Google has chipped in a US$168 million investment in what will be the world's largest solar power tower plant. To be located on 3,600 acres of land in the Mojave Desert in southeastern California, the Ivanpah Solar Electric Generating System (ISEGS) will boast 173,000 heliostats that will concentrate the sun's rays onto a solar tower standing approximately 450 feet (137 m) tall. The plant commenced construction in October 2010 and is expected to generate 392 MW of solar energy following its projected completion in 2013.

Although solar power tower development is currently less advanced than the more common trough systems, they offer higher efficiency and better energy storage capabilities. Parabolic trough systems consist of parabolic mirrors that concentrate sunlight onto a Dewar tube running the length of the mirror through which a heat transfer fluid runs that is then used to heat steam in a standard turbine.

Solar power tower systems such as the ISEGS on the other hand focus a large area of sunlight into a single solar receiver on top of a tower to produce steam at high pressure and temperatures of up to 550 ° C (over 1,000° F) to drive a standard turbine and generator. The ISEGS also uses a dry-cooling technology that reduces water consumption by 90 percent and uses 95 percent less water than competing solar thermal technologies. Water is also recirculated during energy before being reused to clean the plant's mirrors.

Model rendering of the ISEGS heliostats

Overshadowing the 20 MW PS20 solar power tower plant in Spain, the scale of ISEGS can't be overstated. It will be the first large-scale solar power tower plant built in the U.S. in nearly two decades and will single-handedly almost double the amount of commercial solar thermal electricity produced in the U.S. today and nearly equal the amount of total solar installed in the U.S. in 2009 alone.

The entire complex will consist of three separate plants developed by BrightSource Energy that will be built in phases between 2010 and 2013. The energy generated from all three plants will be enough to supply more than 140,000 homes in California during peak usage hours, with the project contracted to provide 1,300 MW to Southern California Edison and 1,310 MW to Pacific Gas and Electric Company.

Google says it has now invested over $250 million in the clean energy sector but its $168 million investment in the ISEGS is the company's largest investment to date. The size of the investment reflects Google's faith in the technology and it hopes that other companies will follow its example and make similar investments in renewable energy.