Wal-Mart has announced its first major purchase of wind energy in the U.S. The company has entered into a four-year agreement with Duke Power to buy enough wind power to meet up to 15% of the retailer's energy load in approximately 360 Texas stores and other facilities.

This is the most recent step in a broad-ranging suite of initiatives by the retailing behemoth to become more sustainable. The company has three major goals—"to be supplied 100 percent by renewable energy, to create zero waste, and to sell products that sustain our resources and the environment." They are "aspirational" (Wal-Mart's term) goals because no hard timelines are associated with them.

The company's wind power purchase inches the company closer to its first aspirational goal of being supplied 100% by renewable energy. It follows on the heels of a solar project announced earlier this year, when the company committed to equipping up to 22 of its locations in Hawaii and California with solar panels, a move that is expected to reduce greenhouse gas emissions by 6,500-10,000 metric tons per year.

Unlikely as it seems, Wal-Mart got the sustainability gospel because of Hurricane Katrina. According to CEO Lee Scott, " For the people of the Gulf Coast, [Katrina] was a devastating event that forever changed the lives of thousands. In a different way, it also changed Wal-Mart forever. Hurricane Katrina showed us our potential to serve our customers, our Associates and our communities by applying our business model to solving major problems. In October 2005, motivated by our experience with the Katrina disaster, we committed to a set of environmental and other goals in a speech titled 'Twenty-First Century Leadership.'"

For years, Wal-Mart was an all-star on environmentalists' list of most despised corporations because of its its problematic social impacts and employee and environmental practices. Now its reputation is improving (even critic Seventh Generation is partnering), thanks in no small measure to its recently-found sustainability commitment.

But how authentic is that commitment? Very much so, if the company's plans for the future are any indication. "At its root," says media manager Kory Lundberg, "sustainability is about eliminating waste from the system and becoming more efficient. That means it's good for Wal-Mart regardless of the economic conditions. We capture those savings and pass them on to our customers."

In a sense, sustainability for Wal-Mart is more than a commitment. It's a strategic asset—a way for the company to identify ways to cut costs and operate more effectively. When a company becomes sustainable because it's the right thing to do, its commitment is on a noble but not all that solid foundation. "Right things to do" can and often do get axed when the going gets tough. But when a company embraces sustainability because of its strategic value,  the commitment is likely to have more staying power. It's kind of like the difference between an affair and a marriage.

Based on its stance during the current economic storm, Wal-Mart appears to have gotten hitched to sustainability.