The Solar Power International wagons have rolled into town again, this time into Chicago, for the annual festival of sunlight.

Perhaps it was the banging 90s techno before the session began, but there seemed to be an unusually heightened state of excitement, if not consciousness, among the audience as the presidents and CEOs of SEIA and SEPA, Rhone Resch and Julia Hamm, burst onto the podium like gameshow hosts to introduce Chicago's mayor, Rahm Emmanuel.

Chicago has recently become a "coal free" city and closed two coal plants in the metropolitan area. Emmanuel's energy deal also included a doubling of wind power and funding for new solar contracts.

But Emmanuel himself, flanked by SPI 2013 logos wreathed with wisps of cloud that looked more like smoke, was restrained in his ambitions for solar. Energy efficiency was the sixth fuel but the priority choice for Chicago, he said. The windy city doesn't look much like turning to the sunny city any time soon.

However, Emmanuel did announce the Chicago Solar Express, which isn't a new high speed rail link to New York, but a fast-track permitting system.

"It will encourage more and more people to have solar here in the city of Chicago on a residential and commercial level,” he said. “On a residential level it will be cheaper, quicker and more efficient for people to put solar in by the express. You will get your permit in one day."

Permitting for commercial systems won't be reduced to a day, but the city council is working on streamlining this process too.

Governor Pat Quinn offered a night in Abe Lincoln's bed at his governor's mansion, but only if "you're really committed to solar power".

Ilinois has an impressive renewable portfolio standard of 25% by 2025, and because wind is such an obvious choice, there's also a solar carve-out for 700MW by 2015.

Resch, meanwhile, laid down the gauntlet to fight for an extension of the Investment Tax Credit, to fight the utilities on net energy metering and protect policies like net energy metering from the American Legislative Exchange Council and the Heartland Institute, funded by the Koch Brothers.

"Simply put, our critics will do everything they can to make sure solar becomes nothing more than a footnote in history," he said. "We cannot let that happen. So buckle up and tighten your chin straps folks, we’ve got a lot of big challenges ahead of us.

"So to the climate change deniers out there and the card-carrying members of the Flat Earth Society, I’ll simply say this: Go ahead. See what happens when you grab the tail of a tiger!"

But Resch also wanted to share the good news from the findings in the annual Solar Means Business Report released by SEIA and Vote Solar.

The report, which identifies major commercial solar projects and ranks America’s top corporate solar users, found that for the second year in a row, Walmart is America’s commercial solar leader with 89 MW installed at 215 locations.

"Today, the list of companies moving to clean, affordable solar energy reads like a ‘Who’s Who’ of the most successful corporations in America," Resch said. "Simply put, these iconic brands – from Apple to General Motors – are leading the way when it comes to efforts to transition to clean, renewable energy."

Hamm compared the solar versus utility battle to that of the cellphone versus the landline.

"As consumers have gravitated to the cell phone the landline telephone in fairly short time has fallen to near obsolescence. In some ways, the analogy is fair and instructive. But there are a few things to keep in mind: the cell phone didn't just allow the consumer to make calls, it provided a host of new dazzling services of value.

"Solar panels may offer consumers the chance to untether from the utility, to be free from the monopoly provider or to be partially free, but in the end the grid and a solar system offer the consumer the same product – electrons."

But I'm not sure that is entirely true. Think of all the other services such as energy efficiency, smart appliances and demand response software companies are trying to package with their solar offerings, SolarCity and Vivint Solar, just to name two.

Hamm also implored the solar and utility industries to become more like one another.

"Companies like AT&T and Verizon have deep roots in the telecommunications industry. They were able to make the conversion to making a successful business with new technology. The question is, can electric utilities do the same?

"We all know solar is sexy, but underlying solar is a lot of important infrastructure… On the surface, the basic business models couldn't be more different. On the one hand, we have very conservative, pragmatic utility industry … on the other hand, solar companies tend to be highly entrepreneurial, fast moving, highly responsive to market and customer shifts, trying to ride the boom and bust cycles."

Despite the drop off in venture capital investment in clean-tech, particularly in solar, Cheryl Martin, deputy director of the Advanced Research Projects Agency–Energy (ARPA-E), pointed out that follow-on funding had been high.

Some US$770 million has been awarded to date across 285 projects, and 17 projects at 14 companies that took US$60 million of ARPA-E funding now have attracted US$450 million of follow-on funding.

"Energy technologies do not mature as fast as we would like them to," she said. "You have to know what you're getting into. Things go bad when you don't have shared expectations and you have to talk about these things. The only failure at the ARPA-E is the failure to act on what you know. When something is not working you stop doing it."

Today another Department of Energy programme, the SunShot Intiative, will announce a further US$60 million in R&D awards to 38 projects; 19 of those companies will be in the show-hall at SPI. SunShot awards are now at US$828 million, a tidy sum towards the US$1/watt goal by 2020.

If the dying embers of heavy industry can catch light here in Chicago, arguably the unofficial capital of the coal-hungry mid-west, it would mean that solar had really come of age in the United States.

The city that was at the heart of America's industrial revolution could also help start a new and cleaner industrial revolution; a second chance from the Second City.