Tag Archives: smart windows

Multifunctional smart windows that lower indoor temperatures without consuming power and can generate electricity from raindrops

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Caption: Figure 1: The main functions of the multifunctional smart windows for implementing Plus Energy (transparent radiative cooling, power generation, and fog and frost removal technology). Credit: © Seoul National University College of Engineering

I’m always a sucker for a ‘smart window’ story and this one from Korea with its reference to harvesting energy from raindrops seems particularly intriguing. From an August 13, 2024 Seoul National University (SNU) press release, also on EurekAlert but published August 22, 2024,

■ Research Necessity

o Recently, with the significant increase in cooling demand due to global warming, a vast amount of energy is being consumed for heat management inside buildings. Existing windows, which have a high solar absorption rate and low reflectance, lead to considerable energy loss. Therefore, energy-saving windows are emerging as a practical solution to global challenges such as responding to climate change and ensuring energy sustainability. These windows not only provide optimal thermal comfort to occupants but also contribute to economic development by reducing dependence on conventional cooling systems.

o For windows to effectively save energy in buildings, it is necessary to adopt energy-efficient cooling technology (Zero Energy) and further ensure energy harvesting methods (Plus Energy) that guarantee sustainable power supply. Additionally, windows must maintain high transparency, which is their fundamental function, even on cold or foggy days.

■ Research Achievements / Expected Effects

o The multifunctional smart windows developed in this research demonstrate their effectiveness as next-generation energy-saving devices by implementing three main functions.

o First, they provide radiative cooling that lowers indoor temperature on sunny days without energy input. Second, they generate electricity using raindrops on rainy days. Third, they implement a transparent heater function to quickly remove frost from the windows on cold days.

■ Research Details 

□ Research Content Overview

o The research team led by Professor Seung Hwan Ko from the Department of Mechanical Engineering at Seoul National University has developed “multifunctional smart window technology” that lowers indoor temperatures without electricity consumption and generates power using the frictional electricity from raindrops. This research is significant in that it pioneers new possibilities for Plus Energy technology, surpassing Zero Energy to contribute to improving energy self-sufficiency in response to global warming.

□ Background

o Recently, implementing Plus Energy Buildings (PEBs) that surpass Zero Energy has become a key task for achieving energy self-sufficiency in buildings. Next-generation PEBs are buildings that go beyond minimizing energy loads and can autonomously produce energy. Buildings inherently consume a massive amount of energy for heat management, and with the rise in cooling demand due to global warming, energy usage has surged dramatically. Furthermore, existing windows with high solar absorption and low reflectivity result in substantial energy losses during cooling. Therefore, to realize economically efficient next-generation Plus Energy Buildings, it is necessary to develop multifunctional smart windows equipped with transparent cooling technology (Zero Energy-based) and further energy-harvesting technology (Plus Energy-based) that ensures sustainable power supply.
o To address these issues, researchers worldwide are focusing on the development of smart windows that maximize energy savings. Smart windows are often thought to adjust internal temperatures by changing color to control sunlight. However, this method has limitations since the windows become opaque during the cooling process, thus failing to maintain high transparency, which is the window’s primary function.

□ Key Research Methods

o The research team is actively working on developing new technologies that improve energy efficiency while preserving the transparency of windows. As part of this effort, Professor Ko’s research team developed a Zero Energy-based “transparent radiative cooling technology” that maintains transparency while enabling cooling without using electricity. Additionally, they developed energy-harvesting technology that produces electricity through the friction generated when raindrops contact the window surface, introducing a Plus Energy-based smart window technology that surpasses Zero Energy. The team also developed a transparent heater technology that quickly clears frost from windows on cold or foggy days, thereby implementing three functions—radiative cooling, power generation, and frost removal—simultaneously in a single device for the first time in the world.
o The research team achieved these three functionalities in a single device by fabricating windows with a layered structure of silver and ITO (Indium Tin Oxide), materials with excellent electrical conductivity and unique optical properties. First, the “transparent radiative cooling technology” minimizes the absorption of sunlight entering indoors while emitting radiant heat outdoors to lower the temperature. Unlike conventional air conditioning systems that use refrigerants, this radiative cooling technology offers cooling performance without consuming electrical energy. The research team focused on allowing only the visible light spectrum from sunlight to pass through the window while selectively reflecting near-infrared sunlight to lower indoor temperatures and maximize cooling. Second, the “frictional electricity-based power generation technology” generates electricity when raindrops contact the window surface on rainy days. For this purpose, an electrode material covering the window surface is necessary, and thanks to the excellent electrical conductivity of the layered silver and ITO structure, the smart window can generate electricity through frictional electricity. Lastly, through “Joule heating,” the transparent electrodes also serve as a heater that quickly removes frost or ice from the window, ensuring clear visibility on cold days. The multifunctional smart windows developed by the research team can provide transparent radiative cooling on sunny days, generate power on rainy days, and remove frost or ice on cold days.

□ Results

o The research team led by Professor Seung Hwan Ko confirmed that the smart windows they developed maintained a temperature approximately 7 degrees lower than regular windows in hot environments under direct sunlight. In an experiment simulating rainy conditions, the smart windows generated 8.3 W m-2 of power with just a single raindrop, while also clearing frost from the window twice as fast as regular windows through Joule heating, demonstrating both high performance and multifunctionality.

□ Expected Effects

o Professor Seung Hwan Ko stated, “This achievement of presenting next-generation smart window technology optimized for responding to the depletion of fossil fuels and global warming offers valuable insights into the technological advancements for Plus Energy buildings and the eco-friendly electric vehicle industry. Smart windows are expected to be applied across various industries because they address environmental pollution, reduce cooling energy, and overcome the limitations of conventional battery technologies through self-power generation.”

□ Achievements

o This research was supported by the Basic Science Research Program through the National Research Foundation of Korea, and it has gained global attention, being published in the October 2024 issue of the prestigious journal Nano Energy (Impact factor: 16.8, Top 5.3%) under the title: “Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities.”

o Meanwhile, Dr. Yeongju Jung, the lead author of this study, is currently conducting follow-up research at Professor Ko’s laboratory in the Department of Mechanical Engineering at Seoul National University and is preparing for a postdoctoral research fellowship abroad.

□ Introduction to the SNU College of Engineering

Seoul National University (SNU) founded in 1946 is the first national university in South Korea. The College of Engineering at SNU has worked tirelessly to achieve its goal of ‘fostering leaders for global industry and society.’ In 12 departments, 323 internationally recognized full-time professors lead the development of cutting-edge technology in South Korea and serving as a driving force for international development.

Here’s a link to and a citation for the paper,

Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities by Yeongju Jung, Ji-Seok Kim, Junhyuk Bang, Seok Hwan Choi, Kangkyu Kwon, Min Jae Lee, Il-Kwon Oh, Jaeman Song, Jinwoo Lee, Seung Hwan Ko. Nano Energy DVolume 129, Part A, October 2024, 110004 DOI: https://doi.org/10.1016/j.nanoen.2024.110004 Available online 25 July 2024, Version of Record 25 July 2024

This paper is behind a paywall.

Excellent electrochromic smart window performance with yolk-shell NiO (nitrogen oxide) nanospheres

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Electrochromic windows hold great promise where energy savings are concerned. So far, it’s still just a promise but perhaps the research in this April 17, 2023 news item on phys.org will help realize it, Note: Links have been removed,

Researchers from Tsinghua University synthesized porous yolk-shell NiO nanospheres (PYS-NiO NSs) via a solvothermal and subsequent calcination process of Ni-MOF. As the large specific surface areas and hollow porous nanostructures were conducive to ionic transport, PYS-NiO NSs exhibited a fast coloring/bleaching speed (3.6/3.9 s per one coloring/bleaching cycle) and excellent cycling stability (82% of capacity retention after 3000 cycles). These superior electrochromic (EC) properties indicated that the PYS-NiO NSs was a promising candidate for high performance EC devices.

Electrochromic (EC) materials (ECMs) are defined as the materials which have reversible changes in their colors and optical properties (transmittance, reflectance, and absorption) under different external voltages. Over the past decades, ECMs show promising advantages and application prospects in many fields such as smart windows, adaptive camouflage, electronic displays, and energy storage, etc., because of their excellent optical modulation abilities.

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This image doesn’t seem all that helpful (to me) in understanding the research,

Caption: Porous yolk-shell nanospheres exhibit a fast coloring/bleaching speed. Credit: Baoshun Wang, Tsinghua University

An April 17, 2023 Particuology (journal) news release on EurekAlert, which originated the news item, does provide more detail, Note: Links have been removed,

Transition metal oxides (TMOs) are one of the most important ECMs which have been widely studied. They have many advantages such as rich nanostructure design, simple synthesis process, high security, etc. Among them, nickel oxide (NiO) is an attractive anode ECM and has attracted extensive research interest due to its high optical contrast, high coloring efficiency, low cost, etc. However, NiO-based ECMs still face the challenges of long EC switching times and poor cycling life which are caused by their poor ionic/electronic diffusion kinetics and low electrical conductivity.

Metal-organic frameworks (MOFs) have attracted enormous attention, because of their high porosity and large surface areas, and could be adjusted to achieve different properties by selecting different metal ions and organic bridging ligands. Due to the porosity and long-range orderliness, MOFs can provide fast and convenient channels for small molecules and ions to insert and extract during the transformation process. Therefore, MOFs can be used as effective templates for the preparation of hollow and porous TMOs with high ion transport efficiency, excellent specific capacitance, and electrochemical activities.

So the authors proposed a new strategy to design a kind of NiO with hollow and porous structure to obtain excellent EC performance and cyclic stability. As a proof-of-concept demonstration, the authors successfully synthesized MOFs-derived porous yolk-shell NiO nanospheres (PYS-NiO NSs) which exhibited excellent EC performance. Ni-organic framework spheres were prepared by a simple solvothermal method and then converted to PYS-NiO NSs by thermal decomposition. The PYS-NiO NSs exhibited relatively high specific surface areas and stable hollow nanostructures, which not only provided a large contact area between active sites and electrolyte ions in the EC process but also helped the NiO to accommodate large volume changes without breaking. Besides, the PYS-NiO NSs also shortened the ionic diffusion length and provided efficient channels for transferring electronics and ions. In addition, the coupling with carbon also rendered the PYS-NiO NSs with improved electronic conductivity and obtained better EC performance. The PYS-NiO NSs exhibited a fast coloring/bleaching speed (3.6/3.9 s). Besides, PYS-NiO NSs also exhibited excellent cycling stability (82% of capacity retention after 3000 cycles). These superior EC properties indicate that the PYS-NiO NSs is a promising candidate for high-performance EC devices. The as-prepared PYS-NiO NSs are believed to be a promising candidate for smart windows, displays, antiglare rearview mirrors, etc. More importantly, this work provides a new and feasible strategy for the efficient preparation of ECMs with fast response speed and high cyclic stability.

Particuology (IF=3.251) is an interdisciplinary journal that publishes frontier research articles and critical reviews on the discovery, formulation and engineering of particulate materials, processes and systems. Topics are broadly relevant to the production of materials, pharmaceuticals and food, the conversion of energy resources, and protection of the environment. For more information, please visit: https://www.journals.elsevier.com/particuology.

Here’s a link to and a citation for the paper, Note: There is an unusually long lead time between online access and print access,

Novel self-assembled porous yolk-shell NiO nanospheres with excellent electrochromic performance for smart windows by Baoshun Wang, Ya Huang, Siming Zhao, Run Li, Di Gao, Hairong Jiang, Rufan Zhang. Particuology Volume 84, January 2024, Pages 72-80 DOI: https://doi.org/10.1016/j.partic.2023.03.007 Available online: April 17, 2023

This paper is open access.

Windows and roofs ‘self-adapt’ to heating and cooling conditions

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I have two items about thermochromic coatings. It’s a little confusing since the American Association for the Advancement of Science (AAAS), which publishes the journal featuring both papers has issued a news release that seemingly refers to both papers as a single piece of research.

Onto, the press/new releases from the research institutions to be followed by the AAAS news release.

Nanyang Technological University (NTU) does windows

A December 16, 2021 news item on Nanowerk announced work on energy-saving glass,

An international research team led by scientists from Nanyang Technological University, Singapore (NTU Singapore) has developed a material that, when coated on a glass window panel, can effectively self-adapt to heat or cool rooms across different climate zones in the world, helping to cut energy usage.

Developed by NTU researchers and reported in the journal Science (“Scalable thermochromic smart windows with passive radiative cooling regulation”), the first-of-its-kind glass automatically responds to changing temperatures by switching between heating and cooling.

The self-adaptive glass is developed using layers of vanadium dioxide nanoparticles composite, Poly(methyl methacrylate) (PMMA), and low-emissivity coating to form a unique structure which could modulate heating and cooling simultaneously.

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A December 17, 2021 NTU press release (PDF), also on EurekAlert but published December 16, 2021, which originated the news item, delves further into the research (Note: A link has been removed),

The newly developed glass, which has no electrical components, works by exploiting the spectrums of light responsible for heating and cooling.

During summer, the glass suppresses solar heating (near infrared light), while boosting radiative cooling (long-wave infrared) – a natural phenomenon where heat emits through surfaces towards the cold universe – to cool the room. In the winter, it does the opposite to warm up the room.

In lab tests using an infrared camera to visualise results, the glass allowed a controlled amount of heat to emit in various conditions (room temperature – above 70°C), proving its ability to react dynamically to changing weather conditions.

New glass regulates both heating and cooling

Windows are one of the key components in a building’s design, but they are also the least energy-efficient and most complicated part. In the United States alone, window-associated energy consumption (heating and cooling) in buildings accounts for approximately four per cent of their total primary energy usage each year according to an estimation based on data available from the Department of Energy in US.[1]

While scientists elsewhere have developed sustainable innovations to ease this energy demand – such as using low emissivity coatings to prevent heat transfer and electrochromic glass that regulate solar transmission from entering the room by becoming tinted – none of the solutions have been able to modulate both heating and cooling at the same time, until now.

The principal investigator of the study, Dr Long Yi of the NTU School of Materials Science and Engineering (MSE) said, “Most energy-saving windows today tackle the part of solar heat gain caused by visible and near infrared sunlight. However, researchers often overlook the radiative cooling in the long wavelength infrared. While innovations focusing on radiative cooling have been used on walls and roofs, this function becomes undesirable during winter. Our team has demonstrated for the first time a glass that can respond favourably to both wavelengths, meaning that it can continuously self-tune to react to a changing temperature across all seasons.”

As a result of these features, the NTU research team believes their innovation offers a convenient way to conserve energy in buildings since it does not rely on any moving components, electrical mechanisms, or blocking views, to function.

To improve the performance of windows, the simultaneous modulation of both solar transmission and radiative cooling are crucial, said co-authors Professor Gang Tan from The University of Wyoming, USA, and Professor Ronggui Yang from the Huazhong University of Science and Technology, Wuhan, China, who led the building energy saving simulation.

“This innovation fills the missing gap between traditional smart windows and radiative cooling by paving a new research direction to minimise energy consumption,” said Prof Gang Tan.

The study is an example of groundbreaking research that supports the NTU 2025 strategic plan, which seeks to address humanity’s grand challenges on sustainability, and accelerate the translation of research discoveries into innovations that mitigate human impact on the environment.

Innovation useful for a wide range of climate types

As a proof of concept, the scientists tested the energy-saving performance of their invention using simulations of climate data covering all populated parts of the globe (seven climate zones).

The team found the glass they developed showed energy savings in both warm and cool seasons, with an overall energy saving performance of up to 9.5%, or ~330,000 kWh per year (estimated energy required to power 60 household in Singapore for a year) less than commercially available low emissivity glass in a simulated medium sized office building.

First author of the study Wang Shancheng, who is Research Fellow and former PhD student of Dr Long Yi, said, “The results prove the viability of applying our glass in all types of climates as it is able to help cut energy use regardless of hot and cold seasonal temperature fluctuations. This sets our invention apart from current energy-saving windows which tend to find limited use in regions with less seasonal variations.”

Moreover, the heating and cooling performance of their glass can be customised to suit the needs of the market and region for which it is intended.

“We can do so by simply adjusting the structure and composition of special nanocomposite coating layered onto the glass panel, allowing our innovation to be potentially used across a wide range of heat regulating applications, and not limited to windows,” Dr Long Yi said.

Providing an independent view, Professor Liangbing Hu, Herbert Rabin Distinguished Professor, Director of the Center for Materials Innovation at the University of Maryland, USA, said, “Long and co-workers made the original development of smart windows that can regulate the near-infrared sunlight and the long-wave infrared heat. The use of this smart window could be highly important for building energy-saving and decarbonization.”  

A Singapore patent has been filed for the innovation. As the next steps, the research team is aiming to achieve even higher energy-saving performance by working on the design of their nanocomposite coating.

The international research team also includes scientists from Nanjing Tech University, China. The study is supported by the Singapore-HUJ Alliance for Research and Enterprise (SHARE), under the Campus for Research Excellence and Technological Enterprise (CREATE) programme, Minster of Education Research Fund Tier 1, and the Sino-Singapore International Joint Research Institute.

Here’s a link to and a citation for the paper,

Scalable thermochromic smart windows with passive radiative cooling regulation by Shancheng Wang, Tengyao Jiang, Yun Meng, Ronggui Yang, Gang Tan, and Yi Long. Science • 16 Dec 2021 • Vol 374, Issue 6574 • pp. 1501-1504 • DOI: 10.1126/science.abg0291

This paper is behind a paywall.

Lawrence Berkeley National Laboratory (Berkeley Lab; LBNL) does roofs

A December 16, 2021 Lawrence Berkeley National Laboratory news release (also on EurekAlert) announces an energy-saving coating for roofs (Note: Links have been removed),

Scientists have developed an all-season smart-roof coating that keeps homes warm during the winter and cool during the summer without consuming natural gas or electricity. Research findings reported in the journal Science point to a groundbreaking technology that outperforms commercial cool-roof systems in energy savings.

“Our all-season roof coating automatically switches from keeping you cool to warm, depending on outdoor air temperature. This is energy-free, emission-free air conditioning and heating, all in one device,” said Junqiao Wu, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of materials science and engineering who led the study.

Today’s cool roof systems, such as reflective coatings, membranes, shingles, or tiles, have light-colored or darker “cool-colored” surfaces that cool homes by reflecting sunlight. These systems also emit some of the absorbed solar heat as thermal-infrared radiation; in this natural process known as radiative cooling, thermal-infrared light is radiated away from the surface.

The problem with many cool-roof systems currently on the market is that they continue to radiate heat in the winter, which drives up heating costs, Wu explained.

“Our new material – called a temperature-adaptive radiative coating or TARC – can enable energy savings by automatically turning off the radiative cooling in the winter, overcoming the problem of overcooling,” he said.

A roof for all seasons

Metals are typically good conductors of electricity and heat. In 2017, Wu and his research team discovered that electrons in vanadium dioxide behave like a metal to electricity but an insulator to heat – in other words, they conduct electricity well without conducting much heat. “This behavior contrasts with most other metals where electrons conduct heat and electricity proportionally,” Wu explained.

Vanadium dioxide below about 67 degrees Celsius (153 degrees Fahrenheit) is also transparent to (and hence not absorptive of) thermal-infrared light. But once vanadium dioxide reaches 67 degrees Celsius, it switches to a metal state, becoming absorptive of thermal-infrared light. This ability to switch from one phase to another – in this case, from an insulator to a metal – is characteristic of what’s known as a phase-change material.

To see how vanadium dioxide would perform in a roof system, Wu and his team engineered a 2-centimeter-by-2-centimeter TARC thin-film device.

TARC “looks like Scotch tape, and can be affixed to a solid surface like a rooftop,” Wu said.

In a key experiment, co-lead author Kechao Tang set up a rooftop experiment at Wu’s East Bay home last summer to demonstrate the technology’s viability in a real-world environment.

A wireless measurement device set up on Wu’s balcony continuously recorded responses to changes in direct sunlight and outdoor temperature from a TARC sample, a commercial dark roof sample, and a commercial white roof sample over multiple days.

How TARC outperforms in energy savings

The researchers then used data from the experiment to simulate how TARC would perform year-round in cities representing 15 different climate zones across the continental U.S.

Wu enlisted Ronnen Levinson, a co-author on the study who is a staff scientist and leader of the Heat Island Group in Berkeley Lab’s Energy Technologies Area, to help them refine their model of roof surface temperature. Levinson developed a method to estimate TARC energy savings from a set of more than 100,000 building energy simulations that the Heat Island Group previously performed to evaluate the benefits of cool roofs and cool walls across the United States.

Finnegan Reichertz, a 12th grade student at the East Bay Innovation Academy in Oakland who worked remotely as a summer intern for Wu last year, helped to simulate how TARC and the other roof materials would perform at specific times and on specific days throughout the year for each of the 15 cities or climate zones the researchers studied for the paper.

The researchers found that TARC outperforms existing roof coatings for energy saving in 12 of the 15 climate zones, particularly in regions with wide temperature variations between day and night, such as the San Francisco Bay Area, or between winter and summer, such as New York City.

“With TARC installed, the average household in the U.S. could save up to 10% electricity,” said Tang, who was a postdoctoral researcher in the Wu lab at the time of the study. He is now an assistant professor at Peking University in Beijing, China.

Standard cool roofs have high solar reflectance and high thermal emittance (the ability to release heat by emitting thermal-infrared radiation) even in cool weather.

According to the researchers’ measurements, TARC reflects around 75% of sunlight year-round, but its thermal emittance is high (about 90%) when the ambient temperature is warm (above 25 degrees Celsius or 77 degrees Fahrenheit), promoting heat loss to the sky. In cooler weather, TARC’s thermal emittance automatically switches to low, helping to retain heat from solar absorption and indoor heating, Levinson said.

Findings from infrared spectroscopy experiments using advanced tools at Berkeley Lab’s Molecular Foundry validated the simulations.

“Simple physics predicted TARC would work, but we were surprised it would work so well,” said Wu. “We originally thought the switch from warming to cooling wouldn’t be so dramatic. Our simulations, outdoor experiments, and lab experiments proved otherwise – it’s really exciting.”

The researchers plan to develop TARC prototypes on a larger scale to further test its performance as a practical roof coating. Wu said that TARC may also have potential as a thermally protective coating to prolong battery life in smartphones and laptops, and shield satellites and cars from extremely high or low temperatures. It could also be used to make temperature-regulating fabric for tents, greenhouse coverings, and even hats and jackets.

Co-lead authors on the study were Kaichen Dong and Jiachen Li.

The Molecular Foundry is a nanoscience user facility at Berkeley Lab.

This work was primarily supported by the DOE Office of Science and a Bakar Fellowship.

The technology is available for licensing and collaboration. If interested, please contact Berkeley Lab’s Intellectual Property Office, ipo@lbl.gov.

Here’s a link to and a citation for the paper,

Temperature-adaptive radiative coating for all-season household thermal regulation by Kechao Tang, Kaichen Dong, Jiachen Li, Madeleine P. Gordon, Finnegan G. Reichertz, Hyungjin Kim, Yoonsoo Rho, Qingjun Wang, Chang-Yu Lin, Costas P. Grigoropoulos, Ali Javey, Jeffrey J. Urban, Jie Yao, Ronnen Levinson, Junqiao Wu. Science • 16 Dec 2021 • Vol 374, Issue 6574 • pp. 1504-1509 • DOI: 10.1126/science.abf7136

This paper is behind a paywall.

An interesting news release from the AAAS

While it’s a little confusing as it cites only the ‘window’ research from NTU, the body of this news release offers some additional information about the usefulness of thermochromic materials and seemingly refers to both papers, from a December 16, 2021 AAAS news release,

Temperature-adaptive passive radiative cooling for roofs and windows

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When it’s cold out, window glass and roof coatings that use passive radiative cooling to keep buildings cool can be designed to passively turn off radiative cooling to avoid heat loss, two new studies show.  Their proof-of-concept analyses demonstrate that passive radiative cooling can be expanded to warm and cold climate applications and regions, potentially providing all-season energy savings worldwide. Buildings consume roughly 40% of global energy, a large proportion of which is used to keep them cool in warmer climates. However, most temperature regulation systems commonly employed are not very energy efficient and require external power or resources. In contrast, passive radiative cooling technologies, which use outer space as a near-limitless natural heat sink, have been extensively examined as a means of energy-efficient cooling for buildings. This technology uses materials designed to selectively emit narrow-band radiation through the infrared atmospheric window to disperse heat energy into the coldness of space. However, while this approach has proven effective in cooling buildings to below ambient temperatures, it is only helpful during the warmer months or in regions that are perpetually hot. Furthermore, the inability to “turn off” passive cooling in cooler climes or in regions with large seasonal temperature variations means that continuous cooling during colder periods would exacerbate the energy costs of heating. In two different studies, by Shancheng Wang and colleagues and Kechao Tang and colleagues, researchers approach passive radiative cooling from an all-season perspective and present a new, scalable temperature-adaptive radiative technology that passively turns off radiative cooling at lower temperatures. Wang et al. and Tang et al. achieve this using a tungsten-doped vanadium dioxide and show how it can be applied to create both window glass and a flexible roof coating, respectively. Model simulations of the self-adapting materials suggest they could provide year-round energy savings across most climate zones, especially those with substantial seasonal temperature variations. 

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I wish them all good luck with getting these materials to market.

Spray-on coatings for cheaper smart windows

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An August 6, 2020 RMIT University (Australia) press release (also on EurekAlert but published August 5, 2020) by Gosia Kaszubska announces a coating that makes windows ‘smart’,

A simple method for making clear coatings that can block heat and conduct electricity could radically cut the cost of energy-saving smart windows and heat-repelling glass [electrochromic windows?].

The spray-on coatings developed by researchers at RMIT are ultra-thin, cost-effective and rival the performance of current industry standards for transparent electrodes.

Combining the best properties of glass and metals in a single component, a transparent electrode is a highly conductive clear coating that allows visible light through.

The coatings – key components of technologies including smart windows, touchscreen displays, LED lighting and solar panels – are currently made through time-consuming processes that rely on expensive raw materials.

The new spray-on method is fast, scalable and based on cheaper materials that are readily available.

The method could simplify the fabrication of smart windows, which can be both energy-saving and dimmable, as well as low-emissivity glass, where a conventional glass panel is coated with a special layer to minimise ultraviolet and infrared light.

Lead investigator Dr Enrico Della Gaspera said the pioneering approach could be used to substantially bring down the cost of energy-saving windows and potentially make them a standard part of new builds and retrofits.

“Smart windows and low-E glass can help regulate temperatures inside a building, delivering major environmental benefits and financial savings, but they remain expensive and challenging to manufacture,” said Della Gaspera, a senior lecturer and Australian Research Council DECRA Fellow at RMIT.

“We’re keen to collaborate with industry to further develop this innovative type of coating.

“The ultimate aim is to make smart windows much more widely accessible, cutting energy costs and reducing the carbon footprint of new and retrofitted buildings.”

The new method can also be precisely optimised to produce coatings tailored to the transparency and conductivity requirements of the many different applications of transparent electrodes.

Global demand for smart glazing

The global market size for smart glass and smart windows is expected to reach $6.9 billion by 2022, while the global low-E glass market is set to reach an estimated $39.4 billion by 2024.

New York’s Empire State Building reported energy savings of $US2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows.

Eureka Tower in Melbourne features a dramatic use of smart glass in its “Edge” tourist attraction, a glass cube that projects 3m out of the building and suspends visitors 300m over the city. The glass is opaque as the cube moves out over the edge of the building and becomes clear once fully extended.

First author Jaewon Kim, a PhD researcher in Applied Chemistry at RMIT,  said the next steps in the research were developing precursors that will decompose at lower temperatures, allowing the coatings to be deposited on plastics and used in flexible electronics, as well as producing larger prototypes by scaling up the deposition.

“The spray coater we use can be automatically controlled and programmed, so fabricating bigger proof-of-concept panels will be relatively simple,” he said.

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Caption: The ultra-thin clear coatings are made with a new spray-on method that is fast, cost-effective and scalable. Credit: RMIT University

That is an impressive level of transparency. As per usual, here’s a link to and a citation for the paper (should you wish to explore further),

Ultrasonic Spray Pyrolysis of Antimony‐Doped Tin Oxide Transparent Conductive Coatings by Jaewon Kim, Billy J. Murdoch, James G. Partridge, Kaijian Xing, Dong‐Chen Qi, Josh Lipton‐Duffin, Christopher F. McConville, Joel van Embden, Enrico Della Gaspera. Advanced Materials Interfaces DOI: https://doi.org/10.1002/admi.202000655 First published: 05 August 2020

This paper is behind a paywall.

Smart film lets windows switch autonomously

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This work from Korean research scientists gives me some hope that smart windows will one day be the norm. From a June 2, 2020 Korea Advanced Institute of Science and Technology (KAIST) press release (also on EurekAlert),

Researchers have developed a new easy-to-use smart optical film technology that allows smart window devices to autonomously switch between transparent and opaque states in response to the surrounding light conditions.

The proposed 3D hybrid nanocomposite film with a highly periodic network structure has empirically demonstrated its high speed and performance, enabling the smart window to quantify and self-regulate its high-contrast optical transmittance. As a proof of concept, a mobile-app-enabled smart window device for Internet of Things (IoT) applications has been realized using the proposed smart optical film with successful expansion to the 3-by-3-inch scale. This energy-efficient and cost-effective technology holds great promise for future use in various applications that require active optical transmission modulation.

Flexible optical transmission modulation technologies for smart applications including privacy-protection windows, zero-energy buildings, and beam projection screens have been in the spotlight in recent years. Conventional technologies that used external stimuli such as electricity, heat, or light to modulate optical transmission had only limited applications due to their slow response speeds, unnecessary color switching, and low durability, stability, and safety.

The optical transmission modulation contrast achieved by controlling the light scattering interfaces on non-periodic 2D surface structures that often have low optical density such as cracks, wrinkles, and pillars is also generally low. In addition, since the light scattering interfaces are exposed and not subject to any passivation, they can be vulnerable to external damage and may lose optical transmission modulation functions. Furthermore, in-plane scattering interfaces that randomly exist on the surface make large-area modulation with uniformity difficult.

Inspired by these limitations, a KAIST research team led by Professor Seokwoo Jeon from the Department of Materials Science and Engineering and Professor Jung-Wuk Hong of the Civil and Environmental Engineering Department used proximity-field nanopatterning (PnP) technology that effectively produces highly periodic 3D hybrid nanostructures, and an atomic layer deposition (ALD) technique that allows the precise control of oxide deposition and the high-quality fabrication of semiconductor devices.

The team then successfully produced a large-scale smart optical film with a size of 3 by 3 inches in which ultrathin alumina nanoshells are inserted between the elastomers in a periodic 3D nanonetwork.

This “mechano-responsive” 3D hybrid nanocomposite film with a highly periodic network structure is the largest smart optical transmission modulation film that exists. The film has been shown to have state-of-the-art optical transmission modulation of up to 74% at visible wavelengths from 90% initial transmission to 16% in the scattering state under strain. Its durability and stability were proved by more than 10,000 tests of harsh mechanical deformation including stretching, releasing, bending, and being placed under high temperatures of up to 70°C. When this film was used, the transmittance of the smart window device was adjusted promptly and automatically within one second in response to the surrounding light conditions. Through these experiments, the underlying physics of optical scattering phenomena occurring in the heterogeneous interfaces were identified. Their findings were reported in the online edition of Advanced Science on April 26 [2020]. KAIST Professor Jong-Hwa Shin’s group and Professor Young-Seok Shim at Silla University also collaborated on this project.

Donghwi Cho, a PhD candidate in materials science and engineering at KAIST and co-lead author of the study, said, “Our smart optical film technology can better control high-contrast optical transmittance by relatively simple operating principles and with low energy consumption and costs.”

“When this technology is applied by simply attaching the film to a conventional smart window glass surface without replacing the existing window system, fast switching and uniform tinting are possible while also securing durability, stability, and safety. In addition, its wide range of applications for stretchable or rollable devices such as wall-type displays for a beam projection screen will also fulfill aesthetic needs,” he added.

Here’s an image illustrating how the composite scatters light (I think),

Caption: Design concept of and fabrication procedures for the 3D scatterer. Credit: KAIST

Here’s a link to and a citation for the paper,

High‐Contrast Optical Modulation from Strain‐Induced Nanogaps at 3D Heterogeneous Interfaces by Donghwi Cho, Prof. Young‐Seok Shim, Dr. Jae‐Wook Jung, Sang‐Hyeon Nam, Seokhwan Min, Dr. Sang‐Eon Lee, Youngjin Ham, Prof. Kwangjae Lee, Prof. Junyong Park, Prof. Jonghwa Shin, Prof. Jung‐Wuk Hong, and Prof. Seokwoo Jeon. Advanced Science DOI: https://doi.org/10.1002/advs.201903708 First published: 26 April 2020

This paper is open access.

‘Smart’ windows in Vancouver (Canada): engineering issues?

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This post was going to focus on the first building in Canada to feature ‘smart’ windows. In this case, they are electrochromic windows and the company, View Dynamic Glass, was mentioned here in a September 17, 2018 posting about the windows’ use at the Dallas/Fort Worth Airport. (The posting includes a link to the View Dynamic Glass report on the windows’ use and a short video.)

However, things changed but, first, let’s start with an explanation as to what electrochromic glass ir. Chris Woodford in a December 5, 2018 article on explainthatstuff.com offers a great overview which includes an explanation, a description of how they work, and more. What follows is a brief excerpt from Woodford’s overview (Note: Links have been removed),

What is electrochromic glass?

Glass is an amazing material and our buildings would be dark, dingy, cold, and damp without it. But it has its drawbacks too. It lets in light and heat even when you don’t want it to. On a blinding summer’s day, the more heat (“solar gain”) that enters your building the more you’ll need to use your air-conditioning—a horrible waste of energy that costs you money and harms the environment. That’s why most of the windows in homes and offices are fitted with curtains or blinds. If you’re into interior design and remodeling, you might think furnishings like this are neat and attractive—but in cold, practical, scientific terms they’re a nuisance. Let’s be honest about this: curtains and blinds are a technological kludge to make up for glass’s big, built-in drawback: it’s transparent (or translucent) even when you don’t want it to be.

Since the early 20th century, people have got used to the idea of buildings that are increasingly automated. We have electric clothes washing machines, dishwashers, vacuum cleaners and much more. So why not fit our homes with electric windows that can change from clear to dark automatically? Smart windows (also referred to by the names smart glass, switchable windows, and dynamic windows) do exactly that using a scientific idea called electrochromism, in which materials change color (or switch from transparent to opaque) when you apply an electrical voltage across them. Typically smart windows start off a blueish color and gradually (over a few minutes) turn transparent when the electric current passes through them.

…

As for the news about its Vancouver debut, I was very excited to see this April 28, 2019 article by Kenneth Chan for dailyhive.com/vancouver,

…

BlueSky Properties’ 10-storey office building at 988 West Broadway [in Vancouver, Canada; emphasis mine] is home to the new Vancouver offices of Industrial Alliance Financial Group, which has leased nine stories and 93,700-sq-ft of office space.

…

One of the building’s unique design features is its use of View Dynamic Glass technology [emphases mine] — a glass technology that controls heat and glare, reduces overall energy consumption and costs, and improves the health and wellness of individuals working inside the building.

These smart windows optimize the amount of natural light to enhance mental and physical well-being without the need for shades or blinds. The application of the technology on this building, the first of its kind in Canada, will result in energy savings of up to 20%, [emphasis mine] with the amount of sunlight streaming through automatically tinted to block glare.

…

Blue Sky Properties (a Bosa Family Company), the local developer for this building, was very excited about the building and the ‘smart’ glass technology, according to its April 23, 2019 news release (here for a short version and here for the full version).

Other than being happy to see the technology being employed in Vancouver, I didn’t spend a lot of time thinking about the property. That changed on reading a May 8, 2019 article by Kenneth Chan for dailyhive.com/vancouver,

A structural engineer based in Vancouver has been stripped of his license to work in British Columbia [emphasis mine] following an investigation that determined his design for a condominium tower in Surrey fell short of the provincial building code.

According to a disciplinary notice posted by Engineers and Geoscientists British Columbia Association (EGBCA) on April 30, John Bryson, a managing partner of Bryson Markulin Zickmantel Structural Engineers (BMZSE), [emphases mine] admitted to unprofessional conduct and acted contrary to the association’s code of ethics that requires its members to “hold paramount the safety, health, and welfare of the public.”

“Mr. Bryson admitted that his structural design for the building did not comply with the 2006 BC Building Code, to which he certified it had been designed, in particular with respect to seismic and wind loads,” reads the notice. [emphases mine]

…

BMZSE has been involved in the design work of a number of projects across Metro Vancouver, including Station Square, Rogers Arena South Tower, Lougheed Heights, River District Parcel 17, The Jervis, Harwood, Plaza 88, Solo District, Burrard Place, Centreview Place, Trump International Hotel & Tower Vancouver, Central, Sovereign, Kings Crossing, and 988 West Broadway. [emphases mine]

You can find the ‘disciplinary notice’ (it’s an account of what Bryson failed to do and the punishment for the failure) here on the Association of Professional Engineers and Geoscientists of the Province of British Columbia (also known as Engineers and Geoscientists British Columbia) website.

Presumably, all of Bryson’s projects have been reviewed since the disciplinary action.

View Dynamic Glass—intelligent windows sold commercially

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At last, commercially available ‘smart’, that is, electrochromic windows.

An April 17, 2018 article by Conor Shine for Dallas News describes a change at the Dallas Fort Worth (DFW) International Airport that has cooled things down,

At DFW International Airport, the coolest seats in the house can be found near Gate A28.

That’s where the airport, working with California-based technology company View, has replaced a bank of tarmac-facing windows with panes coated in microscopic layers of electrochromic ceramic that significantly reduce the amount of heat and glare coming into the terminal.

The technology, referred to as dynamic glass, uses an electrical current to change how much light is let in and has been shown to reduce surface temperatures on gate area seats and carpets by as much as 15 degrees compared to standard windows. All that heat savings add up, with View estimating its product can cut energy costs by as much as 20 percent when the technology is deployed widely in a building.

At DFW Airport, the energy bill runs about $18 million per year, putting the potential savings from dynamic glass into the hundreds of thousands, or even millions of dollars, annually.

Besides the money, it’s an appealing set of characteristics for DFW Airport, which is North America’s only carbon-neutral airport and regularly ranks among the top large airports for customer experience in the world.

After installing the dynamic glass near Gate A28 and a nearby Twisted Root restaurant in September at a cost of $49,000, the airport is now looking at ordering more for use throughout its terminals, although how many and at what cost hasn’t been finalized yet.

…

On a recent weekday morning, the impact of the dynamic glass was on full display. As sunlight beamed into Gate A25, passengers largely avoided the seats near the standard windows, favoring shadier spots a bit further into the terminal.

A few feet away, the bright natural light takes on a subtle blue hue and the temperature near the windows is noticeably cooler. There, passengers seemed to pay no mind to sitting in the sun, with window-adjacent seats filling up quickly.

…

As View’s Jeff Platón, the company’s vice president of marketing, notes in the video, there are considerable savings to be had when you cut down on air conditioning,

View’s April 17, 2018 news release (PDF) about a study of their technology in use at the airport provides more detail,

View®, the leader in dynamic glass, today announced the results of a study on the impact of in-terminal passenger experience and its correlation to higher revenues and reduced operational expenses.The study, conducted at Dallas Fort Worth International Airport (DFW), found that terminal windows fitted with View Dynamic Glass overwhelmingly improved passenger comfort over conventional glass, resulting in an 83 percent increase in passenger dwell time at a preferred gate seat and a 102 percent increase in concession spending. The research study was conducted by DFW Airport, View, Inc., and an independent aviation market research group.

It’s been a long time (I’ve been waiting about 10 years) but it seems that commercially available ‘smart’ glass is here—at the airport, anyway.

ht/ April 20, 2018 news item on phys.org

‘Smart’ windows from Australia

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My obsession with smart windows has been lying dormant until now. This February 25, 2018 RMIT University (Australia) press release on EurekAlert has reawkened it,

Researchers from RMIT University in Melbourne Australia have developed a new ultra-thin coating that responds to heat and cold, opening the door to “smart windows”.

The self-modifying coating, which is a thousand times thinner than a human hair, works by automatically letting in more heat when it’s cold and blocking the sun’s rays when it’s hot.

Smart windows have the ability to naturally regulate temperatures inside a building, leading to major environmental benefits and significant financial savings.

Lead investigator Associate Professor Madhu Bhaskaran said the breakthrough will help meet future energy needs and create temperature-responsive buildings.

“We are making it possible to manufacture smart windows that block heat during summer and retain heat inside when the weather cools,” Bhaskaran said.

“We lose most of our energy in buildings through windows. This makes maintaining buildings at a certain temperature a very wasteful and unavoidable process.

“Our technology will potentially cut the rising costs of air-conditioning and heating, as well as dramatically reduce the carbon footprint of buildings of all sizes.

“Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital.”

Smart glass windows are about 70 per cent more energy efficient during summer and 45 per cent more efficient in the winter compared to standard dual-pane glass.

New York’s Empire State Building reported energy savings of US$2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows. This was using a less effective form of technology.

“The Empire State Building used glass that still required some energy to operate,” Bhaskaran said. “Our coating doesn’t require energy and responds directly to changes in temperature.”

Co-researcher and PhD student Mohammad Taha said that while the coating reacts to temperature it can also be overridden with a simple switch.

“This switch is similar to a dimmer and can be used to control the level of transparency on the window and therefore the intensity of lighting in a room,” Taha said. “This means users have total freedom to operate the smart windows on-demand.”

Windows aren’t the only clear winners when it comes to the new coating. The technology can also be used to control non-harmful radiation that can penetrate plastics and fabrics. This could be applied to medical imaging and security scans.

Bhaskaran said that the team was looking to roll the technology out as soon as possible.

“The materials and technology are readily scalable to large area surfaces, with the underlying technology filed as a patent in Australia and the US,” she said.

The research has been carried out at RMIT University’s state-of-the-art Micro Nano Research Facility with colleagues at the University of Adelaide and supported by the Australian Research Council.

…

How the coating works

The self-regulating coating is created using a material called vanadium dioxide. The coating is 50-150 nanometres in thickness.

At 67 degrees Celsius, vanadium dioxide transforms from being an insulator into a metal, allowing the coating to turn into a versatile optoelectronic material controlled by and sensitive to light.

The coating stays transparent and clear to the human eye but goes opaque to infra-red solar radiation, which humans cannot see and is what causes sun-induced heating.

Until now, it has been impossible to use vanadium dioxide on surfaces of various sizes because the placement of the coating requires the creation of specialised layers, or platforms.

The RMIT researchers have developed a way to create and deposit the ultra-thin coating without the need for these special platforms – meaning it can be directly applied to surfaces like glass windows.

Here’s a link to and a citation for the paper,

Insulator–metal transition in substrate-independent VO2 thin film for phase-change device by Mohammad Taha, Sumeet Walia, Taimur Ahmed, Daniel Headland, Withawat Withayachumnankul, Sharath Sriram, & Madhu Bhaskaran. Scientific Reportsvolume 7, Article number: 17899 (2017) doi:10.1038/s41598-017-17937-3 Published online: 20 December 2017

This paper is open access.

For anyone interested in more ‘smart’ windows, you can try that search term or ‘electrochromic’, ‘photochromic’, and ‘thermochromic’ , as well.

A different type of ‘smart’ window with a new solar cell technology

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I always like a ‘smart’ window story. Given my issues with summer (I don’t like the heat), anything which promises to help reduce the heat in my home at that time of year, has my vote. Unfortunately, solutions don’t seem to have made a serious impact on the marketplace. Nonetheless, there’s always hope and perhaps this development at Princeton University will be the one to break through the impasse. From a June 30, 2017 news item on ScienceDaily,

Smart windows equipped with controllable glazing can augment lighting, cooling and heating systems by varying their tint, saving up to 40 percent in an average building’s energy costs.

These smart windows require power for operation, so they are relatively complicated to install in existing buildings. But by applying a new solar cell technology, researchers at Princeton University have developed a different type of smart window: a self-powered version that promises to be inexpensive and easy to apply to existing windows. This system features solar cells that selectively absorb near-ultraviolet (near-UV) light, so the new windows are completely self-powered.

A June 30, 2017 Princeton University news release, which originated the news item, expands on the theme,

“Sunlight is a mixture of electromagnetic radiation made up of near-UV rays, visible light, and infrared energy, or heat,” said Yueh-Lin (Lynn) Loo, director of the Andlinger Center for Energy and the Environment, and the Theodora D. ’78 and William H. Walton III ’74 Professor in Engineering. “We wanted the smart window to dynamically control the amount of natural light and heat that can come inside, saving on energy cost and making the space more comfortable.”

The smart window controls the transmission of visible light and infrared heat into the building, while the new type of solar cell uses near-UV light to power the system.

“This new technology is actually smart management of the entire spectrum of sunlight,” said Loo, who is a professor of chemical and biological engineering. Loo is one of the authors of a paper, published June 30, that describes this technology, which was developed in her lab.

Because near-UV light is invisible to the human eye, the researchers set out to harness it for the electrical energy needed to activate the tinting technology.

“Using near-UV light to power these windows means that the solar cells can be transparent and occupy the same footprint of the window without competing for the same spectral range or imposing aesthetic and design constraints,” Loo added. “Typical solar cells made of silicon are black because they absorb all visible light and some infrared heat – so those would be unsuitable for this application.”

In the paper published in Nature Energy, the researchers described how they used organic semiconductors – contorted hexabenzocoronene (cHBC) derivatives – for constructing the solar cells. The researchers chose the material because its chemical structure could be modified to absorb a narrow range of wavelengths – in this case, near-UV light. To construct the solar cell, the semiconductor molecules are deposited as thin films on glass with the same production methods used by organic light-emitting diode manufacturers. When the solar cell is operational, sunlight excites the cHBC semiconductors to produce electricity.

At the same time, the researchers constructed a smart window consisting of electrochromic polymers, which control the tint, and can be operated solely using power produced by the solar cell. When near-UV light from the sun generates an electrical charge in the solar cell, the charge triggers a reaction in the electrochromic window, causing it to change from clear to dark blue. When darkened, the window can block more than 80 percent of light.

Nicholas Davy, a doctoral student in the chemical and biological engineering department and the paper’s lead author, said other researchers have already developed transparent solar cells, but those target infrared energy. However, infrared energy carries heat, so using it to generate electricity can conflict with a smart window’s function of controlling the flow of heat in or out of a building. Transparent near-UV solar cells, on the other hand, don’t generate as much power as the infrared version, but don’t impede the transmission of infrared radiation, so they complement the smart window’s task.

Davy said that the Princeton team’s aim is to create a flexible version of the solar-powered smart window system that can be applied to existing windows via lamination.

“Someone in their house or apartment could take these wireless smart window laminates – which could have a sticky backing that is peeled off – and install them on the interior of their windows,” said Davy. “Then you could control the sunlight passing into your home using an app on your phone, thereby instantly improving energy efficiency, comfort, and privacy.”

Joseph Berry, senior research scientist at the National Renewable Energy Laboratory, who studies solar cells but was not involved in the research, said the research project is interesting because the device scales well and targets a specific part of the solar spectrum.

“Integrating the solar cells into the smart windows makes them more attractive for retrofits and you don’t have to deal with wiring power,” said Berry. “And the voltage performance is quite good. The voltage they have been able to produce can drive electronic devices directly, which is technologically quite interesting.”

Davy and Loo have started a new company, called Andluca Technologies, based on the technology described in the paper, and are already exploring other applications for the transparent solar cells. They explained that the near-UV solar cell technology can also power internet-of-things sensors and other low-power consumer products.

“It does not generate enough power for a car, but it can provide auxiliary power for smaller devices, for example, a fan to cool the car while it’s parked in the hot sun,” Loo said.

Here’s a link to and a citation for the paper,

Pairing of near-ultraviolet solar cells with electrochromic windows for smart management of the solar spectrum by Nicholas C. Davy, Melda Sezen-Edmonds, Jia Gao, Xin Lin, Amy Liu, Nan Yao, Antoine Kahn, & Yueh-Lin Loo. Nature Energy 2, Article number: 17104 (2017 doi:10.1038/nenergy.2017.104 Published online: 30 June 2017

This paper is behind a paywall.

Here’s what a sample of the special glass looks like,

Graduate student Nicholas Davy holds a sample of the special window glass. (Photos by David Kelly Crow)

Offering privacy and light control via smart windows

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There have been quite a few ‘smart’ window stories here on this blog but this one is the first to feature a privacy option. From a Nov. 17, 2016 news item on Nanowerk,

Smart windows get darker to filter out the sun’s rays on bright days, and turn clear on cloudy days to let more light in. This feature can help control indoor temperatures and offers some privacy without resorting to aids such as mini-blinds.

Now scientists report a new development in this growing niche: solar smart windows that can turn opaque on demand and even power other devices. …

A Nov. 17, 2016 American Chemical Society (ACS) news release, which originated the news item, goes on to explain the work,

Most existing solar-powered smart windows are designed to respond automatically to changing conditions, such as light or heat. But this means that on cool or cloudy days, consumers can’t flip a switch and tint the windows for privacy. Also, these devices often operate on a mere fraction of the light energy they are exposed to while the rest gets absorbed by the windows. This heats them up, which can add warmth to a room that the windows are supposed to help keep cool. Jeremy Munday and colleagues wanted to address these limitations.

The researchers created a new smart window by sandwiching a polymer matrix containing microdroplets of liquid crystal materials, and an amorphous silicon layer — the type often used in solar cells — between two glass panes. When the window is “off,” the liquid crystals scatter light, making the glass opaque. The silicon layer absorbs the light and provides the low power needed to align the crystals so light can pass through and make the window transparent when the window is turned “on” by the user. The extra energy that doesn’t go toward operating the window is harvested and could be redirected to power other devices, such as lights, TVs or smartphones, the researchers say.

For anyone who finds reading text a bit onerous, there’s this video,

Here’s a link to and a citation for the paper,

Electrically Controllable Light Trapping for Self-Powered Switchable Solar Windows by Joseph Murray, Dakang Ma, and Jeremy N. Munday. ACS Photonics, Article ASAP DOI: 10.1021/acsphotonics.6b00518 Publication Date (Web): October 26, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.