The 6000 sq m solar pond in Bhuj supplied totally about 15,000 m3 of hot water to the dairy at an average temperature of 75oC between September 1993 and April 1995. It is estimated that the beneficiary of the project, Kutch Dairy can save over 935 MT of lignite per year if solar pond is utilized to its full capacity. This translates into monetary savings of the order of US$19,000 per annum.
The Bhuj Solar Pond project was conceived as a research and development project to demonstrate the feasibility of using a salt gradient solar pond to deliver industrial process heat in the Indian context. Another major consideration in setting up the pond was to develop an indigenous and cost-effective lining scheme based on locally available materials. Apart from being cost effective, solar ponds can be effectively used for reducing the consumption of fossil fuel and bringing down pollution emission levels.
The construction of 6000 m2 solar pond was started in 1987 at Kutch Dairy, Bhuj as a collaborative effort between Gujarat Energy Development Agency, Gujarat Dairy Development Corporation Limited and Tata Energy Research Institute under the National Solar Pond Programme of the Ministry of Non-conventional Energy Sources.
A salinity gradient solar pond is an integral collection and storage device of solar energy. By virtue of having built in thermal energy storage, it can be used irrespective of time and season. In an ordinary pond or lake, when the sun's rays heat up the water this heated water, being lighter, rises to the surface and loses its heat to the atmosphere. The net result is that the pond water remains at nearly atmospheric temperature. The solar pond technology inhibits this phenomena by dissolving salt into the bottom layer of this pond, making it too heavy to rise to the surface, even when hot. The salt concentration increases with depth, thereby forming a salinity gradient. The sunlight, which reaches the bottom of the pond, remains entrapped there. The useful thermal energy is then withdrawn from the solar pond in the form of hot brine and is used as industrial process heat.
The highlights are as follows: •
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Establishment of first large scale pond in industrial environment, to cater to actual userdemands. Demonstrated successfully, for the first time in India, the use of solar pond for supplying process heat to an actual industrial user.
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Culmination of laboratory scale testing. Beginning could now be made for commercial exploitation of technology. Created an awareness and interest among the industries with potential for utilizing thermal energy supplied by solar pond.
TERI carried out execution, operation and maintenance of Bhuj solar pond. After its start-up in September 1993, hot water supply to the dairy continued till April 1995. The hot water supply was resumed in August 1996 and in April 1997, the solar pond was handed over to the dairy. An inexpensive lining scheme, consisting of alternating layers of clay and LDPE combination was used for lining the pond. To take care of wind induced disturbances (Bhuj is a windy area with an annual wind speed of over 3.6 m/sec) especially developed Israeli nets were substituted successfully by wave suppressors made of locally available HDPE nets. The salt dissolution process was expedited by means of a system comprising a mixing pond with a mechanical agitator, settling tank and a sand bed filter. This process enabled simultaneous chemical treatment & clarification of brine. Instead of establishing a linear salinity gradient, a non-linear gradient was established in Bhuj Solar Pond, using an injection diffuser which was installed at one end of the pond, the other end being 100 m away. Maximum pond temperature (under stagnation) of 99.8oC was attained in May 1991, leading to development of sudden leakage in the pond. However, even at such high temperatures, the salinity gradient remained stable. It took nearly two years to analyze the problem and re-establish the pond with an improved lining scheme. The improvements in the lining scheme consisted of (i) increase in thickness of clay lining, (ii) membrane liner made of LLDPE & LDPE, and (iii) overlapped joints instead of heat-sealed joints of membrane strips. Since brine transparency is one of the crucial factors as far as thermal behavior of pond is concerned, several steps were taken to maintain it at an optimal level. These included surface skimming, flocculation of suspended particles and algae control through addition of hydrochloric acid and copper sulphate. The heat extraction system consisted of brine suction and discharge diffusers, brine pump, associated piping, controls and instrumentation. Both, suction and discharge diffusers were installed on the same side of the pond. Keeping in view the problem of fouling, a shell and tube type heat exchanger was chosen. Brine was on the tube side, made of cupro-nickle. The pond dissolution of 3500 MT salt within two & half month with is capable of delivering 80000 liters of hot water daily, at 70o C or above. The total cost of construction of the Bhuj Solar Pond was US$90,000 (1997 prices), including heat exchanger and piping etc. This corresponds to a unit cost of $15/m2 of the pond area as compared to $30/m2 of the Beth `ha Arava (Israel) solar pond in 1984. This shows the definite outcome of the research and development efforts in this field. The savings resulting in substitution of lignite with the pond amount to around US$19,000 per annum. Further improvements, especially on the lining method, are expected to reduce the costs even more.
Thus, the simple payback period works out to be less than 5 years without any subsidy or tax incentives. The economics becomes still more attractive if the fuel replaced is not lignite but either oil or coal.
This project succeeded in generating interest among the potential users through actual demonstration, business meet and one-to-one interaction with the decision-makers. Thus, the leading industrial houses like DCW Ltd. (for their Tuticurin plant), Ballarpur Industries Ltd. (for their Bromine recovery plant in Great Rann of Kutch), Excel Industries Ltd . (for their Marine chemicals project in Great Rann of Kutch, near Khavda); Gujarat Heavy Chemicals Ltd . and Sanghi Industries Ltd. (for their Cement Division at Narayan Sarovar, Kutch) etc. evinced keen interest in this technology. Not only that, even the Gujarat Government and the Indian Army too were interested in establishing solar pond water desalination systems to meet drinking water requirements of the interior villages and troops, respectively, all along the Great Rann of Kutch.
! The crucial factors that affect the economic viability of solar ponds include the abundance of inexpensive salt and level land. Thus, it makes economic sense to locate the pond near an inexpensive salt supply, such as salt works, coastal regions, near the source of bittern and natural salt and within an industry that produces brine/bittern as a by-product. When these requirements or inputs are matched with the deliverables of a pond, the following niche areas emerge where this technology can be applied most gainfully: -
Process heating Water desalination Refrigeration Production of Magnesium Chloride and other marine chemicals. Bromine recovery from the bittern Enhancement of the salt yield in the salt farms
Solar ponds located in arid regions where abundant brackish water is available, may be excellent sources of energy for water desalination. There are two reasons for this, first, the solar pond can provide the thermal energy required for the process and second, the pond can be a repository for the concentrated waste brine, disposal of which often prove to be a difficult problem, particularly with anti-pollution laws becoming stricter every day. Apart from industrial applications, solar pond desalination systems can also be employed to solve drinking water problems in areas where fresh water is scarce. The Bhuj Solar Pond, which was dedicated to the nation in May 1994 by then Union Minister for Non-conventional Energy Sources, has demonstrated for the first time in the country, the supply of industrial process heat to an actual user. Thus, a stage has been set from where commercial exploitation of this potential technology could be embarked upon.
BHUJ SOLAR POND
A 6000 m2 solar pond has been constructed at Bhuj, Kutch in a milk-processing dairy. The project, with a total outlay of Rs.8.73 million, sponsored by the Ministry of No n-conventional Energy Sources as a National Project, was a joint venture among Tata Energy Research Institute, Gujarat Energy Development Agency and Gujarat Dairy Development Corporation Ltd. Highlights:
Establishment of first large-scale pond in industrial environment, to cater to actual userdemands. Demonstrated successfully, for the first time in India, the use of solar pond for supplying process heat to an actual industrial user. Completely indigenously developed, cost-effective lining scheme, based on locally available materials. Attained a record temperature of 99.8oC under stagnation. Culmination of laboratory scale testing. Paved way for commercial exploitation of technology. Created an awareness and interest among the industries having potential for utilising thermal energy supplied by solar pond. Achieved design capacity of supplying 80,000 litres of hot water per day to the dairy at 70oC or above. Over 20 million litres of hot water supplied to the dairy between September 1993 and March 1997. The savings to the dairy to the tune of about 935 MT of lignite per year at full capacity utilisation of solar pond. Thus, the simple payback period works out to be less than 5 years without any subsidy or tax incentives.
Niche Applications
A major portion of industrial energy consumption is in the form of thermal energy. Solar pond technology is an alternative that offers various cost-effective end-uses without endangering the environment. The following are the niche applications of solar pond technology:
Process heating Water desalination Refrigeration Production of Magnesium Chloride Bromine recovery from the bittern Enhancement of the salt yield in the salt farms, etc.
" 1. Amit Kumar and Kishore V V N. 1989. Solar Pond Project at Kutch Dairy. Int. Solar Pond Letters, Vol. 3(1) 2. Rao K S, Motiani M, Kishore V V N, Kumar A, Rao K S, and Pawar P R. 1990. Setting Up of Salt Gradient Solar Pond For a Dairy Plant - Phase I. Rao K S, Kishore V V N, Vaja D (Eds.), Solar Pond, GEDA 3. Motiani M, Kumar A, Kishore V V N, and Rao K S. 1990. Constructional Details of a 6000 sq.m. Solar Pond at Kutch Dairy, Bhuj. 2nd International Conference on Progress in Solar Ponds, Rome, Italy 4. Motiani M, Kumar A, Kishore V V N, and (late) Rao K S. 1993. One Year Performance of 6000 sq.m. Solar Pond at Bhuj. 3rd International Conference on Progress in Solar Ponds, El Paso, Texas, USA 5. Amit Kumar, Bhatt R N, and Kishore V V N. 1993. Operation of a 6000 sq.m. Solar Pond for Supplying Process Heat to a Dairy Plant at Bhuj. National Solar Energy Convention, Baroda 6. Amit Kumar and Kishore V V N. 1994. Construction and Operation of a 6000 sq.m. Salt Gradient Solar Pond for Process Heat Application. Salt Research and Iodisation Meet. Regional Research Laboratory. Bhubaneswar. 7. 8.Kishore V V N, and Kumar A. 1996. Solar Pond: An exercise in development of indigenous technology at Kutch, India. Energy for Sustainable Development, Vol. 3(1). 8. Amit Kumar and V V N Kishore. 1998. Utilization of solar pond technology in industry. In Proceedings of National Solar Energy Convention. November 30-December 2. Roorkee. 9.
Amit Kumar and V V N Kishore. 1999. Construction and operational experience of a 2 6000 m solar pond at Kutch, India. Solar Energy Vol 65 (4). pp 237-249.
10.
Amit Kumar and V V N Kishore. 1999. Development of a large solar pond for a dairy plant in India. SunWorld. Vol 23 (1). pp 23-24.
