My research has shown that while many utilities have purchased storage (SCE 250 mW in 2014[1]) it's still very experimental and they do it mostly for research purposes or publicity or because the regulator makes them. However, since the electricity business is slow moving, low margin and very capital intensive it's clear why everyone is very interested in any new potentially disruptive technology. Imagine owning a peaker power plant that you've paid for in full using debt and generates a little profit each year under the condition that it can be amortized for 15 more years - if someone built the equivalent of a peaker plant made of batteries, even in 2025, you'd still go under. Scary.

[1] http://www.greentechmedia.com/articles/read/the-top-10-energ...