Estimation of various heat losses in flat plate solar collectors is important for their thermal performance evaluation under different operating conditions. Upward heat losses have a major contribution in the total heat losses in flat plate collectors (FPC). Equations for estimation of top heat loss coefficient for single and double glazed FPC have already been proposed [1-2]. Top heat loss coefficient is a function of wind heat transfer coefficient. Different forced convection studies [3-6] conducted in indoor and outdoor conditions have been reported for estimation of wind heat transfer coefficient. At sites/locations with very low wind, use of different velocity based correlations [3-6] would give a wrong estimation of wind heat transfer coefficient. In present work wind heat transfer coefficient is estimated by employing an exposed blackened test plate (of size 925mm x 865mm x 2mm) in outdoor conditions. Experiments have been conducted on rooftop of a building in IIT Delhi. Delhi, in general, has low wind throughout the year [9]. From experimental data of test plate, mixed convection effects have been observed at very low wind speeds.