A crowd estimated at more than 120 people gathered across from Duke Energy Florida's headquarters in St. Petersburg on Wednesday, urging the utility to close two coal plants by 2016 and replace them with solar power.

Led by the Sierra Club, which is pushing utilities nationwide to close coal plants, almost two dozen groups participated in the chilly morning rally with banners that read "Sunshine State for Solar Power," "Solar is the Power!" and "Let the Sun shine."

"Duke Energy's Crystal River coal-fired power plant violates air-quality standards for sulfur dioxide pollution that can trigger asthma attacks and cause other respiratory problems," said Kelly Martin, the senior campaign representative for the Sierra Club.

"Clean Energy solutions are here, happening and helping to make our air and water cleaner," Martin said.

In 2011, then-New York City Mayor Michael Bloomberg committed $50 million to the Sierra Club over four years for the organization's campaign to push for the closure of the nation's dirtiest coal plants by 2020.

Duke plans to close Crystal River coal units 1 and 2 by 2020, but the groups want the utility to act sooner because the generators are considered among the nation's worst polluters.

The generation capacity of those two coal units exceeds 840 megawatts. Replacing them with solar power would require more than seven times the current amount of utility-scale solar in the state. And even then, the solar installation would not match the coal units' output because solar doesn't produce any power at night.

In response to the rally, Duke said it was listening to the concerns of its customers.

"At Duke Energy, we support cost-effective solar energy and recognize it plays a vital role in our state's energy future," said Ann Marie Varga, a Duke spokeswoman. Varga's statement echoed an article Duke Energy CEO Lynn Good wrote in the November/December issue of Electric Perspectives:

"Delivering safe, affordable, reliable, and increasingly clean energy must remain central to our mission. Customers are demanding options, such as more flexible rate offerings, distributed and clean generation, such as rooftop solar, and greater control over their power bills."

Several groups frustrated with Duke have organized rallies at the company's Florida headquarters in recent months. Part of the concern stems from a lack of focus by Florida utilities on the use of solar technology. Florida lags behind such not-so-sunny states as Massachusetts and New Jersey in deployment of solar.

R. Alexander "Alex" Glenn, president of Duke Energy Florida, has said intermittent cloud cover is a problem for solar, even in the Sunshine State. "We're also the partly cloudy state," he told state lawmakers.

Duke's critics call the cloudy comments just excuses to avoid developing solar, so they intend to push for action by the utilities.

Before this week, most of the rallies drew a few dozen people, but the Sierra Club used a different tact for Wednesday's gathering by organizing various groups and forming a coalition to bring their concerns to the utility and public officials.

The partnership, dubbed the Sunshine State Clean Energy Coalition, includes such organizations as the Southern Alliance for Clean Energy, the Tampa Bay area chapter of Physicians for Social Responsibility, the Florida Consumer Action Network, Greenpeace and the Florida Public Interest Research Group.

The coalition members pledged Wednesday to collect some 10,000 signatures to press Duke to bring more solar power to the Sunshine State.

The rally attracted St. Petersburg City Council member-elect Darden Rice, who said local elected officials will need to put forth more effort to promote change since state leaders have not moved the utilities to act in the best interest of consumers and the environment.

"I think the time for excuses is running out," Rice said.

Ivan Penn can be reached at ipenn@tampabay.com or (727) 892-2332.