Reflecting bottom solar pond

Abstract

This communication presents an investigation of a three zone solar pond with a diffusely reflecting bottom. The dynamic performance and its optimization as a large scale solar energy collection and long term storage system have been discussed. Numerical computations, corresponding to the data of solar radiation and ambient air temperature of New Delhi during 1974, have been made for two modes of operation, viz (i) constant flow rate of heat removal fluid, and (ii) zone of heat retrieval remaining at constant temperature. At a typical flow rate of 10 −3kg/m 2s, optimal heat retrieval efficiencies of 32.4% (at non-convective zone depth, l 2, of 1.25 m), 25.2% (at l 2 = 0.75 m) and 21.5% (at l12 = 0.6 m) are predicted for bottom reflectivities of 0.0, 0.5 and 0.8, respectively. Furthermore, the variability in flow rate required to keep the temperature of the heat extraction zone constant is less for higher temperatures of the heat extraction zone, and the effect of R is found to be insignificant. In the mode of heat retrieval at constant temperature, the calculations of Sodha et al. [ Energy Res. 5, 321 (1981)] for the case of a completely absorbing surface with no bottom reflection ( α = 1.0, R = 0.0) have yielded the optimal heat retrieval efficiency of 35.5 and 26.5% at extraction temperatures of 40 and 100°C, respectively. However, for the realistic case of a partially absorbing bottom ( α = 0.9 and R = 0.0), these efficiencies are predicted to go down to 32.5 and 23.5%, respectively. The effect of bottom reflectivity on heat collection efficiency has further revealed the fact that the heat collection efficiency decreases with an increase in bottom reflectivity. For a typical value of R(= 0.6) corresponding to the realistic case of a partially absorbing bottom ( α = 0.9), optimum efficiencies decrease further to 22.3 and 12.4% at collection temperatures of 40 and 100°C, respectively.