1. SOLAR PONDS
By :
Sunil Kumar
CH - 6268

2. CONTENTS
 Introduction
 Description of Solar Ponds
 Methods of maintaining layered structure
 Working of solar ponds
 General Construction features
 Applications
 Hindrances and Remedies

3. NORMAL PONDS
 Normal ponds receive sunlight a part of which is
reflected at the surface, a part is is absorbed and
the remaining is transmitted to the bottom
 Due to this the lower part gets heated up and the
density decreases as a result of which it rises up
and convection currents are set up.
 As a result, the heated water reaches top layer
and looses its heat by convection and
evaporation.

4. SOLAR PONDS
 They are large shallow bodies of water that are
arranged so that the temperature gradient are
reversed from the normal.
 This allows the use for collection and storage of
solar energy which may ,under ideal conditions,
be delivered at temperature 40-50 `C above
normal.

5. Zones of Solar Ponds
A salt-gradient non-convecting solar pond consists
of three zones:
1) UCZ ( Upper Convecting Zone) : top layer
2) NCZ ( Non Convecting Zone) : middle
layer
3) LCZ (Lower Convecting Zone) : bottom
layer

6. Schematic of Solar Ponds

7. Upper Convective Zone
 This is a zone, typically .3 m thick, of almost low salinity
which is almost close to ambient temperature.
 UCZ is the result of evaporation, wind induced mixing,
and surface flushing.
 Usually this layer is kept as thin as possible by use of
wave suppressing mesh or by placing wind breaks near
the ponds.

8. NON CONVECTING ZONE
 In this zone both salanity and temperature
increases with depth.
 The vertical salt gradient in the NCZ inhibits
convection and thus gives the insulation effect.

9. LOWER CONVECTING ZONE
 This is a zone of almost constant, relatively high
salinity ( typically 20 % by weight) at high
temperature.
 Heat is stored in the LCZ, which should be sized
to supply energy continuously throughout the
year.

10. DIFFERENT METHODS OF
MAINTAINING LAYERED
STRUCTURE
1) Maintaining Density Gradient by salt water
2) Use of horizontal and vertical membranes.
3) Polymer gel layers.

11. TYPICALL SALANITY GRADIENT

12. Working of Solar Ponds
Maintenance of salt-gradient
• The concentration gradient that exists in pond lead to diffusion from
higher to lower concentration i.e. from bottom to top.
• Therefore, to maintain stability salt must be added to lower layer
and remove from upper layer.
• Now as the sunlight falls on the pond, the part which is transmitted
to the bottom heats the lower layer and as a result inverse
temperature gradients are set up.

13. INVERSE TEMPERATURE
GRADIENT
 It is the temperature gradients are reversed from
normal i.e. hottest zone is at the bottom of the
pond and coldest zone is at the top.
 They are maintained to eliminate convection
currents that set due to temperature difference
during normal temperature gradient.

14. TYPICAL TEMPERATURE
GRADIENTS

15. GENERAL CONSTRUCTION
FEATURE
 They are 1-3 m deep.
 Constructed on level ground by combination of
excavation and embankments.
 Membrane liners are used to make the basin
leek proof.
 Membranes are covered with clay to protect
them and improve their durability.

16. Continued..
 Since solar ponds are horizontal collectors sites
should be at low to moderate northern latitude
and southern latitude i.e. -40 to +40 degree
latitude.
 Evaluation of geological salt character as
underline earth should be free from stresses,
strains and fissures.
 Thermal conductivity of soil increases with
moisture, so water table of site must be low.

17. APPLICATIONS
 Electric power generation
 Desalination process
 Domestic hot water production
 For space heating & cooling of buildings

18. ELECTRIC POWER
GENERATION

19. DESALINATION

20. MAJOR SALT – GRADIENT SOLAR PONDS (in
India)
Location Area (m2) Depth Main Objectives Achievements
(m)
Bhavnagar 1210 1.2 Operating Max. Temp. 800C in
(India) experience and 1972. Worked for
behaviour of two years.
materials
Bhavnagar 1600 2.3 Operating Getting heated,
(India) experience and designed to supply 20
applications for KW. Rankine cycle
power production. turbines.
Pondicherry 100 2.0 Experience, Built in 1980.
(India) material behaviour,
monitoring &
modeling.
Bhuj 6000 3.0 Operating Supplying process
(India) experience, material heat to a dairy
behaviour and
possible applications

21. PERFORMANCE COMPARISON
A= Curve for flat plate collector
B= Solar pond with 1m depth of LCZ from surface
C= Solar pond with 2m depth of LCZ from surface

22. Cont…
1) Difference in intercept represents additional
radiation absorption by the additional meter of
insulation in the UCZ.
2) Slope of C represents additional meter of
information over LCZ.
3) At high operating point the performance of
solar ponds are better than flat plate
collectors.

23. HINDERANCES
 Cleanliness of pond as contaminants can
reduce transmittance.
 Increase in thickness of UCZ ( Upper
convective zone) due to surface waves and
evaporation.
 Algae growth.
 Horizontal temperature gradient caused by
salt solution removal and addition.

24. REMEDIES
 Contaminants can be removed by filtration and
the effect of contaminants can also be minimized
by constructing larger solar ponds.
 Floating nets and wind barriers can reduce
surface waves and mixing of UCZ.
 Algae growth can be minimized by adding 1.5
mg CuSO4 per liter of water.
 Horizontal temperature gradient can be
minimized by injecting and removing salt
solutions very slowly.

25. REFRENCES
 Tsilingiris 1994
 Angeli et al.2006
 Nielsen 1976
 Solar energy engineering – Soteris Kalogirou
 Solar engineering of thermal processes –
Duffie & Beckman

26. THANK YOU

27. QUERIES
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