Solar Thermal Technologies In India
Posted July 8, 2008on:
Solar thermal technologies have a special relevance in India due to high availability of resource, average radiation is 4.5 – 6 kwh/m2/day with average 280 clear days. In view of the increasing energy demand in all the sectors there is immense potential especially in domestic and industrial sector to meet thermal energy demands.
Solar concentrating collector systems for process heating
The solar thermal systems which use concentrating collectors can deliver thermal energy at a higher temperature compared with solar flat plate collectors used in solar water heating systems. Major portion of thermal energy requirements in the Indian industrial sector lies in the temperature range of 100-250 0C which corresponds to the medium temperature range of solar thermal systems. Solar concentrating systems are best suited for such medium-grade thermal applications. Solar thermal energy has a number of attractive features, which make it a very desirable energy source. As far as the proposed technology is concerned, it is still in conceptual stage in India. Under the renewable energy policy has set the goal of installing 1000 systems of 10 ton/day steam generation capacity by year 2012.
Solar thermal power generation
A 50 kW capacity solar thermal power generation plant was installed at Solar Energy Centre, Gualpahari, Harayana, India in 1989. This plant is operating at a de-rated capacity presently. A 140-MW integrated solar combined cycle (ISCC) power plant is planned at Mathania near Jodhpur in the state of Rajasthan. The capacity of solaralone plant is 35 MW and balance 105 MW is based on naptha. The Rajasthan State Power Corporation Ltd. (RSEB), a recently established concern wholly owned by the state government, will implement the project. The world Bank/GEF had agreed to provide a grant of US $49 million while Government of Germany, through KfW, had agreed to provide composite loan of DM 250 million.
Salt-gradient solar ponds (low -cost solar collectors with integral storage) are both appropriate and relevant in the Indian context. In India, though solar pond research dates back to 1971, none of these ponds were connected to any end-use. The 6000 m2 Bhuj solar pond at the Kachch Dairy, Bhuj, was conceived as an R&D project to demonstrate the feasibility of using a salt-gradient solar pond to deliver industrial process heat. The construction of this pond was started in 1987 as a collaborative effort among Gujarat Energy Development Agency, Gujarat Dairy Development Corporation Limited, and TERI. The Bhuj solar pond started supplying hot water to the dairy in September 1993, saving about 935 MT of lignite a year, at full capacity utilization of the solar pond.
The economic viability of a salinity-gradient solar pond is governed by factors such as its size, proximity to sources of inexpensive salt/bittern and water, and land availability. The following niche areas have been identified after careful matching of these requirements with the deliverables: (1) process heating, (2) water desalination, (3) refrigeration, (4) production of magnesium chloride, (5) bromine recovery from the bittern, and (6) enhancement of the salt yield in the salt farms, etc.
The simplest device for desalination using solar energy is solar still. To increase the efficiency various other techniques are also tried, multi-effect desalination is one of the possible solutions.
Solar still imitates a part of the natural hydrologic cycle in that the saline water is heated by the sun’s rays so that the production of water vapor (humidification) increases. The water vapor is then condensed on a cool surface, and the condensate collected as product water. Thus, solar stills are ideal to provide safe drinking water to isolated communities of small villages, islands, lighthouses and salt works. In solar stills plant the only moving part is the pump, to pump saline water from the well. These units can be constructed in modular form and provide a viable option of providing potable water for a single house or a group of families also.
The Central Salt & Marine Chemicals Research Institute (CSMCRI), Bhavnagar initiated research on solar stills in India in 1965. CSMCRI was the first organization to install large capacity solar stills in villages, lighthouses and island to supply drinking water. Apart from CSMCRI, other institutions, such as Bhabha Atomic Research Center (BARC), Bombay and Indian Institute of Technology (IIT), Delhi etc., too have been involved in this field. Solar still plants of capacity varying from 130m3/day to 8000m3/day of distilled water output were installed at various places in the period of 1965 to1983.
Apart from the basin type of solar still other designs of solar still were also tried to increases the efficiency e.g. active solar still coupled with flat plate collector, double basin solar still etc. To further increase the efficiency multiple effect desalination systems are also under development
Solar detoxification process involves the absorption of photons on the surface of a semiconductor, which acts as a catalyst and produces reactive radicals, mainly hydroxyl radicals. These radicals can oxidize organic compounds and completely mineralize them. Only photons with energy equal to or more than band gap of the semiconductor are absorbed on its surface. The energy needed to activate the semiconductor catalyst recommended for the solar detoxification process corresponds to UV component of the solar radiation.
Solar detoxification technology has shown great promise for treatment of toxic compounds in waste water and ground water. The major advantage of this technology is its ability to completely mineralize the organic chlorinated compounds into CO2 and HCl instead of transferring it from liquid stream to gaseous stream in carbon adsorption technology or incineration. Partial combustion during incineration some time results in the formation of compounds which are more toxic than the original compounds.