Perovskite thermochromic windows: the promising solution to save energy in buildings
Net of the construction process, the operation of buildings is responsible for 28% of global CO2 emissions
(sustainabilityenvironment.com) – Perovskite thermochromic windows improve the efficiency of office buildings as well as reduce climate-altering emissions and reduce costs for occupants.
This is stated by a study conducted by the National Renewable Energy Laboratory (NREL) of the Department of Energy of the United States.
The research has inserted in the thermochromic windows a perovskite base to increase solar absorption and accelerate the passage of the transparent surface from the state of the capture of sunlight to the reflective state, and vice versa.
The results of the study are contained in the document “Thermochromic Halide Perovskite Windows with Ideal Transition Temperature”, published in the journal Advanced Energy Materials.
Lance Wheeler, the project’s chief investigator, said that switching to perovskite thermochromic windows saves significant energy per year. This applies to all climates, both cold and temperate and owes its advantages to the demand for less energy for air conditioning. “If all workers in the simulated office building drove an electric vehicle the distance of an average American commute, then the annual energy could be used to fully charge every worker’s car every day throughout the year“
How do thermochromic perovskite windows work
The National Renewable Energy Laboratory team used the Pvwindow modeling software, developed by Wheeler himself, to identify the optimal material to be used in building a high thermal performance window. The result suggested the addition of a thermochromic laminate with a semiconductor-based on a metal halide.
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The use of “active” windows in solar control per se is nothing new. This strategy has been in use since the 1980s in the form of a coating layer that can selectively reflect infrared light while letting visible light filter. The problem though is that visible wavelengths actually carry a significant amount of solar energy, going to weigh on the total energy balance of the building.
By adding perovskite to the equation, the results were reversed.
The researchers used as a model a structure of 12 floors with a 95% dominant vettrata surface on the opaque envelope. They then simulated the consumption needed for air conditioning for eight different US climate zones covering Hawaii, Arizona, California, Colorado, New York, Wisconsin, Minnesota and Alaska.
The results showed that the use of perovskite thermochromic double glass windows improved efficiency in all weather conditions. Winning in terms of savings even against triple glass windows, but without chromatic properties.
The ideal transition temperature is between 20 ºC and 27.5 ºC. “If the transition temperature is too high, then the window may not save energy, and buildings are better off with static windows,” Wheeler said. “It is interesting that this range is valid across many different climates, from northern Minnesota to southern California. This is because dynamic windows reduce solar heat gain in the summers to save air conditioning, and they also increase solar heat gain when heat is needed in winters.”
For the moment, the researchers’ experimentation has proved to be lasting for 200 cycles, testing a perovskite film inserted between two layers of glass.
