This document discusses solar ponds, which are pools of saltwater that collect and store solar thermal energy. Solar ponds work by using layers of saltwater with different densities to prevent convection, trapping heat in the bottom layer. There are two main types - non-convecting ponds, which use salt concentration gradients to stop convection, and convecting ponds, which stop evaporation to trap heat. Applications include heating and cooling buildings, industrial process heat, and desalination. The largest operating solar pond is located in Bhuj, India. While solar ponds provide low-cost thermal energy storage, they also have disadvantages like salt maintenance and low conversion efficiency.

1. Solar Ponds
By-
Sakshi Shah
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2. Introduction
• The sun is the largest source of
renewable energy and this energy is
abundantly available in all parts of the
earth. It is in fact one of the best
alternatives to the non-renewable
sources of energy.
• Solar power in India is a fast-developing
industry.
• One way to tap solar energy is using solar
ponds
• A solar pond is a pool of saltwater which
collects and stores solar thermal energy
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3. What is Solar Pond?
• A solar pond is a pool of saltwater which
collects and stores solar thermal energy
• Solar ponds heat water by impeding this
convection.
• Salt is added to the water until the lower
layers of water become completely
saturated. High-salinity water at the
bottom of the pond does not mix readily
with the low-salinity water above it, so
when the bottom layer of water is heated,
convection occurs separately in the
bottom and top layers, with only mild
mixing between the two
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4. Working Principle
• The solar pond works on a very simple principle. It is well-known
that water or air on heating become lighter and rise upward e.g.,
a hot air balloon.
• In the salt-gradient ponds , dissolved salt is used to create layers
of water with different densities the more salt, the denser water
.Thus a solar pond has three zones with the following salinity
with depth :
1) surface convective zone (0.3-0.5m), ,with salinity<5%
concentration
2) Non-convective zone(1-1.5m , salinity increses with
depth
3) storage zone (1.5-2m , salt=20%)
• The Non-convective zone is much thicker and occupies more
than half the depth of the pond. Both the concentration and the
temp increase with the depth in it. It mainly serve as a insulating
layer and reduces the heat transfer.
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5. Pond Construction
• The site selected for the construction of solar pond should have the following attributes:
• be close to the point where thermal energy from the pond will be utilized.
• be close to a source of water for flushing the surface mixed layer of the pond.
• the thermal conductivity of the soil should not be too high;
• The water table should not be too close to the surface.
• The LCZ IS 0.5 m high from the bottom of the pond with high density brine.
• Approximately 0.1 m of fresh water on the top makes the UCZ containing light density brine
• This region performs the insulation, that is, keeps the stored energy in the bottom zone,
called NCZ (0.3m height)
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6. Types of Solar Ponds
1. Non-Convecting:
• reduces heat loss by preventing convection with the addition of a concentration of 20–30 percent
salt to the bottom level (lower convective zone) of the pond
• When saturated with high amounts of salt in the form of concentrated brine, the temperature of
the bottom level rises to about 100 °C (212 °F) as heat from the sun is trapped.
• The middle level (non-convective zone) receives a lower amount of salt than the bottom level.
Because it is lighter than the bottom level but heavier than the top level, the water in the middle
level is unable to rise or sink. The middle level, therefore, halts convection currents and acts as an
insulator, trapping sunlight in the bottom level. In the top level (upper convective zone), where
there is little salt, the water remains cold. Fresh water is added to that level, and saline water is
drained. Finally, heat from the bottom level is transferred to pipes circulating through the pond to
extract thermal energy.
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7. 2. Convecting:
• In contrast to the non-convecting pond, convecting
solar ponds trap heat by stopping evaporation
rather than by stopping convection
• A well-researched example of a convecting pond is
the shallow solar pond. This pond consists of pure
water enclosed in a large bag that allows convection
but hinders evaporation. The bag has a blackened
bottom, has a foam insulation below, and two types
of glazing (sheets of plastic or glass) on top. The sun
heats the water in the bag during the day. At night
the hot water is pumped into a large heat storage
tank to minimize the heat loss. Excessive heat loss
when pumping the hot water to the storage tank
has limited the development of shallow solar ponds.
Types of Solar Ponds
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8. Example of Solar Pond
In India
• The Bhuj Solar Pond is a research,
development, and demonstration
project. The construction of the 6000
m2 pond started in 1987 at Kutch Dairy,
Bhuj
• The solar pond is 100 m long and 60 m
wide and has a depth of 3.5 m.
• This pond has been successfully
supplying processed heat to the dairy
since September 1993, and is, at
present, the largest operating solar
pond in the world
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9. Applications
• Heating and Cooling of Buildings
• Production of Power
• Industrial Process Heat
• Desalination
• Heating animal housing and drying crops on farms
• Heat for biomass conversion
• Refrigeration
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10. Advantages &
Disadvantages
Advantages:
• No need of separate collector
• The extremely large thermal mass means power is generated
night and day.
• Diffused radiation is fully used
• Thermal storage is incorporated into the collector and is of
very low cost
Disadvantages:
• . The accumulating salt crystals must be removed and can be a
valuable by-product and a maintenance expense
• Relatively low-temperature operation means solar energy
conversion is typically less than 2%
• Due to evaporation, non-saline water is constantly required to
maintain salinity gradients.
• Risk of contamination of ground with high salt levels from
water in ponds.
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11. Conclusion
• Solar pond technology has made tremendous progress in the last fifteen years.
• This technology is cost effective for low temperature process heat needs of industry.
• The generation of electricity using solar ponds is not economically viable as yet .However ,
the new concerns regarding the environment and safety of nuclear power plants and
nuclear wastes disposal may change the picture totally
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12. References
• http://oaji.net/articles/2014/786-1398761822.pdf
• http://edugreen.teri.res.in/explore/renew/pond.htm#:~:text=Solar%20ponds
%20are%20large%2Dscale,on%20a%20very%20simple%20principle
• https://en.wikipedia.org/wiki/Solar_pond
• https://www.britannica.com/technology/solar-pond
• https://www.sciencedirect.com/science/article/abs/pii/S1364032111001456
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13. Thank you
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