One thing that a grid depends upon is all the transmission and distribution infrastructure. This is an incredible expense, but it is amortized over a very long long time.

On the mainland, investment in that infrastructure has gone in a cycle, I think we're coming off a decade of very large investment after a decade of 5x less investment in that infrastructure.

What's going to replace the expansion of transmission and distribution will be storage. It's often cheaper to buy storage at today's (relatively high) prices than to continue to size the transmission infrastructure for peak demand, rather than something closer to average demand. It's that peak demand that is the most costly to serve, batteries help with this immensely. In NYC, Con ED is delaying $1.1B in substation upgrades through the use of storage:

http://www.utilitydive.com/news/coned-seeks-efficiency-distr...

And on the smaller scale, in Arizona, a community that's growing is getting batteries rather than upgrading the transmission lines:

http://www.utilitydive.com/news/aps-to-deploy-8-mwh-of-batte...