Techno-economic optimization of thermosyphonic solar hybrid water heating systems

Abstract

All water heating solar systems can be designed on criteria such as technical performance corresponding to the minimum radiation level and the minimum temperature of the ambient air. The quantity of ultimate importance is the cost of energy delivered, which has to be optimized along with collector area and storage tank capacity by optimal mixing of conventional energy (by electrical heater or boiler) and non-conventional energy by using solar energy collection devices (hybrid energy analysis). Considering this aspect, a simple techno-economic analysis has been developed with the help of a thermal transient model for finding the technical performance of solar energy systems for calculating the percentage of solar energy contribution for a given consumer hot water demand, at a desired temperature for domestic purposes, using a heat exchanger in the collector loop or without a heat exchanger, and for climatic conditions, as in India. A numerical computation has been done for Indian market conditions and climates, as in Delhi. It has been found that the cost of hybrid energy systems is less than for conventional heating systems. The use of an auxiliary heater inside the storage tank results in wastage of energy due to the larger heat loss from the storage tank because the storage tank is always kept at the desired temperature, and hence, the auxiliary energy consumption is higher. It is observed that the use of an auxiliary heater at the load point is economically feasible. In some areas, where the water quality is bad, it is essential to use a heat exchanger in the collector loop with demineralized water. For very cold climates, the use of an antifreeze solution in the collector loop with a heat exchanger and a separate storage tank is recommended. For forced flow water heating systems used for industrial process heat, the cost of useful energy delivered is 15% higher.