(2) The bonds shall be issued from time to time by the board of commissioners in behalf of the district as authorized by the voters, and may be issued in an amount not to exceed one-half of one percent of the real market value referred to in subsection (1) of this section without the approval of the electors. The bonds shall mature serially within not to exceed 30 years from issue date, and shall bear interest not exceeding seven percent per annum payable semiannually as the board shall determine. The bonds shall be so conditioned that the district agrees to pay to the bearer, at a place named, the principal sum of the bonds with interest at the rate named, payable semiannually in accordance with the tenor and terms of the interest coupons attached.

(3) If the district has within its corporate limits a population of 300 or over, it may issue bonds in an amount which shall not exceed in the aggregate 10 percent of the real market value referred to in subsection (1) of this section.

(4) For the purpose of additionally securing the payment of the principal and interest on general obligation bonds issued under this section, the district may, by resolution of its board which shall constitute part of the contract with the holders of the bonds, pledge all or any part of the net revenue of its geothermal heating system. The board may adopt such a resolution without submitting the question of the pledge to the electors of the district. [1975 c.782 §6; 1977 c.188 §7; 1983 c.347 §29; 1991 c.459 §422; 2001 c.215 §17]