All told, batteries can approach 50% efficiency, not much more at this time.

Interestingly, pumped hydro has greater than 80% efficiency. Ought to be considered in a state like CA.

The advantage of battery storage is that the stored power is available immediately. The disadvantage is the cost and the difficulty in recycling batteries after they die. And that's another negative. Batteries don't last forever. Only so many recharging cycles over which their capacity decreases.

I still look at this as a positive as long as CA opens the door to other storage techniques.

The advantage that batteries have is that they can respond to the minor problems in our electric grid cheaper and faster than anything else that is available - even pumped hydro. Everything else takes much longer to respond.

In order for a gas plant to respond they have to have keep boilers up to heat, same with coal. I wonder how much of our capacity is in standby mode, waiting to fill the gaps that nobody can predict? I wonder how much coal, natgas and uranium is being used wastefully just in case?

Batteries are just like any manufactured product - the more you make the cheaper they become and the more money that is available for R&D to make them better.

You need power now, you got it, if there's charge in the cells.

As you say.

The disadvantages are, as I said, cost and lifetime.

For example, The Edmonston Pumping Plant.

When the plant was built it ran more or less continuously, pumping water to Southern California over the Tehachapi Mountain Range.

In 2004 Hitachi was commissioned to build variable speed pumps that would power up when electricity was plentiful and and power down when electricity was scarce.

So much water is moved around the state there are still plenty of hydroelectric opportunities left to exploit, better than batteries. Off channel hydroelectric schemes are still better than batteries, mostly because battery lifetimes are so limited. The harder you use batteries, the quicker they wear out and the sooner they have to be recycled at some negative cost to the environment. Hydroelectric schemes can be built to last centuries.

Unless those huge pipes running up the mountainside above it are for something else (Hetch Hetchy H20, maybe)?

Dunno if 'solar' is involved either in the pumping but I'd not be surprised.

And yeah, I'd think there's lots of opportunities for something like that in CA as you say ... tons of power-producing reservoirs up in the foothills right above areas that get a whole lotta sun ...