Staples Inc. is the biggest retailer of office supplies in the country, and the second biggest online retailer of any sort after

But the Framingham-based company also ranks high on another list: It’s the ninth largest user of solar power of any non-utility business in the U.S.

Wal-Mart Stores was by far the leader in the Solar Energy Industries Association’sranking of the top 25 solar-using companies, with nearly 90 megawatts of installed solar capacity. Costco and Kohl’s were a distant second and third.

Staples remains in the top 10, with roughly 14 megawatts of capacity, ranked below Johnson & Johnson and McGraw-Hill but above Campbell’s and U.S. Foods. Staples is regularly honored by the Environmental Protection Agency for its work in the solar business, and this report offers new insight into how the company stacks up against other big firms. (It’s the only Massachusetts-based company in the top 25.)

For Staples, the journey to becoming a major solar power player dates back to 2004, when it hooked up with SunEdison, a California-based developer and operator of photovoltaic systems. So far, at least three dozen solar projects have been installed at various Staples sites. Many are stores, although some are offices or warehouses. Staples owns some of the properties, but most are leased.

The most recent installations included a 2.2-megawatt project on land next to Staples’ London, Ohio, warehouse, and a 0.7-megawatt installation on a garage roof at its Framingham headquarters. Both went online at the end of 2012.

Staples avoids major upfront costs by agreeing to 20-year power purchasing agreements with SunEdison. The solar company then gets financing from a bank, often Wells Fargo & Co., to build the panels and sell their power to Staples. Jeff Bower, director of strategic accounts at SunEdison, says if more power is produced than Staples needs at a particular site, the excess goes to the local electric utility and Staples gets a credit for use on a future bill.

Mark Buckley, vice president of environmental affairs at Staples, says that in the case of the Framingham location, all the solar power remains on site to support the 650,000-square-foot headquarters complex and the 3,500 people who work there. Solaire Generation designed and installed the Framingham project.

Buckley said Staples is still looking at other potential projects. Predominantly, these solar panels are going up in states like Massachusetts that have requirements that a certain percentage of the electricity come from renewable energy. These solar panels are also going up in places with relatively high power prices. (Again, Massachusetts fits the bill.) Staples, Buckley says, views these projects as part of broader strategies to keep costs contained and to reduce the chain’s environmental impact.

“It’s a model that’s really transformed the solar industry,” Buckley says. “In the early days, systems were purchased by building owners or tenants, tying up a lot of capital. This is a way for us to solarize our buildings and build long-term price certainty in our power supply without having to make capital investments.”