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DoE Researchers Make Smart Window That Promises Energy Efficiency

image credit: Illustration 158599500 © Anton Shaparenko -

Whether to draw window shades up or down on any given day is generally the simplest of decisions. But those options are, in fact, loaded with complexity for the grid. On a hot day in Arizona, drawing down the shades can cool a room and lead to significantly less power consumption. The same decision in Minnesota’s freezing weather may not make much difference. Similarly, the time of the day (afternoon or evening) and the home’s energy consumption metrics also influences grid consumption. 

Smart windows promise to take the guesswork out of those decisions and produce electricity from excessive sunlight while doing so. For utilities, smart windows belong to the Internet of Things (IoT) devices rubric. These are devices that incorporate intelligence to automate and regulate electricity consumption. The market for such devices is expected to multiply in the future. In turn, this will have implications for energy efficiency initiatives at utilities and power consumption in the overall grid. It is also expected to spur a digital transformation at utilities as they integrate more distributed energy resources (DERs) into the grid. 

Designing a Smart Window That Produces Electricity  

The latest iteration of smart window technology comes from a team of research scientists comprising members from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Northwestern University, the University of Chicago and University of Wisconsin-Milwaukee. The idea behind their smart window is to balance energy usage with the matrix of decision-making, such as temperature and light intensity, for an optimal experience. “[Our system] balances multiple functions of a window along with storing energy that is converted into electricity,” says Dr. Junhong Chen, a professor at the Pritzker School of Molecular Engineering at the University of Chicago. The amount of electricity produced using the window’s solar cells is not much but Dr. Chen argues that the window is a device to conserve and not produce electricity. “The idea is to not waste electricity that is produced,” he said.   

To be sure, smart windows that harvest energy are not a new concept; they have been around for some time now. But current integrations of solar cells into smart windows lack “systematic optimization” capabilities, says Dr. Chen. This means that such systems do not take into account differences in ecosystems and geography in their operations. For example, customizing user preferences for lighting while simultaneously ensuring that the facility, in which the building is housed, meets its energy harvesting goals will require a different set of criteria in Arizona as compared to Minnesota. 

Chen says their team has used software for a new approach. The crux of this approach is the Multi-criteria Pareto Optimization algorithm. The algorithm mimics genetic mutation processes for a flexible design to constantly match outside conditions. Thus, the algorithm enables adjustment of the smart window’s parameters, such as regulation of quantity and bandwidth of light passing through, in response to weather conditions. As an example, the quantity of infrared radiation allowed to pass through windows can make a significant difference to energy consumption. The more the infrared radiation, the more the heat and vice versa. 

The research team had three objectives in mind while designing their smart window: efficient energy generation, smart heat management, and sufficient surface transparency. To achieve their goals, the team designed a window with multiple layers, each of a different thickness. Each layer consisted of a different coating of cells. Thus, one layer consists of perovskite cells, a type of solar cells with greater efficiency than photovoltaic cells, to make the window’s surface transparent and another nanophotonic layer regulates the light frequencies which are allowed to pass through it. 

The idea behind the variety of layers is to provide the smart window’s users with customization options. For example, they will be able to vary the amount of infrared radiation used to heat up a given space passing through the window at different times of the day and in different seasons. In prototype experiments, the biggest infrared transmission reduction for a single PV cell in high temperatures was 44 percent and the maximum transmission enhancement in cold temperatures was 33 percent. (It is important to note here that the performance and temperature simulations were conducted using a halogen lamp). 

Dr. Chen says that the framework of menu options can be expanded based on the building or home’s energy goals. For example, certain smart windows in a building can be used to automatically adjust temperatures to regulate energy flow. “The user will have the option to buy in brightness, lighting intensity, and energy consumption preferences,” says Chen.

The Cost Problem 

Before that happens, however, the team’s smart window concept will need to be refined for manufacturing. While the technology and materials used to manufacture the smart window already exist in the market, Dr. Chen says their costs are a major deterrent. Again, this is not a new problem. A decade ago, the nascent industry faced the same problem. “We need to make materials (used in making the smart window) more cost affordable and overall manufacturing cost acceptable to users,” explains Chen. The research also needs further work. For example, the team also has not looked into the implications pertaining to the degradation of perovskite cells, already a well-known issue, due to natural elements and light. It could have implications on the lifetime and overall cost structure of the smart window. For now, Dr. Chen and his team are investigating further federal funding sources to scale out the application and contribute to overall data relating to cost reduction for smart windows. 

Their research can offer pointers to future load management for utilities. Dr. Chen says their smart windows could translate into higher energy efficiency for building loads. To test the smart window, the research team fitted a 2,000 square feet facility in Phoenix, Arizona with a prototype of their smart window. The experiment resulted in annual savings of 13,560 kWh.  


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Rakesh  Sharma's picture

Thank Rakesh for the Post!

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