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Solar pond technology has made substantial progress in the last fifteen years. The research is to review the solar pond development in the world and its technology. The various specific application of solar pond such as process heating, desalination, refrigeration, drying and solar power generation are widely investigate in this report. The factors which influence the technical and economic viability of solar ponds for thermal applications and power generation have been discussed. Solar ponds can have a significant role in paddy processing, greenhouse heating process, vegetable processing and dairy plants apart from meeting the domestic hot water requirements.
The sun has been radiating energy for over 500 million years and is expected to continue for at least the next 50 million years (Charles E.Backus, 1976). By using the largest and green energy sources from the sunlight to replace the traditional power sources like fossil fuel and nuclear not only will saving cost and also will make our earth clean.
The solar pond is using salty water to collect solar radiation not only will produce energy and also saving the aquatic life inside the lake. A saline lake will keep evaporation and the lake water will become toxic to the aquatic life (Jeffrey Gordan, 2005). The byproduct of the solar pond energy like hot water and salt also will fully using in other field. Solar pond not only will generate electricity and also will maintain the balance of the environment. The purpose of this research is to study about the technology of the solar pond apply on the industry.
The solar saline pond is the simplest type of flat-plate collector, combining both of the collection and the thermal storage subsystems. This idea is developed by Bloch (1948) and Tabor et al (1959). The solar saline pond is based upon the observation by a scientist name A.V. Kalecsinsky (1940) that natural saline lakes can have a steep temperature gradient with depth (Aden B. M And Marjorie P. M, 1976). A series of fundamental research about the solar pond was set up in Israel by Tabor and he success to create a mechanism underlying solar ponds. But his research was set back in 1996 because the cost of solar pond was expensive than the fuel oil. After the rise of oil price at 1970s, several countries start to review his propose to development and research widely (Tabor, 1981).
What is Solar Pond?
Solar pond is a salinity gradient pond which collects the heat from the sun light. The heat that collected will be converted into the electricity. Solar pond can represent in many different forms like salt gradient solar pond, solar gel pond or shallow solar pond. All these different types of solar pond are actually only based on one principle, the heat will be trapped in the lowest water level which is high concentrated brine. Thus, the heat is retained in the depth.
Solar pond is divided into 3 layers as shown as figure 1. The top layer is called as upper convective zone. It does not retain any heat but it function as absorbing the solar radiation. The second layer is called as non-convective zone. This layer absorbs the solar energy and also acting as an insulator for prevents heat loss from bottom layer. The bottom layer is called as lower convective zone. Its function is to store the heat and it is belong to the densest salt concentration part. This layer is where all the hot water is locate and heat exchanger converts the heat energy to electric energy. (John A. D & Williama. B, 2006)
Application of Solar Pond
Solar pond can be used in many applications, such as process heating, power generation, water desalination, and refrigeration system (RMIT University, 2010). In the process heating, the solar pond can produce maximum temperature of 90o C. It is useful for industrial for drying agricultural produce, fish, textile process, and space heating. The water desalination also may apply to the solar pond which is very useful in India. It can provide potable drinking water from the desalination of the seawater (Tripod, 2010). It produced through repetitive cycles of evaporation and condensation (Chauhan, 2007). In vapour absorption refrigeration system (VARS), the solar pond act as a cold storage which is good for storing food that are easily to decay, vaccines, and milk.
Where still using Solar Pond
The examples of solar pond are Bhuj which is located at Gujarat, India. It was the first experiment in India. The Bhuj solar pond covering an area of 6000 square meters. It supplying 80000 litres of hot water daily and the water heat reach a record of 99.8o C. They use the hot water for cleaning and washing (Teri, 2010). Besides that, El Paso solar pond is the project that done by the University of Texas at El Paso. It has start since May 1986 and has an area of 3360 square meters (Teri, 2010).
The Usage of Salts
The salt is the main substances for creating a solar pond. It is important which let solar pond be more convenient and cheap. There are various types of candidate salts are suitable use in the solar pond. The first one is the magnesium chloride which is commonly used by almost every solar pond. They are cheap and readily for use because it is the second largest constituent of ocean water (Murthy, 2010). The second one is fertiliser salts like ammonia salts. The characteristic of the fertiliser salts show that it does will also increase the solubility when the temperature of water is increase. The purpose of using fertiliser salts as the solar pond gradient is in case there is the surface runoff, the most of the runoff fertiliser will pump to farm for other uses (Pandey, 2010).
Solar Pond technology
Solar pond technology not only delivers the solar heat but also includes storing the heat. It work at anytime and this let the heat can be taken at any time even there is in the winter season (Greentrust org, 2010). Although there is much benefit which is helping in producing electricity at anytime, but there is some environment effect which is the disadvantages for building a solar pond. The maintenance of water quality and the salt salinity are the problems that need to face by solar pond. When the water turns into cloudy or growing of the microorganisms on the solar pond, it will affect and reduce the solar pond performance.
In summary, solar pond is the new technology resource which is the renewable energy. But it does not give a very big scale to produce power electricity. (John A. D & Williama. B, 2006)
Finding and Discussion
Solar Pond Power Generations
Solar Thermal Power Generation Technology Scan Advanced Technology Group (N.D) concluded the major solar pond power generations are Ein Boqek (Israel), Beith Haââ‚¬â„¢Arava (Israel) and Alice Springs (Australia). Those power generations contain theory of Rankine cycle (Figure 2) which used in heat exchanger and act as evaporator. The power generation can reduce the Global Carbon Dioxide Emission. At the side of cost, the power generations are better carry out than photovoltaic if calculated per kWh.
Desalination System of Solar Pond
Based on Kudish (1991), he said that desalination process can convert brackish and saline water to fresh or drinking water after receiving treatment. Desalination system of solar pond can solve drinking water problem for some countries, such as Singapore, India, and other countries which are all around with sea water. The water is converted by using Solar Pond Multi Effect Distillation (SPMED) system as shown in Figure 3. This system is utilised solar energy to distillate brackish or saline water. It is repetitive cycles of evaporation and condensation even temperature are low from the solar ponds.
Applications of Hot Water
There are many benefits for the agricultural operations by using hot water application from the solar pond. For instance, paddy soaking in parboiling, sugarcane sett treatment, vegetable blanching, washing of cans in dairy industry, domestic hot water consumption and others.
According to the Bhattacharya (1985), he developed a technique, parboiling process, which could reduce many times for soaking process and also less odour associated with traditional method. First, rough rice was soaking in masonry tanks with a constant temperature hot water for 3 days. After that, streamed the drain paddy and also increase the temperature to 70 oC for few hours.
Additional, Sharma el al (1985) found the treat sugarcane setts in hot water before planting will raise the crop free from seed piece diseases. The setts must treat in water with temperature 50oC for 2 hours and also placed it around 4 hours in humid hot air.
When it is a low temperature, solar ponds with great scope also can be function. It is important that always be operation and maintenance so that solar ponds can be properly managed.
Biswas and Goswami (1996) found that hot water could be used for sterilisation and pasteurisation in a dairy plant. They utilised solar pond which average temperature for each day was about 75 oC and 15 million liters hot water had been supplied to dairy plant.
Solar pond can be used to provide heating for community, residential, and commercial purposes. It can provide low-temperature heat for certain industrial and agricultural purposes such as chemical, foods, textile, livestock buildings and others industrial product (Green-trust.org, N.D) as well as being used in preheating applications for industrial processes that require higher temperatures such as dairy industry, fruit, vegetable and grain canning and drying industry (Digtheheat.com, N.D; RMIT University, 2010).
Sokolov and Arbel (1990) used the temperature of the water of the solar pond for the greenhouse heating purpose. The water is chosen as heat transferring during periods of solar radiation. From the upper layer of the pond, the hot water is transferred to greenhouse through a heat exchanger. After that, the water will return to the bottom of solar pond. In another hand, they also studied many about collector materials properties and how to improve the solar pond performance.
By using the heat collected from solar pond through vapour absorption refrigeration system (VARS) Figure 4, can create refrigeration effect which can be used for cold storage products, milk chilling, storage of milk and milk products and also for air-conditioning (D.S. Chauhan, 2007).Â Refrigeration applications have a wide range in a tropical country. Fresh products like agricultural goods and life saving drugs like vaccines can last for longer period of time in cold storage usingÂ solar pond technology and with vapour absorption refrigeration system.
Solar ponds are very availability used as replacement for the non-renewable resource such as nuclear and fossil fuel to generate thermal enegry. Solar ponds can be used for various industry processes to save more electricity cost and more friendly to the environment.
By using the solar pond is considered as a very useful and economically to many industries and agriculture field, but only a few of research and development had been conduct to improve this green energy. The major problem is the precaution to maintain the solar pond system. The salty water or salt crystal will sink at the bottom of the pond and will corrode the soil. So a plastic sheeting is place on the bottom of the pond to separate the salty water and the soil. The material of the plastic sheeting must use high quality plastic to prevent no leakage at bottom. The type of salt use in the solar pond also consider as a main problem to this technology. Different kind of salt will affect the performance of the solar pond like amount of power generate. Another problems is solar pond need a specific location that is not available in all area.
If the solar pond technology rediscover and receive attention by all the country and industry field it will be the most efficiency future energy source.
Solar Pond (John A. D & Williama. B, 2006)
Rankine Cycle system (Solar Thermal Power Generation Technology Scan Advanced Technology Group, N.D)
Solar Pond Desalination (Kumar and Kishore, 1998)
1. Multi stage flash pan 2. Fresh water 3. Brackish water 4.Hot Brine
5. Heat exchanger 6. Cold brine 7. Solar pond 8. Diffuser
Vapour absorption refrigeretion system (D.S. Chauhan, 2007)