Kavli Affiliate: Yi Zhou
| First 5 Authors: Jie Zhu, Yiwei Qiu, Yangjun Zeng, Yi Zhou, Shi Chen
| Summary:
Utility-scale off-grid renewable power-to-hydrogen systems (OReP2HSs)
typically include photovoltaic plants, wind turbines, electrolyzers (ELs), and
energy storage systems. As an island system, OReP2HS requires at least one
component, generally the battery energy storage system (BESS), that operates
for grid-forming control to provide frequency and voltage references and
regulate them through transient power support and short-term energy balance
regulation. While larger BESS capacity increases this ability, it also raises
investment costs. This paper proposes a framework of layered multi-timescale
energy management system (EMS) and evaluates the most cost-effective size of
the grid-forming BESS in the OReP2HS. The proposed EMS covers the timescales
ranging from those for power system transient behaviors to intra-day
scheduling, coordinating renewable power, BESS, and ELs. Then, an iterative
search procedure based on high-fidelity simulation is employed to determine the
size of the BESS with minimal levelized cost of hydrogen (LCOH). Simulations
over a reference year, based on the data from a planned OReP2HS project in
Inner Mongolia, China, show that with the proposed EMS, the base-case optimal
LCOH is 33.212 CNY/kg (4.581 USD/kg). The capital expenditure of the BESS
accounts for 17.83% of the total, and the optimal BESS size accounts for 13.6%
of the rated hourly energy output of power sources. Sensitivity analysis
reveals that by reducing the electrolytic load adjustment time step from 90 to
5 s and increasing its ramping limit from 1% to 10% rated power per second, the
BESS size decreases by 53.57%, and the LCOH decreases to 25.458 CNY/kg (3.511
USD/kg). Considering the cost of designing and manufacturing utility-scale ELs
with fast load regulation capability, a load adjustment time step of 5-10 s and
a ramping limit of 4-6% rated power per second are recommended.
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