Excess capacity or output of a project not then required by any of the members of a joint authority shall be first offered for sale or exchange pursuant to section 70-626.01. Any sale of available capacity and energy from the joint authority's project shall only be for the period required for the joint authority to fully utilize the amount of capacity and energy originally purchased in the project. The limitations provided in this section shall not apply to the temporary sale of excess capacity and energy without the state in cases of emergency or when required to fulfill obligations under any pooling or reserve-sharing agreements, except that sales of excess capacity or output of a project to electric cooperatives, electric or public utilities, and other persons, the interest on whose securities and other obligations is not exempt from taxation by the federal government, shall not be made in such amounts, for such periods of time, and under such terms and conditions as will cause the interest on bonds issued to finance the cost of a project to become taxable by the federal government. This section shall not apply to sales of ethanol or hydrogen.