The exercise of the powers granted by sections 15-120g to 15-120o, inclusive, constitute the performance of an essential governmental function and the authority shall not be required to pay any taxes or assessments upon or in respect of the project, levied by any municipality or political subdivision or special district having taxing powers of the state and the project and the principal and interest of any bonds and notes issued under the provisions of said sections, their transfer and the income therefrom, including revenues derived from the sale thereof, shall at all times be free from taxation of every kind by the state of Connecticut or under its authority, except for estate or succession taxes.