1-33B-8. Written guarantee--Bond--Payment period not to exceed fifteen years. The contract shall include a written guarantee of the qualified provider that either the energy or operating cost savings, or both, will meet or exceed the costs of the energy efficiency measure within fifteen years. A qualified provider shall provide a sufficient bond to the governmental unit for the installation and the faithful performance of all the measures included in the contract covering the first two years of the contract. The guaranteed energy savings, projected for any additional year of the contract, shall be guaranteed by the qualified provider. The qualified provider shall reimburse the governmental entity for any shortfall of guaranteed energy savings projected in the contract. The guaranteed energy savings contract may provide for payments over a period not exceeding fifteen years.