Beginning with the tax year 1965, after the payment of all necessary operating expenses and all annual debt requirements on bonds, notes or other obligations at any time outstanding and the discharge of all obligations arising under finance agreements and indentures or other instruments under which bonds or obligations have been or may be issued, and after payment into the general fund of the State the sum of at least two hundred twenty-five thousand dollars annually, the South Carolina Public Service Authority shall pay annually to the counties of Orangeburg, Calhoun, Sumter, Clarendon, Berkeley, Horry and Georgetown and school districts therein additional sums of money in lieu of taxes on lands acquired prior to the year 1950 for reservoirs, lakes, canals, structures and adjoining properties of the Santee-Cooper Hydroelectric and Navigation Project in amounts equivalent to that paid in 1964 for sums in lieu of taxes on such lands to the counties and school districts therein. Provided, that all additional sums to be paid under this section shall be used for the support of the public schools within the counties and districts involved.