Sage Electrochromics is now a wholly owned subsidiary of French glass giant Saint-Gobain.

Sage makes energy-saving electrochromic smart window products for buildings which are electronically tintable to block light or let light in.

The acquisition doesn't come as an enormous surprise, as Saint-Gobain had made an $80 million strategic investment in Sage back in 2010. That follows a $16 million venture funding round from Good Energies, Applied Ventures, NV Bekaert, and Bekaert Corporation in 2007. The price of the acquisition was not disclosed, and whether this is a venture-scale return for the original private equity investors is unknown.

The company was founded in 1989 and has developed a technology that coats float glass with thin films of metal oxides using sputter deposition to form the active layer. The tintable windows have the potential to lower heating and air conditioning bills (as does the act of closing a shade).

Cost, complexity and performance concerns have been some of the chief challenges of electrochromics. Training glaziers who are likely unfamiliar with handling wire runs will be another challenge. Dealing with wiring and sensors in craft settings unfamiliar with the messy details of installation is an obstacle. But having Saint-Gobain, with its extensive manufacturing and logistics experience, on Sage's side might help to to migrate these types of windows into the mainstream and beyond the showcase stage. Can the installation process be simplified? Will the windows last as long as the building envelope?

According to information offered by the CEO of Sage, John Van Dine, in an earlier interview with Greentech Media, darkening a window takes only 0.28 watts per square foot of glass; maintaining the tint takes about a tenth of a watt.

In July of 2010, Sage rival Soladigm landed a loan and stimulus package to open a factory in Mississippi. Soladigm has taken more than $60 million from Khosla Ventures, General Electric, the Westly Group, Sigma Partners, and DBL Ventures.

A video on installing the Sage windows can be found here.

Sage is building a manufacturing facility in Faribault, MN that is scheduled to start production in January 2013.