Corporations interested in green energy may be frustrated with Washington, but their voices need to be heard in D.C., says former EPA administrator Cathy Zoi.

FORTUNE -- Along with the rest of the country, more big companies are concerned about sustainable energy. The problem is that corporations interested in taking those concerns to policymakers in Washington are frustrated, given the political gridlock they have encountered there.

An audience member from Microsoft (MSFT) asked a panel at Fortune's "Brainstorm Green" conference if it would be more effective for concerned companies such as Microsoft to pursue green energy as they see fit and sidestep Washington altogether.

No, says Cathy Zoi who has worked for the White House and is now a partner at Silver Lake Kraftwerk Fund. "Do what you're going to do, but please do not abandon Washington," she told the audience. "This is important for Microsoft and Google, because you guys are thinking about reliable, affordable electricity, and Washington needs to know that you care about it."

The fossil-fuel industry is a well-oiled machine in this way, she says, and government representatives hear from those companies all the time. Leaders from green-geared companies need to throw their voices in the fray, she says. More