The representation of hydrogen in open-source capacity expansion models

The intermittent nature of wind and solar power has led to a scientific consensus in the international energy research community that a mix of energy sources and carriers is necessary to achieve carbon neutrality. The search for alternatives has sparked renewed interest in Hydrogen (H2) and its derivatives, such as ammonia and methane. It has also motivated researchers to expand their models to study H2 investments in future energy systems. However, despite years of well-motivated research, a single scalable model that captures the unique characteristics of H2 does not yet exist. It is a consequence of the limitations imposed by computational resources and the availability of data. With the above motivation, we review the current literature on relevant aspects for H2. We find that temporal resolution, seasonal storage, spatial resolution and grid representation, uncertainty, and sector-coupling are important to accurately model H2. We then analyze 18 case studies based on 11 open-source Capacity Expansion Models (CEMs) applied to study power or energy systems in developed countries that include H2 and evaluate which models capture these idiosyncrasies best. Although no model covers all aspects simultaneously, some models tend to be more efficient in certain aspects, which ultimately depends on the underlying research questions they aim to address. We also outline potential research directions in this area. © 2024 The Authors