6. Possibility of storage backup

6.1 Energy storage principle for the optimal 100% mix

What should be the minimum size of a storage system capable of supplying the optimal 100% mix. This ideal storage would absorb excess energy from surplus renewable energy production. It would then release this energy to supplement renewable energy production when the latter fails to meet the load. Pumped-storage power stations (PES) are the model for such storage. The surplus is used to lift water from a low reservoir to a high reservoir. This water can then be turbined in times of shortage. Efficiency is 75-80%