Google's commitment to "green" means that the company sources carpet and sofas made without PVC, paints without volatile organic compounds, and cafeteria food from local growers. It's not surprising, then, that they would roll out the largest commercial solar deployment in the US—a 1.6MW installation that covers most of the buildings at Google's campus and extends even to shaded parking spaces. At the ETech conference in San Diego this week, Google's Anthony Ravitz explained how Google did it, and why.

The move to solar made sense for Google, and not just "hippie Gaia-loving" sense. Ravitz said that Google will earn its investment back in 7.5 years, after which it will continue to enjoy inexpensive power for decades. With the company sprawled across a large campus of many low buildings, roof space was easily available. Solar also has the unique property of pumping out more energy when power is the most expensive—peak afternoon hours. When air conditioners across California kick into action on sunny days, Google generates the most power.

It's still an expensive tech to install (though prices are dropping). Ravitz wouldn't give an exact figure for the project, but did say that it was only doable thanks to subsidies from local utility PG&E and a generous federal tax credit.

9,212 Sharp photovoltaic modules now cover the rooftops of the Googleplex, each one capable of pumping out 208W of DC power in full sun. To gain even more solar surface area, Google installed solar panels as "shades" over several of its parking lots, keeping cars cool and generating power at the same time. The installation can generate 30 percent of Google's peak demand power, or enough to light about 1,000 California homes.

The solar modules are wired in series, 14 to each circuit, and their output is sent to 10 SatCon inverters. The inverters transform the DC power to utility-grade AC, and are 96 percent efficient at installation (efficiency drops each year that they are in operation). The inverters are then tied into Google's own power systems and the general electrical grid. The system is set up for "net metering," which means that any excess power generated by the panels is pumped back into the state grid and Google receives a credit for that power.

It's a textbook example of the convergence of business and environmental concerns, and Ravitz hopes that Google's example will inspire other firms to explore alternative energy sources. It seems to have helped: an even bigger 1.9MW installation is going in just down the road.