12-06-2012, 04:06 PM
Solar ponds
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Introduction
Formally known as a salinity gradient solar pond, solar ponds are an alternative source of harnessing the suns energy to heat water that can be converted to electricity. This technology is very basic and easy to use with adequate land space and proper design. For residential use, ponds need to be at least 12x12 feet and 3 feet deep and for commercial use ponds must be sized according to their functionality. Solar ponds require lots of sunlight and salt water. The first solar pond was discovered in the early 1900s in Transylvania and was naturally occurring. Following this discovery these ponds were replicated and dubbed solar ponds.
How they work
Solar ponds can be naturally occurring; however, most ponds are man-made. Once the pond is dug, the pond must be lined with an impermeable lining, preferable one that is insulating. Then the pond is filled with salty water. Once the sun hits the pond the water warms and divides into three layers. The top layer, known as the surface zone, is composed of primarily freshwater due to the fact that salt typically settles at the bottom of water. The middle layer is known as the insulation zone. The insulation zone has a higher salt concentration than the surface zone. Crucial to a solar pond is the bottom layer known as the storage zone. The storage zone is where all the hot water is held and this is what is converted into electricity. The hot salt water produced is similar in chemical characteristics to brine.
Using a solar pond
Solar ponds have a number of uses. They are effective for heating facilities such as industrial complexes, greenhouses, and agricultural building. When used for heat, it is hard to regulate the temperature; therefore solar ponds are typically used in situations that the heat temperature does not have to be regulated.
Solar ponds in India:
Table enlist the various solar ponds constructed in India. The first solar pond in India was constructed at Central Salt and Marine Chemicals Research Institute (CSMCRI) in Bhavnagar, Gujarat in 1971. Extensive studies on heat extraction pattern, effect of rainfall on salinity gradient and overall variation of temperature profiles were conducted at Indian Institute of Science, Bangalore in 1984. Another pond of 400 m² areas was constructed at Mysore, Karnataka around 1990 with the purpose of meeting the hot water requirements of a village. A 6000 m² area solar pond was commissioned by Government of India and executed by Gujarat Energy Development Agency (GEDA), Gujarat Dairy Development Corporation Limited (GDDC) and Tata Energy Research Institute (TERI) at Bhuj, Gujarat State.
Scope of Solar Ponds:
The solar ponds are widely considered as the low temperature energy storage devices having use in wide range of process applications. The following section deals with scope of the applications of solar pond heat adopted in various processes.
Greenhouse heating
Sokolov and Arbel demonstrated the use of fresh water solar pond for greenhouse heating purpose. The pond comprised an excavation in the earth with liner and a thin top cover. The water was used as a heat transferring fluid during periods of solar radiation. Energy was delivered to the greenhouse by pumping hot water from the upper layer of the pond through a heat exchanger. The water returned after heat extraction to the bottom of solar pond. In another study, Arbel and Sokolov studied different collector materials having different material properties and concluded that the use of appropriate material improves the solar pond performance.