Development and application of proton exchange membrane water electrolysis hydrogen production technology under wind and solar power fluctuations I

Development and application of proton exchange membrane water electrolysis hydrogen production technology under wind and solar power fluctuations I

The trend of global warming is more obvious. The development of clean energy can alleviate the large amount of greenhouse gas emissions generated by the use of fossil  fuels. Therefore, the development of renewable energy such as wind energy and solar energy is of great significance to the sustainable development of human society. Renewable energy has strong time and space dependence, intermittency, volatility and other characteristics. It also faces the difficulties of reliability and peak and frequency regulation in grid connection. Therefore, converting renewable energy electricity into chemical energy and storing it before using it is more flexible and is an effective way to coordinate the development of source, network and load.

Hydrogen has the advantages of being clean and having high quality/energy density. It is an efficient energy carrier that can replace fossil fuels such as coal and natural gas in high-carbon emission industries, electricity and other fields, and has broad application prospects. Hydrogen production from renewable energy water electrolysis is an effective way to achieve renewable energy consumption and green hydrogen production. Common technologies include alkaline water electrolysis, proton exchange membrane (PEM) water electrolysis, anion exchange membrane water electrolysis, and solid oxide water electrolysis. Among them, PEM water electrolysis technology has high current density, efficiency (80%~90%), gas purity, low energy consumption and volume, and good safety and reliability. Carrying out research and development of PEM water electrolysis technology is an important part of supporting the realization of renewable energy and electricity coupled hydrogen production.

The article focuses on the development and application of efficient hydrogen production technology by electrolysis of water under wind and solar fluctuating power sources. It systematically discusses the problems existing in hydrogen production by coupling wind and solar fluctuating power sources from the aspects of wind and solar fluctuation characteristics and hydrogen production methods, PEM water electrolysis hydrogen production characteristics and attenuation mechanism, current status of hydrogen production applications, and key technology research and development, in order to provide a basic reference for the corresponding technology development and industrial application research.

I. Renewable electricity, wind and solar power generation, hydrogen production scenarios
The mainstream forms of renewable energy power are wind power and photovoltaic power generation, which have the inherent property of strong volatility. Only by  analyzing the fluctuation characteristics of wind and photovoltaic power can we identify the basic conditions for the development of water electrolysis hydrogen production technology under wind and photovoltaic fluctuating power sources.
1.Wind power coupled with hydrogen production
Wind power coupled hydrogen production is mainly divided into grid-connected and off-grid types. For grid-connected wind power, the power grid realizes voltage and frequency control through the energy management system to ensure that the electrolytic cell produces hydrogen at a relatively stable voltage; the corresponding grid-connected methods mainly include synchronous wind power grid-connected and asynchronous wind power grid-connected. There are three main application scenarios for grid-connected wind power coupled hydrogen production: using surplus wind power to produce hydrogen, which plays the role of "peak shaving" in the power grid; using hydrogen energy and generating electricity through technologies such as fuel cells to play the role of "filling the valley" in the power grid; using grid power supply to solve the intermittent problem of wind power and enhance the stability and reliability of the hydrogen production system.
Compared with the grid-connected method, off-grid wind power eliminates grid-connected auxiliary equipment, can avoid the problems caused by grid connection, and reduce the cost of hydrogen production. Especially for offshore wind power, adopting off-grid power generation can effectively solve the problem of power transmission; oil and natural gas transmission infrastructure can also serve as a transmission channel for offshore wind power hydrogen production, which significantly reduces the investment cost of the corresponding pipeline. Generally, there are two main application scenarios for off-grid wind power-coupled hydrogen production: the obtained hydrogen is exported through gas pipelines or hydrogen tankers, and a microgrid system is built by wind power, converters, electrolyzers, hydrogen storage equipment, fuel cells, etc.

2. Photovoltaic power generation coupled with hydrogen production
Photovoltaic power generation coupled with hydrogen production can also be divided into grid-connected and off-grid types. Grid-connected photovoltaic power generation coupled with hydrogen production connects the electricity generated by photovoltaic modules to the grid, and then obtains electricity from the grid to electrolyze water to produce hydrogen. It is often used for large-scale abandoned light and energy storage; off-grid photovoltaic power generation coupled with hydrogen production refers to directly supplying the electricity generated by photovoltaic modules to electrolyzers for hydrogen production, which is mainly used for distributed hydrogen production. Photovoltaic power generation coupled with PEM water electrolysis hydrogen production technology mainly adopts two ways: photovoltaic DC-DC conversion indirect coupling and photovoltaic direct coupling.
1). Photovoltaic DC-DC conversion indirect coupling hydrogen production
The output power of photovoltaic power generation is affected by multiple factors such as solar radiation, ambient temperature, and external load, making it difficult to directly provide the optimal power for the load. A DC-DC converter is usually added between the photovoltaic module and the electrolytic cell to better match the photovoltaic voltage and the electrolytic cell voltage, thereby improving the efficiency of hydrogen production. The commonly used method is maximum power density tracking, such as using pulse width modulation technology to adjust the duty cycle to track the maximum power point and adjust the robust control of the converter output current. Although the DC-DC converter can effectively improve the efficiency of hydrogen production, the ripple generated by the converter will cause errors in the level judgment of the input current, thereby affecting the working efficiency of the electrolytic cell; the loss caused by DC conversion increases the operating cost and will also affect the durability of the hydrogen production system and the life of the device.
2). Photovoltaic direct coupling hydrogen production
The direct coupling of photovoltaic power generation devices and electrolytic cells simplifies the complexity of photovoltaic power generation coupled hydrogen production systems. For example, the photovoltaic electrolysis system consists of two PEM electrolytic cells directly connected to three-node solar photovoltaic cells, which can generate sufficient voltage to maintain the electrolytic cell hydrogen production process based on solar photovoltaic cells; adjusting the photovoltaic maximum power density point to match the electrolytic cell can make the solar-to-hydrogen conversion efficiency as high as 30%. However, under direct coupling, the voltage and current waveforms of the photovoltaic cell directly act on the electrolytic cell, which poses a challenge to the long-term safe and stable operation of the electrolyzer stack.