Walmart might be an unadulterated, union-busting evildoer in the eyes of organized labor. But when it comes to another liberal priority, green energy, it's becoming something of a corporate hero. For a few years now, Walmart has been installing solar panels on its stores’ capacious rooftops to improve its corporate image while controlling energy costs. Other big-box retailers such as Ikea, Costco, and Kohl’s have done the same. But thanks to its huge real-estate footprint, Walmart’s efforts are reaching enormous scale.

This week, the Solar Energy Industries Association, a trade group, reported that Walmart has installed 105 megawatts of solar capacity, up 16 percent from last year, and more than twice as much as the next closest company, Kohl’s. All told, the 25 corporations with the most solar have added 569 megawatts combined—roughly one-sixth of which belongs to the pride of Bentonville, Arkansas.

Here’s another comparison that puts Walmart’s efforts into perspective: According to SEIA spokesman Ken Johnson, the company now has more solar capacity than 35 states and the District of Columbia. It lags behind California, Arizona, Colorado, Florida, Georgia, Hawaii, Maryland, Massachusetts, North Carolina, Nevada, New Jersey, New Mexico, New York, Pennsylvania, and Texas. That’s it. (Last year, using a different data source, Bloomberg reported that Walmart had more capacity than 38 states).

Walmart’s efforts are also only just beginning—it has pledged to double its solar installations by 2020 and says that, long term, it wants to get all of its electricity from renewables, up from about a quarter of its worldwide consumption today. So while smaller companies like Kohl's and Whole Foods, which according to the Environmental Proection Agency get all of their power from green sources, have made faster progress shifting their own power consumption to renewables, Walmart has the ability to keep growing the solar market.

All of which helps explain why President Obama chose to use one of Walmart's stores for a backdrop during a speech on green energy. At the time, liberal critics savaged the decision, in part because he appeared to be lending respectability to a company with an awful labor record. But Walmart's notoriously ruthless cost-cutting might actually burnish solar power's reputation as an economically viable choice rather than some goofy liberal fixation. The company wouldn't be building out an entire state's worth of capacity if solar didn't make fundamental financial sense. Corporate America doesn't get any more hardheaded—or mainstream—than Walmart, and that's great news for green energy.