PURPOSE: To obtain a solar pond whose absorbing efficiency is high and having no salt water loss from an unconvention layer and effective use of a pool of a transparent fluid as a fish breeding tank or a hot water pool is contrived, by a method wherein unconvection layer is provided above a convection layer of the bottom part, on which the pool of the transparent fluid is arranged through a transparent partition layer.

CONSTITUTION: Energy of insolation S is absorbed partly by a pool 5 of a transparent fluid, a transparent partition layer 4 and unconvection layer 3 and the rest of the same arrives at a convection layer 2 of a solar pond 1. As concentration C of salt of the unconvection layer 3 increases according as a depth becomes deeper and possesses distribution of the concentration which becomes the maximum concentration C1 at a boundary between the convection layer 2, which is the deepest part of the unconvection layer 3, and the unconvection layer 3, a convection is not generated. The convection layer 2, therefore, is turned into a state as if it is covered with a heat insulating layer and solar energy is accumulated as heat. As the unconvection layer 3 does not touch the open air, a disturbance of a concentration gradient of salt close to the surface of the unconvection layer 3 through wind is prevented from occurring and seaweed in both the layers is prevented from growing.