Optimization of Energy Storage Systems and Demand Side Management to Maximize Water Utility Savings: A Hawaii Case Study

Abstract

Energy conservation is a concern in many industries, and consequently, facility operators are turning to various efficiency measures or alternative power sources to reduce electricity costs. With the expanding use of intermittent resources, energy storage systems (ESSs) and demand side management (DSM) options are also gaining interest to maximize potential energy savings. Here, we study the potential of ESSs versus DSM for water utilities through a case study of the National Energy Laboratory of the Hawaii Authority (NELHA). NELHA is a multizone water utility in which most of its electricity usage is dedicated to pumping water. In this study, the optimization of the overall electricity charges for NELHA, using both ESSs or DSM via pump load shifting and optimization of pump house output is investigated. An optimization algorithm is created to determine the optimal size of the batteries for installation considering the water demand and energy costs in each zone. An extended approach of considering the characteristics of individual pumps on each pump house in the optimization model is applied to provide insight into the proper optimization framework for dispatching pumps depending on the current zonal load, given pump efficiencies, and maximum flowrates from each pump. The outcome from mathematical models using general quadratic pump efficiency functions and a simplified linear version of pump efficiency is compared to determine the significance of this difference in modeling methodology in estimations and evaluations. Additionally, the effect of increasing solar power on electricity purchased is analyzed. This work will help to establish the role of ESS and DSM in energy savings for water utility industry as well as show what methods should be used for evaluation of the potential of ESS and DSM interventions.