Proceeds of the bonds issued under authority of this chapter shall be used solely for the payment of the costs of a project or combined projects, and any other corporate purposes of the authority, and shall be disbursed upon requisition or order of the persons and under such restrictions as the resolution authorizing the issuance of the bonds or the trust agreement or indenture may provide. If the proceeds of the bonds of any issue shall exceed the amount required for the purpose for which the bonds are issued, the surplus shall be paid into the fund provided for the payment of principal of and interest on the bonds. In the discretion of the authority, bonds of a single issue or series of any issue may be issued for the purpose of paying the costs of any one or more projects, including a combination of projects.