The transition to a system where an increasing proportion of energy is produced by variable sources, such as solar and wind, requires strategic development of energy storage systems. This chapter introduces various energy storage solutions that are needed to stabilize the variability of wind and solar power production. To reduce the required capacity of the largest storage systems, it is necessary to rethink the energy system as a whole. For instance, it may be more efficient to store energy as low-temperature heat rather than electricity, if this is in line with the end-use. Furthermore, it is essential to assess which components of energy generation and load are already flexible or can be made flexible. Additionally, the chapter addresses the so-called “hard-to-abate” sectors that are challenging to electrify, including heavy road transportation, marine transportation, aviation, and the chemical, cement, and metallurgical industries. These sectors have been constructed entirely on fossil-based raw materials, and as we transition away from fossil resources, it is essential to identify alternative solutions for these sectors. In the context of transportation, e-fuels derived from hydrogen and captured CO2 represent a promising avenue for continued utilization of internal combustion engine and gas turbine systems, which is advantageous in terms of scalability. Similarly, for chemical and metallurgical industries dependent on coal, oil, and natural gas, the potential exists to substitute these with green hydrogen and CO2 as raw materials.