(341t) Design and Optimization of Hybrid Grid System Containing Power-to-X Systems for Renewable Energy Storage

The proportion of renewable energy has risen in a global effort to fight climate change over the past few decades. Due to the intermittent and varying nature of power outputs from renewable energy generation units, a temporal and spatial mismatch between demand and supply can result inevitably. Energy storage system (ESS) which typically comprises batteries and supercapacitors is used to help manage the temporal imbalance in renewable energy supply [1-2]. However, ESS alone is not sufficient for resolving this problem because of its high investment cost and unsuitability for long-term energy storage.

Power-to-X (P2X) technologies are attracting attention as a means to store excess energy in an easily transportable form for a long period of time. P2X technology is a process that converts power generated from renewable energy (especially electrical energy) to chemicals, fuels, and other energy states that are sustainable and easily manageable [3-5]. Furthermore, P2X technologies are believed to be an effective way to mitigate CO₂ emission because many of them consume a significant amount of CO₂ as a feedstock to produce energy-storing chemicals (e.g., syngas and methanol). Thus, P2X technologies offer a sustainable solution to the current energy and environmental problems, by reducing CO₂ emission as well as storing excess energy from renewable energy generation in a stable and transportable form. Furthermore, in certain cases, P2X technologies can produce chemicals in more direct and simpler ways than the respective conventional chemical production processes, e.g., only one step is needed to produce a target chemical in the P2X process while multiple steps are required in the conventional production method [6]. With the reduced number of steps during the chemical production, the P2X system is expected to generate additional economic benefits, resulting from the reduced capital and operation cost.

However, the P2X system is not easy to design so that it can be incorporated directly into the grid with renewable energy generation. Many P2X systems require downstream processes, e.g., separation processes and reaction processes. If combined directly, the P2X system has to be operated to absorb the fluctuating nature of power outputs from renewable energy sources. This in turn will cause intermittent operation of downstream processes, which can be highly inefficient. In addition, the sizing of the downstream process units has to be overestimated because it has to accommodate the maximum level operation of the P2X system. Thus, in order to design and operate a P2X system in an efficient way, the energy supply needs to be stabilized with the aid of ESS.

In order to manage energy outputs from renewable sources in an efficient way, a hybrid grid system being composed of a renewable electricity generation system (including wind turbine and solar panel), ESS (including battery, supercapacitor, and fuel cell), and the P2X process is proposed in this study. A detailed process model for each unit component is developed to analyze the performance of the overall system and its economic feasibility under various scenarios. Model equations are implemented in gPROMs and Python to predict the performance of each component, i.e., power consumption in the P2X process and the electrolyzer, state of charge in batteries, and power output from the wind turbines and photovoltaics panels. Finally, the optimal sizing of each component is identified via model-based optimization. An additional optimization is carried out to determine the best operating conditions and schedules by accounting for the seasonal variations in the renewable energy sources.

References

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