"That's really what we're working on—making it work better small before we make it bigger," said Wheeler. "There are still more fundamental scientific questions that have to be answered," said Tenent. "One of the challenges we've got is that skyscrapers don't have abundant roof space to put PV on," Tenent said. Incorporating PV into the windows is one answer. "The big goal is definitely to get it into your downtown skyline where you have lots of glass and no roof space," said Wheeler.
"If you buy a nice skylight, usually it's going to be electronically controlled to have a rain sensor and actuate if it's open or closed," Wheeler said. "The big problem is you have to tear a wall apart to wire it. If you can put the power on board, that's what this switchable energy generation gives you."
The durability of the switchable component is key to ensuring the adoption of the technology. The device must be able to switch back and forth between transparent and tinted many more times than has been demonstrated in the lab so far. "Eventually, it's got to switch 50,000 times," said Wheeler. "We've shown it can switch around 20–30 times in the lab right now."
"The durability piece of the equation—we actually do a lot of that," said Tenent, an electrochemist. "That's what our core windows program at NREL is based on. We developed the standard for evaluating the durability of electrochromics. The 50,000-cycle threshold is based on the electrochromic standard. It's become kind of a de facto accepted metric."
The initial technology had a power conversion efficiency of 11.3 per cent, aiming to maintain that figure over the thousands of switching cycles. "Right now there are things specific to a window and not to a solar panel, like how much light is let through and what sort of solar heat gain you get when you