Germany gets roughly as much sunlight as Canada, and started installing solar when costs were 5-10x what they are today. They paved the way for future installations at lower costs, but their experience isn't directly applicable.
Energy storage is indeed going to be vital once solar exceeds 10-20% of capacity. Energy storage, fortunately, is also dropping fast in cost:http://rameznaam.com/2015/04/14/energy-storage-about-to-get-...
I have future posts coming with closer looks at the future of storage prices, wind prices, and possibly one on nuclear.
I believe almost 70% of that cost is in feed-in tarriff payments, not network upgrades, and is spread over the next 25 years?
http://www.world-nuclear-news.org/NP-Trillion-Euro_cost_of_G...
They are not trivial. Germany claims one trillion EUR direct costs on network upgrades to cope with renewable energy. They do not take into account energy storage costs. Even now (at least in my country) 75% of energy costs are distribution costs.