With the increase in renewable energy use due to environmental concerns and policy comes the need to make it actually it work (and cost-effective if possible). That is where energy storage comes in. An article in IEEE Spectrum looks at the storage situation today.

In the United States, 97% of utility-scale storage in 2014 was in pumped-storage hydroelectric plants, according to research by Oak Ridge National Laboratory in Tennessee. And in 2015, Citibank estimated that the cost of power from pumped hydroelectric was about 5% of the cost of grid-scale battery-stored electricity. The problem is that there are many places that consume high amounts of power but don’t have geological opportunities to build conventional pumped-storage plants, according to Jochen Bard, an energy processing technology manager at the Fraunhofer Institute for Wind Energy and Energy System Technology in Germany.

So the Spectrum article goes on to list four "new" ways to store renewable energy with water, including the concrete bunker, compressed air bags, energy island and wind turbines with water storage.

All unique and innovative, it remains to be seen whether they will be deployed widespread, or just used in specific instances. But each application is working somewhere and can be suitable alternatives to more expensive battery storage.