Until there is a lot more such generating capacity, it would be stupid to divert capital from building that out to building only minimally useful storage.
Again, what is this "ordinary dirt-cheap storage" technology? Sure, you say it's not going to be built until there's an even bigger energy surplus. But at least just specify what technology is going to provide this dirt cheap storage. Because I'd really want to know. All of the alternatives I know of like compressed air, hydrogen storage, ammonia storage, all have significant drawbacks impeding cost effective deployments.
What is this trash? Excess solar output is already an enormous problem. https://www.latimes.com/projects/la-fi-electricity-solar/
And, an occasional excess, a few hours in a few days out of each month is not the same as enough to usefully charge storage.
Also: 2017.