The Tres Amigas project, while interesting technically, strikes me as yet another example of why renewable power systems should be as widely de-centralized as possible, preferably all the way down to the user, or neighborhood/block level.

The company will spend something like $1 billion to build, in essence, a switch that connects three grids.  This investment, to be paid for ultimately by consumers, adds zero energy generating capacity.  It does allow long distance transmission, however, with all the line losses (not mentioned in the article) that entails. 

In short, the project would actually decrease efficiency compared to having the same generation facilities located near the end users.  A handful of investors, however, will get the opportunity to skim something off the top of every MW-hour that passes through their switch.