Several techniques have been proposed for storing collected solar energy. A study was undertaken to investigate energy losses to the soil surrounding a below grade solar energy storage pond. A three dimensional finite element model was developed to approximate the solution of the differential equation of heat transfer. The Crank-Nicholson central difference scheme was used to solve for the time derivative. Four small ponds were constructed at the VPI & SU Swine Center, Blacksburg, Virginia, to study the effect of insulation on heat losses from a warmed water pond. The water in each pond was warmed with an electric resistance immersion heater. The power consumed by each heater was metered. The uninsulated (control) pond was more thoroughly instrumented with thermocouples than were the other three ponds. These thermocouples provided data that were used as input to the computer model as well as data to verify the model. Based on the conditions under which the model was tested, energy losses to the soil from an uninsulated pond were on the order of 26.H-31-7 MJ/day (25-30 k BTU/day). By providing insulation to the ground surface and to a depth of 0.66 m (2 ft) at a distance of 0.33 m (1 ft) from the pond edge, energy loss to the soil was reduced to about 33 percent of the uninsulated case. Insulation of the pond sides and bottom resulted in energy losses that were about 16 percent of those for the uninsulated pond. / Ph. D.