Exploring the benefits of integrated energy-water management in reducing economic and ecological tradeoffs

Abstract:

Designing multi-reservoir operating policies to balance competing socioeconomic and ecological objectives is a challenging, multi-objective control problem. Multipurpose reservoirs provide water for clean energy, recreation, navigation and flood protection. However, dams also have detrimental ecological impacts, altering the natural flow of water, sediment and nutrients, impeding fish migration, and impairing water quality. Furthermore, operations favoring different ecological objectives can also conflict. For example, maximizing the value of green energy from hydropower leads to hydropeaking (releasing water in short, intense bursts to maximize hydropower revenue) which threatens the sustainability of salmon and other fisheries that depend on natural flows. While these tensions will never disappear, they can be reduced by jointly optimizing the management of energy-water systems.

This study introduces an integrated water-energy optimization model for this purpose. We evaluate the economic and ecological benefits of this integration using the Columbia River Basin (CRB) and Mid-Columbia energy market as a case study. This model couples a simulation model of seven CRB reservoirs and a unit commitment/economic dispatch model of the California and West Coast Power system (CAPOW). We use a model-free, closed loop optimal control method called Direct Policy Search (DPS) to design reservoir operations in conjunction with the dispatch of non-hydropower energy sources (wind, natural gas, and in California, solar). We couple DPS with a multi-objective evolutionary algorithm (MOEA) to optimize three objectives simultaneously: Maximize economic benefits from energy production, maximize energy generation from renewables and minimize environmental flow violations, subject to flood control constraints. Our work illustrates the multi-objective benefits of integrated water-energy management, while also elucidating remaining tradeoffs decision makers must weigh in designing their joint operation.