From time to time, and at least at the close of each fiscal year, the Secretary shall pay from the fund into the Treasury as miscellaneous receipts interest on the value as determined by the Secretary, with the approval of the Comptroller General, of the Government’s equity transferred to the fund pursuant to the first sentence of this subsection plus the cumulative amount of appropriations made available after enactment of this provision as capital and for administration of the programs financed from the fund, less the average undisbursed cash balance in the fund during the year. The rate of such interest shall be determined by the Secretary of the Treasury, taking into consideration the current average yield on outstanding marketable obligations of the United States with remaining periods to maturity comparable to the average maturities of loans made or insured from the fund, adjusted to the nearest one-eighth of 1 per centum. Interest payments may be deferred with the approval of the Secretary of the Treasury, but any interest payments so deferred shall themselves bear interest. If at any time the Secretary determines that moneys in the fund exceed present and any reasonably prospective future requirements of the fund, such excess may be transferred to the general fund of the Treasury.