(459a) Dynamic Modeling and Hierarchical Control of a Microgrid Incorporating Ammonia

A microgrid is an integrated platform for power supply and energy storage, which can be operated either in a non-autonomous way when it is connected to the macrogrid or in an islanded mode if disconnected [1]. Microgrids are receiving significant attention due to their capabilities of utilizing renewable energy sources (RES), such as wind and solar energy. Due to the unpredictable and intermittent nature of RES, energy storage units are needed. Conventional energy storage media include batteries or hydrogen; however, they are uneconomical for long-term storage because of their low energy densities. Ammonia, a chemical that can be easily and safely stored as a liquid, has been considered as an alternative energy storage medium in recent studies [2].

In a microgrid, green ammonia can be synthesized through the Haber-Bosch process with renewable hydrogen obtained from water electrolysis and nitrogen from air separation [3]. For power generation, ammonia can be used as a fuel in combustion engines or ammonia fuel cells [4]. Optimal design and scheduling of microgrids incorporating green ammonia have been studied for different locations in the US [5], suggesting that a combination of hydrogen and ammonia storage is the most economical solution. However, there has been no study of the dynamic operation and control of a microgrid with ammonia.

In this work, the dynamic modeling and hierarchical control of a microgrid incorporating green ammonia for energy storage is considered. The proposed microgrid is operated in an islanded mode. Wind and solar energy are captured and used for meeting residential demands or powering water electrolysis. Hydrogen produced from electrolysis can be further converted to ammonia through the Haber-Bosch process. Generator sets are dispatched for power generation from hydrogen or ammonia. A two-level control architecture is proposed. Local controllers are designed for each module in the framework, taking hourly commands from an upper-level real-time optimization layer. Simulation case studies are conducted for Duluth, MN, Phoenix, AZ and Las Vegas, NV over a 24-hour time horizon for different seasons. The results show that hydrogen is mostly dispatched to address mismatches between the available RES and grid load within a day, while ammonia is preferred when there is need for storing energy across seasons. Compared to a hydrogen-only microgrid, the operating cost of a microgrid with both hydrogen and ammonia is reduced by at least 23%, confirming the economic advantages of the proposed system.

References:

[1] N. Hatziargyriou, Microgrids: architectures and control. John Wiley & Sons, 2014.

[2] R. M. Nayak-Luke and R. Ba ̃nares-Alc ́antara, “Long-term energy storage: What is the need and is ammonia a solution?” in Computer Aided Chemical Engineering. Elsevier, 2018, vol. 44, pp. 1843–1848.

[3] L. Ye, R. Nayak-Luke, R. Banares-Alcantara, and E. Tsang, “Reaction: “green” ammonia production,” Chem, vol. 3, no. 5, pp. 712–714, 2017.

[4] C. Zamfirescu and I. Dincer, “Using ammonia as a sustainable fuel,” Journal of Power Sources, vol. 185, no. 1, pp. 459–465, 2008.

[5] M. J. Palys and P. Daoutidis, “Using hydrogen and ammonia for renewable energy storage: A geographically comprehensive techno-economic study,” Computers & Chemical Engineering, vol. 136, p. 106785, 2020.