Two simple formulations for estimation of net available radiation at a depth in solar pond are proposed. The first formulation uses the correlation of Bryant and Colbeck [Solar Energy 19 (1977) 321] and extends the same to incorporate the reflected part of radiation coming from bottom and surface of the pond. The other formulation is an empirical fourth order polynomial function. The universal functions of Hull [Solar Energy 29 (5) (1982) 385] are taken as a base line for comparison of accuracy in estimation of radiation flux. The proposed formulations provide a substantial saving of computational time, much simplicity in analytical calculations, and reasonably good accuracy in estimation of radiation flux at a depth in solar pond. Their impact of these formulations is also analyzed on accuracy in prediction of pond's long-term thermal behavior and gain in terms of computational speed. It provides a 20-25% saving in computational time as compared to Hull's method with comparable accuracy. (C) 2003 Elsevier Ltd. All rights reserved.