110 ILCS 62/5-15
"Guaranteed energy savings contract" means a contract for: (i) the implementation of an energy audit, data collection, and other related analyses preliminary to the undertaking of energy conservation measures; (ii) the evaluation and recommendation of energy conservation measures; (iii) the implementation of one or more energy conservation measures; and (iv) the implementation of project monitoring and data collection to verify post-installation energy consumption and energy-related operating costs. The contract shall provide that all payments, except obligations on termination of the contract before its expiration, are to be made over time and that the savings are guaranteed to the extent necessary to pay the costs of the energy conservation measures. Energy savings may include energy reduction and offsetting sources of renewable energy funds including renewable energy credits and carbon credits.
110 ILCS 62/5-15