How a New Jersey power company taught NFL owners to love clean energy.

By Brian Dumaine, senior editor-at-large

A ring of solar-powered LEDs atop MetLife Stadium flashes New York Giants blue.

FORTUNE -- A new kind of NFL rivalry is forming, not on the gridiron but in the boardroom. Many NFL owners have suddenly gotten religion about the environmental impact of football: installing solar panels in their stadiums, recycling plastic cups, and even composting garbage. Philadelphia Eagles owner Jeffrey Lurie wants to make his venue an environmental showcase. New York Giants co-owner Don Mara says he wants "to have the greenest stadium in the NFL." Jonathan Kraft, whose family owns the New England Patriots, says: "We hope to lead the way in sustainability."

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It's not just altruism that's driving these business titans. Their plans will help the bottom line. Take the solar systems the Patriots, Giants, Jets, Redskins, and others are installing. About a year and a half ago, David Crane, CEO of the New Jersey-based energy provider NRG (NRG), approached the NFL about converting to renewable energy. NRG, with $9 billion in revenue and a fleet of coal, gas, and nuclear power plants, says he believes that solar will be a disruptive technology. The problem, explains Crane, is that solar, which still counts for less than 1% of U.S. power production, wasn't gaining any traction. If he could get the NFL to embrace solar, he could use America's most popular sport to help spread the word. His pitch: At no capital expense to the NFL owners, NRG would install panels at their facilities. For the deal at Foxborough, Mass., one of seven NFL locales NRG is wiring, the Patriots get to hedge against rising electricity prices by locking into a long-term fixed-price contract. NRG profits from the cash flow. The utility has installed nearly a megawatt of solar panels, enough to supply 60% of the power for the stores and restaurants in the complex.

NFL games still consume lots of power and create lots of waste. But owners say solar is just a first step in a long drive toward sustainability. No word yet on harnessing the energy from the on-field tackles.

This story is from the September 24, 2012 issue of Fortune.