Section 15. The bonds and notes issued under this chapter shall be payable solely from the funds provided therefor under this chapter, the liability of the city or town from other funds being limited to obligations undertaken by it to pay for the electricity used by it, and a statement to this effect shall be included on the face of such bonds and notes. Subject to the provisions of clause (i) of paragraph (1) of subsection (b) of section nine, the bonds and notes and such obligations shall not at any time be included in the debt of the city or town for the purpose of ascertaining its borrowing capacity.