Walmart has 115 rooftop solar installations in seven countries. Earlier this month, the company completed its largest solar project yet, installing 14,000 solar panels on a 1 million square-foot distribution center in Buckeye, a small town west of Phoenix. The panels sit atop the roof and parking canopies. The system will provide up to 30 percent of the center’s energy needs, generating enough electricity to power more than 400 homes. The reduction in greenhouse gas emissions is the equivalent of taking about 600 cars off the road.Walmart is also looking to harness the power of the wind, installing micro-wind turbines in parking lots as part of an alternative energy test program.The shift locks down a major contributor to operating costs and the falling cost of solar energy systems makes the economics even more appealing. The average price of a commercial photovoltaic system as dropped nearly 14 percent in the last year, according to the Solar Energy Industries Association. So companies focused on efficiency are more and more likely to look to the sun for a bargain.