solar pond type

1. Solar pond
What is a Solar Pond A solar pond is a large-area collector of solar energy resembling a
pond that stores heat, which is then available to use for practical purposes, Researched
designs include saltwater ponds, gel ponds, and others such as shallow ponds with covers,
deep ponds with glass or plastic containment devices. Their common features are to store the
energy in the incoming solar radiation in the heated depths of the pond, and to suppress the
convection currents that would otherwise lead to heat loss to the surroundings. The most
common form of solar pond is a salt-water solar pond. Salt water ponds exist naturally in a
variety of locations; the first ponds being discovered in Eastern Europe at the beginning of
the 20th century at a natural Salt Lake in Transylvania. Most of the salt water ponds operated
today, however, are artificial, simulating natural solar ponds but taking advantage of
engineering technologies to advance their operation and application for practical purposes.
Principle of a solar pond in a clear natural pond about 30~ solar radiation reaches a depth of
2 metres. This solar radiation is absorbed at the bottom of the pond. The hotter water at the
bottom becomes lighter and hence rises to the surface. Here it loses heat to the ambient air
and, hence, a natural pond does not attain temperatures much above the ambient. If some
mechanism can be devised to prevent the mixing between the upper and lower layers of a
pond, then the temperatures of the lower layers will be higher than of the upper layers. This
can be achieved in several ways. The simplest method is to make the lower layer denser than
the upper layer by adding salt in the lower layers. The salt used is generally sodium chloride
or magnesium chloride because of their low cost. Ponds using salts to stabilize the lower
layers are called 'salinity gradient ponds'. There are other ways to prevent mixing between the
upper and lower layers. One of them is the use of a transparent honeycomb structure which
traps stagnant air and hence provides good transparency to solar radiation while cutting down
heat loss from the pond.
Designing for an
Application Designing of a
solar pond is to have a
specific application in mind.
This application may be
heating for an industrial,
commercial or agricultural
enterprise. It is in this case
crucial to know whether
water, some other liquid or air
is the medium to be heated.
Also the temperature at which
heat is to be supplied, whether up to say 80°C or as low as 35 or 40°C, is critical information
for the solar pond designer. Alternatively, the application may be electrical power generation

2. or combined heat and power supply. When the desired application is known, the end-use
energy requirements to be supplied by the solar pond can be identified, and the solar pond
designed accordingly. In practice, for example, the characteristics of a solar pond to supply
hot water at say 35°C to an aquaculture facility will be very different from that of a solar
pond to be used to generate electricity where sustained performance at higher temperatures of
80°C or above is essential. Obviously the solar pond must be located as close to its
application as possible.
Types of solar ponds
Solar ponds are primarily grouped into two types: Convective solar ponds
Non-convective solar pond.
Convective solar pond The shallow solar pond and the deep salt less pond are the examples
of convective type.
Shallow solar pond The shallow solar pond uses fresh water and does not need any
addition of salt. They comprise of a black insulation and generally a concrete-made frame
with a plastic tube attached. This plastic tube is filled with fresh water and its black bottom
absorbs as much solar radiation as possible to heat up the water. Mostly, the plastic tube is
covered by another glaze to reduce convection losses to the ambient air.
Saturated solar pond (SSP) These types of pond are saturated with salt at any depth of the
pond. The amount of salt differs simply because of the varying density and the subsequent
higher solubility due to the change in temperature. This implies that by heating up the water
at the bottom of the pond, its solubility increases and the water cannot rise to the surface and
lose its heat content.
Non-convective solar ponds
There are four types of non-convective solar ponds: 1 SGSP, 2 Partitioned solar pond (PSP),
3 Membrane solar pond 4 Polymer gel layers solar pond.
SGSP
The SGSP collects and stores solar energy and its stability is usually maintained by
the salt. The SGSP is a pool of water approximately 1–5m deep, which contains dissolved
salts to create a stable density gradient. There are three layers in a SGSP: upper convective
zone (UCZ), lower convective zone (LCZ) and salinity gradient non-convective zone (NCZ)
in the middle. Incident solar energy is collected and stored, which may be delivered at
temperature near 100°C
PSPs
PSPs use a physical separation of at least the heat storage zone (HSZ) to avoid
interactions with the NCZ, this is so as to increase the temperature in the HSZ and hence
increase the performance of the solar pond. Usually, solar pond faces many complications
such as the biological growth of bacteria and algae, reduced transparency due to dirt and dust
falling into the pond, disturbance of the concentration gradient during heat extraction and
evaporation. The solutions to the biological problem are by adding chemicals, whereas two
transparent partitions can be installed on the top or fairly close to the surface. Polymer gel
layer/viscosity-stabilized solar ponds
(VSSPs)
In this type of pond, a gel is used to make the water thicker which obstructs convection
losses. The necessities for such a gel are relatively high as it should be thick enough to avoid
convection. Also, it must retain its temperature resistance, have a good physical resistance to
withstand precipitation and ensure a satisfying transmittance for solar radiation

3. Membrane-stratified solar pond (MSSP)
MSSP is a non-convective solar pond that uses thin transparent membranes to separate layers
and suppress convection instead of using salt gradient layers. The transparent membrane
thickness has to be small and should have many high transparency films. The weight of water
balances the buoyancy effect in order to convert solar radiation into sensible heat. Three
membrane types were proposed for the MSSP, which are horizontal sheets, vertical tubes and
vertical sheets.
Site Characteristics Sitting of a solar pond assists smooth installation and operability. Many
of the site characteristics for a solar pond are similar to those for location of any artificial
pond. Land that is amenable to forming banks, with soil that is cohesive and either
structurally stable or compactable, within easy access to water and salt or brine supplies, and
environmentally acceptable locations for managing salt recycling or disposal, are the ideal
factors. In addition to geo-environmental considerations, the prevailing weather environment
is also relevant. Locations where the wind is constantly strong would not be as ideal as calm
locations.
 Free draining soil.
 Free salt available
nearby to reduce
costs.
 Easily compactable
soil for structural
stability.
 Low prevailing wind
speeds to minimize
wave-induced mixing
and the depth of the
top mixed zone.
 An environmentally
acceptable disposal
method or recycling
ability for closed-salt
inventory balancing.
 Flat land to minimize
earthmoving
requirements.
 Dry soil for good
thermal insulation.
 Easy access to water
supply for pond
establishment and
surface washing.
 High incident solar
radiation for good
thermal performance.
 Low evaporation to
minimize the need for
make-up water.
 A method to
withdraw heat
readily; and a place
where pond
monitoring and
control system are
locatable.
 A soil with good
cohesion for forming
stable walls (if not
excavating).
 A low amount of
wind-borne debris to
easily maintain
cleanliness.
 A stationary or deep
groundwater table to
minimize heat loss
within the ground.
 Most important some
way in which to use
the heat or power
output usefully.
Desirable characteristics for siting a solar pond
3 Thermal Output and Sizing The thermal performance of a solar pond largely depends on
the nature of the absorption of solar radiation in the layers of the ponds. The water in the
pond needs to be as clear as possible so that the maximum amount of solar radiation reaches

4. the storage zone at the bottom. The more radiation that gets there, the higher the energy
efficiency and operating temperature of the pond will be. In a well- designed and set up solar
pond, upward heat losses from the storage zone are small. The surface area and depth of the
pond determine its operation and performance characteristics.
Submitted by:
Mr. Rajesh Kumar
MSc. Final (EES)
180530180005(28)