Centralised offshore hydrogen production

Abstract

Green hydrogen is expected to play a crucial role in the energy transition as it can be utilised for both storage purposes and as fuel for hard-to-abate sectors. One of the possible configurations for producing green hydrogen is by means of a central offshore hydrogen production platform powered by offshore wind energy. Producing hydrogen offshore facilitates the possibility to eliminate parts of the expensive electrical infrastructure present in conventional offshore wind farms and could result in lower losses.

In collaboration with Vattenfall, this study provides a thorough examination of centralised offshore hydrogen production. The study addresses both the techno-economic feasibility of the centralised configuration and the effects of aggregating the power supplied by individual offshore wind turbines.

In Part 2, the study presents a comprehensive techno-economic analysis of different electrolysis technologies, the optimal hydrogen production unit capacity, and compressor output pressure. The outcomes reveal that an optimal levelised cost of hydrogen can be achieved by reducing the hydrogen production unit capacity compared to the offshore wind farm capacity. Moreover, increasing the hydrogen pressure above the minimum pressure required to overcome the pipeline pressure drop, reduces the levelised cost of hydrogen further. The study reveals a small preference for hydrogen production based on proton exchange membrane electrolysis, in comparison to hydrogen production based on alkaline electrolysis.

In Part 2, the focus is shifted towards hydrogen production solely, influenced by power fluctuations. By using historical offshore wind turbine power output data, it was found that aggregating the power output significantly reduces the normalised power output fluctuations, compared to a decentralised offshore configuration. However, the reduced power fluctuations did not result in a higher hydrogen yield, attributed to the inter-array cable losses of the centralised configuration. Nevertheless, a significant reduction in the number of switches of operational mode and the number of turn-offs of the stacks was observed. Reducing the number of switches and turn-offs will reduce the process of stack degradation.

The study concludes that centralised offshore hydrogen production facilitates the possibility to produce hydrogen at a competitive levelised cost of hydrogen. Furthermore, the reduction of the power fluctuations will benefit this configuration due to the deceleration of the stack's degradation process.