The annual credit determined with respect to any qualified renewable energy bond is the product of— (A) the applicable credit rate, multiplied by (B) the outstanding face amount of the bond. (3) Applicable credit rate For purposes of paragraph (2), the applicable credit rate is the rate which the Secretary estimates will permit the issuance of qualified renewable energy bonds with a specified maturity or redemption date without discount and without interest cost to the qualified issuer. The applicable credit rate with respect to any qualified renewable energy bond shall be determined as of the first day on which there is a binding, written contract for the sale or exchange of the bond. (4) Special rule for issuance and redemption In the case of a bond which is issued during the 3-month period ending on a credit allowance date, the amount of the credit determined under this subsection with respect to such credit allowance date shall be a ratable portion of the credit otherwise determined based on the portion of the 3-month period during which the bond is outstanding. A similar rule shall apply when the bond is redeemed or matures. (c) Limitation based on amount of tax (1) In general The credit allowed under subsection (a) for any taxable year shall not exceed the excess of— (A) the sum of the regular tax liability (as defined in section 26(b)) plus the tax imposed by section 55, over (B) the sum of the credits allowable under this part (other than subpart C and this subpart). (2) Carryover of unused credit If the credit allowable under subsection (a) exceeds the limitation imposed by paragraph (1) for such taxable year, such excess shall be carried to the succeeding taxable year and added to the credit allowable under subsection (a) for such taxable year (determined before the application of paragraph (1) for such succeeding taxable year). (d) Qualified renewable energy bonds For purposes of this subpart— (1) In general The term qualified renewable energy bonds means any bond issued as part of an issue if— (A)