The trouble with Tesla and Elon Musk is that although he is without doubt a visionary and a very capable man he is prone to over-estimate his and his comapnies capability. There are many solar powered ideas that on paper that all look viable and wiring up the desert with solar PVs and Tesla batteries sounds great. The trouble is that Tesla stuff doesn't really work - at least not as good as what is already out there.
There are a number of decent "battery" systems out there for commercial load, A123 Systems and NGK of Japan for example. Unfortunately they are expensive and following Musks' desert idea would require much of the "desert" capacity to charge and maintain the load, also with a lifespan of no more that about 15 years they would be expensive to replace - Tesla batteries are much less... for want of a better phrase "efficient", cost more and last a maximum 10 years.
Batteries are seen as the holy grail of the green power movement but are unfortunately a major issue at the moment in that there is nothing really on the horizon that is going to solve the problem of bulk storeage for commercial load variability.
Tesla Corp is in my humble oppinion a ponzi scheme in that it has thrived on cheap capital over the last decade to service a massive debt producing mediocre goods to an affluent middle class wanting to "do their bit" for the planet. The hype and gush surrounding Tesla has enabled them to obtain mountains cheap credit and as long as the elegant and suave Elon Musk stays in front of the media then great he can maintain his public image and keep selling his junk to the affluent green middle classes.
I'm just thankful that their are still serious people, serious engineers doing the serious research and working hard trying to solve the real problems with RES. These are the people that stand up and say "errrmm well its not that simple really!" These are the people that don't get in front of the cameras but they sure as hell make a serious contribution.