BRIEF ON VARIOUS CONCENTRATED SOLAR HEAT TECHNOLOGIES

Transcription

1 BRIEF ON VARIOUS CONCENTRATED SOLAR HEAT TECHNOLOGIES The various technologies currently in the market are single and dual axis tracked parabolic dishes, single and double axis Scheffler Dishes, Linear Fresnel Reflectors Systems, ETC based NonImaging Concentrators, Parabolic Trough Concentrators (PTC), and Arun Technology. Scheffler Technology: A Scheffler Reflector is a parabolic dish that uses single axis tracking to follow the sun's daily course. Scheffler technology is developed by Wolfgang Scheffler in In 1982 Wolfgang Scheffler started developing a parabolic fixed focus reflector that was later named after him by his friends in India. Working Principle: The reflector is a small lateral section of a much larger Parabolic. The inclined cut produces the typical elliptical shape of the SchefflerReflector. The sunlight that falls onto this section of the Parabolic is reflected sideways to the focus located at some distance of the reflector. Scheffler reflectors have the advantage of having a fixed focal point which improves the ease of cooking & other application and are able to reach temperatures of C. The design procedure is simple, flexible and does not need any special setup, thus offering the end user the prospect of application in domestic as well as industrial configurations. The axis of daily rotation is located exactly in north south direction, parallel to earth axis and runs through the centre of gravity of the reflector. Disadvantages: Require huge space: Beneficiaries require lot of space for the set up of this system. Mostly it is available on roof top for different applications.

2 Depends on the availability of sun: This system does not work without sun, hence it is integrated with LPG or Diesel system at all places in India. Mirror & tracking problem: Breakage is common at all plants but unbreakable mirror for 25 years is available these days. Tracking system does not work properly to get effective reflection of sun rays onto receiver which causes low efficiency of plant. Manufacturers: Unisun Technologies. Thermax Limited Bergen Solar Power & Energy Ltd. K energy Bhagawati International Ltd. Megawatt Solutions Private Limited. Taylormade Solar Solutions Pvt. Ltd. AKSON Solar Equipments (P) Ltd. Arun Technology It is twoaxes tracking mechanism for automatically tracking the sun giving maximum daily output. Testing procedure for this technology is being developed by IITBombay. The technology is much more productive and versatile compared to any other solar thermal concentrator system available. Storage vessel is available for heat delivery any time of the day or night. Working Principle: The ARUN solar concentrator consists of Fresnel Parabolic Reflector with Point Focus (or a focus of small area) with reflector facets fixed on to a tracking surface. The reflectors reflect and concentrate the solar beam radiation at its focus. A receiver designed for minimum thermal loss is provided at the focal point. The fluid outlet temperature can be up to 250 C. An insulated pipeline delivers this heat energy to user. This system has micro processor based control system that automatically drives the dish from east to west to continuously face the Sun which helps in operating the system near its peak capacity for about 8 to 10 hours a day. The tracking system also takes care of seasonal shifting of the Earth s axis with reference to the Sun. Technical Specification: Parabolic Solar Concentrator: Fresnel Parabolic Solar Concentrator System with a Point Focus based on assembly of reflectors and uses solar grade mirrors as reflectors. Central Receiver: The receiver is placed at the focus of the parabolic concentrator. It is an inverted cavity type receiver with MS tubing as per the required pressure. Automatic tracking system: Steam heater pipe transfers steam from receiver to end point where steam is being used for different purpose. Other equipments and material: The other necessary equipment to generate steam or balance of steam generation plant are feed water tank, pressure gauge, backup boiler, tracking system, cooking vessels, etc.

3 Applications of Solar Concentrator: The unit is best suited for the industrial applications using thermal energy from electricity or liquid fossil fuels. The thermal medium can be highh or low pressure process steam, hot water, hot air, hot thermic fluid or oil. It can be used for providing processs heat for a wide range of industries and chemical processing plants using boilers or heaters, textile mills, sugar mills, vegetable oil mills, agro and food processing industries, timber industry, milk processing, drying of horticultural, food and fruits products, drying of chemicals as well as units using vapor absorption refrigeration for space cooling. It is also suitable for hotels and hospitals for providing hot water, steam and cooling Advantages: Small Footprint Area & Retrofits: The small footprint area of ARUN dish (3m x 3m per dish) enables it to be mounted at locations whichh have space limitations. It can also be erected on rooftops of existing buildings. Highest Temperature & Pressure: Delivery ARUN can operate up to C (oil) and 25 bar (steam). NonSolar Hours Operations: ARUN dish can be augmented with a heat energy storage facility for operation during nonsolar hours. High Wind Bearing: Capacity ARUN dish is designedd to operate in wind speeds up to 10 m/s and it can survive in wind speeds up to 45 m/s. High Net Energy Gain: The Net Energy Gain (i.e.. Energy gained from energy source Energy expended in harvesting the energy source) is amongst the highest in the solar manufacturing industry. Disadvantages: Cost of Arun dish system is highh i.e., 50 Lakh with installation. But payback period is less.

4 Manufacturers: Clique Developments Ltd., (Clique Solar) NonImaging Concentrators Working Principle: In this technology, solar rays are not directly reflected to a point or line but they are reflected many times and eventually fall on the tubes placed inside the collector. Solar radiation enters the collector through the transparent cover and reaches the absorber. Here the absorbed radiation is converted to thermal energy. A good thermal conductivity is needed to transfer the collected heat from the absorber sheet to the absorber pipes where the heat is finally transferred to the fluid. Design produces fluids up to C suitable for process heat industries (replacing boiler application) and cold storage applications and HVAC etc. Usually a water/glycol mixture with anticorrosion additives is used as the heat carrying fluid. The fluid also protects the collector from frost damage. A mirror reflector is mounted behind the tubes in order to reflect solar radiation that falls into the area between the tubes on the round absorbers from the back side. The heat transfer from the absorbing inner glass tube of the twin glass tube to the fluid is accomplished by an aluminum heat transfer sheet that is in contact with the circumference of the absorber glass. The aluminum heat transfer sheet is also in contact with the copper Utube. All U- tubes are connected hydraulically in parallel to the header tubes for the collector inlet and the collector outlet. The header tubes are insulated by mineral wool. The casing is made from aluminum sheets. The system is suitable for Industrial processes where heat at a temperature higher than approximately 100 C 130 C (depending on climate conditions) is needed. They can be used to generate steam either in direct steam generation mode or using an indirectly fired steam generator. The steam can be fed into steam heat distribution networks that are used widely in industry. Description: A nonimaging solar collector includes an outer housing transparent to light, a reflector element positioned within the outer housing, an absorber concentrically disposed relative to the outer housing, and a heat conduction fin coupled to the absorber and having a wedge shape which tapers to a smaller thickness as a function of increasing radial. Advantages Higher efficiency and temperature than other collectors. System offers a lower cost solution than systems with other technologies. Disadvantages Entire glass has to be change even if small crack occurs

5 Suitable Applications Process heat requirements Air conditioning Manufacturers Thermax Limited Bergen Solar Power & Energy Ltd. Parabolic Trough Concentrators (PTC) Working Principle: The sun's energy is concentrated by parabolically curved, troughshaped reflectors onto a receiver pipe running along the inside of the curved surface. This energy heats oil/water flowing through the pipe and the heat energy is then used for community cooking/ Process heat/laundry/electricity generation. Description of Technology: The Parabolic trough collectors consist of solar collectors, Heat receivers and structures. The Parabolicshape concentrates incoming sunlight on to central receiver tube at a focal line of a collector. Absorber Tube: Absorber tube is generally a coated stainless steel tube, with a spectrally selective coating that absorbs the solar (short wave) irradiation well, but emits very little infrared (long wave) radiation. This helps to reduce heat loss. Evacuated glass tubes are used because they help to reduce heat losses. Reflector: Reflector is a reflective surface used to collect or project energy such as light, sound, or radio waves. Parabolic reflectors are used to collect energy from a distant source (for example sound waves or incoming star light) and bring it to a common focal point. Solar Field Piping: The piping system consists of header piping, valves, and fittings. In a typical parabolic trough solar field configuration, the flow in the cold header is incrementally drawn off through a collector loop and passed to the hot header.

6 Applications of Parabolic Trough: The different applications of parabolic trough technology are: Low temperature application (>30 C) Swimming pool Heating Ventilation air preheating Medium temperature application (30 C to 100 C) Domestical water and Space Heating. Community Cooking, laundries, Hotels. High temperature application (>loo C) Industrial Process Heating Electricity Generation Advantages of Solar Parabolic troughs: No Fuel Cost No Pollution and Global warming Effects Most suited for all applications like community cooking, process heating etc. Section 2 illustrates the projects in

7 Disadvantages of Solar Parabolic troughs High costs Time constraint (operated only 5 to 6 Hrs Daily). Operation & Maintenance issues exist Continuous monitoring is required Manufactures: Ultra Conserve Pvt. Ltd Thermax Limited Maharishi Solar Technology Pvt. Ltd