Many people may still question the future of solar energy in the United States, but there's little debate in corporate America over whether to go solar. What may surprise you is that the discussion has nothing to do with climate change.

Some of the largest and most influential companies in the country are spending billions of dollars to outfit their businesses with solar energy. And they're doing so in the name of increasing shareholder value.

Verizon takes the telecommunications industry solar

The latest company to make a big investment in solar is Verizon Communications (NYSE:VZ), which is installing 10.2 megawatts of solar power systems from SunPower (NASDAQ:SPWR) at eight network facilities around the country. The investment will cost about $40 million and will nearly double the company's investment in solar energy.

When discussing the investment on Bloomberg TV, James Gowen, Verizon's chief sustainability officer, said "It's not just about going green. It's about driving shareholder value; it's about building redundancy." Today, solar energy created on-site is cheaper than buying energy from the grid, particularly when you include the tax benefits to companies such as Verizon.

Corporate America bets big on solar

Verizon is just the latest in a long line of corporations to go solar by building its own sun-powered energy systems. These include some major U.S. names.

Wal-Mart (NYSE:WMT) has installed over 250 solar energy systems on store and distribution center rooftops, providing 15% to 30% of each location's energy needs. In all, the mega-retailer has built over 335 renewable energy projects around the globe. SolarCity (NASDAQ:SCTY) is one of Wal-Mart's main suppliers of solar, with an agreement to build 60 rooftop systems in California alone.

Apple (NASDAQ:AAPL) is another notable corporate solar and renewable energy supporter. The company has built three 20-megawatt solar systems at data centers around the country and has at least 40 MW more solar in the pipeline. The company also uses fuel cells that run on biogas and other renewable (or at least cleaner) forms of energy to power its business.

Costco had 47 MW of solar installed as of mid-2013, enough to make it the second-largest commercial installer at the time.

These are big, profitable companies that wouldn't put solar on their rooftops or adjacent to data centers if it wasn't profitable. As Verizon's Gowen said, it's about adding shareholder value, and that means saving money.

The tip of the iceberg

If solar energy makes sense anywhere it's on the large rooftops of stores and distribution centers, which is where most of these companies are building the systems. The installations provide energy at the source of demand, and the large scale of the installation brings costs in far lower than a small residential rooftop system. That's why the economics are too good for corporate America to pass up.

Keep in mind that this trend is just beginning. The Center for Environmental Innovation in Roofing estimates there are 50 billion square feet of flat commercial rooftops in the U.S. If only 25% were suitable for solar, that's potential for 125 gigawatts of installations, or more than three times the amount of solar installed in the world in 2013.

To put it another way, 125 GW of solar is enough to power 20.5 million households in the U.S. Corporate America has already started to see the value in turning its rooftop space into power-generating assets, and I think this trend is only going to grow in the future.