A study of ocean thermal energy conversion in the southern Caspian Sea

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1 1 In Int. J.MAr.Sci.Eng., 4(1), 7-14, Winter & Spring 2014 ISSN IAU A study of ocean thermal energy conversion in the southern Caspian Sea 1* V. Niksima; 2 K. Lari; 2 M. Torabiazad 1 Young Researchers Club, Science and Research Branch, Islamic Azad University, Tehran, Iran 2 Department of Physical Oceanography, Tehran North Branch, Islamic Azad University, Tehran, Iran Received 9 February 2013; Revised 27 February 2014; Accepted 2 March 2014 ABSTRACT: Nowadays, in consideration of environmental issues and limitation of fossil fuels, there is a particular consideration of renewable energy including Ocean Energy, that can extracted going through various methods such as Wave Energy, Tidal Energy, Salinity Gradient, OTEC: Ocean Thermal Energy Conversion. Herein this research, operation of OTEC Method in Southern Caspian Sea has been discussed. For this purpose Sea Surface Temperature (SST) Data and Thermocline diagram with respect to 25 stations from east to west coastal area, measured in 1995 in various seasons, have been used. Considering the researches conducted, in order to use OTEC, there must be a difference in temperature between the surface and depth for at least 20 Degrees Centigrade. If such difference in temperature occurs in less depth, closer to the coast, such energy extraction will be more cost-effective. According to investigations conducted, there is a difference in temperature for about 20 Degrees Centigrade in the depth of about 200 m in the Caspian Sea during hot seasons of the year. In summer and early autumn when Thermocline achieves its complete growth, energy extraction from OTEC has a desirable yield. During winter and spring when there is decay in Thermocline, the yield is so low that using this method is not justifiable. Thus, this method can only be used in hot seasons of the year. Finally, hydrographic and temperature investigations have revealed that southeastern coasts especially those of Bandar Neka and Babolsar achieve the desirable difference in temperature, closer to the coast due to high SST and coastal slope, compared to other areas and eventually, using OTECT is cost-effective. Keywords: OTEC; Caspian Sea; Energy; Ocean Thermal Energy Conversion INTRODUCTION industrial communities, energy plays an infrastructure role. Whenever sufficient energy is available, economic development shall be possible. Kinds of fossil fuels such as coal, petroleum and natural gas have mostly been used by humans as the most important sources of energy so far (Aswathanarayana and Harikrishnan, 2010). However, these sources of energy are limited and shall end one day. Even if unlimited fossil fuels are available, we must try utmost to find substitutes for such sources. Because too much use of these sources shall lead to severe raise of such gases as CO 2 in the atmosphere and shall bring about many consequences including climate changes, as one of its results (Knauss, 1997). The substitute, which has been found for the said energy sources, is Renewable Energy. The International Energy Agency defines renewable energy as energy that is derived from natural processes, which are replenished constantly (Jordan- Korte, 2011). From among the most important * Corresponding Author vahidniksima@yahoo.com renewable energies, one may name Solar Energy, Wind Energy, Geothermal Energy, Hydrogen Energy, Fuel Cells Biomass Energy and Ocean Energy. Ocean energies can be extracted going through various methods. From among the respective methods, one may point out energy extraction through waves, energy extraction through tide, energy extraction through salinity gradient, and energy extraction through Ocean Thermal Energy Conversion (OTEC). Oceans absorb over 70% of solar energy, radiated to the earth (Roostampour and Koshesh, 2001). This has caused that the oceans become the greatest solar energy collector. In one usual day, 60,000,000 km 2 of equatorial waters absorbs energy, equivalent of 250 Billion oil barrels. Even if 0.1% of this energy is changed to electricity, it would be huge quantity of energy. One of the methods to use the said source of energy is to hire a thermal machine named OTEC (Ocean Thermal Energy Conversion), which generates electricity through the difference in temperature of surface and deep waters.

2 V. Niksima et al. Energy Resource Table 1: Energy Extraction Method of Ocean Energies Technology Energy Potential (TWh/yr) Economic Global World Europe Ocean Wave Attenuators Collectors Overtopping OWC & OWSC Point absorbers 45, Submerged pressur differential Terminators Rotors Tidal Stream Horizontal/Vertical-turbines Oscillating hydrofoils Venturi Salinity Gradient Semi-permeable osmotic membranes 2000 N/A 28 OTEC Thermo-dynamic ranking cycle 10,000 N/A The fundamentals of the said technology were introduced to the world first in 1881 by a French scientist named Jacques Arsened Arsonval (Patrick, 1991). In 1926, his student, Dr Georges Claude started his research in the field of commercial use of the said technology. Oil crisis in 1970 was a returning point for most of researchers conducting extensive researches on OTEC. It was a great motivation in the United States and Japan, in particular in order to conduct deep researches in the said field. In 1972, the U.S. administration took the first major step in this respect allotting a budget equivalent of 240,000,000.- Dollars. It should be mentioned that it is still regarded as pioneers in development of OTEC technology. In 1979, Mini OTEC project started in Hawaii America. This project consisted of a small device of closed cycle type, with a design similar to a ship. The said device was first tried in 1980 under the name of OTEC-1. It generated a power equivalent of 59 kw. In 1981, Japanese succeeded in testing a power plant of 120 kw in the Republic of Nauru (Khaligh and Omar, 2010). In 1990, International Organization of OTEC was launched by three countries namely Taiwan, America and Japan. In 1993, OTEC open cycle power plant of 210 kw was operated by America on Hawaii coast (Vega, 2003). In Iran, with a coastal border of about 5800 km, a few researches have been conducted to use OTEC technology. The most important reason refers to lack of data required for such researches. The Caspian Sea, with a coast of about 740 km, belonging to Iran, of which depth reaches over 1000 m, can be a desirable source to operate OTEC Technology in case of required difference in temperature. MATERIALS AND METHODS OTEC Technology uses hot surface water of seas (at degrees centigrade) as thermal source with high temperature and cold waters in the depths of m (at 4-8 degrees centigrade) as thermal source with lower temperature. It converts a few quantity of energy, which is transferred from hot to cold source, to mechanical work. It is used to generate electricity. Here, we face a huge source of thermal energy that covers a vast area. This kind of energy is regarded as renewable energy and also it may generate energy for 24 hours. However, due to low difference between the temperature of the two hot and cold sources, the system has a low yield accordingly (Avery and Wu, 1994). In order to calculate maximum yield of the power plant, Formula 1 has been used. The said formula is known as Carnot efficiency. η max = T w T c T w (1) where η max : Maximum yield that is derived from the difference between hot and cold temperature. T w : Absolute temperature of hot water T c : Absolute temperature of cold water In order to use the aforesaid formula, respective temperatures obtained through research tours, done per degree centigrade, are converted based on Kelvin scale. For the best conditions in tropical areas where surface structure is 29 Degrees centigrade and the temperature of cold weather in deep areas are 4.5 Degrees centigrade, the yield of our cycle will be about 8 percents. However, the said calculation is considered in ideal conditions. In practice, such yield, as described above, could not be achieved. Because some quantity of the said energy is lost during conversion process due to such factors as friction, thermal loss, etc. Yield amount, obtained after such losses, is usually given as 3.5-4% which 25-30% of 8

3 Int. J. Mar.Sci.Eng., 4(1), 7-14, Winter & Spring, 2014 this generated energy is used for internal consumptions of the power plant such as water pumping. Finally, (net) output yield of the power plant is given as about 2.5-3%. The said quantity of the yield, compared to common power plants that usually have a yield above 40%, is not too much. However, regarding OTEC power plants, we have a free and huge source of heat that can be used day and night. This has caused that OTEC power plants are of great interest. OTEC Power Systems On a whole, OTEC systems work according to three different cycles. Open, closed and hybrid cycles of which the third cycle is a combination of the two said cycles.fig.s 1 shows the scheme of the said cycles. Open Cycle OTEC use hot surface sea water as both Working Fluid and thermal source. In such system, hot water is evaporated due to vacancy. Steam, with low pressure, enters the turbine and work is done. Then, the steam is condensed in the condenser. In case surface condenser is used, condensed water is used to produce drinkable water. In case spraying condensers or Director Control Condensers are used, the mixture of the said condenses and chilling water of the ocean is discharged. Open Cycle is also called Claude Cycle since it has been used for the first time by Dr. George Claude (Watt, Mathews and Hathaway, 1977). Closed Cycle OTEC devices enjoy anworking fluid except for water. This cycle is called Closed Cycle because the working fluid works in a closed cycle that has no material interaction with environment (Rankin Cycle). Surface sea hot water is pumped into the system. Working fluid, which is usually ammoniac, inside the evaporator, exchanges heat with sea hot water through wall of conversion plates or pipes (pressure is higher than atmosphere). Working fluids boils through indirect contact with hot water and is evaporated. It enters the turbine with a lower pressure, compared to the evaporator. Steam expansion among turbine blades shall rotate it and eventually, the generator moves and power is generated. Output steam of the turbine is pumped into the condenser and is condensed by cold water (Hoseyni, 2000). There is no difference between hybrid cycle OTEC equipments and the said cycles. In fact, it is a device that is made through a series of open or closed cycle with the evaporator and extra condenser. It seems that the most use of thermal energy is for generating electricity and drinkable water. Further to generating electrical power and drinkable water, OTEC devices enjoys various applications as well. From among these applications one may point out Air conditioning using cold water, Hydrogen production, Aquaculture, Chilled-soil agriculture and Mineral extraction. For feasibility study of OTEC in the Caspian Sea, the difference in temperature of surface and deep water of the said coasts must be calculated so that a desirable area for startup of the power plant would be achieved. For this purpose, we use the information of the southern Caspian Sea, obtained by Ecology Research Center of the Caspian Sea, measured in 1995 and The said information covers from the east to the west side of the said coasts. Fig. 2 shows the location of the said stations. First, surface temperature at the said stations has been studied. Then, temperature profiles were drawn based on depth. Fig. 1: Schematic closed cycle (a), open cycle (b) and compound cycle (c) 9

4 A study of ocean thermal energy conversion in the southern Caspian Sea RESULTS AND DISCUSSION Study of temperature changes based on depth is obligatory in order to achieve a desirable depth. Fig. 3 shows temperature profile in the Caspian Sean during four different seasons. The said diagram has been given as sample from among the stations that have been studied. One may observe that Thermocline in the Caspian Sea at depths of m only occurs during hot seasons of the year. When the weather becomes cold, it decays until it completely faded in winter. Fig. 2: Measurement stations in the Caspian Sea Fig. 3: Temperature Profile based on depth in the Caspian Sea 10

5 Temperature (C) Int. J. Mar.Sci.Eng., 4(1), 7-14, Winter & Spring, 2014 Surface temperature of the southern Caspian Sea increases from west through east. We witness the highest temperatures on the entire surface of the Caspian Sea on the southeastern coasts. The said temperature increases from degrees in winter to degrees in summer. The average of difference in surface temperature in summer and winter is given as about 15 degrees. Fig. 4 shows the change in surface temperature with a change in longitude from east to west (stations D6-D14). According to the investigations conducted, it has been found that change in the temperature of the water of the Caspian Sea to a depth of about 200 m is completely evident. The said changes is gradually decreased to a depth of about 500 m. Below the said depth, one can say that there is still cold water where no particular change and difference in temperature occur and that there is less signs of aquatic organisms at the said depths. The results of difference in the temperature of surface and that of depth of 200 m are given in Tables 2-5. Moreover, a maximum yield occurs due to the said difference in temperature Summer Longitude Temp. (C) Expon. (Temp. (C)) Fig. 4: Surface temperature profile with a change in longitude (stations D6-D14) Table 1: Information of stations in Spring Stations seasen Temperature difference (between surface and depth of 200m) Output D1 Spring D2 Spring D3 Spring D4 Spring D5 Spring D6 Spring D7 Spring D8 Spring D9 Spring D10 Spring D11 Spring D12 Spring D13 Spring D14 Spring D15 Spring D16 Spring D17 Spring D18 Spring E Spring M Spring - - L Spring - - K Spring - - I Spring G Spring U1 Spring

6 V. Niksima et al. Table 2: Information of stations in Summer Stations seasen Temperature difference (between surface and depth of 200m) Output D1 Summer D2 Summer - - D3 Summer D4 Summer D5 Summer D6 Summer D7 Summer D8 Summer D9 Summer D10 Summer D11 Summer D12 Summer D13 Summer D14 Summer D15 Summer D16 Summer D17 Summer - - D18 Summer E Summer - - M Summer - - L Summer - - K Summer I Summer - - G Summer U1 Summer Table 3: Information of stations in Autumn Stations seasen Temperature difference (between surface and depth of 200m) Output D1 Fall D2 Fall D3 Fall D4 Fall D5 Fall D6 Fall D7 Fall D8 Fall D9 Fall D10 Fall D11 Fall D12 Fall D13 Fall D14 Fall D15 Fall D16 Fall D17 Fall D18 Fall E Fall M Fall L Fall K Fall I Fall G Fall U1 Fall

7 Int. J. Mar.Sci.Eng., 4(1), 7-14, Winter & Spring, 2014 Table 4: Information of stations in Winter Stations seasen Temperature difference (between surface and depth of 200m) Output D1 Winter D2 Winter D3 Winter D4 Winter D5 Winter D6 Winter D7 Winter D8 Winter D9 Winter D10 Winter D11 Winter D12 Winter D13 Winter D14 Winter D15 Winter D16 Winter D17 Winter D18 Winter E Winter M Winter L Winter K Winter I Winter G Winter U1 Winter - - The difference in required temperature for desirable yield of OTEC power plan is given as 20 Degrees Centigrade (Heydt, 1993). Considering Table 3, even in the warmest seasons of the year, there is rarely a difference in temperature of 20 degrees centigrade to the depth of 200 m in the Caspian Sea. However, such difference in temperature reaches above 19 degrees centigrade to the said depth. It should be noted that respective data studied herein this research has temporarily been measured. For more precise study, constant data in the Caspian sea to the depth of 200 m is required. The yield, calculated for the power plant in Spring and Summer, the yield is so low that it is not possible to use the said power plant. In summer and autumn, we face a relatively desirable yield. We can say that southeastern coast of the Caspian Sea have more potential to use OTEC. Through erection of OTEC coastal power plants in certain areas of the said coast with a desirable continental slope, one may avoid respective expenses spent for development of floating power plants. Because one of the most important byproducts of Open Cycle OTEC devices is drinkable water and since southern coastal areas of the Caspian Sea face no specific problem with respect to precipitation and resources of drinkable water and concerning the fact that respective equipments for producing drinkable water costs too much, Closed Cycle is more suitable for the Caspian Sea and application of Open or Hybrid cycle OTEC devices that enjoys stage of producing drinkable water are placed in the next priority. Close Cycle OTEC devices are capable of generating a huge quantity of electrical power and their technological limitations with respect to development of large ones are less than those of Open Cycle. On a whole, most potential of the southeast coastal regions of the Caspian sea to use OTEC, compared to other regions, is evident. In certain regions of the said coasts such as Neka and Babolsar coasts, with more appropriate continental slope, one can avoid spending too much money for development of floating power plants through erection of OTEC coastal power plants. It should be further added that the said power plant can only be operated during hot seasons of the year and it stops working during other season. CONCLUSION Herein this research, we have studied the possibility of the use of OTEC Technology on the southern coasts of the Caspian Sea. The said technology can only be operated in hot seasons of the year (about five 13

8 A study of ocean thermal energy conversion in the southern Caspian Sea months per year) in the said region and it stops working during other seasons of the year. The average of surface temperature obtained for the southern coasts of the Caspian Sea is given as 26.6 Degrees centigrade in summer and 10.1 Degrees centigrade in winter. The difference in surface temperature in summer and winter reaches 15.5 degrees centigrade. Formation of a strong and seasonal Thermocline in the depths of m in hot months of the year is completely evident. In winter, Thermocline is actually faded due to winger convection. Southeastern coasts of the Caspian Sea enjoy more desirable conditions for operation of the said technology due to high surface temperature (about 26 degrees centigrade on average) compared to other regions (with a temperature of degrees centigrade on average). In certain areas of the said coasts such as Neka and Babolsar coasts, with more continental slope, we reach cold deep waters in the sea and required difference in temperature, required for OTEC System, in a closer distance to the coast. The said regions are most cost-effective accordingly. REFERENCES Aswathanarayana, U.; Harikrishnan, T.; Thayyib Sahini, K.M., (2010). Green Energy: Technology, Economics and Policy, CRC Press. Avery, W. H.; Wu, Ch., (1994). Renewable Energy from the Ocean: A Guide to OTEC, Oxford university press. Heydt, J. T., (1993). An Assessment of Ocean Thermal Energy Conversion as an Advanced Electric Generation Methodology, Proceedings of The IEEE. 81 (3). Hoseyni, R., (2000). OTEC plant design and technical and economic considerations of installation in the Caspian Sea and Persian Gulf, University of Sistan and Baluchestan Jordan-Korte, K., (2011). Government Promotion of Renewable Energy Tecnologies, Gabler Publishing House Knauss, J. A., (1997). Introduction To Physical Oceanography, Prentice Hall Press Khaligh, A.; Onar, O. C., (2010). Energy harvesting: solar, wind, and ocean energy conversion systems, CRC Press. Patrick k., (1991). Ocean thermal energy conversion: Its promise as a total resource system, Journal of Energy, 17 (7), Roostampour, V.; Koshesh, P., (2001). Optimized application of thermal energy in southern coastal area of Caspian Sea to generate electricity, Third National Energy Conference. Vega, L. A., (2003). Ocean Thermal Energy Conversion Primer, Journal of Marine Technology Society, 6 (4), Watt, A. D.; Mathews, F. S.; Hathaway, R. E., (1977). Open cycle ocean thermal energy conversion: a preliminary engineering evaluation, United States. Dept. of Energy. Division of Solar Energy. How to cite this article: (Harvard style) Niksima, V *.; Lari, K.; Torabiazad, M., (2014). A study of ocean thermal energy conversion in the southern caspian sea. J. Mar. Sci. Eng., 4 (1),