I can't endorse this perspective enough. The amount of energy storage we need is staggering and ever-growing. We've someone convinced ourselves that the 'baseline' is consuming with abandon millennia worth of stored energy and anything even slightly less responsive than that is too inconvenient. Given those parameters, we need any and all energy storage options and efficiency is not a priority. Tesla powerwalls were never going to power the world, but giant caverns full of sand might.