Big chain stores have big roofs, and they’re being put to good use.

A new report [PDF] from the Solar Energy Industries Association and Vote Solar puts Walmart at the top of the corporate heap in installing solar power on its buildings, with 65 megawatts, followed by four other major retailers: Costco, Kohl’s, Ikea and Macy’s.

retailer solar installations
Ikea’s 31st solar installation, in Boomington, Minn. (image via Ikea)

The top 20 U.S. companies in onsite solar energy capacity cumulatively have installed 1.2 million solar panels, adding up to 279 MW in capacity and capable of producing $47.3 million worth of electricity a year, the report said.

And here’s a startling fact that ought to make Walmart and Costco proud (while also shaming Florida): The two companies combined have more installed PV capacity than the so-called Sunshine State.

While Walmart leads in sheer bulk, it’s also got a big advantage: It has more than 4,000 retail outlets in the United States. Measured by percentage of stores with solar power systems, Ikea comes out the big winner. It has solar at 79 percent of its stores, far outdistancing second-place REI at 20 percent, followed by Costco (14 percent) and Kohl’s (11 percent).

What’s driving this move to solar? There’s good PR in it, no doubt. Trust us, all of these major players put significant energy into getting out the word about their solar installations, and their other green initiatives. But the biggest factor is that it saves them money, now more than ever as prices for solar continue to slide.

“Between the second quarter of 2011 and the second quarter of 2012, the average price of a completed commercial PV system fell by nearly 14 percent,” the report says. “The economics of PV have become so attractive that many of the best managed companies … are adopting solar energy on a massive scale in the U.S.”

Here’s the full list of the top 20:

  1. Walmart: 65 MW, 7 states, 144 systems
  2. Costco: 38.9 MW, 5 states, 62 systems
  3. Kohl’s: 36.5 MW, 10 states, 124 systems
  4. Ikea: 21.5 MW, 17 states, 31 systems
  5. Macy’s: 16.1 MW, 4 states, 41 systems
  6. McGraw-Hill: 14.1 MW, 1 state, 2 systems
  7. Johnson & Johnson: 11.6 MW, 2 states, 12 systems
  8. Staples: 10.8 MW, 5 states, 35 systems
  9. Campbell’s: 9.9 MW, 3 states, 3 systems
  10. Walgreen’s: 8.1 MW, 6 states, 134 systems
  11. Bed Bath & Beyond: 7.5 MW, 1 state, 4 systems
  12. Toys R Us: 5.7 MW, 1 state, 4 systems
  13. GM: 5.6 MW, 5 states, 13 systems
  14. FedEx: 4.9 MW, 2 states, 5 systems
  15. White Rose Food: 4.9 MW, 1 state, 1 system
  16. Dow Jones: 4.1 MW, 1 state, 1 system
  17. Snyder’s of Hanover: 3.5 MW, 1 state, 1 system
  18. Prologis: 3.5 MW, 1 state, 10 systems
  19. Hartz Mountain Industries: 3.4 MW, 1 state, 5 systems
  20. Crayola: 3.4 MW, 1 state, 1 system