(a) In determining the allocation of tax savings derived from liberalized depreciation and amortization, the investment tax credit, and the application of similar methods, the commission shall:
(1) balance equitably the interests of present and future customers; and
(2) apportion accordingly the benefits between consumers and the public utility.
(b) If a public utility retains a portion of the investment tax credit, that portion shall be deducted from the original cost of the facilities or other addition to the rate base to which the credit applied to the extent allowed by the Internal Revenue Code.