Crazy as it seems, with all the new renewable power and the battery storage systems being developed and tested, the 2000-year-old technology of flowing water to generate power is still the biggest mass storage solution we have. In fact, California is now pushing forward with a new pumped-water solution: Simply place pump water uphill when excess solar power exists during the day and power is generated (for free) as it runs it back downhill through turbines when you need power.
We have also seen a new type of rail car solution. Pull a heavily-loaded rail car uphill and use its engine to generate power when needed going to go downhill. This application doesn’t require all the water management and storage solutions both up top and down below, but it is still technically complex. We hope this can be deployed in a scalable fashion in the near future.
Of course, battery cost and technology are trying very hard to go to smaller and to produce more power-dense solutions while still being safe. Tesla is one of the first mega battery factories coming on line and we expect to see many more in Asia coming on line soon.
Deciding which storage system solution works best is always an interesting discussion. In the long run, the technology will win out.