Optimization of solar thermal systems with a thermocline storage tank

The solar thermal-based hot water system has established itself as one of the prominent options to achieve sustainable energy systems. Optimization of the solar water-heating system focuses mainly on two major decision variables, the solar collector area and the storage tank volume, and leads to a significant reduction in the capital investment. In conventional design practice, a well-mixed storage tank is considered for storing the heat. A thermocline tank offers benefits like the uniformity of the output temperature and reduction in thermal losses from the solar collector, through the establishment of thermal stratification. A holistic approach to optimize the overall system is missing in the literature. A methodology is proposed in this paper to optimize the solar water-heating systems, incorporating a thermocline storage tank, with the application of the design space framework. The design space was proposed initially to design and optimize energy systems as it helps in identifying different design constraints through a graphical representation. The design space, graphically represented on a storage volume versus collector area diagram, incorporates variations of the thermocline zone with the change in solar irradiation, thermal load, and other system-level constraints. The effects of various system parameters on system design through sensitivity analysis are also studied. It is observed that the solar collector area requirement and the overall capital investment can be reduced by 57% and 28%, by optimally integrating a thermocline tank. [GRAPHICS] .