Those new signboards at Wednesday's USA-Mexico game were for China-based company Yingli Green Energy, which signed a multi-year deal to be the first "Official Renewable Energy Partner" of U.S. Soccer.

Yingli ran a text-messaging campaign, offering fans a chance to win soccer prizes -- and also a free quote on solar installation. "The intent here is not only to raise awareness but to educate people on how to go solar," says Helena Kimball, head of U.S. marketing communications for Yingli.

The deal was a natural for Yingli. Four of the five largest solar markets are also among the top five in U.S. Soccer attendance: California, New Jersey, Pennsylvania and Massachusetts.

"We chose this platform because we wanted to reach out to the broadest audience possible from a national level," says Kimball. "And we saw a strong correlation between growth of soccer and growth of solar in U.S."