A new type of solar collector was developed and its short term thermal performance was investigated. The solar collector, which exhibited a net solar aperture area of 1.44 m(2), consisted of two adjoining sections one filled with water and the other with a phase change material with a melting and freezing range of about 45-50degreesC, i.e. paraffin wax in this study. The phase change material functioned both as an energy storage material for the stabilisation, theoretically, of the water temperature and as an insulation material due to its low thermal, conductivity value. The results of the study indicated that the water temperature exceeded 55degreesC during a typical day of high solar radiation and it was kept over 30degreesC during the whole night. Covering the collector surface with an insulation blanket at a time when the water temperature was at its maximum improved the energy conservation of the water significantly. The instantaneous thermal efficiency values were between about 22% and 80%. The present solar collector was much advantageous over the traditional solar hot water collectors in Turkey in terms of total system weight and the cost in particular. (C) 2002 Elsevier Science Ltd. All rights reserved.