The energy transition is the topic on everyone's lips. But how can green energy be stored for use when the wind is not blowing and the sun is not shining? Power-to-X (P2X) might be the answer.

By Nikolaus Fecht

© NEA GroupWorldwide efforts to protect the climate and reduce the cost of generating electricity from renewable energies are heralding a new phase in the energy transition and its country-specific initiatives all over the world. Up to now, renewable energies have mainly been used to generate electricity, but climate-neutral energy sources are increasingly being sought for transport and heating (process and buildings). For the time being, there are many applications that can use direct electrification, which seems very probable given the rapid progress of battery technology. The most obvious example is the battery-powered electric car, which can cover a large proportion of individual mobility. Applications like shipping, air transport, trucks and industrial processes, however, demand energy sources with a high energy density and appropriate storage capacity.

Chemistry is the answer here - hydrogen and especially hydrocarbons, which can be formed from hydrogen and carbon dioxide, have proved to be useful energy sources. All fossil fuels consist of hydrocarbons. The crucial aspect is that hydrogen can be produced from water in a proven electrolysis process, using energy. Renewable electricity and water thus form the basis of emission-free or at least emission-neutral gaseous substances such as "green hydrogen" and methane (power-to-gas), liquid fuels (power-to-liquid) and chemical raw materials (power-to-chemicals). "This would make an important contribution to decarbonization in the chemicals industry and in the transport sector," says Ragnar Strauch, Process Technology Consultant at VDMA. A single term has become established to cover the diverse applications: power-to-X, or P2X for short.

P2X and gas network storage for renewable energies

Both relevant quantities of hydrogen and unlimited quantities of methane can be safely stored in the natural gas grid and in underground cavities for the long term. This means that a greenhouse gas-neutral fuel is available at any time - as long as the carbon dioxide used to create the methane does not come from burning fossil fuels. Even then, repeated use is kinder to the environment.

In today's system, increasingly shaped by renewable energies, this is currently the only storage solution that can bridge the times when there is insufficient wind or sun - sometimes for up to two weeks. The fact that alternative energy sources can also be a huge help during temporary dips in supply on electricity networks will be a vital aspect, at least over the next few years.

Green gas is the answer

Even local solutions have enormous potential. "All these interesting approaches have inspired us to pay more attention to P2X. After all, it enables clean, climate-neutral alternatives to be developed on the basis of existing, highly-developed engine technologies," explains Peter Müller-Baum, Managing Director VDMA Engines and Systems. "In shipping, for example, battery-powered electric drives will only be suitable for use in a few niche applications in the foreseeable future. Green gas generation is at the heart of it all."

Andreas Rupieper © LindeAndreas Rupieper, Head of Group R&D and Portfolio Management, Technology & Innovation at Linde AG in Munich, sees green hydrogen as one of the key factors in achieving the energy transition, as the gas is a central P2X element that is suitable for sector coupling. In the long term, he could even imagine "separate hydrogen pipelines, as end users generally limit the amount that can be added to the existing natural gas grid to ten percent."

Hydrogen is suitable not only for storage, but also for supplying classic and new fields of application, such as power-to-liquid/chemicals, especially for fuel cell vehicles. "H2 mobility is a good opportunity to decarbonize the transport sector early, both on road and rail," says Rupieper.

When it comes to H2 mobility, the Munich-based company is using beacon projects to create early inspiration and positive examples for the switch to this environmentally-friendly technology. Linde is using his long-standing expertise in hydrogen supply, for example, to pave the way for fleet operators to use fuel cell technology. "Together with our partners, we are investing heavily in the establishment of a network of hydrogen filling stations in Germany."

Expansion of the hydrogen filling station network

Linde is working with partners in the H2 mobility consortium to support the establishment of a comprehensive network of 400 filling stations for hydrogen. Vehicles will soon be able to fill up with hydrogen at around 100 filling stations in Germany. "We hope that this will increase acceptance among consumers. Even today, customers already need less than five minutes to fill up their fuel cell vehicles for ranges of up to 500 kilometers."

Dr. Andreas Hartbrich, Managing Director of Silica Verfahrenstechnik GmbH in Berlin, sees coordinating the various fields as the biggest challenge for the energy transition. This complex jigsaw of different technologies needs to be brought together into a useful overall picture, he says. "I would like to see some support from policy makers here. So far, all they have contributed to the energy transition is the power lines for distributing green electricity."

But processes have already developed further, with the Berlin-based company's technologies being used not just for power-to-gas, but also for power-to-chemicals systems. "For example, one of the largest variable five-megawatt electrolysis systems in northern Germany recently began working with one of our systems for cleaning and drying the hydrogen generated," reports Hartbrich. If someone operated a system like this with regenerative wind or solar electricity, refineries could use the emission-free "green" hydrogen generated to produce fuels and oils. This would be an excellent alternative to E10 gasoline, he continues.

Hartbrich sees methanation as a second interesting option. "We have just handed over a pilot system that uses green hydrogen from an electrolysis system and excess CO2 from a biogas system to produce methane," he explains.

Andreas Hirschter © NEA GroupNeuman & Esser Verwaltungs- und Beteiligungsgesellschaft mbH (NEA Group) from Übach-Palenberg, near Aachen, builds gas storage systems. A subsidiary of this Rhineland-based family company is active in integrated energy, in which different industries that are usually separate work together.

Condensed hydrogen powers buses

Systems that provide hydrogen at an extremely high operating pressure of 1000 bar for filling fuel cell vehicles with green fuel are already being built. While this application is already being implemented, storing gas and transporting it via existing gas networks is still a long way off in North Rhine-Westphalia. Andreas Hirschter, Head of Strategic Marketing: "I am sure that the NEA Group will be more active in this field in future, including with a view to power-to-X."

Stephan Schmidt, Product Manager Fuels at Chemieanlagenbau Chemnitz GmbH (CAC), sees the switch from fossil fuels to a climate-friendly economy as the biggest challenge. "We need to focus on decarbonization, i.e. on processes that prevent or compensate the release of carbon dioxide. Technologies suitable for industrial use already exist, but there are no investors building the relevant systems and acting as pioneers." However, he says, there is a need to motivate the entire population to take part in this process.

The Saxony-based company is already demonstrating how this can work with systems for fuel synthesis. "Together with our partners, we have demonstrated how synthetic gasoline can be produced from hydrogen and CO2, reducing emissions by at least 80 percent," says Schmidt. "At one euro per liter (in favorable conditions), the production costs are higher than those usual for fossil gasoline, but still less than the end price usually paid at filling stations." The regulatory conditions now need to be adapted to make the transition to the fuel market tolerable. As a technology provider, CAC develops and builds systems that produce synthetic gasoline.

Establishing alternative energy sources

Stephan Schmidt © CACSynthetic fuels are only climate-neutral, however, if the electricity needed for production comes from renewable energy sources. "The alternative energy sources currently available are insufficient," emphasizes Schmidt. "Renewable energy generation therefore needs to be expanded further in order to ensure sufficient supply for the production of synthetic fuels." The Chemnitz-based company not only plans and builds this kind of system, but also provides support in project development and the development of new business models. Since synthetic gasoline has very similar properties to fossil gasoline, no significant changes need to be made to engines currently common on the roads. Car manufacturers plan to test the synthetic gasoline in existing fleets and are demonstrating great interest in this kind of concept.

For Rolls-Royce Power Systems AG in Friedrichshafen, P2X is also an important opportunity to back up volatile alternative energies and use them better. Dr. Daniel Chatterjee, Head of Product Management "Small, Large and Classic Engines"/"Green & High-Tech Programs", says, "furthermore, electrification in the heavy goods or high-performance off-highway segment is only possible to a limited extent." However, according to Chatterjee, the evolution of the combustion engine combined with hybridized drives and alternative fuels could reduce CO2 emissions considerably.

Rolls-Royce Power Systems is taking a two-pronged approach with its green and high-tech strategy. On the one hand, the Friedrichshafen-based company is researching and developing new gas generators that have the power shift behavior of diesel generators and are also highly efficient. "The aim is to use gas as control energy," explains Chatterjee. "On the other hand, our approach to mobility - especially in shipping - is moving towards gas engines." The first achievement here is a specially-developed gas engine that offers the same performance and properties as a diesel generator.

Natural gas as a bridging technology

Dr. Daniel Chatterjee<br>© Rolls-Royce Power Systems The first potential fuel is liquefied or compressed natural gas (LNG/CNG), a bridge technology that enables a start in P2gas. In the next step, these fossil gases will be replaced with green, synthetic fuels.

The company is pursuing the same goal with diesel fuels. "Synthetic diesel is much cleaner when burned," the expert reports. Given the increasingly-strict emissions guidelines, the exhaust gases will probably still need to be treated - although clean combustion means that this treatment will last longer. "As a manufacturer of full drive and energy solutions, we need to think beyond the engine. We are currently launching a joint project looking at the entire chain, from P2X generation to use. This type of sector coupling is the key to the future," emphasizes Chatterjee.

"For us as a producer of ships' engines, P2X is one of the key technologies for the maritime energy transition. After all, the shipping sector also wants to, and indeed must, contribute to implementing the Paris climate accord,§ says Dr. Matthias Auer, Head of Department in Pre-Development at MAN Diesel & Turbo SE in Augsburg. §Given the enormous freight volume and ranges in container shipping, full drive electrification is not technically feasible in the foreseeable future." However, he continues, electrifying the fuel would enable the switch to climate-neutral shipping without changing the drive technology.

Need for clarity from policy makers

Auer believes that there are still regulatory issues to be resolved with regard to P2X, including promoting the expansion of regenerative energies and regulations for CO2 trading. "There is a lot of uncertainty for potential investors in P2X systems here," he stresses. "Providing clarity and planning certainty here is a task that policy makers urgently need to address in the coming legislative period." Investment in P2X will only come once this issue is resolved, says Auer.

Matthias Auer © MAN Diesel & Turbo "We are taking a systematic approach to the topic. We developed the heart of the Audi e-Gas project in Werlte - the reactor for producing methane - and are now operating it successfully." As part of this project, electrolysis and green electricity are used to produce hydrogen, which the car manufacturer uses for methane production. The system has been feeding the green gas into the regular gas network since fall 2013, compensating for the natural gas used by Audi customers. The Augsburg-based company has high hopes of the 25 million-euro E2Fuels project, in which MAN acts as consortium coordinator, working with 16 partners from industry and research to advance electricity-based fuels even further. Auer says, "taking a holistic approach, we are working on the efficient production of P2X fuels and their use in engines."

Association platform P2X4A

This fits in well with the work of VDMA, which is already thinking about the next practical step - the foundation of an Association platform P2X4A. 4A stands for "for applications" in various fields. "There is no way to accurately predict how P2X4A will develop over the next 20 years or more, so we are ensuring that the legal framework is formulated in a technology-neutral way," says Peter Müller-Baum. "For this to work, policy makers need to move away from defining a single technology to the detriment of all other developments. They need to be open to all technologies, so that industry itself can develop the best solutions."


Further Information

VDMA Process Plant and Equipment   |   VDMA Engines and Systems   |   CAC   |   Linde Group   |   MAN Diesel&Turbo   |   NEA Group   |  Rolls-Royce Power Systems   |   Silica    

Ragnar Strauch, VDMA Process Plant and Equipment.
Peter Müller-Baum, VDMA Engines and Systems.