Chinese Researchers Create Transparent Solar Panels for Windows. (Credit: Flickr @ Brenda Gottsabend http://www.flickr.com/photos/gottgraphicsdesign/)Researchers at the Shanghai University have integrated solar cells into a “smart” window. These solar panels can intelligently regulate the transmission of heat while maintaining visible transparency.
The authors of the paper, published in Scientific Reports (see footnote), say that most efforts to efficiently utilize solar energy have been focused on improving the efficiency in the conversion and storage using solar cells and large capacity batteries, respectively. However, these cells, which have been used on housetops and wall periphery, could not be integrated into windows that require the material to be transparent. Traditionally designed energy-saving windows, such as electrochromic thermochromic, and gasochromic, typically function by exterior stimuli involving either an electric field, heat stimulus or a gas. It is not possible to alter the optical performance, which involves intelligently passing or blocking solar energy in response to environmental changes, and simultaneously generate electricity.
There were, however, several proposals to create “smart windows” that would not not require an external power source. One of them is the bioinspired microfluidic circulatory system for windows developed by researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University. The other is the new nanocrystal material to be embedded in window glass that can dynamically modify sunlight as it passes through a window. This material was developed at Berkeley Lab.
The smart window, described in the journal Scientific Reports, combines energy saving and generation in a single device.
Vanadium oxide (VO2) is an attractive material for the fabrication of smart windows because of the reversible, temperature-dependent phase transitions it undergoes. Below a critical temperature of 68 °C (154 °F), the material is insulating and transparent to infrared light, but above 68 °C it becomes metallic and reflective to infrared light. The origin of this metal to insulator transition remains controversial and is of interest in condensed matter physics.
Previously, it was a challenge to integrate solar cells that can efficiently harness and store solar energy into windows that require the material to be transparent. In this study, Yanfeng Gao and colleagues from the Chinese Academy of Sciences positioned vanadium oxide films around glass panels to regulate solar infrared radiation in response to environmental temperature and scatter partial light to solar cells. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and efficiently utilize solar radiation.
The researchers say that their device may someday contribute towards reducing energy costs for heating, lighting and cooling buildings.
Zhou J, Gao Y, Zhang Z, Luo H, Cao C, Chen Z, Dai L, & Liu X (2013). VO2 thermochromic smart window for energy savings and generation. Scientific Reports, 3 PMID: 24157625
