Section 5. The organization of a corporation to be formed under this chapter shall be effected in accordance with the requirements of section twelve of chapter one hundred and fifty-six B and section six. A certified statement of the fact of incorporation by the state secretary shall be conclusive evidence of incorporation. Nothing contained in this chapter shall authorize the organization of a combined gas and electric company, unless the department, after notice and a public hearing, shall certify to the state secretary that it deems the public convenience will be promoted thereby.