(1) The property of all nonprofit cooperative electric power associations organized heretofore or which may be hereafter organized under any of the laws of this state for the purpose of selling, transmitting, distributing or generating electricity, electric current or power, and which shall engage in any such business or businesses shall be exempt from ad valorem taxes, and such association shall be exempt from franchise, privilege, net income or other excise taxes imposed by the state or any of its political subdivisions. Provided, however, that this exemption shall not extend to or include exemptions from payment of gas taxes, motor vehicle privilege and motor vehicle ad valorem taxes, and sales and use taxes.

(2) This exemption shall apply to all property which may be used or useful in the transaction of any such business or businesses including, but not limited to, office buildings, warehouses, office equipment and supplies, maintenance, operating and construction equipment, supplies and materials, and all electrical distribution and transmission lines and component parts thereof. Provided, however, that nothing contained in this section shall be construed so as to grant exemption from municipal ad valorem taxes or taxes levied for the benefit of the particular municipal school district on any real estate owned by such associations and located within the corporate limits of the municipality, nor construed so as to grant exemption from municipal ad valorem taxes on electrical transmission and distribution lines and component parts thereof owned by such associations which do not purchase the electricity which they sell in the municipality from any agency or instrumentality of the United States.

(3) In the event any such association shall engage in the sale of commodities, goods, wares or merchandise as a business, the foregoing exemption shall not apply to that part of the business so done.

(4) In the event any part of any office building owned by such an association shall be rented or subrented by any such association, such building shall not be exempt from ad valorem taxes, but may be assessed by the county tax assessor and board of supervisors of the county in which it is situated and by the taxing authorities of any municipality in which it may be situated.