Signalling the cost of intermittency: What is the value of curtailed renewable power?

Curtailment of renewable power, which results from the intermittency of renewable sources, is inevitable from an economic perspective, especially for islanded systems. This work explores the economic value of curtailed renewable power using methanol production with a dedicated renewable power system as a basis. A cascade design of methanol plants is proposed that the first plant is powered by renewable energy directly from renewable power generation, whereas the subsequent plants are powered using the curtailed energy from the previous plant. The size of the subsequent plants and energy storage units are optimised using a modelling approach. When the first and the second plant are compared, it is found that the levelised energy cost of the second plant is significantly reduced by 34.9%. However, the reduction in levelised cost of methanol is negligible since the optimal size of the second plant is only 2.8% of the first plant, which in turn reduces its economic potential due to economies of scale. After the second plant, the economic optimality of the subsequent plants has shown a dramatic increase in the production cost, meaning that the utilisation of the renewable power curtailed twice or more is economically infeasible. The cost breakdown shows that the main hurdle in curtailed renewable power utilisation is the electrolysers, which are designed with excess rated power in order to accommodate the enhanced variability of the curtailed power. The analysis concludes that the curtailed renewable power has promising economical potential; however, the portion of the curtailed power that can be used economically is insignificant.