Yangjun Zeng

Yiwei Qiu, Jiatong Li, Yangjun Zeng et al.

An emerging approach for large-scale renewable hydrogen production is integrating multiple alkaline water electrolysis (AWE) stacks into one balance-of-plant (BoP) system, sharing gas-lye separation and lye circulation components. While this configuration, termed $N$-in-1, reduces cost and complexity, its dynamic performance under fluctuating power remains unclear compared with conventional 1-in-1 systems. This paper develops a state-space model of the multi-stack AWE system, capturing lye circulation, temperature, and hydrogen-to-oxygen (HTO) dynamics, calibrated via experiments on a 4,000 Nm$^3$/h-rated 4-in-1 system. A nonlinear model predictive controller (NMPC) is then designed to coordinate inter-stack current distribution, lye flow, and cooling for load tracking and operational stability. Simulations on the experimental-validated model show that a $4$-in-1 system can achieve very similar performance compared to four parallel 1-in-1 systems. Differences in load-tracking error, temperature stabilization, and specific energy consumption remain below 0.015 MW, 0.346 K, and 0.001 kWh/Nm$^3$ under wind power supply.

Yiwei Qiu, Qingjie Sun, Yangjun Zeng et al.

In renewable power-to-ammonia (ReP2A) systems, the intermittency of wind and solar generation propagates through electrolytic hydrogen production and induces thermal instability in the ammonia synthesis reactor (ASR). The resulting temperature cycling accelerates fatigue and shortens service life, while reactor thermal inertia limits flexible start-up, shutdown, and load adjustment. To address this issue, this study integrates molten-salt thermal energy storage (MS-TES) into the Haber-Bosch synthesis loop and develops a coordinated electro-hydrogen-thermal scheduling framework. MS-TES decouples hydrogen supply fluctuations from reactor thermal dynamics by enabling hot standby operation and sustained thermal support during start-up and low-load conditions. A state-space model is established to capture the thermal dynamics of the ASR and MS-TES. Based on this model, an optimal scheduling program coordinates ammonia synthesis operation with hydrogen production, battery energy storage (BES), and hydrogen storage (HS). The problem is formulated as a mixed-integer linear program (MILP) and extended with information gap decision theory (IGDT) to address renewable uncertainty. Case studies based on an industrial-scale project in northern China show that MS-TES enhances reactor thermal stability and system-level flexibility, while diminishing the marginal benefit of large BES capacity. As a result, a configuration combining small BES, HS, and MS-TES achieves near-equivalent performance to large-BES systems, with lower investment and improved economic returns. Year-round simulations further show that MS-TES avoids ASR start-up and shutdown and delivers consistently higher net revenue under variable renewable conditions.

Yangjun Zeng, Yiwei Qiu, Xiaocong Sun et al.

Integrating renewable generation, hydrogen production, and renewable ammonia (RA) synthesis into power-to-ammonia (P2A) systems creates interactions across electricity and hydrogen markets. Limited operational flexibility, however, places RA at a disadvantage at the Nash equilibrium (NE). Recent advances in ammonia synthesis reactor design enable hot standby (HSB) operation, improving flexibility but introducing integer decision variables that complicate market equilibrium analysis. To address this challenge, we develop a potential game model and derive a convergent ε-approximate equilibrium via an iterative best-response approach. Case studies show that HSB reduces RA's reliance on hydrogen purchases and increases its profit by 20.14%. More importantly, HSB shifts the market equilibrium toward a more mutually beneficial outcome.

Yangjun Zeng, Huayan Geng, Yiwei Qiu et al.

Renewable power-to-ammonia (ReP2A) production offers a viable pathway to decarbonize the power and chemical sectors and is increasingly supported by carbon-emission policies. However, a carbon-related mechanism that links ReP2A producers with fossil-based gray ammonia (GA) competitors while aligning the interests of renewable power, green hydrogen, and green ammonia producers in the ReP2A process chain remains unexplored. To fill this gap, we propose a hierarchical carbon-driven incentive mechanism (PCIM) to improve the market competitiveness of green ammonia. We first construct a trading framework in which ReP2A and GA participate in both the carbon allowance (CA) and ammonia markets, which forms the outer layer. These interactions, together with electricity and hydrogen transactions in the ReP2A chain, which form the inner layer, are modeled as a hierarchical game. For tractability, the inner layer is characterized via decomposable equivalent optimization, and the outer layer is solved as a mixed-integer linear program (MILP) derived from Karush-Kuhn-Tucker conditions. Based on the resulting equilibrium, we identify the carbon-related revenue of ReP2A and propose an incentive-compatible CA allocation mechanism (PCAM) %to ensure equitable benefit sharing across the ReP2A chain. Simulations show that the PCIM reduces carbon emissions by 12.9\% at a cost of only a 1.8% decrease in sectorwide revenue, and results from the PCIM provide guidance for carbon pricing. Furthermore, the application of the PCAM increases stakeholders' willingness to participate in ReP2A production.

Huayan Geng, Yangjun Zeng, Yiwei Qiu

Renewable power-to-ammonia (ReP2A), which uses hydrogen produced from renewable electricity as feedstock, is a promising pathway for decarbonizing the energy, transportation, and chemical sectors. However, variability in renewable generation causes fluctuations in hydrogen supply and ammonia production, leading to revenue instability for both ReP2A producers and conventional fossil-based gray ammonia (GA) producers in the market. Existing studies mainly rely on engineering measures, such as production scheduling, to manage this risk, but their effectiveness is constrained by physical system limits. To address this challenge, this paper proposes a financial instrument termed \emph{renewable ammonia futures} and integrates it with production decisions to hedge ammonia output risk. Production and trading models are developed for both ReP2A and GA producers, with conditional value-at-risk (CVaR) used to represent risk preferences under uncertainty. A game-theoretic framework is established in which the two producers interact in coupled ammonia spot and futures markets, and a Nash bargaining mechanism coordinates their production and trading strategies. Case studies based on a real-world system show that introducing renewable ammonia futures increases the CVaR utilities of ReP2A and GA producers by 5.103% and 10.14%, respectively, improving profit stability under renewable uncertainty. Sensitivity analysis further confirms the effectiveness of the mechanism under different levels of renewable variability and capacity configurations.