A system is provided to recover unutilized energy as electric power in hydraulic turbine power generation. The system includes a heat storage tank, a pump for pumping water from the heat storage tank and to air conditioning loads, a first water feed pipe connected between an outlet of the storage pump and the air conditioning loads, and a second water feed pipe for returning the water discharged from the air-conditioning loads. A hydraulic turbine driven generator is provided on a lower portion of the second water feed pipe at such a position as to recover the potential energy of the water discharged from the air conditioning loads.