You have to design a thermal system for the storage of thermal energy using an underground tank of water. The tank is buried with its top surface at a depth of 2.5 \(\mathrm{m}\). It is a cube of \(1.5 \mathrm{~m}\) on each side. The water in the tank is heated by circulating water through a solar energy collection system. The heat input to the water is due to the solar energy flux. Characterize the design problem in terms of the fixed quantities and design variables.