Seasonal energy storage is key to the future of fully decarbonised energy systems. Geological features capable of storing hydrogen at low costs are not universally available, and solutions to store renewable energy above ground will be required. In this study, an isolated energy hub investment optimisation model is developed with a constant demand centre of 100 MW, and different aboveground seasonal energy storage solutions are evaluated with different minimum load operation levels. In addition, the effects of different temporal optimisation resolutions and optimisation windows are evaluated. The results show that the current utility-scale lithium-ion battery system performs poorly in techno-economic terms at the seasonal storage level. Similarly, compressed hydrogen tanks are among the least competitive options. In contrast, ammonia and methanol are the most cost-effective solutions for new development sites reaching break-even electricity selling prices of 116€/MWh. However, for power generation sites with existing infrastructure like gas turbines, storage and pipelines, Fischer-Tropsch fuels become the most competitive option. Process capacity flexibility is also studied, and it is shown that it significantly decreases the costs. For these evaluated processes to reach commerciality, developing flexible production processes is crucial and should be prioritised. Finally, it is shown that seasonal storage investment is lower when lower temporal optimisation resolutions are used and increased when longer optimisation windows are considered. • Ammonia and methanol are the most cost-effective solutions for new developments. • Fischer-Tropsch fuels are preferred for existing power generation sites. • Lithium-ion batteries are the worst-performing option in all scenarios. • Capacity flexibility is key to decreasing energy storage costs. • Low temporal resolution and short optimisation periods decrease storage investment.