Optimal Demand Response Scheduling for Water Distribution Systems

As energy intensive infrastructures, water distribution systems (WDSs) are promising candidates for providing demand response (DR) and frequency regulation services in power systems operation. However, models that tap the full flexibility of WDSs to provide the services while respecting the operational constraints of water networks are remained scarce. This paper proposes a comprehensive framework for optimizing the participation of water distribution system operators (W-DSOs) in DR and frequency regulation markets, which captures the joint flexibility of variable frequency pumps and water tanks and takes into account the underlying hydraulic operating constraints of WDSs. The proposed framework consists of two optimization models, where the first-step model optimizes the operation of water pumps and tanks for minimizing the W-DSO's water procurement cost, and the second-step model optimizes the DR and frequency regulation up and down offers by modifying the operation of water pumps and tanks, such that the W-DSO's profit of providing the services is maximized. The proposed model ensures the availability of services by taking into account the interdependence and compatibility of the DR load reduction and load recovery and the frequency regulation up and down services. In addition, the proposed models incorporate a detailed formulation of water distribution networks and the associated hydraulic constraints, ensuring deliverability of the services to power systems. The nonlinear terms appearing in the WDS constraints are linearized to convert the proposed models to instances of mixed-integer linear programming problems. The proposed model is implemented on a 15-node WDS, using the energy and ancillary service prices of the California ISO. The results reflect significant profit opportunities for the W-DSO by providing DR and frequency regulation services in the markets.