysis of the situation is necessary. 3 Salt Water Energy Literature Review Electricity and Capacitors Voltage/Current/Resistance Voltage is the force on electrons. A current is a flow of moving electrons, indicating their speed and quantity. In a suitable analogy, electricity can be compared with the water in a river. A stronger river current has more water and greater water speed. Similarly, a stronger electrical current has more electrons traveling at a greater speed. Voltage is similar to the on water; water moves due to a gravitational force, while electrons move due to an electrical force called voltage. Voltage, current, and resistance are related and dependent upon each other. In a complete circuit, the voltage causes a current of electrons to flow through a resistance at a certain speed and quantity. In a river, gravity causes water to flow through a river bed at a certain speed and quantity. In this water analogy, voltage is analogous to gravity, current is analogous to the speed/quantity, and the resistance is analogous to the river bed. In the metric system, the units of voltage, current, and resistance are respectively Volts (V), Amps (I), and Ohms (R). In any electrical circuit, V = I*R; this allows for calculations of voltage, current, or resistance when only two of the quantities are known. This is also a principle equation used when designing electronic circuits (“Electricity”, 2009, p. 4). Energy Energy is a measurement of the amount of work that can be performed by a force. The work may include anything from driving a motor to shining light. Kinetic energy refers to the energy in moving objects, and potential energy refers to stored energy that has the potential to be converted to other forms of energy. The Law of Conservation of Energy states that energy cannot be created or destroyed; it can only be converted to different forms (mass may be regarded as a condensed form of energy. The standard metric unit of energy is the Joule (J) (“Electricity,” 2009, p. 15). Power Power is the rate at which work is performed, or in this case, energy is converted. It is the product of voltage and current, and it is the quotient of work (energy) and time. The standard unit of power is the Watt (W). Charge Electrical charge is a characteristic property of subatomic particles, indicating the electromagnetic reaction between them. Particles with a negative charge, such as electrons, attract particles with a positive charge, such as protons. Particles of the same charge repel each other. An electrically charged object contains charged particles. A moving charge, such as a 4 Salt Water Energy transfer of electrons, defines electricity. The standard unit of charge is the Coulomb, which is defined as the amount of charge transported in one second by a current of one ampere. Capacitors Capacitors are electronic components that can store charge. They are essential to nearly all electronic circuits, especially audio devices, radios, timers, and camera flash systems. The fundamental idea utilized by a capacitor is that a combination of two metals (electrodes) separated by an electrical insulator (a dielectric) can store charge (see Figure 1). One electrode is positively charged and is referred to as the cathode. The other is negatively charged and is called Figure 1. Basic capacitor design. These components consist of two conductive plates separated by an insulator. the anode. When connected to a battery or other power source as shown in Figure 2, the electrons of the metal on one side of the capacitor move to the battery anode, thus leaving a positively charged void in that portion of the capacitor. In return, the electrons from the battery cathode rush to fill this void and charge up the other side of the capacitor. In this way, the capacitor becomes charged: positively charged on one metallic surface and negatively charged on the other. The electrons of the capacitor cathode are unable to fill in the anode because of the insulation. However, when both terminals of the capacitor are connected as shown in Figure 2, the capacitor will act as a battery, spilling out the stored charge. The driving force behind this phenomenon relates to the properties of metals and insulators. When a capacitor is being charged, electrons leave one metallic end for the battery Figure 2. Circuit Configuration. To Charge a capacitor, simply connect the electrodes to the terminals of the battery. A resistor may be used to slow the charging rate. 5 Salt Water Energy anode. Electrons can leave the metal because they are generally in small quantities in the valence shells of metals. They can easily break away from the atoms if they are attracted by some other force, such as a battery. When they break away from their atom, they are considered free. Electrons in an electrical current are free because they are not bonded to any atom. Thus, in a capacitor they break away from the metal. In response, the electrons from the battery cathode rush to neutralize the positive charge of the capacitor. Capacitors differ mainly in their capacitance values, measured in farads. This is a ratio of the charge on each plate to the potential voltage difference between them. A farad is the charge in Coulombs a capacitor will accept in order for the voltage potential to increase one volt. The voltage potential is the voltage difference across the two plates. For example, if one plate is charged to 4.5 volts, and the other plate is charged to -4.5 volts, then the voltage potential is 9 volts. This is what a voltmeter will measure when connected to a capacitor. Thus: