Batteries are only the most expensive of a wide array of storage choices that today vie for which will end up cheapest, overall. Pumped hydro is mature, but underground and underwater compressed air are being proven; mine-shaft gravitic similarly; low-pressure LH2 is newly practical with aerogel insulation; carbon-captured LCH4, likewise; catalytic ammonia; and even powdered iron. None of these require any theoretical breakthroughs, just workaday engineering. In some cases combining them makes sense, such as mineshaft gravitics and compressed air in the same mineshaft. In other cases the storage medium is itself directly useful, as for example LH2 as aircraft fuel, and ammonia as both fertilizer and fuel.

Some depend on geography, particularly pumped hydro and mineshaft gravitic, and to a lesser degree compressed air. Catalytic improvements will bring rapid cost decline in LH2 and ammonia production. And, finally, battery technology, still the most immediately practical for home systems, is still improving fast. Any breakthroughs not anticipated only improve the picture.

The cost for utility-scale solar is many times less than roof-mounted, battery-backed home systems, but in places where distribution is expensive (rural) or unreliable (3rd world and California) it has strong appeal.