AbstractThree types of no‐salt solar ponds, which do not exhibit environmental or operational problems of the kind observed for salt ponds, are examined on a laboratory scale. The negative temperature gradient necessary for heat storage was obtained by using appropriate arrangements in such a way that narrow passages appear which reduce substantially the heated water currents, or by using two (or more) transparent immiscible liquids which constitute a density gradient serving the same purpose. The influence of the dissolved air in the water mass is discusse