I think Matt Roberts makes a key point here. Many people, myself included, have made the association between Solar PV in the mid 2000's and energy storage now. It's an obvious one to make, especially as it's in recent memory, and many of us experienced that journey, or Solarcoaster. It doesn't take much thinking though to realise the similarity is skin deep.  Solar has grown enormously over the last ten years, but in reality the technology change has been slow. Slight improvements in efficiency, and big reductions in cost and therefore deployment.  Energy storage is an entirely different ball game, the growth and advance in technolgies, as well as rapid cost reductions play one part, but so does the whole set of different grid and service opportunities. Decentralised energy is coming at pace. Solar and wind have done a great deal to path the way, but storage is about to change the world as we know it.