Buildings and Cities
A one-time luxury, glass windows are now standard across the world, bringing light and visibility into the built environment without inviting in the weather. Except windows do let in the weather, in the form of heat or cold. They are much less efficient than insulated walls at keeping room temperature in and outside temperature out—by a factor of ten or more.
Various measures can improve a window’s efficiency: layered panes, reflective low-emissivity coatings, insulating gas between panes, and tightly sealed frames. More adaptive technologies, dubbed “smart glass,” make windows responsive in real time to sunlight and weather, reducing a building’s energy load for lighting and improving heating and cooling efficiency.
Smart glass relies on chromism, the term for any process that causes material to change color. Electricity triggers it in electrochromic glass: When exposed to a brief burst of voltage, ions move into another layer of glass and the tint and reflectiveness change. Thermochromic glass is triggered by heat: Based on outside temperature, it transitions automatically from transparent to opaque and back again. Photochromic windows operate similarly, on the basis of light exposure. Currently challenged by cost, smart glass will become much more common in the coming decades.
Roman glass: Deviren, A. Senem, and Phillip James Tabb. The Greening of Architecture: A Critical History and Survey of Contemporary Sustainable Architecture and Urban Design. Farnham, Surrey, UK: Ashgate Publishing Limited, 2013.
windows…less efficient insulated walls: Gunn, Dwyer. “This Sustainable New Tech Will Make You See Windows in a Whole New Light.” The Guardian. November 10, 2016.
most efficient windows…U-value: Energy Star. “ENERGY STAR Most Efficient.” https://www.energystar.gov/products/most_efficient.
Electrochromic glass…developed in the 1970s and ’80s: “Researchers Develop ‘Smart’ Window to Cut Energy Consumption.” New York Times. September 29, 1992.
nanoscale metal oxides: Hickey, Shane. “Smart Glass Offers Window of Opportunity for View.” The Guardian. November 23, 2014.
disaggregate light and heat: Korgel, Brian A. “Materials Science: Composite for Smarter Windows.” Nature 500, no. 7462 (2013): 278-279.
Japan…[drop in] cooling loads: Yoshimura, Kazuki, Kazuki Tajima, and Yasusei Yamada. “Development of Switchable Mirror Glass.” Synthesiology 5, no. 4 (2013): 262-269.
electrochromic line…[vs.] traditional windows: Gunn, “Windows.”
Project Drawdown defines smart glass as: glass that dynamically changes its opacity to reduce or increase the amount of light and heat that is allowed to pass through. This technology replaces conventional, non-dynamic glass.
Smart glass promises energy savings for both thermal and lighting systems in buildings and transportation. Applications include sunlight regulation in buildings and glare reduction on rear-view mirrors. There are many technologies that allow this, including those that automatically change in response to light, heat, or an electrical current (that is, by human control). Smart glass can greatly reduce the inefficiency of building windows and other glazed surfaces and can also eliminate the need for shading, resulting in an increase in natural lighting in buildings. In this report, we examine the potential financial and climate impact of increased adoption of smart glass instead of plain glass for commercial building applications.
Total Addressable Market 
The total addressable market for commercial architectural glass was determined based on the estimated growth in commercial floor area and the average window-to-floor-area ratio from the Global Buildings Performance Network. Recent sales data of smart glass from four market research sources was used to estimate the solution’s current adoption  in square meters.
Adoption Scenarios 
Impacts of increased adoption of smart glass from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.
For smart glass, three scenarios were developed based on near-term projections and long-term targets from international organizations:
- Plausible Scenario: For near-term forecasts to 2022, historical and trend data estimated by Navigant Research (2012) was used, and interpolated with a far future forecast guided by the World's Green Buildings Council target of 100 percent net zero buildings by 2050.  A more conservative number of 30 percent adoption in 2050 was chosen.
- Drawdown Scenario: The same procedure was performed as in the Plausible Scenario, but 50 percent adoption in 2050 was used.
- Optimum Scenario: The same procedure was performed as in the Plausible Scenario, but 75 percent adoption in 2050 was used.
Lighting and cooling energy data for commercial buildings was obtained from the International Energy Agency’s data (IEA ETP, 2016), combined with that of the US Energy Information Administration (EIA CBECS). Only grid emissions from lighting and cooling electricity were included, and a weighted reduction in electricity use was found of 30 percent for these two applications.
First costs of smart glass are almost three times those of plain glass based on a total of 20 data points, but a learning rate of 8 percent was applied for smart glass.  As the technology is still relatively new, and as some types of smart glass do use small amounts of electricity whereas other do not, operating costs of the glass itself were not included. Cooling and lighting costs, however, were included for commercial areas with smart glass and with plain glass.
The smart glass solution was integrated with others in the Buildings and Cities Sector by first prioritizing the solutions according to the point of impact on building energy usage (with building envelope solutions first and building systems last).  The impact on building energy demand was calculated for highest-priority solutions, and the smart glass input value was reduced to represent the impact of higher building envelope solutions. The output from the smart glass model was used as the input in lower-priority solutions.
The Plausible Scenario forecasts that just under 3 billion square meters of smart glass could be installed by 2050, thereby avoiding 2.2 gigatons of carbon dioxide-equivalent greenhouse gas emissions. The marginal capital cost compared to the Reference Scenario would be $932 billion,  but this scenario saves $325 billion in operating costs by 2050 due to reduced energy consumption.
The Drawdown and Optimum Scenarios show 3.6 and 6 gigatons of emissions reduced, respectively.
It is clear that smart glass would have to drop significantly in price to be economically viable, but it does have the potential to contribute to emissions reductions. Some aspects that may affect this result have not been examined, however, such as the regional nature of adoption due to smart glass’s high price and weather application. Realistically, architectural smart glass will be mainly adopted in wealthier regions with higher average temperatures, such as Australia and the southern and western areas of the US. Additionally, there are likely some residential applications that would increase the impact of smart glass. Emissions impacts could be higher if heating is included, especially since some building heating systems use natural gas instead of electricity.
The high upfront cost of smart glass has inhibited its growth. As new competitors enter the market (including for transportation applications of smart glass, which were not included in our model), the price of smart glass is expected to drop and adoption is expected to accelerate. Growth could be further driven with government support and the development of programs that demonstrate the benefits of smart glass to consumers.
 For more on the Total Addressable Market for the Buildings and Cities Sector, click the Sector Summary: Buildings and Cities link below.
 Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.
 To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Buildings and Cities Sector-specific scenarios, click the Sector Summary: Buildings and Cities link.
 All buildings consume net zero energy/produce onsite or produce net zero carbon emissions.
 Although no learning rate data was found on smart glass, another cooling technology (air-conditioning units) had a learning rate of 13 percent, so a rate was used that was bounded by this.
 For more on Project Drawdown’s Buildings and Cities Sector integration model, click the Sector Summary: Buildings and Cities link below.
 Although we used the term “priority”, we do not mean to say that any solution was of greater importance than any other, but rather that for estimating total impact of all building solutions, we simply applied the impacts of some solutions before others, and used the output energy demand after application of a higher-priority solution as the energy demand input to a lower-priority solution.
 All costs are presented in US2014$.