A city or district may contract to purchase from an operating agency electric power and energy required for its present or future requirements. For projects the output of which is limited to qualified alternative energy resources as defined by RCW 19.29A.090(3), the contract may include the purchase of capability of the projects to produce electricity in addition to the actual output of the projects. The contract may provide that the city or district must make the payments required by the contract whether or not a project is completed, operable, or operating and notwithstanding the suspension, interruption, interference, reduction, or curtailment of the output of a project or the power and energy contracted for. The contract may also provide that payments under the contract are not subject to reduction, whether by offset or otherwise, and shall not be conditioned upon the performance or nonperformance of the operating agency or a city or district under the contract or other instrument.