Solar Desalination Systems Soteris Kalogirou Department of Mechanical Engineering and Materials Sciences and Engineering Cyprus University of Technology Water The most important element for the preservation of life on earth. 3/4 of the earth surface covered with water. 97% of this water is salty. 3% is potable water found in: Underground reservoirs lakes rivers Polar ice Biggest problem today: Water pollution. 1
Water shortage problem Humanity has been dependent on rivers, lakes and underground water for the clean water requirements in domestic life, agriculture and industry. Causes of water shortage: Worldwide population explosion (mainly for use in the production of adequate quantities of food) - expected increase in the population from 4.7 billion in mid 80 s to 8.2 billion in 2020. Rapid industrial growth and pollution of rivers and lakes by industrial wastes. The large amounts of sewage discharged (due to the increased population). Uneven distribution, countries like Canada which have a tenth of the world s surface fresh water are inhabited by less than 1% of the world population. Water and Energy History proves that water and civilization are two entities which are highly related. All great civilizations were developed and flourished near sources of fresh clean water. Historical records prove the importance of water in the preservation of life and development of the civilization (typical example of this influence is the Nile River in Egypt which provided water for irrigation and mud full of nutrients to raise crops). Energy is as important as water for the development of good standards of life as it is the source that powers all human activities. Water is also by itself a power generating force in the form of hydraulic power. All manmade desalination processes require large quantities of energy to achieve separation of salts from seawater. 2
Seawater The oceans is the only inexhaustible source of water. Sea water desalination could solve the water shortage problem. Desalination can be achieved with: Phase change or thermal processes. Membrane or single-phase processes. Desalination Methods Thermal Processes: (Solar Stills-SS) Multi Stage Flash Evaporators-MSF Multiple Effect Distillation Evaporators-MED Vapour Compression Evaporators-VC Membrane Processes: Reverse Osmosis-RO Energy Recovery-ER/RO Electrodialysis-ED Other less developed methods: Freezing Humidification-dehumidification 3
Desalination during the ancient times Solar Stills 100% solar system Most of these systems are combined with rain collection. 4
Multi Stage Flash Evaporators Steam from a solar steam generation system A photo of an actual MSF plant 5
Multiple Effect Distillation Evaporator Steam from a solar steam generation system Multiple Effect Stack (MES) type evaporator This is the most appropriate type for solar energy applications. Advantages: Stable operation between virtually zero and 100% output even when sudden changes are made (most important). Its ability to follow a varying steam supply without upset. Actual MES plant 6
Mechanical Vapor Compression Mechanical compressor is used Mechanical energy can be from PV or wind system Principle: By pressurizing the steam condensation temperature increases thus steam can be used to provide energy for the evaporation of more seawater. Thermal Vapor Compression Jet ejector is used 7
ΙΟ ΙΩΝ ΜΟΡΦΩ Ν ΗΠ Ε ΓΕΙΑ ΕΡ Ν & ΤΟ Σ Σ ΕΡΓΑ ΣΤ ΗΡ Reverse Osmosis-element ΠΡ Ο ΣΤ ΑΣ Ν ΛΟ ΙΑΣ ΠΕΡΙΒΑΛ Reverse Osmosis system Variation (energy recovery RO) Only energy required is for pumping seawater (PV or wind). ΙΩΝ ΜΟΡΦΩ Ν ΗΠ Σ & ΠΡ Ο ΣΤ ΑΣ Ε ΤΟ Σ ΙΟ ΓΕΙΑ ΕΡ Ν ΕΡΓΑ ΣΤ ΗΡ Very complex pre-treatment systems is required. Ν ΛΟ ΙΑΣ ΠΕΡΙΒΑΛ 8
Reverse Osmosis - Banks System easily expandable +ve (anode) Electrodialysis -ve (cathode) Electrodialysis unit during maintenance -ve ions (anions) +ve ions (cations) Fresh water compartment Anion permeable membrane Cation permeable membrane DC current is required for its operation supplied directly from PV panels. Some other systems, like the humidification/dehumidification are industrially matured yet 9
Current status of industry The installed capacity of desalinated water systems in year 2010 is about 60 million m 3 /day. Due to the continuing problems of climate change (droughts) this is expected to increase significantly in the next decades. The increase of desalinated water supply will unavoidably create a series of problems; most significant: increased energy consumption and environmental pollution caused by the use of fossil fuels. These create a chain reaction as this is the reason why more desalinated water is required (climate change). It has been estimated that the production of 60 million m 3 /day requires about 495 million tons of oil per year. Environmental Effects Therefore, significant quantities of energy are required to achieve salt separation. Even if conventional fuels were cheap we would not be able to use them for sea water desalination. Reason: Pollution of the environment. Fortunately, there are many parts of the world that suffer from water shortage problems but have abundant renewable sources of energy that can be used to power desalination processes. 10
Solar Energy Sources and Desalination Combination of Technologies Photovoltaic panels: Reverse Osmosis Electrodialysis Vapour compression systems Solar Collectors (FP, CPC, ETC, PTC): Multistage flash evaporators Multiple effect distillation evaporators PTC FP CPC ETC Combination of a RE system with conventional Renewable Energy System Conventional System Storage Device Desalination System Storage smoothens also the variation in the supply Many pilot RES-powered desalination plants tried 11
Desalination in Cyprus Suffered from water shortage problems for millennia. First desalination plant erected in 1996 (Dhekelia). Originally 20,000 m 3 /day - capacity doubled 2 years later Other plants followed which solved permanently the problem. All plants are reverse osmosis type and NO renewable energy is used. 25% of the cost of water is for ENERGY. It is estimated that every 2m 3 of purified water 3 liters of petrol are required. Contribute 5-6 kg of CO 2 per m 3 produced. Solar desalination can be used in many islands of the eagean Desalination a new perspective Combination of CSP with desalination CSP plants need to be located near the sea Desalination systems are also near the sea In water-short areas power stations are also near the sea Energy and water are both required The system is more flexible produces either commodities or both at the same time 12
Conclusions There are available technologies both for desalination and for the collection and use of solar energy. The point is how to combine them in order to produce desalinated water in the lowest possible cost. The pollution of the planet should not be underestimated. We need to protect our planet. We own it to the future generations. Thank you for your attention. ΕAny questions????? ΡΓΑΣΤΗΡΙΟ ΗΠΙΩΝ ΜΟΡΦΩΝ ΕΝΕΡΓΕΙΑΣ 13