Hydrogen electrolysis on a grand scale

Hydrogen is the fuel of the future. The only question is: where are we going to get the huge quantities needed to overcome the climate crisis? The answer is electrolysis – lots of electrolysis. This electrochemical process uses electricity to break water into its constituent parts: hydrogen and oxygen.  

Rolls-Royce is developing mtu electrolyzers with outputs of up to 2 MW that can be scaled up to over 100 MW. Now the company has acquired a stake in Hoeller Electrolyzer, a specialist company that develops and manufactures the cell stack, the core component of the electrolyzer. The shared aim of Rolls-Royce and Hoeller Electrolyzer is to develop a solution to produce hydrogen cheaply and on a large scale using green electricity. This is an ideal add-on for an mtu microgrid. It creates the possibility to store and use solar and wind power, thus making an important contribution to the energy transition.

Large-scale electrolysis works on the same principle as those electrolysis experiments in physics and chemistry lessons, in which two electrodes are suspended in a water bath: In an electrolyzer, water is broken down into its components hydrogen and oxygen by an electrochemical reaction. In contrast to the electrolysis experiment from physics or chemistry lessons, however, a membrane is used here instead of electrodes. Current is passed through this membrane into the water, producing hydrogen at the negative cathode and oxygen at the positive anode. This process takes place in a so-called cell, hundreds of which are stacked on top of each other in such a way that they produce the required amount of hydrogen as economically and effectively as possible.

Why hydrogen?

“Because it contains no carbon and cannot produce harmful carbon dioxide (CO2) when powering fuel cells or hydrogen engines. Sounds fairly straightforward. The trick, though, is to ensure that no CO2 is produced during production of the hydrogen – as is partly the case when hydrogen is obtained from natural gas,” explained Armin Fürderer, who heads up net zero solutions at Rolls-Royce Power Systems.

This calls for 'green' hydrogen produced in ways that give off no carbon emissions, and that's where solar parks and wind turbines come in – supplying the electrolyzers with electricity generated with zero CO2 emissions. The collected hydrogen from the electrolyzers can be used in a variety of ways: In fuel cells, the hydrogen is used to generate electrical energy again as needed. Or it is used to power hydrogen engines. Either way, electricity can be fed into the grid or used to power vehicles or ships. Alternatively, the green hydrogen can be used in industry and replace so-called gray hydrogen - i.e. hydrogen from natural gas.

Combustion engines run climate-neutral

Another possibility is to use further energy from renewable sources to produce methanol from hydrogen and CO2 in the air. If this methanol is used in a future mtu methanol engine, CO2 is released again, but in quantities equivalent to those extracted from the air during the methanol production – meaning the whole process is 'net zero carbon'. The synthesis of other sustainable fuels such as e-kerosene or e-diesel is also possible with hydrogen. Thus, other sectors such as heavy-duty transport or aviation can also be decarbonized.    

There is still some work to be done to make this process cost-effective. Stefan Höller, Managing Director and the resourceful mind behind Hoeller Elektrolyzer, wants to change that. “With our stack, you're going to be able to produce hydrogen in a way that's so inexpensive it's so far been thought impossible,” he said.  

This is no accident, because over 25 years of expertise and pioneering work by company founder Stefan Höller have gone into the Hoeller stack. He has continuously refined his technology and holds several patents on it – always with the aim of reducing the production cost of green hydrogen. The innovative design of the cells and stack boosts its efficiency. The stack also uses significantly less platinum and iridium than usual, and a higher output pressure makes it even more powerful.

Anything but pie-in-the-sky

It won't be long until the first mtu electrolyzer is producing hydrogen.  Development work on the first mtu electrolyzer using a Hoeller stack has been underway for some time. It is set to go into operation at the Validation Center in Friedrichshafen in 2023, showing the part an electrolyzer can play in the overall architecture of a microgrid. An initial customer project is already planned for 2024. “We're going to be launching electrolyzers with several megawatts of power right from the word go. A total output of over 100 MW is conceivable by combining several electrolyzers,” said Armin Fürderer.  

Rolls-Royce and Hoeller combining their strengths  

Rolls-Royce Power Systems and Hoeller Elektrolyzer are ideal partners, with Hoeller developing the specialist technology of the electrolysis stack and Rolls-Royce using it to develop the complete electrolyzer, initially housed in containers. Rolls-Royce's global sales and service network will ensure access to a wide range of customers across the world. Discussions with the first customers are already underway, with the first customer projects expected to kick off in 2024 – all aimed at making hydrogen green, its production economical and the future climate-friendly.