Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1 (2016), pp.63-67 IIJET SOLAR THERMAL POWER PRODUCTION USING HELIOSTATS PrithivieRaaj T*, Gobinath M**

*,**Department of Mechanical Engineering, Adhiyamaan College of Engineering, Tamilnadu

*[email protected], **[email protected]

Abstract activate turbines that produce electricity. The focusing of solar power can be achieved by parabolic dishes. Solar This paper is based on the solar technology which deals thermal power production is basically done by the following with the heating of the salt or fluids by the use of the components is explained in the schematic diagram. heliostat, receiver (solar salt tower) which includes a receiver and many no thin walled tubes. The salt can be melted and their temperature increased and then passed through a receiver by focusing a point focus method on the receiver as it collects and heat the salt to high temperature of 868K. It is further used in the steam production by the use of the turbine and heat exchanger.

The salt which is used is a mixture of potassium nitrate and sodium nitrate as they can hold high temperature for more than 14 hours. We can store the heat in the salt, even we can use it in the night time also. This technology Figure 1: Solar Power Production Components 100% eco-friendly. The salt which we are using is initially A. Heliostat Mechanism melted by thermal oil it can also be heated by the solar arrays which are naturally available. The salt which we A heliostat is a mechanism that includes a dual axis sun- using can be reused for a prolonged period until the tracking mirrors mirror, usually a plane mirror which turns so power plants maintenance break. as to keep reflecting sunlight toward a defined target, compensating for the sun's apparent motions in the sky. The I. Introduction target may be a physical object, distant from the heliostat, or a direction in space. To do this, the reflective surface of the This research paper vividly explains about the solar mirror is kept perpendicular to the bisector of the angle technology by the use salt and heliostat mirrors. This energy between the directions of the sun and the target as seen from is a largely available on the earth. Renewable energy is a eco- the mirror. The target is stationary relative to the heliostat, so friendly energy when compared to energy produced by the light is reflected in a fixed direction. Nowadays, most nuclear energy, coal and other fossil fuels. Renewable energy heliostats are used for day lighting or for the production of resources exist over wide geographical area, in contrast to concentrated solar power, usually to generate electricity. other energy sources. Rapid deployment renewable energy They are also sometimes used in solar cooking. A few are and energy efficiency is resulting in significant energy used experimentally, or to reflect motionless beams of security, climatic change, mitigation and economic benefits. sunlight into solar telescopes. Before the availability of lasers Solar thermal energy is arising as a leading power production and other electric lights, heliostats were widely used to technology using renewable resources. This technology produce intense, stationary beams of light for scientific and which produce electricity by concentrating solar energy in other purposes. Most modern heliostats are controlled by single focal point this concentrated energy is then used to computers. The computer is given the latitude and longitude develop heat on salt and use it to produce the steam and of the heliostat's position on the earth and the time and date.

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Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1 (2016), pp.63-67 IIJET

From these, using astronomical theory, it calculates the Heliostat costs represent 30-50% of the initial capital direction of the sun as seen from the mirror, e.g. its compass investment for solar power tower power plants depending on bearing and angle of elevation. Then, given the direction of the energy policy and economic framework in the location the target, the computer calculates the direction of the country. It is of interest to design less expensive heliostats for required angle-bisector, and sends control signals to motors, large scale manufacturing, so that solar power tower power often stepper motors, so they turn the mirror to the correct plants may produce electricity at costs more competitive to alignment. This sequence of operations is repeated frequently conventional coal or nuclear power plants costs. Besides cost, to keep the mirror properly oriented. percent solar reflectivity and environmental durability are factors that should be considered when comparing heliostat B. Mirror designs. Most are countries are attempting to lower the costs of heliostats is by replacing the conventional heliostat design These are parabolic mirrors shaped like half pipe.The sun with one that uses fewer, lighter materials. A conventional shines onto the panels made up of glass which is 94% design for the heliostat's reflective components utilizes a reflective where as ordinary mirrors are only 70% reflective. second surface mirror. The sandwich-like mirror structure It is automatically tract the sun throughout day. The source of generally consists of a steel structural support, an adhesive mirror breakage is wind. We can protect it from those layer, a protective copper layer, a layer of reflective silver, breakages by turning it during intense wind storms which and a top protective layer of thick glass. This conventional often occurs in deserts. Another factor which reduce its heliostat is often referred to as a glass/metal heliostat. efficiency is deposition of sand on the mirror it can be Alternative designs incorporate recent adhesive, composite, rectified by automated washing mechanism at regular and thin film research to bring about materials costs and interval. A curved mirror 2m*3m which is about a thickness weight reduction. Some examples of alternative reflector of 3mm is more effective. There are two types of focusing designs are silvered polymer reflectors, glass fiber reinforced mirrors, they are line focus, point focus mirror. Line focus is polyester sandwiches (GFRPS), and aluminized reflectors. less expensive, technically less difficult, but not as efficient Problems with these more recent designs include as point focus. The basis for this technology is a parabola- delaminating of the protective coatings, reduction in percent shaped mirror, which rotates on a single axis throughout the solar reflectivity over long periods of sun exposure, and high day tracking the sun. The point of focus in a line focus mirror manufacturing costs. array can only reach temperatures around 300°C. Point focus, though initially costlier and technically more nuanced. The II. Solar salt tower point focus technique requires a series of mirrors surrounding a central tower, also known as a power tower. The mirrors The solar power tower, also known as 'central tower' power focus the sun's rays onto a point on the tower, which then plants or 'heliostat' power plants, is a type of solar furnace transfers the heat into more usable energy. We can obtain using a tower to receive the focused sunlight. It uses an array more energy in point focus mirror. In the northern of flat, movable mirrors (heliostats) to focus the sun's rays hemisphere, evacuated tube collectors should be installed upon a collector tower. Concentrated solar thermal is seen as pointing towards true south. This is, however, not the same as one viable solution for renewable, pollution-free energy. magnetic south or the south that your compass shows us. This Early designs used these focused rays to heat water, and used difference between magnetic south and true south is called the resulting steam to power a turbine. Newer designs using the azimuth. Depending on the longitude of your location liquid sodium have been demonstrated, and systems using (direction East and West) determines your azimuth. Azimuth molten salts (40% potassium nitrate, 60% sodium nitrate) as is different from location to location, and we should align our the working fluids are now in operation. These working solar collector on the azimuth for optimum performance. In fluids have high heat capacity, which can be used to store the addition, solar collectors must be installed at the right angle energy before using it to boil water to drive turbines. These in order to ensure that they perform with the highest possible designs also allow power to be generated when the sun is not efficiency and deliver the highest returns on investment and shining. the shortest payback period possible. The optimum installation angle for solar collectors is your latitude plus 15 A. Design degrees. For instance, we live at 30 degrees North Latitude; It is a tower which is about a height of 640 feet and hold a our solar collectors should be installed at 45 degrees – 30 solar energy receiver at the upper part. It appears like circular degrees plus 15 degrees. but actually consist of 14 panels, each made of 66 thin walled C. Design straight tubes. Some Concentrating Solar Power Towers are

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Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1 (2016), pp.63-67 IIJET air-cooled instead of water-cooled, to avoid using limited Molten salt has already proved itself as a storage medium. desert water.Flat glass is used instead of the more expensive The use of similar salt as a heat transfer medium not only curved glass. Thermal storage to store the heat in molten salt leads to considerable storage in power plant technology but containers to continue producing electricity while the sun is also allows the operating temperature to be increased relative not shining. Steam is heated to 500 °C to drive turbines that to the thermal oil. This enables greater process efficiencies are coupled to generators which produce electricity. Control and higher storage capacity for the same storage volume. In systems to supervise and control all the plant activity periods without radiations, special precautions are necessary including the heliostat array positions, alarms, other data in order to prevent the molten salt from freezing. The acquisition and communication. Generally, installations use simplest measure us to permanently recirculated warm salt in from 150 hectares (1,500,000 m2) to 320 hectares (3,200,000 order to keep the plant at the right temperature. The incurs m2). corresponding heat loses. It also needs to be ensured that these mixture remains at stable at high temperature, are not B. Working of solar salt tower corrosive and cheap nitrate salt mixture with three or more component look highly promising. Chloride mixture are also The solar energy reflected from the mirror is focused against being investigated, but these implicate increased corrosion the receiver tower continuously throughout the day. The problem. Molten salt is circulated from thorough highly receiver consists 14 absorbing panels each made up of 66 specialized nickel pipes in the receiver during the day time, thin walled straight tubes. The receiver are made up of a and held in the storage tank at night. The store the molten salt proprietary high nickel based alloy steel finished high at the atmospheric temperature. It can also store it for a absorptive black coating. The cold storage tank consists of period of few months also. Whenever the electricity is salt mixture of potassium nitrate 40% and sodium nitrate needed, molten salt is dispatched from the hot tank through 60%. This salt mixture is melted at238 and maintained at a the heat exchanger to create super- heated stream as it then temperature of 290 in cold storage tank.it is then travelled power a stream turbine. The salt still contain some heat and it through the receiver where it is heated up to 565 then it is passed to the cold storage tank passed to the hot salt storage tank . Line focus is less expensive, technically less difficult, but not as efficient as D. Cold storage tank point focus. The basis for this technology is a parabola- shaped mirror, which rotates on a single axis throughout the At the cold storage tank initially the salt mixture of day tracking the sun. The point of focus in a line focus mirror potassium nitrate and sodium nitrate is kept and the thermal array can only reach temperatures around 300°C. There are oil which circulating at the outer circumference of the tank two types of receiver i.e.,fixed and mobile receiver, fixed heated by the series of arrays of sun. When salt is melted at tower is permanently fixed on the top of the tower as it is 573K and then it is transferred to solar salt tower. fixed it cannot absorb more energy from the collector where in case of mobile receiver it tracks along the collector axis. III. Surface and above ground technology Hence it receives more energy when compared to fixed receiver. Heat storage system have two main tasks in solar Pit storages. Lined, shallow dug pits that are filled with thermal power plants, on the one hand relatively small gravel and water as the storage medium are used for STES in storage system can be used to balance out the fluctuating many Danish district heating systems. Pit storages are irradiation and facilitates stable plant operation on the other covered with a layer of insulation and then soil, and are used hand large storage system can extend the operating time of for agriculture or other purposes .Initially providing 20% of power plant blocks beyond the periods when there is a the village’s year-round heat but now being expanded to irradiation or enable it to completely decoupled .the storage provide twice that. The solar heat to provide 50% of the size is often specified in full load hours: that is the number of annual energy for the world's largest solar-enabled system. hours in which the power plant could be operated at full Large-scale water storages. Large scale STES water storage power solely from the storage system. Buffer storage system tanks can be built above ground, insulated, and then covered typically have a capacity of half to one full load hour, with soil. Horizontal heat exchangers. For small installations, whereas large storage system with 8-12 full load hours enable a “slinky” heat exchanger of plastic pipe can be shallow- power plant operation around the clock. buried in a trench to create an STES. Earth-beamed buildings, with passive heat storage in surrounding soil C. Hot storage tank (further described below).

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Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1 (2016), pp.63-67 IIJET

leads to a larger overall shell diameter, which leads to a more expensive heat exchanger. Tube corrugation: this type of tubes, mainly used for the inner tubes, increases the turbulence of the fluids and the effect is very important in the heat transfer giving a better performance. Tube Layout: refers to how tubes are positioned within the shell. There are four main types of tube layout, which are, triangular (30°), rotated triangular (60°), square (90°) and rotated square (45°). The triangular patterns are employed to give greater heat transfer as they force the fluid to flow in a more turbulent fashion around the piping. Square patterns are employed where high fouling is experienced and cleaning is more regular. Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle. A. Steam generation system They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They The molten salt from the hot storage tank taken into the can also prevent the tubes from vibrating. The most common super heater.Super heaters are widely used for the purpose is type of baffle is the segmental baffle. The semicircular to raise steam temperature from saturation conditions to the segmental baffles are oriented at 180 degrees to the adjacent desired final temperature, which can be as high as 1,000°F in baffles forcing the fluid to flow upward and downwards some cases. When used in steam turbines, superheated steam between the tube bundles. Baffle spacing is of large decreases steam heat rate of the turbine and thus improves thermodynamic concern when designing shell and tube heat the overall plant power output and efficiency. Also, steam exchangers. Baffles must be spaced with consideration for conditions at the turbine exit will have no moisture, the conversion of pressure drop and heat transfer. For thermo depending on the pressure. It is then passed to the heat economic optimization it is suggested that the baffles be exchanger. The Heat exchangers consist of series of tubes. spaced no closer than 20% of the shell’s inner diameter. One set of these tubes contains the heated molten salt. The Having baffles spaced too closely causes a greater pressure second fluid runs over the tubes that are being heated by the drop because of flow redirection. Consequently, having the tubes. A set of tubes is called the tube bundle and can be baffles spaced too far apart means that there may be cooler made up of several types of tubes: plain, longitudinally spots in the corners between baffles. It is also important to finned, etc. Shell and tube heat exchangers are typically used ensure the baffles are spaced close enough that the tubes do for high-pressure applications. This is because the shell and not sag. The other main type of baffle is the disc and tube heat exchangers are robust due to their shape. Several doughnut baffle, which consists of two concentric baffles. thermal design features must be considered when designing An outer, wider baffle looks like a doughnut, whilst the inner the tubes in the shell and tube heat exchangers: There can be baffle is shaped like a disk. This type of baffle forces the many variations on the shell and tube design. Typically, the fluid to pass around each side of the disk then through the ends of each tube are connected to plenums through holes in doughnut baffle generating a different type of fluid flow. The tubesheets. The tubes may be straight or bent in the shape of super-heated stream from the heat exchanger is fed into the a U, called U-tubes. Larger tube diameter makes the heat turbine. exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster. To B. Turbine prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, A turbine is a rotary mechanical device that extracts the available space, cost and fouling nature of the fluids must be considered. The thickness of the wall of the tubes is energy from a fluid flow and converts it into useful work. usually determined to ensure:There is enough room for A turbine is a turbo machine with at least one moving part corrosion. That these tubes can have resistance to flow- called a rotor assembly, which is a shaft or drum with induced vibration. It can have axial strength and it also blades attached. Moving fluid acts on the blades so that withstand the internal tube pressure.Heat exchangers are they move and impart rotational energy to the rotor. There usually cheaper when they have a smaller shell diameter and are two types of turbine i.e., reaction and impulse turbine. a long thin tube length. Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch (i.e., the Impulse turbines change the direction of flow of a high centre-centre distance of adjoining tubes) is not less than velocity fluid. The resulting impulse spins the turbine and 1.25 times the tubes' outside diameter. A larger tube pitch leaves the fluid flow with diminished kinetic energy. There

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Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1 (2016), pp.63-67 IIJET is no pressure change of the fluid in the turbine blades (the winding generate electricity. The armature can be rotor or moving blades), as in the case of a steam, all the pressure stator. drop takes place in the stationary blades (the nozzles). Field: The magnetic field component of an electrical Before reaching the turbine, the fluid's pressure head is machine. The magnetic field of the dynamo or alternator can changed to velocity head by accelerating the fluid with a be provided by their electro magnets or permanent magnet nozzle. Impulse turbines do not require a pressure mounted on either the motor or stator. casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blades on the rotor. D. Condenser Newton's second law describes the transfer of energy for Condenser is device or a unit which converts the vapor into impulse turbines. Reaction turbines develop torque by the liquid. There are two types of condenser Surface reacting to the fluid's pressure or mass. The pressure of the condenser, is a heat exchanger which can be installed in a fluid changes as it passes through the turbine rotor blades. stream electric power station to condense turbine exhaust A pressure casement is needed to contain the working fluid steam into water. The condenser which converts the heated as the turbine must be fully immersed in the fluid flow molten salt is then passed to the cold storage tank and (such as with wind turbines). The casing contains and maintained at a temperature of 290 as it doesn’t crystallize. Hence it can be used for another cycle of power production. directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. For compressible IV. Conclusion working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. Newton's third law In this research paper the solar power is pointly focused on describes the transfer of energy for reaction turbines. the receiver and the salt mixture which is fed in the cold When the stream strikes the turbine and due to the kinetic storage tank is heated by the use thermal oil under the action energy. According to the law of energy conservation of the solar arrays. Then it is fed into the receiver on the top kinetic energy is converted to mechanical energy then of the tower (solar salt tower). Due to the action of point stream is passed to the condenser. focus the salt is heated up to 868K and that heat can be used in the power production by the normal thermal power C. Generator production. This method of power production is pretty much effective and eco-friendly than any other power production. Generator is device which converts mechanical energy into electrical energy. The turbine is coupled with the generator by the shaft mechanism. A generator is combination of a V. Acknowledgement turbine and directly connected to electric generator for the The authors are grateful for financial support and approval of generation of power. Large stream powered turbo generator publication for this paper from the Adhiyamaan college of has been across the world Electromagnetic generators fall Engineering, Tamilnadu. into one of two broad categories DYNOMOS AND ALTERNATORS. Dynamos: it generate direct electric References current usually with voltage and by use of commutator. Alternator: It generates alternating current which may be [1] Feldhoff J. F., Schmitz K., Eck M., Laing D., Schnatbaum- rectified by another system. Lauman L., D. Laing, Ortiz-Vives F., Schulte-Fischedick J.: Comparative System Analysis of Direct Steam Generation and Mechanical part of generator: Synthetic Oil Parabolic Trough Power Plants with Integrated Thermal Storage, Solar Energy, No. 86 (2012) pp. 520-530. Rotor: The rotating part of an electrical machine [2] Laing D., Bahl C., Bauer T., Lehmann D. Steinmann W.-D.: Stator: The stationary part of the electrical machine Thermal energy storage for direct steam generation, Solar Energy, No. 85 (2011)pp. 627-633. Electrical parts of the generator: [3] BINE informatiopn service-themen info/2013. Armature: The power producing component of the electrical machine in a generator alternator or dynamos the armature

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