This paper proposes a model for optimizing the energy flexibility of water distribution systems (WDSs) in day-ahead power systems operation. The water distribution system operators (W-DSOs) are considered as energy-conscious entities, who run the proposed WDS operation model to optimize the operation of pumps and tanks for minimizing the operation cost of local WDSs, given the expected water demand and electricity prices of the next day. A WDS energy flexibility model is proposed that is used by W-DSOs in order to calculate and offer the feasible flexible energy capacity to the power system operator. The proposed WDS operation model takes into account the hydraulic operating constraints of water networks, thus ensuring deliverability of the WDS energy flexibility. Further, a network-constrained unit commitment model is proposed that integrates and optimizes the energy flexibility of WDSs in the day-ahead operation of power systems. The proposed model is implemented on a 15-node WDS that is powered by a 6-bus power system and the results are presented to study the impacts of optimized WDS energy flexibility on power and water systems operation.

This paper proposes a comprehensive framework for optimizing the participation of water distribution system operators (W-DSOs) in demand response (DR) and primary frequency regulation markets, which captures the joint flexibility of water pumps and tanks considering 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 primary frequency regulation up and down offers by modifying the operation of 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 considering the interdependence of the load reduction and load recovery and the frequency regulation services. The proposed model is implemented on a 15-node WDS, using the energy and ancillary service prices of the California ISO.

This paper proposes a fundamental model for defining and optimizing distributed energy flexibility in distribution buses, as well as deliverable energy flexibility as the aggregate distributed flexibility that is available for offering to the day-ahead energy market by distribution system operators (DSOs), without jeopardizing the operational constraints of the distribution network. The distributed energy flexibility is provided by flexible loads in distribution buses, which are modeled by clustered queuing systems representing the aggregation of large population of flexible loads with different energy and service quality requirements. Further, controllable inverters interfacing distributed solar generation provide reactive power flexibility in distribution buses. The deliverable energy flexibility is optimized by the proposed model that coordinates the energy flexibility of queued flexible loads and controllable inverters to maximize DSO’s profit of participating in the day-ahead energy market, while satisfying the service quality constraints of flexible loads, the operational limits of controllable inverters, and power flow constraints of distribution network that are formulated using the branch flow model. Moreover, an index is proposed to calculate the contribution of each distribution bus in providing the deliverable energy flexibility. The proposed model is implemented on the IEEE 33-bus distribution network. The numerical results exhibit profit opportunities for DSOs from providing the deliverable energy flexibility in the day-ahead energy market.

As freshwater resources progressively decline, desalination capacities around the world are projected to increase. However, high electricity consumption costs hinder the broader development of desalination plants. A promising solution to offset a portion of these costs is to enable water distribution system operators (W-DSOs) to offer the flexibility of their water desalination plants in electricity markets. This article proposes a model to integrate the available flexibility of water desalination plants in W-DSOs operation and optimize their participation in electricity demand response (DR) and frequency regulation markets. The proposed model co-optimizes the operation of desalination plants with variable speed pumps and water storage tanks in order to optimally allocate the available WDS flexibility between the day-ahead energy and frequency regulation markets. The proposed model takes into account the hydraulic operating constraints of the WDS, thus ensuring the delivery of DR and regulation services in the markets while supplying the water demand at the desired pressure. In addition, the proposed model considers the unavailability of freshwater resources when providing flexibility services to the grid, thus enabling W-DSOs to balance their profits against water shortages. The numerical studies, conducted on a test 15-node water network, show that the proposed model effectively utilizes the operational flexibility of desalination plants to offer DR and regulation services in the markets, considering the hydraulic constraints of the WDS, freshwater availability conditions, and desalination plants’ freshwater recovery rates.