Stabilizing green hydrogen

Abstract

To mitigate the effects of climate change, CO2-emmissions will have to be reduced. This can be done by substituting the use of fossil, CO2-heavy by the use of renewable, CO2-neutral energy carriers. Hydrogen is such a renewable energy carrier that can be produced in a CO2-neutral way. The potential of hydrogen is recognized by the European Commission as specific renewable hydrogen goals are stated in their Fit for 55 package, which is a plan to reduce greenhouse gas emissions within the European Union with 55% by 2030. These goals relate to both the production and use of renewable hydrogen within the European Union.  For hydrogen to be qualified as renewable, the European Commission has proposed a set of requirements that its production has to comply with. One of them is temporal correlation, requiring the amount of energy used by a hydrogen production plant to match the amount of energy generated by one or more connected renewable energy plants. Renewable energy plants generate a variable output of energy as they rely on variable energy sources such as wind. This causes the production of renewable hydrogen to be variable as well. The fact that this production of hydrogen is variable can be problematic as some industrial processes require or perform better with a constant input of hydrogen. Energy storage systems, such as lithium-ion batteries, can be integrated in hydrogen plants to stabilize the hydrogen production from a renewable energy source. This works through locally storing part of the energy generated during peaks to be used at times when there is a deficit of energy. The purpose of this study is to see how different energy storage systems influence the performance of wind-hydrogen plants. A wind-hydrogen plant is a hydrogen plant producing hydrogen with an electrolyzer powered with energy from a wind park. Based on the outcomes of the study, wind-hydrogen plants can be designed incorporating the most adequate energy storage system for its purpose. The outcomes of the study can also be used by policy-makers to see how the temporal correlation requirement of the European Commission influences the feasibility of the hydrogen goals in the Fit for 55 package. The performance of wind-hydrogen plants with different energy storage methods is evaluated using a simulation model. After performing experiments for wind-hydrogen plants with different types of energy storage systems, their influence on the performance of the wind-hydrogen plant can be analyzed.  Results show that the hydrogen production from a variable energy source is lower and less stable than that from a continuous source. These effects can be mitigated with the use of energy storage systems. However, the introduction of these systems makes wind-hydrogen plants less efficient and drive up the costs of hydrogen production. This illustrates a trade-off as energy storage systems do increase and stabilize hydrogen production, but at a lower efficiency and higher cost.  Comparing the performance of individual energy storage systems shows that the use of lithiumion batteries to store energy results in the highest and most stable hydrogen. At the same time, the use of lithium-ion batteries is by far the most expensive option. The use of a hydrogen energy storage system results in the most efficient and cheapest hydrogen production. This shows that another trade-off is at play when selecting an energy storage system to integrate in a wind-hydrogen plant.

Based on the results, the effects of the temporal correlation requirement on the feasibility of the Fit for 55 renewable hydrogen goals can be analyzed. The requirement makes the hydrogen goals in the Fit for 55 package less feasible as it causes a decrease in renewable hydrogen production. It also makes it less fit for use by the industry as the hydrogen supply will become less stable. Energy storage systems can be used to mitigate these negative effects, however, these cause a decrease in hydrogen plant efficiency and therefore an increase in loss of renewable energy. Also, it drives up the production cost, making renewable hydrogen less attractive to use by industry and increasing barriers for new renewable hydrogen production to enter the market. The recommendation is for the European Commission to investigate an alternative requirement than the temporal correlation to ensure the renewable production of hydrogen.