Google is investing $168 million to help build the world's largest solar power plant in California's Mojave Desert. The project, being developed by BrightSource Energy, is also being financed with $1.6 billion in federal loans and $300 million from NRG Energy. Why is the web giant making such a big bet on thermal energy? Here, a brief guide:

What is this project?
It's called the Ivanpah Solar Electric Generating System, and it actually consists of three power plants. When it's completed in 2013, the site will generate 392 gross megawatts of power. "That's the equivalent of taking more than 90,000 cars off the road over the lifetime of the plant, projected to be more than 25 years," says Rick Needham, Google's director of green business operations. At full capacity, the power plant will be able to generate enough electricity for 140,000 California homes.

How will it work?
Ivanpah will be home to the world's largest solar power tower, at about 450 feet tall. Sunlight will be reflected off a field of 173,000 special mirrors onto a receiver on the tower. A water-filled boiler will use that heat to generate steam, which will then spin a traditional turbine to generate electricity. This type of set-up is "very efficient," Google says. "Think about burning a tuft of grass with a magnifying glass, only multiplied by thousands."

But why is Google involved?
The web giant has been interested in clean energy for years — it launched a subsidiary called Google Energy in 2010 — and this latest deal brings its total investment in clean energy to $250 million. "Google has always put its money where its ideals have been," says Barbara E. Hernandez at NBC Bay Area.

Surely there must be something in it for Google, right?
There is. It takes a lot of electricity to power the data centers behind Google's online services, so "solar facilities like Ivanpah have the potential to lower costs for Google," says Chris Barth in Forbes. And Google's clean-energy portfolio could help the company make money. The energy being generated at the Ivanpah plant will be sold to PG&E and Southern California Edison. "Every indication is that by 2013, the solar industry will be booming, and Google will be making a pretty penny on those clean watts," says Ariel Schwartz at Fast Company.

Sources: Fast Company, Financial Times, Forbes, NBC Bay Area, San Francisco Chronicle, Google Blog, Wall St. Journal, GigaOm, WebProNews