The system being considered is the one dimensional heat transfer problem through a parallel piped whose base is a unit surface area of the pond, and its height is the depth of the pond. To obtain better results from the model developed, it is more convenient to address each zone in respect to the boundary conditions. For this purpose, the pond is considered to have three zone, as in Fig 3. The UCZ and LCZ are considered as single grid points which have a thickness of Z0 and ZA, respectively. The total depth of the pond is Z. Conservation of energy is then applied on each zone. For NCZ, the energy equation ca be written as follow;

For LCZ, the energy equation is also written as follow;

dT

PCpADL^7 = QR — Qup — Qs — Qg — Ql (2)

dt

By assuming that the pond is well insulted, heat loss around the pond is small comparative with amount of heat extraction. The equation (2), thus, can be written as follow;

AT

Qsolar = Qs + mCp — (3)

From the fact that extracted heat from the solar pond is equal to the heat extracted by thermosyphon. Substitute (3) into (2), we got;

Estimation of solar pond’s heat absorption is expressed by Rubin et al.(1984), the heat from solar radiation of any location can be often.

Where ф is the rate of the solar radiation at any wave length pass though the pond in any depth z, can be obtained.

ф = ф0 n exp(-M z /c°s<92)

J =1

Substitute ф0and constant value from (6) into (5). Therefore, it follows that

4 Mj — p. z/cos# (7)

Ч(А = ф0 ^ exp J

0J=1 cos#

Hence, the calculation of energy balance at LCZ can be obtained from (4).