Professor Andrew Blakers and Professor Ricardo Rüther (UFSC) have published an article in PV Magazine discussing the need for energy storage to support variable renewable installations around the world. The Global Pumped Hydro Atlases, available within this website, show 820,000 possible pumped hydro systems around the world. These pumped hydro systems can be effectively combined with battery systems to create superior hybrid storage systems, as detailed in the extract below:
Hybrid storage systems that combine batteries and PHES are superior to either technology alone. Batteries are relatively inexpensive for storage power ($/GW) but are expensive for energy storage ($/GWh). PHES is more expensive than batteries for storage power ($/GW) but much cheaper for energy storage ($/GWh). A hybrid system has both cheap energy (GWh) and cheap power (GW).
In a hybrid system, storage can charge storage. A large PHES reservoir can trickle charge batteries 24/7 for a week during a calm and cloudy period. For example, a PHES system with 350 GWh of energy storage and 2 GW of generation power can trickle charge twelve 4-hour batteries (48 GWh) every day for a week. Such a hybrid system effectively has energy storage of 370 GWh and storage power of 12 GW. A battery-only system would run out of energy after the first day, while a PHES-only system would be underpowered.
The article can be accessed here.
The above image is from Sirbatch, via Wikimedia Commons.