(a) The rates charged by the electric utility on the 185th day after the date the utility files the rate-filing package required by Section 36.153 automatically become temporary rates if:
(1) the 185-day period has been extended under Section 36.154(b); and
(2) the regulatory authority has not issued a final order or established temporary rates for the electric utility on or before the 185th day.
(b) On issuance of a final order, the regulatory authority:
(1) shall require the electric utility to refund to customers or to credit against future bills:
(A) money collected under the temporary rates in excess of the rate finally ordered; and
(B) interest on that money, at the current interest rate as determined by the commission; or
(2) shall authorize the electric utility to surcharge bills to recover:
(A) the amount by which the money collected under the temporary rates is less than the money that would have been collected under the rate finally ordered; and
(B) interest on that amount, at the current interest rate as determined by the commission.