Public utilities are authorized to contract for the sale, on an interruptible basis, of utility services at agreed prices for a definite term not to exceed twenty-five (25) years with customers whose use of the service is for manufacturing, generation, processing, preparation of products, or industrial purposes. However, the contracts shall be subject to approval by the Arkansas Public Service Commission before becoming effective. These contracts, after approval by the commission, shall continue in full force and effect for the term thereof.