Researchers from the U.S. Department of Energy's (DOE) Argonne National Laboratory, Northwestern University, the University of Chicago and the University of Wisconsin-Milwaukee created a new customizable smart window that uses solar power to save energy costs.
Scientists developed a smart window device for concurrently harvesting and regulating solar energy. Source: Peter Allen/University of Chicago
The team combined solar cell technology with a new optimization algorithm to create a smart window that meets a range of criteria. Their algorithm uses physical models and computational techniques to maximize overall energy usage and balance building temperature and lighting requirements. The aim is to create windows that can meet needs and optimize energy usage across all locations and seasons. The window’s design framework is customizable and can be applied to any building.
The team used an approach called multicriteria optimization to design the windows and maximize overall energy efficiency while also considering the building’s light and temperature needs. Multicriteria optimization adjusts the thickness of the solar cell layers in the window's design.
The windows reduce the energy needed to cool a building in the summer by minimizing the amount and type of light that passes through while maintaining the building’s lighting needs. In the winter, the windows increase energy savings by maximizing the amount of sunlight that passes through, thereby reducing the energy needed to heat the building.
To determine the best design for a given building, the team’s algorithm incorporates physics-based models of interactions between light and materials in the smart windows and how those processes affect energy conversion and light transmission. It also takes into account the various angles of sun as it hits the window.
To test the algorithm and design, the team created a small prototype window made of dozens of material layers. The material layers control the amount and frequency of light let through and the amount of solar energy being converted into electricity. The first group of layers is a perovskite, which harvests solar waves to create energy. The second group of layers is a nanophotonic coating, which tunes the frequency of light that passes through the window. The layers are very thin, only 10s of microns thick, with a periodic design that creates varying levels of thickness. The design allows the window performance to follow the sun as it changes while keeping in mind the season and the user’s preference.
The team optimized a prototype for a 2,000 sq ft, single story home in Phoenix, Arizona. They calculated annual energy savings the window generated and compared it to the commercially available window technology. The calculations were created using the EnergyPlus building model that estimates realistic power consumption over time.
In the future, the team wants to create a flexible version of the window that can be fitted to cover preexisting windows.
A paper on this technology was published in Cell Reports, Physical Science.
