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Converting electricity into hydrogen in order to store sustainable energy over a longer period of time is a hot topic. With the help of the expertise and tools of Empa researchers, a master's student at ETH Zurich has investigated whether it makes sense to use a so-called "power-to-hydrogen-to-power" system in an apartment building.

How do you bring surplus energy from summer to winter? This is one of the central questions with regard to how we want to guarantee our energy supply in the future in a sustainable and at the same time secure way - especially because we want to manage without fossil energies in the future. This topic is also on the mind of master's student Josien de Koning. "The Swiss power grid currently has excess production in the summer, while we rely on imports in the winter. This imbalance will be exacerbated by electrification and the replacement of nuclear power plants with renewable energy sources such as solar energy. It's important that we find solutions to counteract this." In her master's degree in "Integrated Building Systems" at ETH Zurich, she therefore wanted to take a closer look at one of the possible solutions in a term paper at the beginning of 2022. She was supported in this by experts from Empa's "Urban Energy Systems Lab".

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De Koning focused on the integration of a so-called "power-to-hydrogen-to-power" (P2H2P) system. This is used to convert electricity - ideally surplus electricity - into hydrogen, store it and generate electricity from it again when needed. Accordingly, it includes various components, such as PV systems, an electrolyzer, hydrogen tanks and fuel cells. The big advantage here is that, unlike other storage methods such as batteries, the energy can thus be stored for months without any losses. "In my work, I wanted to find out whether it makes sense to integrate such a solution into an energy system. I chose an apartment building in Obersiggenthal as the object of investigation," explains de Koning.

The first step was to model the system using software. To do this, the master's student used the so-called "ehub tool", which Empa researchers had developed in recent years and from which the spin-off "Sympheny" ultimately emerged. The tool maps energy systems and performs calculations on them. First, de Koning defined in the software which components should be installed, which energy sources are available and what the building's energy requirements are. After this modeling, the system was to be optimized. To do this, the student fed the software with data from various databases. These included, for example, solar radiation, CO₂ emissions and electricity prices from the Swiss power grid, as well as various technical data for the individual components.

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The optimal solution

The software then used the input data to calculate the costs and emissions of a P2H2P system and a conventional system without the hydrogen components - once for the present and once for the year 2040. The aim was to see whether the solution, if this is not the case today, might have potential in the future.

On the one hand, it was shown that the P2H2P system was able to balance the energy imbalance as desired. Batteries and thermal storage were able to absorb the daily fluctuations, while the hydrogen storage was able to absorb the seasonal fluctuations. On the other hand, however, the P2H2P system was not identified as the optimal solution in any of the scenarios - thus, its integration was more expensive and had higher emissions than the conventional system in both 2020 and 2040. The main problem was the storage tank for the hydrogen, the size of which had a strong impact on costs and emissions.

Nevertheless, Josien de Koning is convinced that the system could have potential in the future: "It is quite possible that the P2H2P system in 2040 could be in an acceptable range in terms of price and CO₂ emissions. However, to achieve this, we must manage to significantly reduce the size of the hydrogen tank. The key factors here are technological improvements and price reductions in the system itself, as well as reducing consumption in general."

So if certain conditions change in the future, "power-to-hydrogen-to-power" could well help move surplus energy from summer to winter. In any case, it is clear that the topic will continue to accompany Josien de Koning in future work: "From my work at Empa, I am taking away many valuable insights and follow-up questions for my further academic path."

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