Solar Tower (by pradeep)

SOLAR POWER TOWER TECHNOLOGY: 

SOLAR POWER TOWER TECHNOLOGY Presented by: Pradeep Kumar K.R V SEM, MECH 1SV09ME037

CONTENTS: 

CONTENTS Introduction Overview on SPTT History System Description Rankine's cycle Benefits of SPTT Advantages & Disadvantages Applications Conclusions

Introduction: 

Introduction Solar power towers generate electric power from sunlight by focusing concentrated solar radiation on a tower-mounted heat exchanger (receiver). It uses an array of flat, moveable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a substance that can store the heat for later use. The more recent heat transfer material that has been successfully demonstrated is liquid sodium. Sodium is a metal with a high heat capacity, allowing that energy to be stored and drawn off throughout the evening. Stored energy can be used to boil water for use in steam turbines.

Overview: 

Overview The largest power towers ever built are the 10 MW (Solar One and Solar Two plants). Assuming success of the Solar Two project, the next plants could be scaled-up to between 30 and 100 MW. As non-polluting energy sources become more favored, molten-salt power towers will have a high value because the thermal energy storage allows the plant to be dispatch able. The value of power is worth more because a power tower plant can deliver energy during peak load times when it is more valuable New peaking and intermediate power sources are needed today in many areas of the developing World. One possible concern with the technology is the relatively high amount of land and water usage.

History: 

History Solar technology is not new process. Its history spans from the 7thCentury B.C. to today. We started out concentrating the sun’s heat with glass and mirrors to light fires. Today, we have everything from solar-powered buildings to solar powered vehicles. Solar One, which operated from 1982 to 1988, was the world’s largest power tower plant. It proved that large-scale power production with power towers was feasible. During the operation of Solar One, research began on the more advanced molten-salt power tower design described. This development culminated in the Solar Two project. Solar Two, which is currently going through its startup phase, will generate (in addition to electric power) information on the design, performance, operation and maintenance of molten-salt power towers. Solar Two is expected to begin routine daily power production in late 1997.

System Description: 

System Description Solar power tower convert sunshine into clean electricity. The technology uses many large, sun-tracking mirrors commonly referred as heliostats to focus sunlight on a receiver at the top of a tower. The enormous amount of energy, coming out of the sun rays, concentrated at one point (the tower in the middle), produces temperatures of approx. 550°C to 1500°C. The gained thermal energy can be used for heating water or molten salt, which saves the energy for later use. Heated water converts to steam, which is used to move the turbine-generator. This way thermal energy is converted into electricity. Water is the oldest and simplest way for heat transfer. But the difference is that the method in which molten salt is used, allows storing the heat when the sun is behind clouds or even at night.

Continued….: 

Continued…. As already mentioned there are two main fluids which are used for the heat transfer, water and molten salt. If water is used as Heat transfer fluid then it is First generation of solar power tower plant. (i.e. Solar One) If Molten salt is used as Heat transfer fluid then it is Next generation of solar power tower plant. (i.e. Solar Two) HELIOSTAT Heliostat is termed Greek word Helios- sun stat - stationary A Heliostat is a device that tracks the movement of the sun. The reflected sunlight from the heliostats can generate an enormous amount of heat if all are oriented towards the same target. These are also called as sun tracking mirrors.

Solar one : 

Solar one Solar One was the world’s largest power tower plant. In that plant, water was converted to steam in the receiver and used directly for conventional Rankine-cycle steam turbine to generate power. The Solar One thermal storage system works by storing heat in the form of steam generated using solar energy in a tank which is filled with rocks and sand and using oil as the heat-transfer fluid. The Solar One thermal storage system extended the power generation capability of the plant into the night and provided heat for generating low-grade steam for keeping parts of the plant warm during off-hours and for morning startup. Disadvantage of solar one technology Solar One thermal storage system was complex and thermodynamically inefficient. Solar One also showed the disadvantages of a water/steam system, such as the intermittent operation of the turbine due to cloud transience and lack of effective thermal storage.

Solar Two : 

Solar Two The conversion of Solar One to Solar Two required a new (molten-salt) heat transfer system and a new control system. This includes the receiver, thermal storage, piping, and a steam generator. The Solar Two power tower is composed of a series of panels (each made of 32 thin-walled), stainless steel tubes, through which the molten salt flows in a serpentine path. A black Pyromark paint which is robust, resistant to high temperatures and thermal cycling and absorbs 95% of the incident sunlight is used to coat the external surfaces of the tubes. The design including laser-welding, a tube clip design that facilitates tube expansion and contraction, and non-contact flux measurement devices, allows the receiver to rapidly change temperature without being damaged.

Advantages of Using Molten Salt : 

Advantages of Using Molten Salt A variety of fluids were tested to transport the sun's heat, including water, air, oil, and sodium. In that, molten salt was selected as best. Molten salt is an efficient, low cost medium to store thermal energy. Molten salt operating temperatures are compatible with today’s high-pressure and high-temperature steam turbines. it is non-flammable and nontoxic.

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Rankine cycle

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A Rankine cycle describes a model of the operation of steam heat engines most commonly found in power generation plants. Common heat sources for power plants using the Rankine cycle are liquid salts, natural gas, oil etc. The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The Rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. This cycle generates about 80% of all electric power used throughout the world

Continued….: 

Continued…. There are four processes in the Rankine cycle, each changing the state of the working fluid. The working fluid is pumped from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy. The high pressure liquid enters a boiler where fluid is heated at constant pressure by an external heat source to become a dry saturated vapor. The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. The wet vapor then enters a condenser where it is condensed at a constant pressure and temperature to become a saturated liquid..

Benefits of Solar Power Towers : 

Benefits of Solar Power Towers Solar power towers are fueled by sunshine and do not release greenhouse gases. Solar power towers are unique among solar electric technologies in their ability to efficiently store solar energy and dispatch electricity to the grid when needed, even at night or during cloudy weather. Environmental Benefits of Solar Power Towers No hazardous gaseous or liquid emissions are released during operation of the solar power tower plant. Salt can be recycled if necessary. If the power tower is hybridized with a conventional fossil plant, emissions will be released from the non-solar portion of the plant.

Continued…. : 

Continued…. Metal Corrosion in the Molten-Salt Environment All pipes, valves and vessels for hot salt were constructed from stainless steel because of its corrosion resistance in the molten-salt environment, while the cold-salt system is made from mild carbon steel.

Advantages of SPTT: 

Advantages of SPTT Solar energy comes directly from the sun it is not only renewable, but also accessible in any part of the world. Solar power is also one of the cleanest forms of energy, since it creates no pollution, and produces no greenhouse gases or waste products. Solar Power is safer alternative to WIND & HYDRO POWER. Not only solar energy is non-pollutant, in terms of gases, but it also causes zero noise pollution – since there are no moving parts in any of the devices which are used to capture the sunlight. Maintenance costs are low as well – only occasional cleaning and periodic battery replacements are needed. Most manufacturers of solar panels provide twenty-year warranties for their equipment, guaranteeing long-life operation.

Disadvantages : 

Disadvantages The most obvious drawback of solar energy is its sole dependence on the sun.  Once the weather becomes cloudy or night time strikes, energy collection comes to a halt. Solar panels can also be expensive, because of the materials that are used to create them. This includes portable devices that utilize solar energy. Fortunately, there are some people who sell damaged solar cells, which are much cheaper. These damaged solar cells are be used to build solar panels. It is also true that direct sunlight is needed in order to make the most of the sun’s energy– and to generate the highest amounts of power.  This significantly restricts the placement of solar panels Huge amount of water and land is required.

Applications Of SPTT: 

Applications Of SPTT Solar Powered LED lighting system provides bright light charged by sunlight. Suitable for wherever the grid electricity is unreliable or unavailable. In order to supply Electricity for street lights, solar power tower technologies are used. Solar Power can be used as Alternative for Wind & Hydro power. These plants are best suited for utility-scale applications in the 30 to 400 MW range. Provides rough enough Electricity for night use & during Cloudy weather. Solar tower technology produces air above 1000°C or synthesis gas for gas turbine operation.

SOLAR TWO POWER TOWER TECHNOLOGY: 

SOLAR TWO POWER TOWER TECHNOLOGY

Conclusions : 

Conclusions It is very efficiency system can be increased by hybridizing it with the other conventional plants. Very economy excluding initial cost. Can be implemented with alternative like WIND and HYDRO power generation. Molten salt has the best Heat capacity. Non pollutant power technology. It will be the power source for developing countries.

REFERENCES : 

REFERENCES 1 . Solar power engineering By B.S Magal 2.Solar energy fundamentals and applications By H P Garg and J Prakash 3.www.wikepedia.org 4.Stoddard, M.C., et. al., SOLERGY - A Computer Code for Calculating the Annual Energy from Central Receiver Power Plants, Sandia National Laboratories, Livermore, CA: May 1987. 5.Meinecke, W., and M. Bohn, Solar Energy Concentrating Systems: Applications and Technologies, edited by M. Becker, and B. Gupta, Muller Verlag, Heidelberg, Germany, 1995. 6.Anderson, D. And K. Ahmed, The Case for the Solar Energy Investments, World Bank Technical Paper Number 279 - Energy Series, World Bank, Washington D.C.: February 1995

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