Nora Han, Head of Hydrogen Product Group, ABB System Drives, examines how the right choice of power supplies can enable more efficient and affordable green hydrogen production.
Estimates from the Hydrogen Council and McKinsey suggest that clean hydrogen has the potential to reduce global carbon dioxide (CO2) emissions by 80 gt by 2050. This means that renewable and low-carbon hydrogen could contribute up to 20% of the annual emissions reductions required to reach net-zero by 2050.
However, today’s hydrogen production is not compatible with a sustainable future. This is because 99.6% of hydrogen comes from processes that involve petroleum and natural gas. The waste carbon released into the atmosphere negates hydrogen’s carbon-neutral benefits.
Fortunately, this is not the only option: hydrogen can also be produced using electrolysis. When the electricity comes from a renewable source, such as wind or solar, the process does not emit any carbon and the resulting product is green hydrogen.
Hydrogen must be generated sustainably if we are to successfully decarbonise, meet our climate goals, and improve the resilience of our energy systems. To achieve these essential goals and make green hydrogen production into a scalable and economically viable approach, operators depend on highly-efficient and reliable power supplies.
Energy efficiency: the key to green hydrogen
Assuming water is relatively affordable, electricity is the most significant operating expense, accounting for approximately 80% of OPEX. This means that energy efficiency is key to driving down the levelized costs of hydrogen production from electrolysis. By optimising energy usage, green hydrogen production becomes more affordable and accessible.
There are many components required to produce green hydrogen, and each introduce potential inefficiencies. Components include electrolysers, power supply systems, protection equipment, cooling systems, enclosures, auxiliary equipment, and more – and all of it must work in harmony to achieve optimal efficiency.
Among these components, an efficient power supply – which consists of transformers, rectifiers, compensation equipment, and more – makes up around 20 – 30% of the price of an electrolysis system. Therefore, it offers the greatest potential for reducing hydrogen costs. According to IRENA, as the scale of hydrogen production increases, standard utility scale power supply systems become available from leading manufacturers of electrical equipment. Using these can significantly reduce cost and increase the performance of the power supply for electrolysers.
Power supply systems convert alternating current (AC) from the grid to direct cur-rent (DC) at the appropriate voltage for the electrolyser. The choice of power supply can affect overall system efficiency up to 20% in some cases.
Selecting the perfect power supply
There are several types of electrolyser technology. The three most common are alkaline/proton exchange membranes (PEM), and solid oxide electrolyser cell (SOEC) systems. Although specific requirements vary based on the technology, electrolysers today are classified as low-voltage (LV) equipment.
To power an electrolyser, electricity must be changed from medium-voltage (MV) AC to LV DC. There are several ways to achieve this. The first uses transformers to step down the voltage, and then rectifiers convert the LV AC directly to DC at the appropriate voltage for the electrolyser.
Other solutions combine a rectifier with a DC-DC converter to achieve greater overall performance. These solutions first convert the AC power to DC and then perform a DC-DC voltage conversion to achieve the appropriate voltage. Alternatively, if the electrolyser is connected to a DC distribution system, it only requires DC-DC converters to match the voltage level. Operators should consider modular options, as these make it easier to scale up production in the future.
The industry is still in need of standardisation. Analysis by IRENA finds that optimisation can be achieved by careful system integration of different components in the electrolyser facility, optimising the entire facility rather than individual components. Therefore, to identify the appropriate solution to minimise costs and maximise reliability and performance, operators must work with expert partners to create an ideal solution. Green hydrogen, by definition, uses electricity from a renewable source. These sources often behave dynamically and can be intermittent, which poses challenges for system integration. To overcome these, power supplies must react rapidly to input and output signals, even under challenging conditions. Specialised power electronics controls react quickly to unpredictable behaviour under even the harshest conditions, enabling plants to maximise uptime.
Understanding power factor and harmonics
Reactive power is a critical consideration in the electrical network supplying electrolysis systems as it has a significant impact on energy efficiency. It represents the power that flows back toward the grid without doing any work while using up system capacity. The efficiency of the network is measured by the power factor (PF), which is the ratio of the true power (supplied by the network) to the actual power (used to do the work). An ideal PF is unity. This is rarely achieved, with 0.95 generally considered an acceptable figure. It is often well below this, meaning that facilities are paying for power they do not use. In some cases, grid operators impose significant penalties for excess reactive power. The solution can be to install power factor correction equipment such as capacitors, STATCOMs and synchronous condensers.
Another power quality risk is harmonic distortion, which can significantly decrease the system’s energy efficiency. As a rectifier draws power, it introduces noise to the network. When this noise occurs at a multiple of the fundamental frequency, it is called a harmonic wave.
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