World's largest power-to-gas plant of its kind: A blueprint for sector coupling? 

The big question about future energy systems is how to design them so that they’ll remain stable despite volatile energy generated from wind and solar power. One important solution are Power-to-X technologies. Armin Schnettler, head of the Research in Energy and Electronics unit, and Gabriele Schmiedel, head of Hydrogen Solutions at Siemens Energy, discuss the functionality, opportunities, and prospects of this technology. A plan by the German transmission system operator Amprion plays an important role.

By Ulrich Kreutzer

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Everybody’s talking about power-to-gas technologies. What does the term mean and why is it becoming increasingly important?

Schmiedel: Power-to-gas technologies are the bridge between energy generation out the volatile energy and other sectors. The principle is simple: “Green” electricity and water are converted to carbon-neutral hydrogen and oxygen in an electrolysis process. The hydrogen can then be stored in existing gas infrastructures and used as fuel or as a raw material in industry. Power-to-gas technologies can thus balance volatile renewable energy generation and make a vital contribution to the success decarbonization of every sector.

Schnettler: Take Germany, for example: Today, renewable energies make up more than 30 percent of the overall power supply. The higher the percentage grows, the greater the demands on our grids, which have to accommodate the volatile energy. This is where power-to-gas comes in. Today there’s already a number of plants in regular operation in the single-digit megawatt class. So we’re already headed in the right direction! But to guarantee grid stability and security of supply with 50 or more percent renewable energy, the size of plants must increase considerably in the future.

Does this also mean that grid expansion, which is also necessary for the integration of wind and solar power, can be completely replaced by power-to-gas technologies?

Schnettler: No, this isn’t an either-or situation. We need an immense grid expansion worldwide, especially over the next 10 to 15 years. In 15 years at the latest, expanding the grid infrastructure will no longer be sufficient in itself. We need storage facilities and new consumers – a variety of them. One is power-to-gas. The background is obvious: The percentage of renewable energies will grow worldwide, while at the same time its levelized cost will drop considerably. The PV price in Europe today is already under 4 US cents per kilowatt hour. 


In windier and sunnier locations such as the Middle East, it’s even less than 2 cents! At the same time, the goal is to decarbonize all sectors – to which power-to-gas can make an important contribution. The generation of carbon-neutral hydrogen and its further use is a major contributor for this sector coupling, meaning the increasing interconnection of all sectors, including electricity, heating/cooling, gas, industry, and mobility.

" It’s important that we be equipped to deal with the requirements of a future energy supply. We expect renewable plants to grow further. "
Armin Schnettler, head of the Research in Energy and Electronics unit
The transmission system operator Amprion recently revealed plans for a power-to-gas plant with a power rating of up to 100 megawatts in Germany. What does this announcement mean for the industry as a whole and for Siemens Energy in particular?

Schmiedel: We consider Amprion’s plans to build a plant with an output of up to 100 megawatts a strategic milestone! It’s crucial that we scale the size of existing plants, and quickly. Our goal regarding the electrolyzer power is to grow by a factor of ten every four to five years. It’s the only way that we can keep pace with the steep growth of renewable energies. Our electrolysis system at an oil refinery in Hamburg – based on the Silyzer 200 – with a 5 megawatt continuous power rating is now the largest plant in continuous operation in the world. We’re currently working on the new Silyzer 300 product generation as part of the EU research project H2Future in Linz, Austria. That plant will have a 6 megawatt capacity. We’ll then rely on a modular design to advance to the 100 megawatt performance class, based in Silyzer 300.

Schnettler: It’s important that we be equipped to deal with the requirements of a future energy supply. We expect future renewable plants to grow further. In some regions it could increase more than ever before, especially by plants more than a few 100 megawatt. That’s why we have to be willing to provide plants in precisely this performance class, and to do so we need to acquire well-grounded operational experience as quickly as possible. Amprion’s plan is the logical next step in the right direction if we want to accelerate power-to-gas technologies and launch them on the market.

What’s special about Siemens Energy’s Silyzer solution?

Schmiedel: We use PEM electrolysis, which is based on a proton-conducting membrane. In contrast to traditional alkaline electrolysis, it’s ideally suited to harvesting power that’s irregularly generated because it can be quickly switched on and off without preheating. The heart of the system is the proton exchange membrane. Its special property is that it’s permeable to protons but not to gases such as hydrogen and oxygen. In an electrolytic process, it functions, among other things, as a separator that prevents the product gases from mixing. On the front and back of the membrane are electrodes made of noble metal that are connected to the positive and negative poles of the voltage source. That’s where the water molecules are split.

Where is the carbon-neutral hydrogen that’s generated used?

Schnettler: Hydrogen is multifunctional. The good thing about hydrogen is that it’s easy to store, to add and to transport – for example, in the existing gas grid, which has a total length of 511,000 kilometers. According to the DVGW (the German association for gas and water), Germany currently already has the capacity to store about 200 terawatt hours of energy in underground gas storage facilities – which is about 23,000 times the capacity of a state-of-the-art pumped storage power plant.

Schmiedel: Hydrogen is also used as a process gas in industry, as an alternative fuel in mobility, and as feedstock for valuable chemical substances. In the future, even reconversion is worthwhile.

Let’s talk about fuel: What role can power-to-gas play in changing mobility?

Schmiedel: In the future, synthetic fuels will play a key role in the mobility sector as “green” fuels. In particular, hydrogen is an ideal energy source for the long-distance transport of freight by rail or road. It can be supplied via a pipeline system but can also be generated on site at the gas station using an electrolyzer. Moreover, “green” hydrogen can be used in chemical plants, which are producing synthetic methane or “green” fuels.

From today’s perspective, what are the greatest challenges on the way to power-2-gas plants in the three-digit megawatt range?

Schnettler: Naturally, the price is key. But I’m confident that with the cost of renewable energies continuing to drop, “green” hydrogen will already be able to compete with traditional hydrogen generation within just a few years. And with total carbon neutrality, of course, whereas normal production produces about 10 kilograms of CO2 per kilogram of hydrogen! Projects as the one of Amprion can help to bring technology on the right level of industrialization. That’s what we need to retain our leading technology position, to gain more knowhow and expertise and to strengthen economic output.  

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July 05, 2018

By Ulrich Kreutzer


Combined picture credits: Siemens Energy