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Solar still project report


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Report on Double Slope Type Solar Still

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Solar still project report

  2. 2. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 2 ACKNOWLEDGEMENT We take this momentous opportunity to express our heartfelt gratitude, ineptness & regards to vulnerable and highly esteemed guide, Mr. Amit Shukla, Lecturer, Department of Mechanical Engineering, MITS for providing us an opportunity to present our project on “CONSTRUCTION OF DOUBLE SLOPE TYPE SOLAR STILL”. We with full pleasure converge our heartiest thanks to Project coordinators Mr. Kunal Gupta and Ms. Prachi Dixit, Lecturer, Department of Mechanical Engineering, MITS for their invaluable advice and wholehearted cooperation without which this project would not have seen the light of day. We attribute hearties thanks to all the faculty of the department of Mechanical Engineering and friends for their valuable advice and encouragement. Devendra Pratap Singh Kunwar Veer Vikram Singh Vinay Singh Chauhan
  3. 3. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 3 CERTIFICATE This is to certify that project report entitled “Construction of Double Slope Type Solar Still”, which is submitted by “Devendra Pratap Singh, Kunwar Veer Vikram Singh and Vinay Singh Chauhan” in partial fulfillment of the requirement for the award of degree B.Tech in Department of Mechanical Engineering of Maharana Institute Of Technology And Sciences, affiliated to Uttar Pradesh Technical University, Lucknow is the record of candidates own work carried out by them under my supervision. The matter embodied in this project work is original and has not been submitted for the award of any other degree. DATE - Mr. Amit Shukla (Lecturer) Head of Department Department of Mechanical Engineering Mr. ANUJ SINGH MITS, LUCKNOW
  4. 4. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 4 DECLARATION We here by certify that the work which is being presented in the project entitled “Double Slope Type Solar Still”, by “Devendra Pratap Singh, Kunwar Veer Vikram Singh and Vinay Singh Chauhan” in partial fulfillment of the requirements for the award of degree B.Tech in Department of Mechanical Engineering of Maharana Institute Of Technology And Sciences, affiliated to Uttar Pradesh Technical University, Lucknow is an authentic record of our own work carried out during the period from 28/01/2014 to 08/05/2014 under the guidance of Mr. Amit Shukla. The matter embodied in this project work is original and has not been submitted by us in any other university/ Institute for the award of B .Tech Degree. Devendra Pratap Singh (Roll No.1043040016) Kunwar Veer Vikram Singh (Roll No. 1043040025) Vinay Singh Chauhan (Roll No. 1043040050)
  5. 5. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 5 CONTENTS S.No TOPIC PAGE NO. 1. Abstract 1 2. Introduction 2 3. Non-Conventional Energy Resources & Types 3-9 4. Water Impurities And Purification 10-11 5. Inspiration And Motivation 12 6. Solar Water Distillation 13-15 7. Principle Of Solar Still 15-16 8. Working Of Solar Still 16-17 9. Design Of Solar Still 18-19 10. Literature Review 20 11. MODES & MECHANISM Of Heat Transfer 21-22 12. Conduction, Convection And Radiation 23-27 13. Concept For Good Solar Still 27-28 14. Design Types And Performance 28-32 15. Material Requirements 33 16. Capabilities And User Experiences 34-36 17. Cost, Material And Manufacturing 37-39 18. Components Of Solar Still 40-41 19. Increasing Efficiency Of Solar Still 42-48 20. Dimension & Performance Analysis 49 21. Water Purifiers & Types Of Filters 50-54 22. Solar Panels 55-56 23. Would Solar Still Suits Our Need 57 24. Advantages & Disadvantages 58 25. Pictures Of Working Model 59-60 26. Conclusion And References 61-62
  6. 6. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 6 LIST OF FIGURES Figures Page No. • Earth Energy Budget……………………………………………………………2 • Non-Conventional Energy Resources…………………………………………...3 • Solar Energy System…………………………………………………….............5 • Bio-Gas Plant…………………………………………………………………....6 • Ocean Thermal Energy Conversion……………………………………..............7 • Geo-Thermal Energy…………………………………………………………....8 • Wind Energy………………………………………………………………….... 9 • Principle of Solar Still………………………………………………….............15 • Working of Solar Still………………………………………………………….16 • Conduction, Convection and Radiation Process…………….22, 23, 24, 26 • Design Types of Solar Still……………………………………...29,30 • Cad Model of Solar Still…………………………………………………..…..39 • Components of Solar Still……………………………………………………..41 • Double Slope Glass Cover…………………………………………………….42 • Sealants…………………………………………………………………..........46 • Reflectors………………………………………………………………………47 • Temperature Sensor……………………………………………………………48 • Solar Panel………………………………………………………………..........55 • Pictures of Working Model………………………………………….............59, 60
  7. 7. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 7 ABSTRACT The purpose of this project is to design a water distillation system that can purify water from nearly any source, a system that is relatively cheap, portable, and depends only on renewable solar energy. The motivation for this project is the limited availability of clean water resources and the abundance of impure water available for potential conversion into potable water, In addition, there are many coastal locations where seawater is abundant but potable water is not available. Our project goal is to efficiently produce clean drinkable water from solar energy conversion. Distillation is one of many processes that can be used for water purification. This requires an energy input as heat, electricity and solar radiation can be the source of energy. When Solar energy is used for this purpose, it is known as Solar water Distillation. Solar Distillation is an attractive process to produce portable water using free of cost solar energy. This energy is used directly for evaporating water inside a device usually termed a “Solar Still”. Solar stills are used in cases where rain, piped, or well water is impractical, such as in remote homes or during power outages. Different versions of a still are used to desalinate seawater, in desert survival kits and for home water Purification. For people concerned about the quality of their municipally- supplied drinking water and unhappy with other methods of additional purification available to them, solar distillation of tap water or brackish groundwater can be a pleasant, energy- efficient option. Solar Distillation is an attractive alternative because of its simple technology, non- requirement of highly skilled labour for maintenance work and low energy consumption. The use of solar thermal energy in seawater desalination applications has so far been restricted to small-scale systems in rural areas. The reason for this has mainly been explained by the relatively low productivity rate compared to the high capital cost. However, the coming shortage in fossil fuel supply and the growing need for fresh water in order to support increasing water and irrigation needs, have motivated further development of water desalination and purification by renewable energies.
  8. 8. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 8 INTRODUCTION Due to environmental issues and limited fossil fuel resources, more and more attention is being given to renewable energy sources. In the recent years solar energy has been strongly promoted as a viable energy source. One of the simplest and most direct applications of this energy is the convergence of solar radiation into heat. Figure.1.1: Earth’s Energy Budget Solar radiation can be widely used for water heating in hot water systems, swimming pools as well as a supporting energy sources for central heating installations. The energy of the solar radiation is in this case converted to heat with the use of solar panel. Using the sun’s energy to heat water is not a new idea. More than one hundred years ago, black painted water tanks. Water is a basic necessity of man along with food and air. Fresh water resources usually available are rivers, lakes and underground water reservoirs. About 71% of the planet is covered in water, yet of all of that 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps and 0.001% in the air as vapor and clouds, Only 2.5% of the Earth's water is freshwater and 98.8% of that water is in ice and groundwater. Less than 1% of all freshwater is in rivers, lakes and the atmosphere.
  9. 9. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 9 NON-CONVENTIONAL ENERGY RESOURCES Energy is a crucial input in the process of economic, social and industrial development. Energy plays a vital role in our daily life. The degree of development and civilization of a country is measured by the utilization of energy by human beings for their needs. Energy is available in different forms like electrical energy, mechanical energy, chemical energy, heat energy and nuclear energy etc. Day by Day the energy consumption is increasing very rapidly. The world’s fossil-fuel supply i.e. coal, petroleum and natural gas will be depleted in few hundred years. The rate of energy consumption increasing, supply is depleting resulting inflation and energy shortage. This is called the Energy Crisis. Alternative or non-conventional or renewable energy resources are very essential to develop for future energy requirements. Energy can be extracted from various resources i.e. bio-energy, human energy, mechanical energy, kinetic energy and animal energy. Energy having many properties. According to law of conservation of energy “Energy can neither be created nor it can be destroyed but can be transformed from one form to another form. Energy can be transported from one place to another place. The energy demand increases day by day because of population increasing, industrialization increases and transportation increases etc.
  10. 10. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 10 CLASSIFICATION OF ENERGY RESOURCES 1. COMMERCIAL AND NON-COMMERCIAL ENRGY RESOURCES These are also called as primary energy resources. These are available in nature in raw form e.g. coal, natural gas, wind and water etc. The other resources which are freely available to us like solar energy, agricultural wastes etc. are known as non-conventional energy resources. Hydroelectric power and nuclear power also comes under commercial resources. In many developed countries the non-commercial resources are used to produce energy. 2. RENEWABLE AND NON-RENEWABLE ENERGY RESOURCES Renewable resources are those resources are those resources which can be used to produce energy again and again e.g. solar energy, geothermal energy, tidal energy etc. Non-renewable resources cannot be replaced once they are used e.g. coal, oil, gas etc. These energy resources (coal, oil, gas etc.) are limited and would be exhausted within prescribed period of time. Greater usage of such fuels would result in energy crisis and supply cannot be adjusted according to demand. 3. CONVENTIONAL & NON-CONVENTIONAL ENERGY RESOURCES Coal, oil and gas are commonly known as conventional energy resources. As the population is increasing and standard of living rising, more energy needs will be in future. The scope of meeting these energy demands through conventional (also known as commercial resources) resources is limited due to their insufficient availability. Therefore, a large amount of energy can be derived from non-commercial resources like agricultural wastes, firewood, solar, wind etc. These resources are known as non-conventional energy resources. Conventional energy resources are used conventionally and can be stored. The non-conventional energy resources cannot be easily stored.
  11. 11. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 11 NON-CONVENTIONAL ENERGY RESOURCES 1. SOLAR ENERGY The earth receives radiation from sun in the form of electromagnetic radiations. Solar energy is cheap and free from pollution. India receives solar energy equivalent to more than 5000 trillion kWh per year, which is far more than its total annual consumption. Solar energy can be used in following applications:- Heating and cooling of buildings Air conditioning and Refrigeration Solar cookers Solar water heaters Solar water pumping systems Solar energy is collected by a device called Solar Collectors. Solar Collectors collect radiation and transfer the energy to a fluid passing in contact with it. The device which converts solar energy into electrical energy is called Solar Cell.
  12. 12. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 12 2. BIO-GAS AND BIO-MASS Bio gas plant is a device for conversion of fermentable organic matter, in particular cattle dung, into combustible gas and fully matured organic manure. This is achieved by subjecting the material to anaerobic fermentation. The main sources for production of Bio-Gas are cattle dung, night soil, poultry or piggery droppings. These materials are confined in a place, out of contact with oxygen, give rise to a large number of bacteria. These bacteria convert Carbohydrates, Proteins and Fats into volatile acid and Carbon dioxide. Biogas has many applications such as cooking, lighting etc.
  13. 13. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 13 3. OCEAN ENERGY AND TIDAL ENERGY The vast potential of energy of the seas and oceans, which cover about 3/4th of our planet, can make a significant contribution to meet our energy requirements. The various forms of energy from seas and oceans which are receiving attention at present are Tidal Power, Ocean Thermal Energy Conversion (OTEC), Waves and Ocean Currents. The ocean contains vast potential in its waves, in its tides and in the temperature difference between cold deep waters and warm surface water. Tides are the result of gravity of sun, moon and rotation of the earth working together. Tides can be used to produce electrical power which is known as Tidal Power.
  14. 14. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 14 4. GEOTHERMAL ENERGY Geothermal energy is another energy source that can be harnessed for power generation and thermal applications in the near future. Geothermal energy is the natural heat generated from within the earth. The steam and hot water comes naturally to the surface of the earth at some locations. The main source of geothermal energy is Magma. The extraction of heat from earth’s interior needs a natural or artificial heat exchanger. Water is injected by injection well into hot dry rocks inside the earth to extract the hot water and steam from production wells. Water injected into the well acts as heat collecting and heat transporting medium. The hot springs are found in North-West Himalayan region, M.P. and Gujarat.
  15. 15. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 15 5. WIND ENERGY Winds are caused by pressure gradient. The kinetic energy of wind can be changed into Mechanical or Electrical energy. Wind’s energy is used to generate electricity by wind turbines. Blowing wind spins the blades on a wind turbine. The blades of turbine are attached to a hub that is mounted on a turning shaft. The shaft goes through a Gear transmission box where the turning speed is increased. The transmission is attached to a high speed shaft which turns a generator. Energy storage is provided by a DC battery sets connected via AC/DC converter. If the wing gets too fast, the turbine has a break that will keep the blades from running too fast and being damaged. Coastal regions of Tamil Nadu, Gujarat, Andhra Pradesh and Maharashtra are favorable for wind power generation.
  16. 16. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 16 WATER IMPURITIES • Suspended particles- Suspended solids refer to small solid particles which remain in suspension in water as a colloid or due to the motion of the water. Suspended solids are important as pollutants and pathogens are carried on the surface of particles. Removal of suspended solids is generally achieved through the use of sedimentation and/or water filters (usually at a municipal level). • Dissolved inorganic salts- Compounds that do not contain CARBON. Eg- Sodium chloride, sodium sulphate, magnesium chloride, magnesium sulphate, calcium chloride, calcium sulphate. • Dissolved organic compounds- Compounds that contain CARBON. Eg- Hydrocarbons. • Micro-organisms- Includes Fungi, Algae, Bacteria etc. • Pyrogens- Fever inducing substances. • Dissolved gases- Eg- Argon, Methane, Ethylene, Carbon Mono-oxide, Carbon dioxide, Hydrogen, Helium, etc WATER PURIFICATION DISTILLATION: The saline water is evaporated using thermal energy and the resulting steam is collected and condensed as final product. VAPOR COMPRESSION: Here water vapor from boiling water is compressed adiabatically and vapor gets superheated. The superheated vapor is first cooled to saturation temperature and then condensed at constant pressure. REVERSE OSMOSIS: Here saline water is pushed at high pressure through special membranes allowing water molecules pass selectively and not the dissolved salts.
  17. 17. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 17 Benefits of Distillation:- Finally we decided to go by distillation method owing to the following benefits:- 1. It produces water of high quality. 2. Maintenance is almost negligible. 3. Any type of water can be purified into potable water by means of this process 4. The system will not involve any moving parts and will not require electricity to Operate. 5. Wastage of water will be minimum. NEEDS AND SPECIFICATIONS OF WATER PURIFICATION Our project centers on converting the roughly 99.6% of water that is, in its natural form, undrinkable, into clean and usable water. After researching and investigation, we outlined our needs to be the following:- 1. Able to purify water from virtually any source, included the ocean 2. Relatively inexpensive to remain accessible to a wide range of audiences 3. Easy to use interface 4. Intuitive setup and operation 5. Provide clean useful drinking water without the need for an external energy source 6. Reasonably compact and portable Our aim is to accomplish this goal by utilizing and converting the incoming radioactive power of the sun's rays to heat and distill dirty and undrinkable water, converting it into clean drinkable water. A solar parabolic trough is utilized to effectively concentrate and increase the solid angle of incoming beam radiation, increasing the efficiency of the system and enabling higher water temperatures to be achieved.
  18. 18. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 18 INSPIRATION AND MOTIVATION Solar still is a device that produces pure water without the use of any conventional source of energy. We have non-conventional sources of energy (sunlight, wind etc.) available in abundant amount especially sunlight which can be harnessed for useful purposes. The demand for pure water is rising and we have an abundant amount of brackish or saline water which can be used for harnessing usable water to meet the present demand. Solar energy being a cheap source of energy can be utilized for producing fresh water. It is also an eco-friendly process and does not require any skilled labour for its operation or maintenance. The installation cost is also low. Despite being uneconomical it has proved to be one of the best desalination systems. A number of basin-type solar still plants having areas greater than 100 m2 are in operation in many parts of the world. About 70% of the planet is covered in water, yet of all of that, only around 2% is fresh water, and of that 2%, about 1.6% is locked up in polar ice caps and glaciers. So of all of the earth’s water, 98% is saltwater, 1.6% is polar ice caps and glaciers, and 0.4% is drinkable water from underground wells or rivers and streams. And despite the amazing amount of technological progress and advancement that the current world we live in has undergone, roughly 1 billion people, or 14.7% of the earth’s population, still do not have access to clean, safe drinkable water. A few of the negative results of this water crisis are: • Inadequate access to water for sanitation and waste disposal • Groundwater over drafting (excessive use) leading to diminished agricultural yields • Overuse and pollution of the available water resources harming biodiversity • Regional conflicts over scarce water resources In addition to these problems, according to Water Partners International, waterborne diseases and the absence of sanitary domestic water is one of the leading causes of death worldwide. For children less than 5 years old, waterborne disease is the leading cause of death, and at any given moment, roughly half of all hospital beds are filled with patients suffering from water-related diseases. Clearly, having affordable potable water readily available to everyone is an important and pressing issue facing the world today.
  19. 19. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 19 SOLAR WATER DISTILLATION Solar energy is a very large, inexhaustible source of energy. The power from the sun intercepted by the earth is approximately 1.8×1011MW, which is many thousands times larger than the present all commercial energy consumption rate on the earth. Thus in principle, solar energy could supply all the present and future energy needs of the world on a continuous basis. This makes it one of the most promising of all the unconventional energy sources. In addition to its size, solar energy has two other factors in its favor. Firstly, unlike fossil fuels and nuclear power, it is an environmentally clean source of energy. Secondly, it is free and available in adequate quantity. Solar water distillation is a solar technology with a very long history and installations were built over 2000 years ago, although to produce salt rather than drinking water. Documented use of solar stills began in the sixteenth century. An early large-scale solar still was built in 1872 to supply a mining community in Chile with drinking water. Mass production occurred for the first time during the Second World War when 200,000 inflatable plastic stills were made to be kept in life-crafts for the US Navy. Human beings need 1 or 2 liters of water a day to live. The minimum requirement for normal life in developing countries (which includes cooking, cleaning and washing clothes) is 20 liters per day .Yet some functions can be performed with salty water and a typical requirement for distilled water is 5 liters per person per day. Therefore 2m2 of solar still are needed for each person served. Solar stills should normally only be considered for removal of dissolved salts from water. For output of 1m3/day or more, vapour compression or flash evaporation will normally be least cost. Solar distillation systems can be small or large. They are designed either to serve the needs of a single family, producing from ½ to 3 gallons of drinking water a day on the average, or to produce much greater amounts for an entire neighborhood or village. In some parts of the world the scarcity of fresh water is partially overcome by covering shallow salt water basins with glass in greenhouse-like structures. These solar energy distilling plants are relatively inexpensive, low- technology systems, especially useful where the need for small plants exists. Solar distillation of potable water from saline (salty) water has been practiced for many years in tropical and sub-tropical regions where fresh water is scare. However, where fresh water is plentiful and energy rates are moderate, the most cost-effective method has been to pump and purify.
  20. 20. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 20 Distillation is one of many processes available for water purification, and sunlight is one of several forms of heat energy that can be used to power that process. To dispel a common belief, it is not necessary to boil water to distill it. Simply elevating its temperature, short of boiling, will adequately increase the evaporation rate. In fact, although vigorous boiling hastens the distillation process it also can force unwanted residue into the distillate, defeating purification. Solar distillation is a relatively simple treatment of brackish (i.e. contain dissolved salts) water supplies. In this process, water is evaporated; using the energy of the sun then the vapour condenses as pure water. This process removes salts and other impurities. Solar distillation is used to produce drinking water or to produce pure water for lead acid batteries, laboratories, hospitals and in producing commercial products such as rose water. It is recommended that drinking water has 100 to 1000 mg/l of salt to maintain electrolyte levels and for taste. Some saline water may need to be added to the distilled water for acceptable drinking water. Generally, solar stills are used in areas where piped or well water is impractical. Such areas include remote locations or during power outages .Distillation are therefore normally considered only where there is no local source of fresh water that can be easily pumped or lifted. One of the main setbacks for solar desalination plant is the low thermal efficiency and productivity. In areas that frequently loss power, Solar stills can provide an alternate source of clean water. A large use of solar stills is in developing countries where the technology to effectively distill large quantities of water has not yet arrived. BASIC CONCEPT OF SOLAR WATER DISTILLATION The basic principles of solar water distillation are simple yet effective, as distillation replicates the way nature makes rain. The sun's energy heats water to the point of evaporation. As the water evaporates, water vapor rises, condensing on the glass surface for collection. This process removes impurities such as salts and heavy metals as well as eliminates microbiological organisms. The end result is water cleaner than the purest rainwater. The Sol Aqua still is a passive solar distiller that only needs sunshine to operate. There are no moving parts to wear out. The energy required to evaporate water, called the latent heat of vaporization of water, is 2260 kilojoules per kilogram (kJ/kg). This means that ‘to produce 1 litre (i.e. 1kg as the density of water is 1kg/litre) of pure water by distilling brackish water requires a heat input of 2260kJ.’
  21. 21. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 21 The distilled water from a Sol Aqua still does not acquire the "flat" taste of commercially distilled water since the water is not boiled (which lowers pH). Solar stills use natural evaporation and condensation, which is the rainwater process. This allows for natural pH buffering that produces excellent taste as compared to steam distillation. Solar stills can easily provide enough water for family drinking and cooking needs. Solar distillers can be used to effectively remove many impurities ranging from salts to microorganisms and are even used to make drinking water from seawater. Sol Aqua stills have been well received by many users, both rural and urban, from around the globe. Sol Aqua solar distillers can be successfully used anywhere the sun shines. The Sol Aqua solar stills are simple and have no moving parts. They are made of quality materials designed to stand-up to the harsh conditions produced by water and sunlight. Operation is simple: water should be added (either manually or automatically) once a day through the still's supply fill port. Excess water will drain out of the overflow port and this will keep salts from building up in the basin. Purified drinking water is collected from the output collection port. PRINCIPLE OF SOLAR STILL Solar still works on the principle of solar distillation. A solar still duplicates the way as rain water i.e. evaporation and condensation. Saline water is filled in the black painted basin of the solar still. This is enclosed in a completely air tight surface. A sloping transparent cover is provided at the top. Then solar radiations are allowed to fall on it. Solar radiation is transmitted through the cover and is absorbed in the black lining. The distillator is designed so that an efficient amount of solar radiations get trapped inside it. This increases the internal temperature of distillator causing the saline water to evaporate leaving behind all the salt contents, insecticides, herbicides, bacteria, viruses etc.
  22. 22. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 22 The resulting vapour rises and condenses as pure water on the underside of the cover and is collected in the condensate channel due to the inclination provided to the glass covers. Finally fresh water is obtained. • Solar still works on the principle of evaporation and condensation. • Solar radiation falls on the solar still. • These radiations are trapped inside the solar still. • This evaporates the water leaving behind all the salt contents and other impurities. • Resulting vapour rises and condenses on the glass cover and is collected in the condensate channel. WORKING OF SOLAR STILL
  23. 23. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 23 Solar stills are called stills because they distill, or purify water. A solar still operates on the same principle as rainwater: evaporation and condensation. The water from the oceans evaporates, only to cool, condense, and return to earth as rain. When the water evaporates, it removes only pure water and leaves all contaminants behind. Solar stills mimic this natural process. A solar still has a top cover made of glass, with an interior surface made of a waterproof membrane. This interior surface uses a blackened material to improve absorption of the sun's rays. Water to be cleaned is poured into the still to partially fill the basin. The glass cover allows the solar radiation (short-wave) to pass into the still, which is mostly absorbed by the blackened base. The water begins to heat up and the moisture content of the air trapped between the water surface and the glass cover increases. The base also radiates energy in the infra-red region (long-wave) which is reflected back into the still by the glass cover, trapping the solar energy inside the still (the "greenhouse" effect). The heated water vapor evaporates from the basin and condenses on the inside of the glass cover. In this process, the salts and microbes that were in the original water are left behind. Condensed water trickles down the inclined glass cover to an interior collection trough and out to a storage bottle. There are no moving parts in Solar still and only the sun’s energy is required for operation. The still is filled each morning or evening, and the total water production for the day is collected at that time. The still will continue to produce distillate after sundown until the water temperature cools down. Feed water should be added each day that roughly exceeds the distillate production to provide proper flushing of the basin water and to clean out excess salts left behind during the evaporation process. The most important elements of the design are the sealing of the base with black.
  24. 24. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 24 DESIGN OBJECTIVES OF SOLAR STILL For high efficiency the solar still should maintain:- A high feed (undistilled) water temperature A large temperature difference between feed water and condensing surface Low vapour leakage. A high feed water temperature can be achieved if:- A high proportion of incoming radiation is absorbed by the feed water as heat. Hence low absorption glazing and a good radiation absorbing surface are required. Heat losses from the floor and walls are kept low. The water is shallow so there is not so much to heat. A large temperature difference can be achieved if:- The condensing surface absorbs little or none of the incoming radiation Condensing water dissipates heat which must be removed rapidly from the condensing surface by, for example, a second flow of water or air, or by condensing at night.
  25. 25. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 25 DESIGN CONSIDERATIONS Different designs of solar still have emerged. The single effect solar still is a relatively simple device to construct and operate. However, the low productivity of the Solar still triggered the initiatives to look for ways to improve its productivity and Efficiency. Solar Stills may be classified into passive and active methods. Passive Solar Still- Passive methods include the use of dye or charcoal to increase the solar absorptivity of water, applying good insulation, lowering the water depth in the basin to lower its thermal capacity, ensuring vapor tightness, using black gravel and rubber, using floating perforated black plate, and using reflective side walls. Active Solar Still- Active methods include the use of solar collector or waste heat to heat the basin water, the use of internal and external condensers or applying vacuum inside the solar still to enhance the evaporation/condensation processes, and cooling the glass cover to increase the temperature difference between the glass and the water in the basin and hence increases the rate of evaporation. Single-basin stills have been much studied and their behavior is well understood. The efficiency of solar stills which are well-constructed and maintained is about 50% although typical efficiencies can be 25%. Daily output as a function of solar irradiation is greatest in the early evening when the feed water is still hot but when outside temperatures are falling. At very high air temperatures such as over 45ºC, the plate can become too warm and condensation on it can become problematic, leading to loss of efficiency. Some problems with solar stills which would reduce their efficiency include:- Poor fitting and joints, which increase colder air flow from outside into the still. Cracking, breakage or scratches on glass, which reduce solar transmission or let in air. Growth of algae and deposition of dust, bird droppings, etc. To avoid this still need to be cleaned regularly every few days. Damage over time to the blackened absorbing surface. Accumulation of salt on the bottom, which needs to be removed periodically. The saline water in the still is too deep, or dries out. The depth needs to be maintained at around 20mm.
  26. 26. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 26 LITERATURE REVIEW The various factors affecting the performance of the solar still are solar intensity, wind velocity, ambient temperature, water glass temperature difference, free surface area of water, absorber plate area, temperatures of inlet water, glass angle and depth of water. The solar intensity, wind velocity and ambient temperature cannot be controlled as they are metrological parameters whereas the remaining parameters, free surface area of water, absorber plate area, temperatures of inlet water, glass angle and depth of water can be varied to enhance the productivity of the solar stills. By considering the various factors affecting the productivity of the solar still, various modifications are being made to enhance the productivity of the solar still. Bassam et al. used sponges to increase the free surface area of the water in the solar still. Due to capillary action, water is sucked by the sponges. The yield of solar still mainly depends on the difference between water and glass cover temperatures which acts as a driving force of the distillation process. Productivity of the solar still also increases with increase in absorber area. A single-stage basin–type solar still, a storage tank and a conventional flat-plate collector were connected together in order to study the effect of augmentation on the still. This increased the temperature of saline water. Voropoulos et al. Studied the behaviour of a solar still in which a thermal storage tank with hot water is integrated. On evaluation it lead to higher distilled water output due to higher basin water temperature as a result of hot storage tank water. The integration of the storage tank is done in such a way that a compact solar distillation system is formed. Singh and Tiwari found that annual yield of the solar still is maximized when the condensing glass cover inclination is equal to the latitude of the place.
  27. 27. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 27 MODES OF HEAT TRANSFER Heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat. Systems which are not isolated may decrease in entropy. Most objects emit infrared thermal radiation near room temperature. The fundamental modes of heat transfer are conduction or diffusion, convection, advection and radiation. The exchange of kinetic energy of particles through the boundary between two systems is at a different temperature from another body or its surroundings. Heat transfer changes the internal energy of both systems involved according to the First Law of Thermodynamics. [1] The Second Law of Thermodynamics defines the concept of thermodynamic entropy, by measurable heat transfer. Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system. The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential, designated by the letter "H” that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V). Joule is a unit to quantify energy, work, or the amount of heat. Heat transfer is a process function (or path function), as opposed to functions of state; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process. In engineering contexts, the term heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (caloric) that can be transferred by various causes, and that is also common in the language of laymen and everyday life. The fundamental modes of heat transfer are:- 1-CONDUCTION 2-CONVECTION 3-RADIATION
  28. 28. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 28 MECHANISMS OF HEAT TRANSFER CONDUCTION The transfer of energy between objects that are in physical contact. Thermal conductivity is the property of a material to conduct heat and evaluated primarily in terms of Fourier's Law for heat conduction. CONVECTION The transfer of energy between an object and its environment, due to fluid motion. The average temperature is a reference for evaluating properties related to convective heat transfer. RADIATION The transfer of energy from the movement of charged particles within atoms is converted to electromagnetic radiation.
  29. 29. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 29 CONDUCTION On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact. Steady state conduction (see Fourier's law) is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further. In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out. Transient conduction occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.
  30. 30. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 30 CONVECTION The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means. Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming. The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction. Free, or natural, convection occurs when bulk fluid motions (steams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.
  31. 31. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 31 RADIATION Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws. Earth’s radiation balance depends on the incoming and the outgoing thermal radiation, Earth's energy budget. Anthropogenic perturbations in the climate system are responsible for a positive radiative forcing which reduces the net long wave radiation loss out to Space. Thermal radiation is energy emitted by matter as electromagnetic waves, due to the pool of thermal energy in all matter with a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space. Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface. The Stefan-Boltzmann equation, which describes the rate of transfer of radiant energy, is as follows for an object in a vacuum: For radiative transfer between two objects, the equation is as follows Where Q is the rate of heat transfer, ε is the emissivity (unity for a black body), σ is the Stefan- Boltzmann constant, and T is the absolute temperature (in Kelvin or Rankine). Radiation is typically only important for very hot objects, or for objects with a large temperature difference. Radiation from the sun, or solar radiation, can be harvested for heat and power. Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation. For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F). Radiation can be of two types:-
  32. 32. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 32 DIRECT RADIATION - The solar radiation that reaches the earth surface without being diffused i.e. reaches the surface of earth directly, is called Direct or Beam radiation. DIFFUSE RADIATION - As sunlight passes through the atmosphere, some part of it is absorbed, scattered and reflected by air molecule, water vapour, clouds, dust and pollutants. This is called Diffuse or Sky radiation. RADIATION PROPERTIES TRANSMITIVITY The fraction of radiation transmitted by the surface is termed as Transmitivity. It is denoted by ‘τ’. REFLECTIVITY The fraction of radiation reflected by the surface is termed as Reflectivity. It is denoted by ‘ρ’.
  33. 33. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 33 ABSORPTIVITY The fraction of irradiation absorbed by the surface is termed as Absorptivity. It is denoted by ‘α’. EMMISITIVITY It is the measure of ability of a surface to emit radiation energy in comparison to a Black body at the same temperature. It is denoted by ‘ε’. IRRADIATION Process by which an object is exposed to radiation is called Irradiation. For opaque body, τ=0. Therefore α + ρ=0. For transparent body, α=ρ=0. Therefore τ=1. For white body, τ=0, α=0. Therefore ρ=1. For a black body, τ=0, α=1, Therefore ρ=0. CONCEPTS FOR MAKING A GOOD SOLAR STILL The cover can be either glass or plastic. Glass is preferable to plastic because most plastic degrades in the long term due to ultra violet light from sunlight and because it is more difficult for water to condense onto it. Tempered low-iron glass is the best material to use because it is highly transparent and not easily damaged (Scharl & Harrs, 1993). However, if this is too expensive or unavailable, normal window glass can be used. This has to be 4mm think or more to reduce breakages. Plastic (such as polyethylene) can be used for short-term use. Stills with a single sloping cover with the back made from an insulating material do not suffer from a very low angle cover plate at the back reflecting sunlight and thus reducing efficiency. It is important for greater efficiency that the water condenses on the plate as a film rather than as droplets, which tend to drop back into the saline water. For this reason the plate is set at an angle of 15° to 25º. The condensate film is then likely to run down the plate and into the run off channel. α+ ρ+ τ=1
  34. 34. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 34 Brick, sand concrete , waterproofed concrete, copper or Aluminium (highly efficient) can be used for the basin of a long-life still if it is to be manufactured on-site, but for factory- manufactured stills, prefabricated Ferro-concrete can be used. Moulding of stills from fiberglass was tried in Botswana but in this case was more expensive than a brick still and more difficult to insulate sufficiently, but has the advantage of the stills being transportable. By placing a fan in the still it is possible to increase evaporation rates. However, the increase is not large and there is also the extra cost and complication of including and powering a fan in what is essentially quite a simple piece of equipment. Fan assisted solar desalination would only really be useful if a particular level of output is needed but the area occupied by the stills is restricted, as fan assistance can enable the area occupied by a still to be reduced for a given output. Sufficient Insulations of wool, Thermocol, sealants etc. are provided inside the Basin in order to prevent loss of heat. DESIGN TYPES AND THEIR PERFORMANCE Single-basin stills have been much studied and their behavior is well understood. Efficiencies of 25% are typical. Daily output as a function of solar irradiation is greatest in the early evening when the feed water is still hot but when outside temperatures are falling. Multiple-effect basin stills have two or more compartments. The condensing surface of the lower compartment is the floor of the upper compartment. The heat given off by the condensing vapour provides energy to vaporize the feed water above. Efficiency is therefore greater than for a single-basin still typically being 35% or more but the cost and complexity are correspondingly higher. In a wick still, the feed water flows slowly through a porous, radiation-absorbing pad (the wick). Two advantages are claimed over basin stills. First, the wick can be tilted so that the feed water presents a better angle to the sun (reducing reflection and presenting a large effective area). Second, less feed water is in the still at any time and so the water is heated more quickly and to a higher temperature. Simple wick stills are more efficient than basin stills and some designs are claimed to cost less than a basin still of the same output.
  35. 35. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 35 Emergency still - To provide emergency drinking water on land, a very simple still can be made. It makes use of the moisture in the earth. All that is required is a plastic cover, a bowl or bucket, and a pebble. Hybrid designs - There are a number of ways in which solar stills can usefully be combined with another function of technology. Three examples are given: a) Rainwater collection:-By adding an external gutter, the still cover can be used for rainwater collection to supplement the solar still output. b) Greenhouse-solar still:-The roof of a greenhouse can be used as the cover of a still. c) Supplementary heating: - Waste heat from an engine or the condenser of a refrigerator can be used as an additional energy input. CONCENTRATING COLLECTOR STILL MULTIPLE TRAY TILTED STILL
  36. 36. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 36 TILTED WICK SOLAR STILL BASIN STILL After going through the various existing designs of solar stills there are a few facts that come to picture: 1. The efficiency of single stage still is around 25%. 2. The efficiency of multistage stills is higher than 35%. 3. Mostly people use three staged stills because for more stages the cost outweighs the utility. 4. Most of the losses can be attributed to heat transfer losses. 5. Thermal losses are mostly in form of conduction and convection and very little by radiation – owing to low temperatures. So we can assume radiative losses to be negligible. Also the cost of a solar still which produces reasonable amount of purified water is high. The cost of water produced by the still is high. This fact attributes to almost negligible penetration of solar stills in Indian villages. While pursuing and pondering about the ways to reduce costs the first factor that comes to mind is why not increase the efficiency. But as we all know this is much easier said than done. After giving it a considerable thought we came up with a design that can greatly improve the efficiency of a solar water distillation system by minimizing thermal losses.
  37. 37. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 37 The equations governing the heat transfer rates are:- a. Conduction b. Convection Both the losses are greatly dependent on the area and temperature difference between the medium i.e., water and ambient. Hence if we can reduce temperature of the whole system we can reduce the heat loss and hence improve the efficiency. But reducing operating temperature will come at the cost of lower rated of evaporation and consequently lower rated of condensation leading to slower distillation. So now the problem boils down to increasing the rated of evaporation at lower temperature. The Vapor Pressure of a liquid at a given temperature is a characteristic property of that liquid. Vapor pressure of a liquid is intimately connected to boiling point. Q = - k A dT / dx Q = h A (Tsurface- Tambient) (Mass loss rate) / (Unit area) = (Vapor Pressure - Ambient Partial Pressure) * Sqrt ((Molecular Weight)/ (2*pi*R*T))
  38. 38. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 38 Vapor Pressures are influenced by Temperature logarithmically and this relationship is defined with the Clausius Clapyron Equation: Where: R = universal gas law constant = 8.31 J/mol-K = 8.31 X 10-3 KJ / mol-K P1 and P2 = vapour pressure at T1 and T2 T1 and T2 = Kelvin Temperature at the initial state and final state At 373K the pressure is 1 atm. We all know that boiling takes place when the ambient temperature equals that of the vapour pressure of the liquid. This means that we can increase the rate of evaporation by reducing the pressure of the vessel. This will ensure higher rates of evaporation even at low temperatures. ESTIMATION OF THE QUANTITY OF OUTPUT WATER Empirical relationship given by Schumacher Center For Technology & Development, UK A = Aperture area of the still in m2 E = Efficiency of the still usually taken as 50% G = Global radiation energy in MJ/m 2 (Approx. 18 MJ/m 2 ) Log P2 / P1 = Delta H vaporization [1 / T1 - 1/T2] / 2.303 (R) Estimate: 3.91 liters/m 2 /day.
  39. 39. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 39 MATERIAL REQUIREMENTS OF BASIN STILLS The materials used for this type of still should have the following characteristics: • Materials should have a long life under exposed conditions or be inexpensive enough to be replaced upon degradation. • They should be sturdy enough to resist wind damage and slight earth movements. • They should be nontoxic and not emit vapors or instill an unpleasant taste to the water under elevated temperatures. • They should be able to resist corrosion from saline water and distilled water. • They should be of a size and weight that can be conveniently packaged, and carried by local transportation. • They should be easy to handle in the field. Although local materials should be used whenever possible to lower initial costs and to facilitate any necessary repairs, keep in mind that solar stills made with cheap, unsturdy materials will not last as long as those built with more costly, high quality material. With this in mind, you must decide whether you want to build an inexpensive and thus short-lived still that needs to be replaced or repaired every few years, or build something more durable and lasting in the hope that the distilled water it produces will be cheaper in the long run. Of the low cost stills that have been built around the world, many have been abandoned. Building a more durable still that will last 20 years or more seems to be worth the additional investment. Choosing materials for the components in contact with the water presents a serious problem. Many plastics will give water off a substance which can be tasted or smelled in the product water, for periods of anywhere from hours to years.
  40. 40. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 40 CAPABILITIES A solar still operates using the basic principles of evaporation and condensation. The contaminated feed water goes into the still and the sun's rays penetrate a glass surface causing the water to heat up through the greenhouse effect and subsequently evaporate. When the water evaporates inside the still, it leaves all contaminants and microbes behind in the basin. The evaporated and now purified water condenses on the underside of the glass and runs into a collection trough and then into an enclosed container. In this process the salts and microbes that were in the original feed water are left behind. Additional water fed into the still flushes out concentrated waste from the basin to avoid excessive salt build-up from the evaporated salts. A solar still effectively eliminates all waterborne pathogens, salts, and heavy metals. Solar still technologies bring immediate benefits to users by alleviating health problems associated with water-borne diseases. For solar stills users, there is a also a sense of satisfaction in having their own trusted and easy to use water treatment plant on-site. Solar still production is a function of solar energy (insolation) and ambient temperature. Typical production efficiencies for single basin solar stills on the Border are about 60 percent in the summer and 50 percent during the colder winter. Single basin stills generally produce about 0.8 liters per sun hour per square meter. Given the smaller product water output for a solar still, the technology calls for a different approach to providing purified water in that it only purifies the limited amounts of water that will be ingested by humans. Water used to flush the toilet, take a bath, wash clothes, etc. does not need to meet the same high level of purity as water that is ingested, and thus does not need to be distilled. Solar stills have proven to be highly effective in cleaning up water supplies and in providing safe drinking water. The effectiveness of distillation for producing safe drinking water is well established and long recognized. Distillation is the only stand-alone point-of-use (POU) technology with NSF (National Sanitation Foundation) certification for arsenic removal, under Standard 62. Solar distillation removes all salts and heavy metals, as well as biological contaminants.
  41. 41. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 41 USER EXPERIENCES Surveys were conducted on user satisfaction with project participants receiving cost- shared solar distillers. Users were nearly unanimous that owning a solar still was good for them. Some owners prized the idea of using alternative, clean energy to achieve their purposes, while at the same time leaving only a small “footprint” on the planet. All were very enthused about the economic benefits of using a solar distiller. They found that paying a relatively low price for a still was a favorable alternative to having to buy water on a regular basis with no end in sight to this routine. Others valued the independence and fascination they experienced from being involved in the production of their own purified water. Most colonials residents often do not trust their local water supply in those cases when there is one available (e.g., Columbus). While many have noted a concern over local water supply color or odor, the overwhelming characteristic that gains their attention is poor taste. There is a good deal of concern with taste, and most of those interviewed noted that one of the reasons for wanting a water purification system was to improve the taste of their local water supply. Since many of the local water supplies are high in salts and minerals (e.g., iron or sulphur), they often have a marginal or poor taste. The solar stills were considered useful by colonial residents to improve drinking water taste. Solar distillers were able to meet all of the drinking and cooking water needs of a household. Not all of the households receiving solar stills through pilot projects had stills optimally sized to meet all of their wintertime water production needs, but about 40 percent of the households were completely satisfied with their still water production. All households had sufficient water during the high summertime production period, and it was during the wintertime where some families had insufficient still water. Generally, it appears that for most Border households about 0.5 m2 meter of solar still is needed per person to meet potable water needs consistently throughout the year. Those households with insufficient wintertime still water production typically had 0.35 m2 or less of still area per person. Survey results clearly indicate that only about a third of colonials residents are willing or able to pay the full price of the solar still up front, because most simply could not afford the higher up-front capital cost. However, interest mounted greatly when the possibility of financing was mentioned. Thus, water districts and others interested in providing potable water to Border colonials should consider offering an option for still financing. To bolster interest, a clear, easy-to-follow breakdown of cost payback should be provided. Prospective customers interest is peaked when they realize that even at full price, a solar still can pay for itself in less than two years as compared to purchasing bottled water. Some prospective customers would be delighted to know that savings over a decade or more could be substantial and amount to thousands of dollars. Almost all of those surveyed were using their solar stills regularly, thus now meeting most or all of their drinking water and cooking water supply needs via solar distillation.
  42. 42. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 42 Occasionally, still users had to supplement their still supply with store-bought water, especially in the winter, when still production decreases to about half of summertime production. Yet the need for purchasing bottled water from a store was greatly mitigated in all cases. Solar still savings were approximately $150 - $200 a year per household instead of purchasing bottled water. Solar still technology has gradually improved over the past decade along the Border. The greatest problem for the first generation stills designed by EPSEA in the mid-1990‟s (an improvement on the original McCracken solar still) was that when they dried out, the inner membrane silicone lining would outgas. This in turn deposited a fine film on the underside of the glass, causing the water droplets to bead up and falls back into the basin rather than trickle down the glass to the collection trough and thus still water production drops dramatically (about 80% or more drops). The first still used a food grade silicone and were made out of plywood and concrete siding. It was found that the stills (3‟ x 8‟) were often producing far more water than the users needed, especially in the summer. As time evolved, a second generation solar still was developed made out of aluminum and smaller (3‟ x 6‟ and 3‟ x 3‟). The still was lighter, but expensive to build. ECONOMICS Compared to purchasing comparable quantities of bottled water, the average return on investment on a solar still for a family is typically a couple of years. Factoring in the health costs of contaminated water, payback for a solar still can be immediate. Solar distillation is the cheapest way to clean water for a household and is quite economical as compared to reverse osmosis and electric distillation. A square meter for a single basin solar still costs about $400. Many families in the U.S. colonies often spend from $8 to $12 per week on bottled water. Likewise, in northern Mexico families often spend $3 - $5 per week on purified water. This represents an investment of anywhere from $150 to $600 per year for bottled water. Thus, simple payback on a solar still strictly compared to purchasing bottled water is typically within two to three years. The levelized energy cost of solar distilled water is about US$.03 per liter, assuming a ten year still lifetime. The first EPSEA stills have now been operating for a decade and are still going strong. The presented high performance solar distilled water plant can be a very economical, cost effective, minimum maintenance and the zero energy cost option. Moreover, there is no pollution involved.
  43. 43. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 43 COST & MATERIALS FOR SOLAR STILL Materials:- 1. The side and bottom walls need to be insulated. This can be achieved by using multilayered insulator. Glass wool/Thermocol will be sand-witched between two metallic plates. This will ensure negligible heat loss to the surroundings. 2. The main frame is composed of ALUMINIUM owing to its corrosion resistance, low weight, long life and easy cleanability. 3. The inside of the complete distiller is coated with carbon black to increase absorption of radiation. 4. The cover on the top is made of tempered glass so that the birds can’t see their reflection and hence avoid nuisance. Cost Analysis:- 1. Total cost of Aluminium box = Rs 1500 2. Cost of carbon black paint = Rs 100 3. Cost of tempered glass = Rs 1000 4. Cost of Reflector = Rs. 2000 5. Cost of insulation and sealing (UV Glue & Silicon Glue) = Rs. 2500 6. Cost of the hoisting mechanism and other auxiliaries = Rs 500 7. Cost of labour and machining = Rs 600 8. Cost of Temperature Sensor = Rs 2200 9. Cost of other parts (Table, Base, Pipings etc.) = Rs 450 10. Cost of Report Writing= Rs. 1500 (Typing, Editing, Color Printing, Binding) Net cost of the Project = Rs 12350
  44. 44. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 44 COST ANALYSIS AND MANUFACTURING The per-liter cost of solar-distilled water can be calculated as follows: (a) Estimate the usable lifetime of the still; (b) Add up all the costs of construction, repair and maintenance (including labour) over its lifetime; and (c) Divide that figure by the still's total expected lifetime output in liters. Such a cost estimate is only approximate since there are large uncertainties in both the lifetime and the yield estimates. Costs are usually considerably higher than current water prices–which explain why solar backyard stills are not yet marketed widely in India. ASSEMBLING AND MANUFACTURE Fabrication of the whole unit is pretty straight forward and involves metal cutting, welding, glass cutting, sealing, painting and drilling. All these processes can be done at any local workshop using simple machines – lathe, drill, welding, milling etc. The steps in the process of assembling are outlined as follows: 1. The outer box made of ALUMINIUM will be fabricated first. It will be made of double wall and will be filled with Thermocol to provide insulation. 2. Top Cover (Double slope Type) will be fabricated then. It will be supported by Aluminium Fittings. 3. Condensate Channels will be made on the Top of Basin for the passage of condensed pure water. 4. Water Inlet and Outlets have been made in Basin and Top Glass cover.ONE water inlet and TWO water outlet. 5. Reflectors in order to increase efficiency are then fixed on two sides of glass cover. 6. Thermocouples which will indicate temperature inside still at various levels are then attached. 7. The whole system is sealed using sealant to prevent the air from leaking in from the atmosphere.
  46. 46. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 46 COMPONENTS OF SOLAR STILL Solar still is a simple device which can convert available water or brackish water into portable water by using solar energy. Main components of solar still are: 1. BASIN: It is the part of the system in which the water to be distilled is kept. It is therefore essential that it must absorb solar energy. Hence, it is necessary that the material has high absorptivity or very less reflectivity and very less transmitivity. These are the criteria for selecting the basin materials. 2. CONDENSATE CHANNEL: It is the part of the system in which condensed water is collected. Sheet of required dimension is first cut out, and then it is folded by using the folding machine. 3. BLACK LINER: Solar radiation transmitted through transparent cover is absorbed in the black lining. Black bodies are good absorbers. Black paint is used as liner. 4. TRANSPARENT COVER: Glazing glass is used and thickness of 5 mm is selected. The use of glass is because of its inherent property of producing greenhouse effect inside the still. Glass transmits over 90% of incident radiation in the visible range. 5. INSULATION: Thermocol is used as insulator to provide thermal resistance to the heat transfer that takes place from the system to the surrounding. 6. SEALANT: M seal and putty is used as sealant to make the distiller leak proof and air tight. UV Glue is used to join Metal to Glass. Silicon Glue is used to join Glass to Glass. 7. SUPPLY AND DELIVERY SYSTEM: Three holes are made in the basin, one for supply and two for delivery. 8. TABLE: Pine wood table is used to support whole setup. Pine wood has good surface finish. Base of Ply wood is used because of its good strength. 9. SQUARE BOX: Iron Square Box is used to hold side (threaded) stand.
  47. 47. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 47 10. REFLECTOR: Reflecting Mirror is used with one side silver coated and is supported by ply wood to prevent its breakage. 11. TEMPERATURE SENSOR: LM35 Temp Sensor along with its complimentary components is used. LCD reflecting temperature in °C.
  48. 48. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 48 HOW TO INCRESE EFFICIENCY OF SOLAR STILL We have increased the efficiency of solar still through following ways:- • Double slope glass cover • Top reflectors • Bottom reflectors • Insulation • Black liner • Sealant DOUBLE SLOPE GLASS COVER Double Glass Cover is used so there is no requirement of rotating set up as per sun’s location all the time, as in case of Single Slope stills.
  49. 49. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 49 INSULATION Thermocol insulation is provided on all four sides of Basin in order to prevent Heat losses from system to surrounding. PROPERTIES OF THERMOCOL Thermocol is a commercial name like Coca-Cola. In 1951 the researchers of a German company named BASF successfully restructured chemical bonding of polystyrene (a synthetic petroleum product) molecules and developed a substance named stretch polystyrene. This substance was named Thermocol, which nowadays is manufactured through a simple process. Thermoplastic granules are expanded through application of steam and air. Expanded granules become much larger in size but remain very light. Thermocol is a good resister of cold and heat but since it is a petroleum product it dissolves in any solvent of petroleum. As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100 °C, its glass transition temperature. It becomes rigid again when cooled. This temperature behavior is exploited for extrusion, and also for molding and vacuum forming, since it can be cast into molds with fine detail. It is very slow to biodegrade and therefore a focus of controversy, since it is often abundant as a form of litter in the outdoor environment, particularly along shores and waterways especially in its foam form. (STRUCTURE OF THERMOCOL) (I.U.P.A.C. NAME -: Poly1-phenylethylene)
  50. 50. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 50 BLACK LINER The bottom of Basin is painted Black in order to absorb maximum radiation. Black paint at the bottom of the basin acts as the black body and absorb maximum heat. A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition. A black body in thermal equilibrium has two notable properties: It is an ideal emitter: it emits as much or more energy at every frequency than any other body at the same temperature. It is a diffuse emitter: the energy is radiated isotropically, independent of direction An approximate realization of a black surface is a hole in the wall of a large enclosure (see below). Any light entering the hole is reflected indefinitely or absorbed inside and is unlikely to re-emerge, making the hole a nearly perfect absorber.
  51. 51. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 51 PRINCIPLE OF BLACK BODY Black body works on Kirchhoff’s law-: Kirchhoff in 1860 introduced the theoretical concept of a perfect black body with a completely absorbing surface layer of infinitely small thickness, but Planck noted some severe restrictions upon this idea. Planck noted three requirements upon a black body: the body must (i) Allow radiation to enter but not reflect; (ii) Possess a minimum thickness adequate to absorb the incident radiation and prevent its re- emission; (iii) Satisfy severe limitations upon scattering to prevent radiation from entering and bouncing back out. As a consequence, Kirchhoff's perfect black bodies that absorb all the radiation that falls on them, cannot be realized in an infinitely thin surface layer, and impose conditions upon scattering of the light within the black body that are difficult to satisfy. SEALANT A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary action. Anaerobic acrylic sealants generally referred to as impregnates are the most desirable as they are required to cure in the absence of air, unlike surface sealants that require air as part of the cure mechanism that changes state to become solid, once applied, and is used to prevent the penetration of air, gas, noise, dust, fire, smoke or liquid from one location through a barrier into another. Typically, sealants are used to close small openings that are difficult to shut with other materials, such as concrete, drywall, etc. Desirable properties of sealants include insolubility, corrosion resistance, and adhesion. Uses of sealants vary widely and sealants are used in many industries, for example, construction, automotive and aerospace industries. Application of sealant-: 1-: It fills a gap between two or more substrates 2-: It forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate. 3-: It maintains sealing properties for the expected lifetime, service conditions and environments.
  52. 52. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 52 Sealants used in Solar Still- M-Seal is used to make Basin and Glass Cover leak proof. UV Glue is used to join Metal to Glass and Metal to Metal. Silicon Glue is used to join Glass to Glass. UV GLUE SILICON GLUE M-SEAL
  53. 53. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 53 REFLECTORS Top and Bottom Reflectors are used so that more of the solar radiations are allowed to fall on the glass cover. Concave type Reflecting mirrors were used as top and bottom reflectors. Hence more heat energy would be supplied to the basin water, which will help in conducting fast evaporation. Hence increasing efficiency of Solar Still. BOTTOM REFLECTORS TOP REFLECTORS
  54. 54. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 54 AUXILLARY DEVICE TEMPERATURE SENSOR LM 35 Temperature sensor along with its complimentary components is used. It is operated by a 6V battery. LCD of the sensor reflects temperature of following areas in °C:- • Temperature of incoming brackish water. • Temperature of outgoing potable water. • Temperature at the top of glass cover.
  55. 55. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 55 DIMENSIONS OF SOLAR STILL USED S.No. Parameters Double Slope 1. Area of Basin 0.90x0.45 m2 2. Height of Basin 0.1 m 3. Area of Glass 0.90x0.52 m2 4. Thickness of Glass Cover 0.004m 5. Angle of Glass 25° 6. Thickness of Insulation 0.01 m 7. Height of Still from Ground 0.20 m PERFORMANCE ANALYSIS Basin is filled with 10 liters of Brackish Water and then performance of our Solar Still was checked. The result is tabulated below:- TIME QUANTITY OF OUTPUT WATER (ml) 0800-1000 Hours 350 1000-1200 Hours 550 1200-1400 Hours 800 1400-1600 Hours 700 1600-1800 Hours 400 Total Quantity of Potable water achieved= 2.8 liters.
  56. 56. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 56 WATER PURIFIERS History of drinking water filtration During the 19th and 20th centuries, water filters for domestic water production were generally divided into slow sand filters and rapid sand filters (also called mechanical filters and American filters). While there were many small-scale water filtration systems prior to 1800, Paisley, Scotland is generally acknowledged as the first city to receive filtered water for an entire town. The Paisley filter began operation in 1804 and was an early type of slow sand filter. Throughout the 1800s, hundreds of slow sand filters were constructed in the UK and on the European continent. An intermittent slow sand filter was constructed and operated at Lawrence, Massachusetts in 1893 due to continuing typhoid fever epidemics caused by sewage contamination of the water supply. The first continuously operating slow sand filter was designed by Allen Hazen for the city of Albany, New York in 1897. The most comprehensive history of water filtration was published by Moses N. Baker in 1948 and reprinted in 1981. In the 1800s, mechanical filtration was an industrial process that depended on the addition of Aluminium sulphate prior to the filtration process. The filtration rate for mechanical filtration was typically more than 60 times faster than slow sand filters, thus requiring significantly less land area. The first modern mechanical filtration plant in the U.S. was built at Little Falls, New Jersey for the East Jersey Water Company. George W. Fuller designed and supervised the construction of the plant which went into operation in 1902. In 1924, John R. Baylis developed a fixed grid backwash assist system which consisted of pipes with nozzles that injected jets of water into the filter material during expansion.
  57. 57. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 57 TYPES OF FILTERS Water treatment plant filters Media Filters Screen Filters, Disk Filters, Slow Sand Filter Beds, Rapid Sand Filters and Cloth Filters. Point-of-use filters for home use include granular-activated carbon filters (GAC) used for carbon filtering, metallic alloy filters, micro porous ceramic filters, and carbon block resin (CBR), microfiltration and ultrafiltration membranes. Some filters use more than one filtration method. An example of this is a multi-barrier system. Jug filters can be used for small quantities of drinking water. Some kettles have built-in filters, primarily to reduce lime scale buildup. Point-of-use microfiltration devices can be directly installed at water outlets (faucets, showers) in order to protect users against Legionella spp., Pseudomonas spp., Nontuberculous mycobacteria, Escherichia coli and other potentially harmful water pathogens by providing a barrier to them and/or minimizing patient exposure. CERTIFICATION OF WATER FILTERS Three organizations are accredited by the American National Standards Institute, and each one of them certifies products using ANSI/NSF standards. Each ANSI/NSF standard requires verification of contaminant reduction performance claims, an evaluation of the unit, including its materials and structural integrity, and a review of the product labels and sales literature. Each certifies that home water treatment units meet or exceed ANSI/NSF and Environmental Protection Agency drinking water standards. ANSI/NSF standards are issued in two different sets, one for health concerns (such as removal of specific contaminants (Health Effects) and one for aesthetic concerns (Aesthetic Effects, such as improving taste or appearance of water). Certification from these organizations will specify one or both of these specific standards. NSF International: The NSF Water treatment Device Certification Program requires extensive product testing and unannounced audits of production facilities. The goal of this program is to provide assurance to consumers that the water treatment devices they are purchasing meet the design, material, and performance requirements of national standards.
  58. 58. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 58 Underwriters Laboratories: Underwriters Laboratories, Inc. is an independent, accredited testing and certification organization that certifies home water treatment units which meet or exceed EPA and ANSI/NSF drinking water standards of contaminant reduction, aesthetic concerns, structural integrity, and materials safety. Water Quality Association: The Water Quality Association is a trade organization that tests water treatment equipment, and awards its Gold Seal to systems that meet or exceed ANSI/NSF standards for contaminant reduction performance, structural integrity, and materials safety. PORTABLE WATER FILTERS Water filters are used by hikers, by aid organizations during humanitarian emergencies, and by the military. These filters are usually small, portable and light (1-2 pounds/0.5-1.0 kg or less), and usually filter water by working a mechanical hand pump, although some use a siphon drip system to force water through while others are built into water bottles. Dirty water is pumped via a screen-filtered flexible silicon tube through a specialized filter, ending up in a container. These filters work to remove bacteria, protozoa and microbial cysts that can cause disease. Filters may have fine meshes that must be replaced or cleaned, and ceramic water filters must have their outside abraded when they have become clogged with impurities. These water filters should not be confused with devices or tablets that are water purifiers, some of which remove or kill viruses such as hepatitis A and rotavirus. WATER POLISHING The term water polishing can refer to any process that removes small (usually microscopic) particulate material, or removes very low concentrations of dissolved material from water. The process and its meaning vary from setting to setting: a manufacturer of aquarium filters may claim that its filters perform water polishing by capturing "micro particles" within nylon or polyester pads just as a chemical engineer can use the term to refer to the removal of magnetic resins from a solution by passing the solution over a bed of magnetic particulate. In this sense, water polishing is simply another term for whole house water filtration systems. Good materials to create a filter are sand, gravel, activated carbon and window screens. “The next world war-if ever-will not be over land, but on WATER.” Globally more than one billion people lack access to safe drinking water, nearly all of them in the developing countries, including India. Nearly one-third of the population worldwide live in areas which are water stressed. This figure is expected to increase further by a fold by 2025. Approximately 80% of diseases in India are caused by water borne microorganisms. This is true in rural as well as urban India. However, awareness of health risks linked to unsafe water is still very low among the rural population. The few who treat water resort to boiling or use domestic candle filters. With more & more number people are becoming conscious about contaminated drinking water; the demand for water purifiers is rapidly rising especially in India. In the past few years, Indian water purifier industry has seen an exponential growth of 22% CAGR (Compounded Annual Growth Rate).
  59. 59. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 59 There are three types of Water Purifiers in the market: 1. Ultra Violet Based 2. Reverse Osmosis Based 3. Chemical Based The UV segment constitutes more than 55% of the industry and has its key focus area for water Purifier manufacturers because of higher margins it offer. The Indian water purifier market has tremendous potential with a market size of approximately INR 1400 Crore. It is more evident from the fact that global majors such as Philips and Hindustan Unilever have stepped in the area. In the years to come, we can expect to see others entering the battle. FEATURES OF A GOOD PURIFIER • It should retain natural quality of water • User friendly features. • Absolutely safe for drinking purpose as per WHO standards. • Long Life. • In-built storage tank • Avoids all contamination with last point purification. • Low Maintenance. AN EXAMPLE OF HOME BASED WATER PURIFIER:- PUREIT Pure-it is the world’s most advanced in-home water purifier. Pure-it, a breakthrough offering of Hindustan Unilever (HUL), provides complete protection from all water-borne diseases, unmatched convenience and affordability. Pure-it’s unique Germ kill Battery technology kills all harmful viruses and bacteria and removes parasites and pesticide impurities, giving you water that is “as safe as boiled water". It assures your family 100% protection from all water –borne diseases like Jaundice, Diarrhoea, Typhoid And Cholera. Pure-it not only renders micro- biological safe water, but also makes the water clear, odorless and good-tasting. Pure-it does not leave any residual chlorine in the output water.
  60. 60. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 60 The output water from Pure-it meets stringent criteria for microbiologically safe drinking water from one of the toughest regulatory agencies in the USA, EPA (Environmental Protection Agency). The performance of Pure-it has also been tested by leading scientific and medical institutions in India and abroad. This patented technological breakthrough has been developed by HUL. Pure-it runs with a unique, Germ kill Battery Ki that typically lasts for 1500 liters of water. Consumer will get 4 liters of water that is as safe as boiled water for just one rupee. Pure-it in- home purification system uses a 4 stage purification process to deliver “as safe as boiled water” without the use of electricity and pressurized tap water. Pure-it purifies the input drinking water in four stages, namely; 1. MICRO-FIBER MESH- Removes visible dirt. 2. COMPACT CARBON TRAP- Removes remaining dirt, harmful parasites & pesticide Impurities. 2. GERM KILL PROCESSOR– Uses 'programmed chlorine release technology’ and its Stored Germ kill process targets and kills harmful virus and bacteria. 4. POLISHER – Removes residual chlorine and all disinfectant by-products, giving clear odorless and great tasting water. 5. BATTERY LIFE INDICATOR -Ensures total safety because when the germ kill power is exhausted, the indicator turns red, warning you to replace the battery. ‘SOLAR PANELS’ CAN BE USED IN SOLAR STILL FOR CONTINUOUS SUPPLY OF POTABLE WATER DURING DAY & NIGHT
  61. 61. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 61 SOLAR PANEL A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged connected assembly of photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Each panel is rated by its DC output power under standard test conditions, and typically ranges from 100 to 320 watts. The efficiency of a panel determines the area of a panel given the same rated output - an 8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel. Because a single solar panel can produce only a limited amount of power, most installations contain multiple panels. A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and or solar tracker and interconnection wiring.
  62. 62. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 62 Theory and construction Solar panels use light energy (photons) from the sun to generate electricity through the photovoltaic effect. The majority of modules use wafer-based crystalline silicon cells or thin-film cells based on cadmium telluride or silicon. The structural (load carrying) member of a module can either be the top layer or the back layer. Cells must also be protected from mechanical damage and moisture. Most solar panels are rigid, but semi- flexible ones are available, based on thin-film cells. Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired current capability. The conducting wires that take the current off the panels may contain silver, copper or other non-magnetic conductive transition metals. The cells must be connected electrically to one another and to the rest of the system. Externally, popular terrestrial usage photovoltaic panels use MC3 (older) or MC4 connectors to facilitate easy weatherproof connections to the rest of the system. Bypass diodes may be incorporated or used externally, in case of partial panel shading, to maximize the output of panel sections still illuminated. Solar cells become less efficient at higher temperatures and installers try to provide good ventilation behind solar panels. Efficiencies Depending on construction, photovoltaic panels can produce electricity from a range of frequencies of light, but usually cannot cover the entire solar range (specifically, ultraviolet, infrared and low or diffused light). Hence much of the incident sunlight energy is wasted by solar panels, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into different wavelength ranges and direct the beams onto different cells tuned to those ranges. This has been projected to be capable of raising efficiency by 50%. Currently the best achieved sunlight conversion rate (solar panel efficiency) is around 21% in commercial products, typically lower than the efficiencies of their cells in isolation.
  63. 63. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 63 WOULD A SOLAR STILL SUIT OUR NEEDS? Human beings need 1 or 2 liters of water a day to live. The minimum requirement for normal life in developing countries (which includes cooking, cleaning and washing clothes) is 20 liters per day (in the industrialized world 200 to 400 liters per day is typical). Yet some functions can be performed with salty water and a typical requirement for distilled water is 5 liters per person per day. Therefore 2m² of still are needed for each person served. Solar stills should normally only be considered for removal of dissolved salts from water. If there is a choice between brackish ground water and polluted surface water, it will usually be cheaper to use a slow sand filter or other treatment device. If there is no fresh water then the main alternatives are desalination, transportation and rainwater collection. Unlike other techniques of desalination, solar stills are more attractive, the smaller the required output. The initial capital cost of stills is roughly proportional to capacity, whereas other methods have significant economies of scale. For the individual household, therefore, the solar still is most economic. For outputs of 1m³/day or more, reverse osmosis or electro dialysis should be considered as an alternative to solar stills. Much will depend on the availability and price of electrical power. Solar distillation Practical Action for outputs of 200m³/day or more, vapour compression or flash evaporation will normally be least cost. The latter technology can have part of its energy requirement met by solar water heaters. In many parts of the world, fresh water is transported from another region or location by boat, train, truck or pipeline. The cost of water transported by vehicles is typically of the same order of magnitude as that produced by solar stills. A pipeline may be less expensive for very large quantities. Rainwater collection is an even simpler technique than solar distillation in areas where rain is not scarce, but requires a greater area and usually a larger storage tank.
  64. 64. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 64 DISTILLATION PURIFICATION CAPABILITIES Solar stills have proven to be highly effective in cleaning up water supplies to provide safe drinking water. The effectiveness of distillation for producing safe drinking water is well established and recognized. Most commercial stills and water purification systems require electrical or other fossil-fueled power sources. Solar distillation technology produces the same safe quality drinking water as other distillation technologies; only the energy source is different: the sun. ADVANTAGES OF SOLAR STILL • Free of charge sun energy (during sunlight it eliminates 500 Watt electric consumption per one hour of sunlight). • There are no moving parts; it is therefore reliable and almost maintenance free (cleaning is required though). • Water taste is claimed to be better since the device act as a Solar Water Vaporizer and it doesn’t boil the water (resembling rain water). • Neutral pH is claimed (like rainwater), not like the not neutral pH of steamed distilled water. DISADVANTAGES OF SOLAR STILL • Low distillate output per unit area. • Leakage of vapour through joints. • High maintenance. • Productivity decreases with time for a variety of reasons. • Cost per unit output is very high.
  65. 65. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 65 PICTURES OF WORKING MODEL
  66. 66. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 66 OUR DOUBLE SLOPE TYPE SOLAR STILL
  67. 67. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 67 CONCLUSION Distillation is a method where water is removed from the contaminations rather than to remove contaminants from the water. Solar energy is a promising source to achieve this. This is due to various advantages involved in solar distillation. The Solar distillation involves zero maintenance cost and no energy costs as it involves only solar energy which is free of cost. It was found from the experimental analysis that increasing the ambient temperature from 32°C to 47°C will increase the productivity by approx. 12 to 23%, which shows that the system performed more distillation at higher ambient temperatures. When inverted type absorber plate was used thermal efficiency of single slope solar still was increased by 7 %. It was observed that when the water depth increases from 0.01m to 0.03m the productivity decreased by 5%.These results show that the water mass (water depth) has an intense effect on the distillate output of the solar still system. Solar still productivity can also increase by use of reflector by 3%. The use of the mirror reflector will increase the temperature of the solar still basin; such an increase in the temperature is because of the improvement in solar radiation concentration. The solar radiation increase from 0 MJ/m2 /h to 6 MJ/m2 /h has increased the productivity of the still by 15 to 32%. However the increase of the solar radiation parameter will increase the solar energy absorbed by the basin liner. The main disadvantage of this solar still is the low productivity or high capital cost per unit output of distillate. This could be improved by a number of actions, e.g. injecting black dye in the seawater, using internal and external mirror, using wick, reducing heat conduction through basin walls and top cover or reusing the latent heat emitted from the condensing vapour on the glass cover. Capital cost can be reduced by using different designs and new materials for construction of solar stills.
  68. 68. DOUBLE SLOPE TYPE SOLAR STILL Department Of Mechanical Engineering Page 68 REFERENCES 1. Non-Conventional Energy Resources book by S.Hasan Saeed and D.K Sharma. 2. Principles of thermal collection and storage, solar energy, second edition book by S.P Sukhatme. 3. 4. 5. 6. Use-A-Solar-Still.aspx 7.