A salt gradient solar pond offers an economical means of both collecting summer solar heat, and storing it in water over periods of a few months for use in winter space heating. The vertical gradient of salt density prevents convection in the pond and makes it self-insulating against heat losses. The solar pond project at the university of Sussex aimed to study the design, construction, filling, and operation of a salt gradient solar pond, and to develop inexpensive instrumentation for the harsh environment of hot salt water solution, for monitoring behaviour and performance. A new method of heat extraction, from both the insulation and storage layers of the pond, was tested, and a computer program was developed to model pond behaviour under non-steady techniques. Construction, filling, and operation of indoor and state conditions, using finite difference outdoor pilot solar ponds is described and a simple means of maintaining salt density gradient, as well as work on achieving good pond transparency over the two-year period of operation of the pond. To improve the efficiency of the pond successful experiments were carried out to extract heat from both the convecting storage layer and the non-convecting insulation layer of the pond. This permits interception and extraction of heat flow in the non-convecting layer which would otherwise be lost to the surface. Laboratory and outdoor exper iments were car ried out to test whether this causes unwanted convective mixing and increased upward diffusion of salt in the non-convective zone of the pond. Heat transfer coefficients were measured with the heat exchanger placed in the non-convecting insulation layer. Both steady-state and finite difference model calculations are presented to indicate the improvements in operating efficiency and temperatures that are achievable with the new method of heat extraction. Theoretical results from the finite difference model are in good agreement with observed performance.