HOELLER Electrolyzer – German Engineering Advances Climate-Neutral Energy from Hydrogen

By April 24, 2020 5   min read  (842 words)

April 24, 2020 |

Hoeller 1
  • German startup opens a new chapter in water electrolysis with eight patent applications
  • 25 years of know-how lead to economical PEM electrolysis stacks
  • Prometheus: high performance, low costs – thanks to innovations in construction & materials
  • Clear Goal: Green hydrogen below 4 euros/kg of climate-neutral energy – generate it, store it efficiently, and make it available again. One of the central questions of the energy transition to achieve global climate goals.

Hydrogen has long been considered the ideal solution here – but has not yet made its final breakthrough. Although the principle of splitting water (electrolysis) for energy is not new.

Various companies around the world are working to increase the economic viability, possible applications and efficiency levels of the technology to such an extent that it will find its way into the everyday life of private individuals and companies as a clean energy alternative. There is a particularly high energy requirement in industry, which will have to be covered in a climate-neutral and cost-effective manner in the future.

This is exactly where the German company HOELLER Electrolyzer comes in with Prometheus. A range of extremely compact electrolysis stacks based on 25 years of know-how in PEM technology (polymer electrolyte membrane) and eight pending patents. The first Prometheus will go into test operation in the third quarter of 2020.

Prometheus makes green hydrogen available on almost every company site, whether it is wind turbine operators, industrial companies with truck and forklift vehicle fleets, freight trains or hydrogen filling stations. In the future, they will all need energy solutions that can be used cost-effectively and reliably.

Prometheus electrolysis stacks offer this solution. They are the easy-to-integrate, cost-effective and high-performance centerpiece for climate-friendly hydrogen and therefore energy production.

The goal of company founder Dipl.-Ing. (FH) Stefan Höller: “We want to enable every company to be able to produce green hydrogen independently, economically and decentrally on the company premises. Thanks to Prometheus, the price per kilogram of hydrogen will be less than 4 euros.”

HOELLER Electrolyzer offers Prometheus stacks for this purpose in three compact sizes and nominal outputs.

The smallest stack is the size of a water bubbler and 76 kW – the largest 1.4 megawatt

  • Prometheus S – achieves a nominal output of 76 kW, produces 34 kg of hydrogen per day, with a footprint of 25 x 21 cm. It is about the size of a bubbler. With 1,500 full load hours a year, seven cars or two forklifts can be operated. A car can be filled up within three minutes.
  • Prometheus M – has a rated output of 325 kW, produces 147 kg per day, has a footprint of 42 x 29 cm and is roughly the size of a mineral water tank. With 1,500 full load hours a year, 32 cars, seven forklifts or a traffic bus can be operated.
  • Prometheus L – has a nominal output of 1.4 megawatts, 635 kg of hydrogen per day, has a base area of ​​60 x 48 cm and is therefore roughly the size of four mineral water boxes. The most powerful PEM stack from HOELLER can refuel 140 cars, 30 forklifts, five traffic buses, two trucks or half a train with 1,500 full load hours per year.
  • Prometheus stacks take up 25 percent less space.

In addition to performance and economy, the small space requirement and a reduced overall weight are decisive competitive advantages. The electrolysis stacks from HOELLER save around 25 percent in space and weight, which, for example, enables integration into the rotor head of a wind turbine.

HOELLER PEM electrolysis stacks: the technology, innovations and patents behind them

But what exactly makes Prometheus stacks more economical and powerful than other electrolysis stacks?

HOELLER StacksIn brief: HOELLER has succeeded in considerably reducing the cost-intensive use of the precious metals platinum and iridium. This is made possible thanks to an in-house innovation. By improving the surface structures, the reaction area is increased – this in turn leads to an increase in the performance of the HOELLER stacks.

There is also a fundamentally innovative structure for the electrolysis cells in order to further increase efficiency. Since fewer precious metals are used, production is also significantly cheaper and possible in large quantities.

Another factor is to achieve the highest possible outlet pressure of 50 bar and more in order to reduce the energy expenditure for compressing the hydrogen for storage.

In these points, HOELLER is already ahead of some of its competitors and is constantly optimizing its PEM electrolysis stacks in order to take a leading position in this technology in the future.


With its innovative PEM technology, HOELLER Electrolyzer GmbH is developing the future source of green hydrogen. More than 25 years of know-how and pioneering work by the managing director and development manager Dipl.-Ing. (FH) Stefan Höller now flow into Prometheus. These are innovative PEM electrolysis stacks. With the addition of electricity, water is broken down into hydrogen and oxygen. They thus represent the core component of future electrolysis or power-to-X systems. At Prometheus, HOELLER primarily focuses on a convincing price-performance ratio, minimized hydrogen production costs, impressive maximum performance, excellent service life and high hydrogen output pressure.


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