Of all fuels, hydrogen has the highest energy content¹, is relatively easy to produce and easy to transport. In the context of the energy transition, hydrogen is therefore a beacon of hope for mobile and energy-intensive applications. Its use in industry, transport, heating and electricity supply should preferably take place where it is superior to green electricity or even represents the only option.² Only "green" hydrogen, produced exclusively by means of renewable energies, is climate-neutral.

Relevance of the field of application

In terms of industrial applications, the chemical industry in Germany is leading the way in hydrogen use, with a current demand of 1.1 million t (37 TWh). According to estimates, this demand will increase to 7 million t (227 TWh) by 2050, particularly for the CO₂-based synthetic production of naphtha, which is used as an intermediate product in a wide range of production processes.² Among the frontrunners of future hydrogen demand in industry are also the steel industry, which wants to substitute fossil gases in the blast furnace line with hydrogen³ (2 million t or 70 TWh in 2050)² and the cement industry, which wants to convert captured CO₂ into chemical feedstocks or synthetic fuels.²

In the mobility sector, hydrogen will play a role above all in the area of heavy goods transport by truck, ship and rail. A pioneering role for rail transport is played by the company Alstom, which was nominated for the German Sustainability Award Design 2022 for the presentation of the world's first fuel cell train "Coradia iLint".⁴ A hydrogen demand in the mobility sector of 0.8 million t (25 TWh) is already considered plausible for 2030, with an increase to 6.1 million t (203 TWh) by 2050.² A significant increase in hydrogen demand is also expected in the heating and electricity supply sectors due to the substitution of fossil gases as well as an increasing hybridisation of regulating power plants.²

However, only green hydrogen contributes to the climate neutrality of the economy, as only its production relies exclusively on renewable energies. In contrast, the hydrogen used today is mainly produced from fossil fuels and the CO₂ produced is released into the atmosphere ("grey" hydrogen) or permanently stored underground ("blue" hydrogen). "Turquoise" hydrogen relies on the thermal fission of methane with the capture of solid carbon - a process that could theoretically be climate-neutral, but in practice also leads to significant greenhouse gas emissions, mainly because of extraction and transport losses of methane, a potent greenhouse gas.^5,6

Use of battery storage

The production of green hydrogen is based on electrolysis. It is the technically simplest production approach and at the same time has a relatively high energy efficiency.¹ The electrolysis processes differ in the electrolytes used and the operating temperatures for the respective optimum efficiency: alkaline electrolysers operate with aqueous caustic potash solution at 80 °C, membrane electrolysers with a proton-conducting membrane at 80 °C and steam electrolysers with a ceramic membrane as oxygen ion conductor at 650-1000 °C.¹ In general, the production of hydrogen is extremely energy-intensive. For example, the production of 1 g of hydrogen requires 145 kJ of energy. On the other hand, the high energy content of hydrogen is an advantage: the combustion of 1 kg of hydrogen releases the same amount of energy as the combustion of 2.75 kg of petrol.¹

Green hydrogen has already been produced from surplus wind power for some time under the name "wind gas". In the future, however, hydrogen will be produced primarily by means of renewable energy plants that have been built specifically for this purpose. A particularly attractive feature of the direct coupling of electrolysers to generation plants is that even strong, short-term fluctuations, such as those caused by gusts of wind, can be used for hydrogen production by electrolysis without delay.¹ It is true that the efficiency of electrolysers is generally highest in part-load operation. However, an undersupply of electricity in the lower partial load range is detrimental to product quality.¹ The increase in energy efficiency in hydrogen production makes the use of battery storage systems advantageous: load peaks occurring in the generation plants can be smoothed out by intermediate storage, periods of undersupply of electrical power can be reduced compared with direct coupling to the generation plant, and the number of productive hours in the optimum operating range of the electrolysers can thus be increased overall. The coupling of generation plants, electrolysers and battery storage is currently also being discussed for the hybridisation of PV plants.⁷

The design of battery storage systems to increase the efficiency of hydrogen production depends on the plant specifics of the electrolysers used, the load profiles of power generation and the battery technology used.

Performance requirements

Enormous amounts of renewable energy are required for the large-scale production of green hydrogen. Therefore, the use of battery storage for hydrogen electrolysis is basically a high-load application in which the longevity of the battery plays a central role. In conjunction with the high energy content and the corresponding explosion risks when handling hydrogen, the safety of the battery technology is also crucial.

As the production of green hydrogen focuses on the sustainability of the future energy supply, the battery storage systems used should also meet high sustainability standards. An important, often overlooked point here is the size of the required energy storage unit: the combination of specific energy, longevity, fast-charging capability and deep-discharge resistance is decisive for the dimensioning - and thus also for the corresponding environmental impacts.