In the present study, an attempt was made to evaluate the performance of a solar and wind aided cross-flow evaporator prototype as an alternative to conventional evaporators for concentrating reverse osmosis (RO) rejects. The performance of the solar and wind aided cross-flow evaporator was evaluated for different operating conditions such as (i) wind velocity, (ii) relative humidity in the ambient air, (iii) temperature of inlet water, (iv) trickling rate and (v) different packing geometries. Empirical correlations for evaporation loss were developed, as a function of the above variables. Among the various synthetic and natural media tried, plastic flexi ring was the most effective. Solar and wind aided cross-flow evaporator with random packing performed better than that with structured packing, as long as the air flow is not blocked by the packing. Studies revealed that the exposed surface area and depth of packing in the direction of wind are the important dimensions of the natural evaporator. It was also found that solar pre heating significantly increased the evaporation rate. Evaporation rate decreased as the concentration of salt in the water increased. (C) 2013 Elsevier B.V. All rights reserved.