Power tells you how large of a gap in grid capacity-vs-demand storage can cover while renewables are below peak production. That’s the important number, as long as the energy stored is sufficient to last until renewable output goes back up.

Giving an energy storage number by itself could be misleading because it seems the batteries that have been built take longer than an hour to discharge. So for example 26 GWh storage does not equal 26 GW grid capacity.

But this article, like many others does seem to be loose with the power-vs-energy metrics:

If 6,600 MW doesn’t sound like that much, consider it is enough to supply electricity to about 6.6 million homes in California for 4 hours

Maybe the implication is that the total energy storage is 26,400 MWh?