referred following article

https://ieeexplore.ieee.org/abstract/document/4603654/

Thank you dear Dr.D.S.Bhagat

Dear Frie,

Please check out this article: A new improved algorithm for optimal sizing of battery-supercapacitor based hybrid energy storage systems.

https://ieeexplore.ieee.org/document/8405059

Thank you dear Dr.Bashar Abdulrahman Mahmoud

Interesting question Frie Ayalew.

Not being an electric engineer, I think about the big picture, the fact we need energy storage, say some 10 times that of national consumption . The reason is , I believe, we need ligate energy storage with what you need most, water, and shifting it to where it's needed in the next 150 years of increasing droughts, not batteries to do it.

Super batteries and capacitors as such in my mind will never do it. Though of course important buffers locally. Or if I'm wrong please tell me?

One strategy is to use super sized water tanks in the perimeter of nations, even sea water will do to shunt water up say 200 to 400m high from renewable energy. Though the same strategy can be used along major rivers, or aquifers in conjunction where dams are environmentally or physiographically unfeasible. Water storage similar to decentralized city water tanks, orders of magnitude larger and or blocked physiography and gullies in multitudinal mini dams to reduce environmental footprints of major ecosystems.

Of course fresh water would be better then salt water in reticulating energy and water nationally with both electric lines and fresh water pipe lines, regional facilities connected, shunting power-water storage and delivery optimally in such proposed national Grid. A national fresh water (and energy) storage system if you like, harvested from various sources, such as flood runoff wasted to coastal areas, aquifer (with net recharge from coastal runoff waters), supplement desalination if needed locally, etc, powered by massive renewable energy.

Think of the population explosion and environmental needs of Mega cities and nations coming to Africa in the next 200 years.

The advantages are: economic diversity; agriculture, aquaculture, silviculture, environmental -wildlife corridors, fire retardation strategies, desalination of soils, carbon fixation in soils, food security and clean water for hydrogen generation (needs clean fresh water) with electric driven industry and transport having access to water-power storage and their output nodes everywhere.

Dear Bernhard Rupert Hochwimmer  thank you so much for your intersting description as well answers too...