The transient thermal characteristics of a solar tank (a shallow solar-pond water heater) with a silica aerogel surface insulation have been examined both experimentally and theoretically. It is found that the temperature drop of the water within the solar tank after sunset can be appreciably suppressed by introducing the aerogel surface insulation system and that the proposed theoretical model can predict sunny-day hourly variations in the hot-water temperature within the solar tank with acceptable accuracy.