Two years ago, Greentech Media reported, “U.S. companies are adopting solar power faster than ever before,” based on a survey of commercial solar installations from the Solar Energy Industries Association. At the time, commercial solar installations were up more than 40 percent from the year before.

Now in its fourth year, the 2015 Solar Means Business survey shows that that trend has not waned. SEIA sampled Fortune 100 businesses in 37 states and found a nearly 60 percent increase in installed solar from 2014.

Wal-Mart continues to lead the push for commercial solar installations in the U.S., with 142 megawatts installed onsite, far ahead of No. 2 Prologis, which has nearly 98 megawatts of solar capacity.

Large retailers, car manufacturers and grocery stores -- all companies with acres of rooftops -- make the list of biggest solar installers, with tech companies such as Apple and Intel, which run energy-hungry data centers, also making SEIA’s top-25 list. The decision to go solar was once centered on sustainability, but it is increasingly an economic decision as well as the cost of solar continues to fall.

The snapshot of the largest corporations in the U.S. shows that many are taking advantage of rooftop solar as prices continue to decline and with the increasing sophistication of financing options, such as power-purchase agreements, both traditional and virtual.  

Earlier this year, GTM Research senior solar analyst Cory Honeyman noted that Fortune 500 partnerships, such as Target’s portfolio-wide PPA with Greenskies, were one of the keys to the rebound of commercial solar in 2015.

Another issue for the rebound of commercial solar is smaller-scale projects under 1 megawatt, which continue to be challenging to scale.

Walgreens might be an example of a company with a national footprint that has cracked the code. Walgreens has an average system size of less than 500 kilowatts, yet it installed solar at 85 of its stores in this year alone, according to SEIA. “Walgreens is setting the pace for going solar,” the report states.

In terms of placement, roof-mounted systems continue to dominate large corporate solar systems, but one subsector of roof systems is growing rapidly: carports. The average size of carport installations is increasing, from about 600 kilowatts in 2012 to nearly 800 kilowatts today

Wal-Mart is at the head of the pack, with more than 20 carport installations in the past three years. Others, such as Intel, AT&T and GM, have followed suit, and more are likely to come.