Any municipality is authorized to pay for the construction of a heating plant and system by the issuance and sale of revenue bonds payable solely from the revenue derived from the operation thereof. These bonds shall bear interest at the rate of not to exceed the maximum rate authorized by the Bond Authorization Act, as amended at the time of the making of the contract, payable semi-annually, and shall mature within 20 years from the date thereof.
     With respect to instruments for the payment of money issued under this Section either before, on, or after the effective date of this amendatory Act of 1989, it is and always has been the intention of the General Assembly (i) that the Omnibus Bond Acts are and always have been supplementary grants of power to issue instruments in accordance with the Omnibus Bond Acts, regardless of any provision of this Act that may appear to be or to have been more restrictive than those Acts, (ii) that the provisions of this Section are not a limitation on the supplementary authority granted by the Omnibus Bond Acts, and (iii) that instruments issued under this Section within the supplementary authority granted by the Omnibus Bond Acts are not invalid because of any provision of this Act that may appear to be or to have been more restrictive than those Acts.
     The amendatory Acts of 1971, 1972 and 1973 are not a limit upon any municipality which is a home rule unit.