There are two things you notice when you see a Google Maps view of a big-box store: a lot of parking lot and a lot of roof. That first thing is a problem: Big-box stores are a symptom and a facilitator of sprawl, encouraging people to drive in and consume. For most such stores, even someone living across the street would have to walk about five minutes across asphalt before they could make a purchase.

Panels on a Sam’s Club in Puerto Rico. Walmart (parent company of Sam’s) has a large gallery of images of its solar rooftops.

But those roofs? The roofs are an opportunity — for the company and for the environment. As The New York Times reports:

Led by the likes of Walmart, Costco and Kohl’s, commercial installations of solar power have increased sharply in recent months. More than 3,600 nonresidential systems were activated in the first half of 2012, bringing the number of individual solar electric systems to 24,000, the report said.

Whether driven by brand identity or cost concerns, almost half of the top 20 commercial solar customers are major retailers like Bed Bath & Beyond and Staples.

Ikea, one of the chains in the top 20, plans to have solar arrays on almost all of its furniture stores and distribution centers by the end of the year, Joseph Roth, a spokesman, said.

This is obviously good news. Looking down on a big-box site and seeing a parking lot surrounding an array of solar panels isn’t ideal, but it’s better.

The Solar Energy Industries Association put together this graphic, depicting the largest corporate users of solar. As noted above, it’s mostly big box.

Walmart’s focus isn’t only on solar. In Portland, the company is building a new 90,000-square-foot store which will feature the city’s largest green roof. The roof will “have three sections with different soil levels to test the most effective green roof practices” — not only employing the concept, but expanding it. Amazon, the online version of a big-box store, is building Seattle’s largest development ever, topped with a green roof.

As Batman or someone said, with great roof space comes great responsibility. If we’ve gotta have big stores (which we don’t), we might as well put those big roofs to use.