In a sensible storage system, energy is stored based on the distribution of energy and exergy at the specified conditions. It is believed that the least temperature gradient leads to a higher exergy availability and lower entropy generation in a storage system. An energy storage unit with multiple passages fitted with wire coil inserts is evaluated in the present work by assessing the exergy stored and the entropy generation number for heat transfer fluid (HTF) inlet temperature range of 45–75 °C and HTF flowrate of 0.022–0.029 kg/s. The wire coil inserts have a (p/d) ratio in the range of 0.25–0.75. The maximum exergy storage rate in the energy storage unit is found to be 55.43 W corresponding to an energy storage unit having wire coil insert (p/d = 0.25) at the HTF inlet temperature of 75 °C and HTF flowrate of 0.029 kg/s. Entropy generation number of the system with wire coil inserts (p/d = 0.5), compared to smooth HTF passage, is found to be 42.32% at HTF flowrate and inlet temperature of 0.026 kg/s and 45 °C, respectively.