Section 94A. No gas or electric company shall hereafter enter into a contract for the purchase of gas or electricity covering a period in excess of one year without the approval of the department, unless such contract contains a provision subjecting the price to be paid thereunder for gas or electricity to review and determination by the department in any proceeding brought under section ninety-three or ninety-four; provided, that nothing herein contained shall be construed as affecting a contract for the purchase of gas or electricity from a person or corporation engaged in manufacturing, where the manufacture, sale or distribution of gas or electricity by such person or corporation is a minor portion of his or its business, and which contract is made in connection with a contract to supply such person or corporation with gas or electricity, or as affecting a contract for the purchase of electricity from an alternative energy producer. In any such proceeding the department may review and determine the price to be thereafter paid for gas or electricity under a contract containing said provision for review. Any contract covering a period in excess of one year subject to approval as aforesaid, and which is not so approved or which does not contain said provision for review, shall be null and void. The department is authorized to exempt any electric or generation company from any or all of the provisions of this section upon a determination by the department, after notice and a hearing, that an alternative process or incentive mechanism is in the public interest.