In three or four years, you’ll be able to turn a dial and stop the heat from pouring in through your home’s skylight — without cutting off the visible light. Flip the dial to a different position, and your skylight’s glass will go dark, blocking both infrared and visible light. Turn it back, and the glass will go back to letting both light and heat in.
Last week, the journal Nature published details of a research breakthrough making this feat possible. Today, a company called Heliotrope Technologies, cofounded by one of the researchers, is announcing plans to commercialize the technology.
Heliotrope, based in Berkeley, Calif., is led by chief executive Mike Clary, president and cofounder Jason Holt, and chief technology officer and cofounder Guillermo Garcia, who was one of the researchers behind the Nature paper. Garcia contributed to the research at Lawrence Berkeley Labs as part of his Ph.D. dissertation in mechanical engineering at UC Berkeley.
“We were aiming to develop a material that can be deposited in a cheaper way but also add functionality,” compared to existing “smart” windows, Garcia told me in a phone interview.
And, while the Nature research has some practical limitations (it uses a liquid electrolyte, for instance, which wouldn’t fly in a real building), Garcia said that his company had moved far beyond the research already in making the technology practical and market-ready. For example, it now uses a solid-state electrolyte and can be manufactured relatively cheaply.
How Heliotrope’s smart glass works
Current “smart glass” technologies, which have been out for about ten years, use an electric current to switch the glass between transparent and shaded modes. Heliotrope’s technology adds the ability to also block heat, independent of visible light.
The technology starts with extremely tiny crystals of indium tin oxide, a compound also used in making flat-panel displays. When you apply current to indium tin oxide, it acts as a heat blocker, stopping 35 percent of the infrared radiation passing through it. The researchers embedded a layer of indium tin oxide in glass made out of niobium oxide, which darkens (blocking visible light) when you apply current to it.
What they found was that the heat- and light-blocking performance of both materials increased when they were mixed together. When you zap it with electricity, the composite blocks more than 50 percent of the heat and 70 percent of the light passing through the glass.
“The electrochromic performance of the composite is much better than expected from a simple sum of the optical absorption of its two separate components, because of both the nanostructure of the material and synergistic interactions that occur at the interface between the components,” Nature wrote, rather drily, in an assessment of the research.
Or, as Holt put it when explaining things to me, “It’s not 1+1 = 2, it’s like 1+1 = 5.”
The windows have three modes:
- In one, which the company calls “bright,” it is completely transparent to both light and heat.
- In the “cool” mode, the window blocks infrared (heat) while still allowing visible light through.
- And in the “dark” mode, it blocks both heat and light.
(There is currently no way to block visible light while still allowing infrared to pass through.) The glass changes mode depending on the voltage applied to it. Once the glass changes modes, it stays there, so you don’t have to keep applying current.
Why it looks promising
It takes about 1 watt of current and a few minutes to switch between modes, which is comparable to the rate at which current electrochromic glass products change their brightness. However, current technologies only have two modes: They block light or let it through.
Also, electrochromic glass that’s currently on the market costs about $200 per square foot, installed. Ordinary double-paned windows with static coatings cost $75 per square foot, according to a construction estimator contacted by VentureBeat, or $100 per square foot, according to Heliotrope.
As a result, the market for smart glass is very, very small: less than 1 percent of the annual $15 billion market for architectural glass, according to Heliotrope. In fact, they said, 90 percent of electrochromic glass sold today is used in cars’ rearview mirrors, and the remaining 10 percent probably shows up in the houses of the very rich, who are not worried about its exorbitant cost.
Heliotrope’s goal is to offer its smart glass at half the price of current electrochromic glass or less, or about $100 per square foot, at which point it will become competitive with ordinary windows. And, by potentially eliminating the need for shades or curtains, and by increasing heating/cooling efficiency by blocking or transmitting heat, even slightly more-expensive smart glass could pay for itself.
It’s going to take some hard work, though
The company has to cross several significant barriers between now and then, however. It hopes to be producing samples of its product for its manufacturing partners to test by the end of this year. Then, assuming the company gets funding, it will start pilot projects with its partners in 2014 and enter the commercial market by 2017.
“Our goal is to make larger-format devices, potentially large enough for a skylight, in the next 3-4 years,” Holt said.
Heliotrope will also face stiff competition from established smart glass makers such as Sage Glass and View Inc. View has raised more than $140 million from a variety of backers, including glass giant (and Gorilla Glass maker) Corning. Additionally, Heliotrope doesn’t own the patent to its smart glass — that is held by LBL, which licenses it non-exclusively to Heliotrope.
On the other hand, the researchers who discovered the new three-phase smart glass tech are all working with Heliotrope, which gives it a leg up on the competition even if the others license the same patents.
Heliotrope has raised $2 million in seed funding to date, from anonymous individual and institutional ventures, as well as an award from Advanced Research Projects Agency – Energy (ARPA-E, a sort of energy-focused equivalent to DARPA) and a $50,000 prize from the Nova Innovations Challenge, an energy efficiency competition.
It plans to raise a first round of venture funding in Q1 2014.
Fun fact: The heliotrope is a pinkish-purplish flower, and the word also names that flower’s color. Its name comes from Greek, and is based on the idea (not true, apparently) that these flowers turn to face the sun, like sunflowers.