The La Paz project will be the first full-scale plant of its kind in the world (a similar, though much smaller-scale, plant ran for eight years in Spain).  I'm no engineer, so I can't speak to how likely the project is to really work on such a large scale (the Arizona plant will generate 200MW).  Regardless, it's a concept that's mind-boggling.  Imagine driving along a highway in western Arizona and spotting this monolith from miles away.  The view will be jaw-dropping.  

Here's how it works (theoretically, anyway):  The sun beats down on a four square-mile covered greenhouse area at the bottom of the tower, warming the air underneath the greenhouse. Hot air naturally wants to rise, so it rushes toward the tower in the middle.  There, at the base of the tower, are 32 turbines that generate electricity as the air rushes upward through them.

Because the tower is so tall (and air cools about 1 degree every hundred meters), there is a huge temperature differential between the air at the bottom underneath the greenhouse and the air at the top of the tower.  The greater the temperature differential, the harder the tower sucks in the hot air at the bottom and the more energy the turbines generate.

What's so cool about hot air

• Compared to other forms of renewable energy, the solar tower's estimated capacity factor of 60% is incredible (the capacity factor of wind is about 30-50%; solar PV is about 20-30%)
• The plant emits no pollution and creates no hazardous waste
• Unlike some other forms of solar power generation, water use is minimal (important in a state that has very little)
• Operating costs are relatively minimal
• With only basic maintenance, the plant should have a lifespan of at least 80 years
• Because it works on the temperature differential, not on absolute temperature, it works in any weather
• The sun's heat during the day warms the ground underneath the greenhouse, which keeps the air there warmer than in the tower - so the plant works at night as well

That said, there are some issues (or potential issues anyway)

• The plant's footprint is huge (4 square miles) - that works okay in the middle of undeveloped desert but isn't practical everywhere
• The technology is untested on this scale (the pilot project in Spain ran for eight years, but on a much smaller scale - and that was more than 20 years ago)
• Though EnviroMission has a power purchase agreement, it's not clear yet who's going to fund the project (with estimated construction costs around $750 million)
• The "project" at this stage is really just a concept - in addition to securing financing, EnviroMission also needs to conduct environmental impact and engineering feasibility studies, acquire the land, and get approval from the Arizona Corporation Commission

So there's plenty that could derail the project.  But I've written quite often about our desperate need for more innovative ideas.  This is certainly one.

Update side note: I've written a few posts on hydraulic fracturing (fracking) - see The Case for Regulating Safety and The Fate of Fossil Fuels - so an article in the New York Times about it caught my eye: A Tainted Water Well, and Concern There May Be More (part of the Times' "Drilling Down" series).  The article talks about a 1987 report of groundwater contamination that resulted from fracking, but details of the contamination report were sealed from the public.  Worth a read.