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| Fig. 1: Illustration of the two different cross sectional arrangements of Vitwell's Smart Section Blind product, showing the different layers of PDLC, with ITO or solar film positioned underneath glass, and adjacent to the polymer matrix (Source: "Wikimedia Commons"). |
Smart glass is an emerging technology applicable in a variety of settings. As the energy industry witnesses shifts towards energy conservation and user-friendly technologies, smart glass will be recognized for its wide-ranging benefits, and will continue to grow in demand. Controlling visible light transmission through currents running in smart glass panels can benefit worker productivity by providing added control over lighting environments. Smart glass can also control UV and infrared ray transmission, enhancing its value to commercial, hospitality, and healthcare buildings, as well as to consumer products like automobiles, where heat and UV glare matter. Smart glass product offerings will continue to improve with time, and its superior value proposition virtually ensures that it will someday replace regular windows.
There are two main types of smart glass, active and passive. Passive glass is thermochromic and photochromic. Active smart glass involves electric stimulus. There are three key categories of smart glass: electrochromic, suspended-particle, and liquid crystal glass. Electrochromic glass is the most prevalent type as electrochromic materials have the ability to change their optical properties with the addition of voltage. Creating electrochromic glass has allowed one to control the transmissivity, absorptivity, and reflectivity of windows, making it the most predominant form on the market. In contrast to suspended-particle smart glass, electrochromic smart glass, the glass reverts to its original state of transparency when the voltage is removed. [1]
For suspended-particle smart glass, the glass becomes transparent when voltage is applied, because the particles move from their random placement into a minimum energy state, allowing light to pass through. Finally, the last category of smart glass to be discussed is polymer-dispersed liquid crystal smart glass (PDLC). Like suspended-particle smart glass, PDLC windows need voltage to appear transparent. In its original state, the liquid crystal molecules are randomly distributed throughout the polymer, and appear slightly opaque. PDLC has a larger transition time compared to other smart glass material. [1] Hence, electrochromic glass enjoys strong demand in the smart glass market, mainly due to its original transparent state. In terms of energy properties, the U-value for PDLC coats on glass windows range anywhere between 2.8 W m-2 °K-1 for transparent states, and 2.4 W m-2 °K-1 for the translucent state, which is significantly lower than the U value for regular glass (5.8 W m-2 °K-1), facilitating energy conservation. [2]
Smart glass can be applied to a diverse variety of settings. It can be used as soundproof partitions for office or living spaces, as shown in Fig. 1, which shows glass that is both transparent and cloudy for enhanced transparency. Active, electrically-switchable glass technology can be used for office partitions, in hotel buildings, in hospitals, in residential buildings, in retail, and in the automotive industry. Within each of these settings, various types of smart glass can be useful. Though difficult to measure precisely, utility savings can be significant, since interior heat can be better managed through changes to exterior glass windows.
A recent study showed that sunlight shining on semi-transparent silicon thin-film solar cell (Si-TFSC) creates a current changing the color of the photovoltaic electrochromic (PV-EC) device, and generates electricity in the process, creating both a solar cell module and self-powered smart glass. Thus, smart windows can generate the electricity needed to operate their own currents. [3] In contrast, passive thermochromic windows can change their color and optical properties solely based on temperature variation. [4]
In summary, smart glass holds tremendous potential in the energy industry. I believe more commercial buildings will start to feature smart glass exteriors. Since buildings use a significant fraction of overall energy, my hope is that electricity usage will go down, as renewable energy sources gain in prevalence. Thus, smart glass will become an important innovation for maintaining environmental sustainability.
© Brandon Lutnick. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] K. V. Wong and R. Chan, "Smart Glass and Its Potential in Energy Savings," J. Energy Resour. Technol. 136, 012002 (2014).
[2] A. Hemaida et al., "Evaluation of Thermal Performance for a Smart Switchable Adaptive Polymer Dispersed Liquid Crystal (PDLC) Glazing," Solar Energy 195, 185 (2020).
[3] L.-M. Huang et al., "Photovoltaic Electrochromic Device for Solar Cell Module and Self-powered Smart Glass Applications," Sol. Energ. Mat. Sol. C. 99, 154 (2012).
[4] M. Kamalisarvestani et al., "Performance, Materials and Coating Technologies of Thermochromic Thin Films on Smart Windows," Renew. Sust. Energ. Rev. 26, 353 (2013).
