>EV batteries...
I'm not even sure of that: EV batteries tend to be expensive - What does it cost you in terms of incremental battery expense to store a single kWh of power? Tesla claimed a replacement price for an 8 year old 85kWh battery of ~$12,000 (probably on the assumption that production costs will fall), at which point you're probably *really* wanting a new battery. Let's be generous and say that's based on one full "new" deep-discharge cycle on a daily basis - that's $12,000 / (85kWh/dy*8yr*365dy/yr) = $0.0483/kWh. So at least 5 cents worth of battery expense for every kWh stored. You really think the power company is going to be willing to pay you more than that much to store a single kWh of power for a while? I'll bet you purpose-built alternatives can store a kWh of power MUCH cheaper that that.
> Adding a big storage battery to every solar install is a pretty big chunk of cash...
Right. It also only really makes sense if your production routinely exceeds consumption, or you just want to get off the grid for other reasons.
It makes much more sense, for the transitional future, to have at least a few minutes, preferably a few hours, of grid-tied power-buffer, and on-demand power generating facilities available to take up the slack when buffers run low. In essence you rent your batteries and back-up generator from the power company, who also handle operation and maintenance, and can harness economies of scale. Solar generating on the other hand, by necessity, requires a large exposure area. Rooftop solar is a convenient way to co-locate generating facilities in residential and commercial areas, and the legal logistics are much simpler if you own the panels on your own roof.
Such buffers only barely makes sense now, except in places where high solar uptake is stressing residential power systems. But we have to start investing in deploying them if we're going to drive down the cost of producing them. There's a whole industry that needs to scale up, that can't happen overnight. And we have some promising technologies with the potential to drive down stationary storage costs dramatically - after a few generations of maturation.