Microgrid Integrated Solar and Storage Technology

 By Aleksi Paaso, Manuel Avendano and Shay Bahramirad

The landscape in the energy industry is changing. Conventional forms of power supply and delivery are currently being complemented and, at times, challenged by distributed energy resources (DERs). While DERs can potentially provide significant benefits to the grid, their inclusion also may pose challenges to the conventional transmission and distribution (T&D) systems operation and planning. Often these challenges are associated with renewable energy resources, particularly wind and solar. Unlike traditional forms of generation, these resources cannot be dispatched to achieve desired power generation.

As deployments of microgrids are now being considered for resiliency and reliability purposes, there is a strong push to include higher penetrations of solar photovoltaic (PV) and wind generation systems in these installations to meet specific emission and energy efficiency goals. Similar to the traditional grid, the intermittent and sometimes unpredictable nature of renewable generation requires further design considerations, as swings in generation output can have major impact on the microgrid stability, particularly under the islanded mode of operation.

In some cases these “power swings” may even exceed the ramping capabilities of the other DERs within the microgrid boundary, potentially leading to a major curtailment of the renewable generation to avoid stability issues. In this situation, energy storage systems provide a considerably more attractive alternative to curtailment; as these systems can be used to balance out the pockets of variable generation.

In order to advance the state-of-the-art in utilizing energy storage in combination with PVs, Commonwealth Edison (ComEd) received a $4 million award from the U.S. Department of Energy SunShot Initiative in January 2016 to design and deploy solar and battery storage technology within its planned community microgrid demonstration project in Chicago’s Bronzeville neighborhood. The DOE funding allows ComEd to research, develop, deploy, and test microgrid-integrated solar-storage technology (MISST) system at ComEd’s planned microgrid demonstration site. The technology will allow for the widespread use of low-cost, flexible, and reliable solar PV generation, as well as the use of battery energy storage systems with a focus on integrating these systems to microgrids.

The proposed MISST solution will address availability and variability issues inherent in the solar PV technology by utilizing smart inverters for PV and battery storage systems while working synergistically with other components within a microgrid community. The smart inverter technology in MISST is based on a robust control strategy to integrate both solar PV and energy storage systems. The control strategy allows the power electronic converters to function as they were conventional synchronous machines in the electricity grid to further enhance the grid stability. MISST allows the coordination of solar PV and energy storage systems with smart devices and loads, thus providing a reliable and dispatchable solar PV solution for microgrid applications. The MISST solution will be scalable to significant levels of penetration with standardized and proven interoperability capabilities.

One of the key barriers for the high penetration of solar PV system to be addressed via this project is the seamless integration of these systems in utility distribution grids. This means that solar PV systems are both intended to operate without deterioration of reliability, power quality, and operational security of T&D grids, and are also expected to help improve efficiency by supplying loads locally and providing grid services such as controlled active power ramping, dynamic reactive power control, and soft starting by means of smart inverters featuring advanced functionalities. The core MISST solution is the utilization of smart inverters that would offer robust control strategies to enable PV and storage systems appear as they were synchronous machines. Such smart inverters in MISST offer an autonomous frequency control of the solar PV and energy storage system which can be used for grid services and enhancing the economics of solar-storage technology in distribution grids.

The technical tasks in the three-year MISST project will include the design of the integrated solar-storage technology, development of the smart inverter solution, integration of the MISST to the existing microgrid controller, design, engineering, and deployment of the solar PV and energy storage system within the Bronzeville Community Microgrid, and finally the operational data collection and analysis to further demonstrate the merits of the MISST solution. The MISST project will also focus on development of a strategic plan and detailed design methodology for the technology, recommended practices, processes, and considerations for practical implementation and scaling up for high power applications of similar solutions. The project will achieve the technical and financial performance metrics required for the SHINES solution, including consistent component lifetimes, energy storage cycling (for energy shifting and smoothing PV variability), cost reduction, utility-friendly interoperability, communication and control, and grid interconnection cost and time reduction.

As the energy landscape evolves, DERs and microgrids are envisioned to become major components of the future electric grid. The community microgrid setting proposed in Bronzeville, to be developed under the leadership of ComEd, will provide an excellent opportunity to leverage and demonstrate the merits of the solar PV and battery energy storage investment, and showcase how these technologies will improve grid performance and provide sustainable alternatives to reliably operate an efficient and increasingly distributed power system.

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