Section 40. The authority shall have the power to procure electric utility services, including the purchase, generation, transmission, transformation and distribution of the supplies of electricity necessary to operate its mass transportation facilities and equipment, at the lowest reasonable cost consistent with the provision of public transportation services in an efficient, reliable and economic manner. In procuring such electric utility services, the authority may solicit offers and proposals to provide such electric utility services from owners or operators, including the New England power pool, of facilities that generate, transmit, transform, or distribute electric power and energy, and shall take into consideration factors relating to the public interest, including but not limited to the following:

(a) the lowest prices that may be offered by responsible bidders, including electric companies, municipal lighting plants, political subdivisions, and alternate energy producers as defined in chapter 164;

(b) the demonstrated ability of any prospective supplier of electric utility services to provide reliable and continuous service and stability of price; and

(c) consistency with the environmental and conservation goals of the commonwealth; provided, however, the authority must fulfill all obligations of contracts and agreements lawfully entered into and now in force.