Section 9A. An electric company may, in its agreement of association or, in case of a company already organized, at any time and from time to time, by vote of two thirds in amount of all its stockholders at a meeting duly called for the purpose, state that it is organized for, or that thereafter its corporate purpose shall be, the generating and buying of electricity and the transmitting and selling of the same to two or more corporations specified in said agreement or vote as engaged in the electric light or electric power business, or both, in this commonwealth or adjoining states, including other purposes incidental thereto. Upon the approval of said statement by the department, such company shall be limited, in respect to its rights and obligations to transmit and sell electricity, to such transmission and sale as are authorized by this section. Such electric company shall have authority to transmit electricity to or for and to sell electricity to such of the corporations specified as aforesaid as are stockholders of said company, upon such terms as the department shall approve. Such electric company shall also have authority to transmit electricity to or for and to sell electricity to other corporations, municipal electric departments and other entities, engaged in the electric light or electric power business, or both, within or outside this commonwealth, provided that any such sale of electricity for delivery within this commonwealth shall be made upon such terms as the department, on application of such electric company, shall approve. With the consent of the department and to such extent and upon such terms as it may approve, any corporation specified as aforesaid may subscribe for, acquire, own and dispose of stock, bonds or other securities of such electric company, and may, with the consent of the department and upon such terms as it may prescribe, and in compliance with all provisions of law relative thereto, issue and sell its own stock, bonds or other securities to obtain the capital necessary to acquire the same.