The impact of power management strategies and module sizing for offshore wind turbine integrated electrolysis

Abstract

Solar and wind will displace fossil fuels as the main source of energy in a net-zero world. However, renewable energy sources provide intermittent power, hence an energy carrier that enables the balancing of demand and supply is needed. Here green hydrogen comes in place.
In addition, the demand for green hydrogen is expected to rise in the coming decades.
Given the geographical wind resource availability combined with supportive policy, the supply of green hydrogen can be delivered through offshore electrolysis. Moreover, in addition to higher yield, going further offshore creates a stronger case for hydrogen export as power export would become impracticable.
The energy industry is investigating what kind of typology and system configuration is most suitable for offshore green hydrogen production. This report provides insight into the performance of a single wind turbine integrated electrolysis system. For which the effect of different control strategies, electrolyser dimensioning and electrolyser capacities are analysed.

The study comprehends the requirements for transforming a single wind turbine into decentralised hydrogen producing wind turbine. This configuration is designed for an offshore application, but is not restricted to an offshore location. This novel system is equipped with a power conversion system, to power the electrolyser and auxiliaries. Seawater lift with water treatment for desalination and demineralisation. And ultimately, the electrolyser with accompanying balance of system.
This study selects a PEM electrolyser with three parallel modules of 5 MW capacity each. The individual components are separately modelled and combined to complete the system into a mathematical model. Furthermore, a power management strategy is included. The power management strategy determines which, how much and how many modules are powered. The enhanced results are measured by key performance indicators, which are total annual yield, number of start-stop events and power fluctuation within a module. These KPI's are inspired by the drivers of Shell to get the lowest levelised cost of hydrogen. More hydrogen production drives down the costs and the two other KPI's ensures less degradation on the modules, therefore extending the longevity.

This report shows that the use of a power management strategy improves the annual yield, but is also capable of minimising the effect of degradation caused by start-stop events and power fluctuation. The equal power division strategy increases the annual yield by at least 2%. The total number of power fluctuations can be significantly reduced by using the segmented start strategy. Finally, a strategy is developed to enhance the longevity of the system and diminish the degradation of the modules.
Moreover, independent of the strategy, a higher annual yield is achieved by decreasing the size of the modules with the same total electrolyser capacity. However, only when it is operated on the right setpoint.
Furthermore, over-sizing of the electrolyser capacity results in under-utilisation of the electrolyser. While under-sizing the electrolysis capacity leads to an increase in performance as the system is utilised more efficiently. The results are tested and strengthened in a sensitivity study, where other wind conditions and design parameters are applied to the system.