Optimized Integration of Solar and Battery Systems in Water Distribution Networks ^†

Abstract

Water Distribution Networks (WDNs) are traditionally known as significant energy users, leading to numerous studies aimed at enhancing their energy efficiency. However, despite the growing attention towards renewable energy, there has been limited focus on seamlessly incorporating sustainable energy solutions into WDNs. We present an optimization framework for designing and operating WDNs that integrate renewable energy sources. This model considers the unique constraints and needs of each system component. Drawing from realistic capital and operational cost estimates, this combined system refines the arrangement of both water and energy elements (for instance, determining the appropriate size for solar panels and battery systems and the capacity of pumping stations). It also suggests optimal daily operational strategies for the different seasons of the year, such as when to charge batteries or when to activate/deactivate pumps. Our findings highlight that when water and renewable energy systems are cohesively designed and operated, it can markedly boost the energy efficiency of WDNs, furthering the sustainability goals of both the water and energy sectors.

1. Introduction

The integration of renewable energy sources into traditional infrastructure, such as Power Supply Systems (PSSs) and Water Supply Systems (WSSs), has become a pivotal element of sustainable and efficient infrastructure development [1]. Aligning the design and operational strategies of PSSs with WSSs offers multiple benefits, including balancing supply and demand and minimizing energy consumption costs. WSSs, which ensure the provision of clean water to communities, require optimization in infrastructure investments (sizing of pipes, tanks, and pumps) and operational costs, notably the energy costs associated with pumping. With pumping stations accounting for a substantial portion of the electrical energy usage in WSSs, optimizing and designing energy-efficient water systems have attracted considerable research attention [2,3]. However, despite the growing acknowledgment of renewable energy’s potential, its optimized integration into the design and operation of WSSs has not been extensively explored [4,5]. This study introduces a new optimization model for WSSs, incorporating solar plants and battery storage systems. This model transforms the conventional design and operational approaches of WSSs, aiming to minimize total costs while ensuring operational and design efficiency through the integration of clean energy resources [6].

2. Methodology

The methodology presented in the paper outlines a comprehensive approach to integrating renewable energy sources, specifically solar power and battery storage, into WSSs to enhance their efficiency and sustainability. This approach encompasses the simultaneous design and operation of Combined Water and Power Systems (CWPS), aiming to minimize the total costs, including capital and operational expenditures.

The model considers a CWPS comprising pumping units, tanks, pipes, and energy sources, including solar power, battery storage, and the power grid (Figure 1). The objective is to achieve an optimized design and operation that meets consumer demands within the technological, operational, and physical constraints. The objective function is to minimize the overall cost of the CWPS, considering the capital costs of the infrastructure components (pumping stations, pipes, tanks, solar plants, and batteries) and the operational costs (energy consumption and revenue from selling excess energy). The methodology incorporates various constraints related to the physical properties of the system (e.g., pipe diameters, pump efficiency, solar irradiance) and operational guidelines (e.g., minimum and maximum states of charge for the battery and time-of-day energy tariffs). Various parameters such as the efficiency factors (of pumps, battery charging/discharging, inverter) and time-based energy pricing are incorporated in the optimization process. Cost functions are provided in

Table 1. Cost functions for the system’s elements.

Function	Description	Source
CPUC	Cost of pump	[7]
CPC	Cost of pipe	[7]
CTC	Cost of tank	[7]
COBc	Capital cost of battery	[8]
COBo&m	O&M cost of battery	[9]
COSc	Capital cost of solar panels	[10]
COSo&m	O&M cost of solar panels	[9]

for each component of the CWPS, including the pumping station, pipes, tanks, battery system, and solar plant. These functions account for both the capital and operational and maintenance costs, enabling a comprehensive financial analysis of the system.

A mixed-integer linear programming (MILP) problem is formulated, and the Gurobi solver is employed to find the optimal solution. The model is implemented in MATLAB, utilizing the Yalmip toolbox for optimization modeling. The code and data are available at https://github.com/SWSLAB/CWDN (accessed on 1 June 2024).

3. Results

The methodology was applied to the case study outlined in Figure 1. The pump’s energy utilization in the different seasons during the weekdays (WD) is given in Figure 2. $E_{SP}$, $E_{GP}$, and $E_{BP}$ are the pump’s energy supplied by the solar panels, grid, and battery, respectively. In the summer, when water demands are high, the pumps operate almost the entire day. Grid energy is mostly used to supply the pump at night. During the day, the pump is mostly supplied by solar energy, which is also used to charge the battery. In the afternoon, when grid energy is expensive and solar energy production decreases, the battery is used to supply the pump’s power consumption. During the winter, when the water demand is lower, the pump can be turned off during the peak energy tariffs, and the battery will not be required to feed the pump. However, excess solar energy may be stored and sold back to the grid during peak hours.

4. Discussion and Conclusions

In summary, the methodology provides a structured framework for designing and operating WSSs integrated with renewable energy sources, emphasizing cost minimization and sustainability. Through careful modeling of energy and water dynamics and the strategic optimization of system components, the approach offers a path towards more efficient and environmentally friendly water supply systems.