"Power-to-gas" is the name of the concept aimed at connecting the power network to the natural gas network. Researchers at the Paul Scherrer Institute hope that it will enable solar and wind energy to be stored longer. Collaborating with industrial partners, they are testing procedures under real conditions on a platform with containers packed full of high-tech equipment.

Marcel Hofer, Head of the Realisation project and ESI coordinator (left) and Peter Jansohn, Head of ESI. (Photo: Kellenberger Kaminski Photographie)

On the site of the Paul Scherrer Institute (PSI) in Villigen, the future of energy is housed in six white containers, which are lined up on a platform called "Energy System Integration", or "ESI" for short. The containers consist of compact, state-of-the-art systems. They can be used to produce hydrogen and natural gas, and the hydrogen can be converted back into electricity in the fuel cells if needed. There are tanks beside it containing hydrogen, oxygen and carbon dioxide, which are connected to the platform. The board in front lists the names of over twenty project partners, users and support institutions, including the ETH Board, EPFL, ETH Zurich and Empa, as well as the new site of the Swiss Innovation Park, PARK INNOVAARE, which is located close by, and Swissgrid, the electricity network operator.

"If photovoltaic systems and wind turbines are developed as expected, in future we will have to store several terawatt hours of energy in the summer to use in the winter", explains Peter Jansohn.

"The conversion of electricity into hydrogen or methane is central to the ESI platform," explains Peter Jansohn, Head of Energy System Integration at the PSI. If nuclear power is to be replaced by renewables as part of the government's 2050 Energy Strategy, new storage facilities will have to be developed. Solar and wind energy do not only deliver power when it is actually used. The potential of pumped storage hydro power stations has already been exhausted in Switzerland, and batteries are not suitable for storing energy over long periods. Peter Jansohn explains that "If photovoltaic systems and wind turbines are developed as expected, in future we will have to store several terawatt hours of energy in the summer to use in the winter."

The surplus, electrical energy is to be used to produce chemical sources of energy, a concept known as power-to-gas. Therefore, one of the ESI containers houses an electrolyser, which splits water into hydrogen and oxygen. The plant has an output of 100 kilowatts. "Consequently, it is big enough to only require one further scaling step to make it suitable for commercial use", explains the Head of the ESI.

A new exhibition lets visitors experience for themselves the complex challenges of supplying energy with new, renewable energy sources, together with approaches to solving these problems. (Photo: Kellenberger Kaminski Photographie)

A fuel cell system in one of the containers opposite, in turn, produces electricity from the gases. This can be deployed on a stationary basis for a household energy supply, for instance. A fuel cell can also power a vehicle electrically. In the case of both the electrolyser and the fuel cell system, the PSI is using technology with which it has decades of experience. At the heart of the systems are cell stacks with a polymer electrolyte membrane (PEM). In addition, the fuel cell system is operated with pure oxygen instead of air, a process which was developed at the PSI and which is particularly efficient.

There’s even potential in using biomass

The PSI researchers also produce methane from the hydrogen using carbon dioxide from the tank beside the platform. This artificial, CO2-neutral natural gas can be stored with excellent results and can be fed directly into the existing Swiss pipeline network. "The natural gas network itself acts as a reservoir because the pressure can be varied seasonally, easily enabling it to accommodate several terawatt hours," explains Peter Jansohn. "Consequently, we regard the power network and the natural gas network as a perfect, complementary pairing.”

With the help of the interactive model town Esiville, the path to a future energy supply for Switzerland is presented as a story. (Photo: Paul Scherrer Institute/Mahir Dzambegovic)

The methanation plant on the ESI platform has already been put to major external use. In January 2017, Cosyma (short for "Container-based system for methanation") was lifted by crane through a gap in the platform roof, loaded onto a transporter and taken to the Werdhölzli fermentation and sewage-treatment works (project partner is Energie 360°) in Zurich. During 1000 hours of continuous testing, Cosyma produced 60% more biogas from biowaste than conventional methods. Here's the secret: hydrogen is fed into a fluidised-bed reactor where it combines with carbon dioxide that is contained in the raw biogas. This creates biomethane which can be fed directly into the natural gas network. In January 2018 the Swiss Federal Office of Energy (SFOE) awarded the PSI and Energie 360° with the Watt d’Or in the “Renewable energy” Category.

Cosyma has been returned to the PSI in the meantime, and Peter Jansohn is taking stock: "Biomethane production is such an efficient process that the method has great potential to be put into practical application." It would enable about 100 sewage-treatment plants in Switzerland to produce green methane.