"I like to say that the new energy technologies could be the largest economic opportunity of the 21st century," Doerr explained.
He told Stahl it was the firm's first clean energy investment.
Many followed, and the clean tech revolution in Silicon Valley was off and running with start-ups that produce thin flexible solar panels, harness wind with giant balloons, or develop new fuels from algae.
But Bloom is among the most expensive. "I heard actually so far, not just from Kleiner Perkins, but total $400 million," Stahl remarked.
"You're in the ballpark," Sridhar acknowledged.
With that kind of money comes a lot of buzz. "In Silicon Valley, every time a company raises over $100 million, and they haven't come out with a product yet, everybody starts getting the heebie-jeebies," Michael Kanellos, editor-in-chief of the Web site GreenTech Media, told Stahl.
Kanellos admitted he is skeptical. "I'm hopeful but I'm skeptical. 'Cause people have tried fuel cells since the 1830s," he explained. "And they're great ideas, right? You just need producing energy at an instant. But they're not easy. They're like the divas of industrial equipment. You have to put platinum inside there. You've got zirconium. The little plates inside have to work not just for an hour or a day, but they have to work for 30 years, nonstop. And then the box has to be cheap to make."
One thing stoking his skepticism: Sridhar has been hyper-secretive - there's no sign on his building, a cryptic Web site, and no public progress reports.
Given the stealthiness, we were surprised when Sridhar showed us - for the very first time - how he makes the "secret sauce" of his fuel cell on the cheap.
He said he bakes sand and cuts it into little squares that are turned into a ceramic. Then he coats it with green and black "inks" that he developed.
Sridhar told Stahl there is a secret formula. "And you take that and you apply that. You paint that on either side of this white ceramic to get a green layer and a black layer. And…that's it."
Sridhar told Stahl the finished product, a skinny fuel cell, would generate power.
One disk powers one light bulb; the taller the stack of disks, the more power it generates. In between each disk there's a metal plate, but instead of platinum, Sridhar uses a cheap metal alloy.
The stacks are the heart of the Bloom box: put 64 of them together and you get something big enough to power a Starbucks.
Sridhar offered to give Stahl a sneak peek inside the Bloom box.
"All those modules that we saw go into this big box. Fuel goes in, air goes in, out comes electricity," he explained.