Prepared by Ziad Alaywan P.E, Zaher Harkous P.E., & Nicole Ramos
Executive Summary
The decision between DC-coupled and AC-coupled storage offers distinct advantages and considerations for hybrid projects involving Battery Energy Storage Systems (BESS), such as Solar/BESS, Wind/BESS, or other hybrid combinations. DC-coupled storage typically provides higher energy production rates, while both configurations support grid services and scalable capacity. AC-coupled storage, however, allows for independent operation of the photovoltaic (PV) system and the battery, enabling increased capacity with minimal system modifications.
Choosing between AC and DC coupling is not straightforward and depends on specific project goals and future plans. For projects that require grid charging capabilities—whether standalone BESS or hybrid systems—AC-coupled storage is often the preferred option. Conversely, if maximizing energy production is the primary objective, DC-coupled storage tends to be the better choice.
Ultimately, each project must be evaluated individually, taking into account factors such as land availability, utility regulations, market conditions, and reliability needs to make an informed decision between AC and DC-coupled storage solutions.
Introduction
As the integration of renewable energy sources increases, the need for efficient and reliable energy storage has become crucial. Battery Energy Storage Systems (BESS) play a vital role in stabilizing energy grids, particularly by storing energy for use during peak demand periods. When considering (a) Standalone BESS, (b) Hybrid projects where the BESS is not allowed to charge from the grid and the BESS exclusively charges from the onsite generating facility, and (c) Hybrid projects where the BESS is allowed to charge from the grid as well as from the onsite generating facility, one of the key decisions is between alternating current (AC) and direct current (DC) coupling between the battery and the PV system. This case paper explores the differences between AC and DC design solutions, focusing on cost, efficiency, applications, and flexibility, and providing a comparative analysis to help stakeholders make informed decisions.