From the StarTribune: Guaranteed energy-savings contracts work like this:
A city chooses a company to evaluate energy improvements. The company then oversees the installation of projects the city wants and guarantees that energy savings will cover the work, the company’s fee, and up to 20 years of debt service on money the city borrows to pay for the projects. The company posts a performance bond to ensure that it will pay the difference if the savings are less than promised.
See also, Minn. Stat. §16C.144