Accepted Papers - 3.pdf - UNESCO

Figure 1a. Schematic diagram of solar pond
Figure 1b. Energy extraction through solar pond
radiation into heat, but the heat is quickly lost through
convection in the pond and evaporation from the
surface. These are large-scale energy collectors with
integral heat storage for supplying thermal energy.
It can be use for various applications, such as process
heating, water desalination, refrigeration, drying and
Figure 2. Various temperature zones of a solar pond
375
power generation.
A solar pond has three zones. The top zone is
the surface zone, or UCZ (Upper Convective Zone),
which is at atmospheric temperature and has little
salt content. The bottom zone is very hot, 70°– 85°
C, and is very salty. It is this zone that collects and
stores solar energy in the form of heat, and is,
therefore, known as the storage zone or LCZ (Lower
Convective Zone). Separating these two zones is the
important gradient zone or NCZ (Non-Convective
Zone). Here the salt content increases as depth
increases, thereby creating a salinity or density
gradient. If we consider a particular layer in this
zone, water of that layer cannot rise, as the layer of
water above has less salt content and is, therefore,
lighter. Similarly, the water from this layer cannot
fall as the water layer below has a higher salt content
and is, therefore, heavier. This gradient zone acts as
a transparent insulator permitting sunlight to reach
the bottom zone but also entrapping it there. The
trapped (solar) energy is then withdrawn from the
pond in the form of hot brine from the storage zone.
4.1 Convective Solar Pond
The convective solar pond reduces heat loss
by being covered by a transparent membrane or
glazing. One type of solar pond uses a plastic tube
filled with water. Each pond module includes a long
narrow plastic bag measuring container water 5-10
cm deep. The bag has a transparent top to allow
transmission of sunlight and to prevent evaporation
losses. The bottom of bag is black to absorb sunlight.
An insulation layer is provided beneath the plastic
bag to minimize heat losses to the ground. One or
two layers may be arched over the bag of water to
suppress convective and radiative losses. In this type