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Soladigm has emerged as a startup to watch in the smart window space, yet not much is known about its technology. The Silicon Valley company is developing electrochromic windows, which can control the amount of light and heat that pass through the glass, making it a promising method of cooling and heating a room. It turns out, the 3-year-old startup, which announced its first commercial factory plan in Mississippi last week, has been amassing both technologies and patents.
Electrochromic windows can darken or lighten the windows to control the amount of light that enters a room, and one of the goals is to make sure the windows remain transparent so as not to block any view. Soladigm doesn’t say much about its technology and puts nothing on that subject on its website. But we do know that Soladigm did sign a licensing agreement with the Lawrence Berkeley National Laboratory in 2008 for a set of processes for modulating light. According to researchers there, Soladigm is working on materials that could absorb or reflect light.
What’s intriguing about the Berkeley Lab’s technology is the use of a novel material for the electrochromic layer. Instead of absorbing the light, a more common smart window technology, the material reflects it, says Delia Milliron, a nanoscience researcher at Berkeley Lab, during a lecture on smart windows on Monday. The reflective film is based on magnesium, and when it reacts with hydrogen gas to become magnesium hydride, its reflective property changes to become transparent and allow the light in, Milliron said.
Tom Richardson, a Berkeley Lab researcher, is an inventor of this material. Here is a YouTube video explaining his research.
The magnesium hydride material isn’t what Soladigm plans to use to make its first commercial products, however, Milliron said. Instead, the company plans to use tungsten oxide as the electrochromic layer for absorbing light. Tungsten oxide is a well-known material for smart windows. The film makes up one of several layers of materials, such as transparent conductive oxide and lithium ions, that are sandwiched between glass.
Tungsten oxide does its magic of blocking the light when it’s flooded with ions that are activated by applying a voltage to the transparent conductive oxide. So, to darken a window, a voltage sends the ions to the electrochromic layer. To lighten it, the process is reversed to drive ions out of it.
The use of Tungsten oxide creates two key technical hurdles. The material does “a decent good job” of dealing with visible light, but not so much when it comes to near infrared light (which radiates heat), Milliron said. And, because it absorbs light, the material actually heats up the window itself.
“It’s like wearing black and going out on a sunny day. You are trying to prevent heating, but your window gets very hot. They have a secondary heating problem where they need to find a way to reject that heat,” she said. The use of the magnesium hydride helps to solve those technical challenges.
Soladigm also has gotten patents for its own work. The U.S. Patent Office and Trademark Office granted a patent in March this year that outlines the use of tantalum-nitride as an ion-blocking layer between a transparent conductive oxide and the electrochromic layer. Another patent, granted in January this year, looks at the use of antimony alloy as the electrochromic layer (this nanotech patent blog offers more details).
Soladigm has a lot to prove. Research into electrochromic glass has been around for several decades, but it remains expensive to make. The technology has gradually showed up in windows in recent years, but at $50-$100 per square foot, it’s too expensive for consumers or building managers, said Berkeley Lab researcher Steve Selkowitz, during the lecture. The goal is to get the price down to less than $20 per square foot.
The startup has attracted a fair amount of funding to take its know-how out of the lab and into the market. The company has raised about $30 million in equity and debt and a $3.5 million grant from the Department of Energy. For the proposed $130 million factory in Mississippi, Soladigm is getting a $40 million loan from the state and $4 million more in other state incentives. It still needs to raise more money to complete it, however.
Given the government’s focus on technologies to create energy-efficient buildings, many other companies are eying opportunities in the window business. Sage Electrochromics in Minnesota has commercial products, and it recently won a $1.6 million DOE grant. Applied Materials has gotten nearly $2 million from the same DOE grant program to figure out ways to quickly and cheaply coat the glass with various layers of materials. EControl-Glas in Germany also is selling electrochromic glass.
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