Energy and exergy analysis of passive solar distillation systems

Abstract

In this communication, a comprehensive thermodynamic model for exergy analysis of a passive solar distillation system is presented. Temperatures of basin-liner, saline water body and inner and outer glass cover are estimated theoretically with the help of a computer program using a set of typical design and operating parameters. Energy and exergy analysis of a single-effect, single-slope horizontal passive solar still has been carried out under climatic conditions of India. It has been shown that the passive solar still can produce 4.17 l/m2 of freshwater daily. Energy and exergy efficiency of the solar still are 30.42 and 4.93%, respectively. Causes, quantity and place of exergy destruction have also been explored for further research and improvement in the design and performance of solar stills. Exergy destruction or irreversibility in the process of each component, i.e. basin-liner, saline water body and glass cover, has been evaluated as 3353, 1633 and 362 W/m2, respectively, corresponding to the total solar exergy input of 6958 W/m2 on a typical day. Their corresponding exergy efficiencies are found to be 3.91, 17.67 and 42.36%. The global exergy efficiency of the solar still is also estimated as 23.14%, taking these exergy destructions into account. The basin-liner is identified as the component around which there is highest possibility of improvement.