The University of Nanjing has published in Photonix magazine a transparent coating that converts common glass into a directed solar concentrator, without dyeing or distorting the window, that is, it is a solar plate spice. The technology, based on choleric liquid layers (CLC), selectively diffracts part of the light and conducts it through the inside of the glass to the song, where small photovoltaic cells convert that energy into electricity.
The scientific article reports an average transmission of 64.2% in the visible spectrum, a chromatic reproduction index of 91.3% and a collection of up to 38.1% of the green light energy energy in the edge of the glass, maintaining the “colorless” appearance of the glazing. In a prototype of an inch, the set directly moved a 10 miliwatty fan low, and the theoretical models project that a two -meter window could concentrate the light up to 50 times.
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The team led by Wei Hu and with Dewei Zhang as co -author proposes a diffractive solar concentrator (CUSC) that stacks several CLC layers with different helical periods. This architecture expands the “photonic band” to the entire visible and, together with a submicrometric lateral alignment, force that the diffracted light is guided in a single sense inside the glass. Thus, the capture is unidirectional and the user’s field of vision remains clear. “The Clc movie separates the light by circular polarization and introduces it into the glass wave guide at pronounced angles,” explains the article.
The authors also have a key fact to dimension the state of maturity: in real lighting conditions, the conversion efficiency of the experimental system (window more cells in the song) stood between 3.1% and 3.7% at the maximum point of the day, descending when the irradiance varies. Long -term laboratory stability remained around 95% of the peak value after 1,500 hours of LED lighting in controlled environment. The publication itself admits that, to climb, there are challenges in materials and processes: optimize thicknesses and periods, introduce opposite helical hand layers, and develop “Roll -to-Roll” photo
International context and competition
The work is inscribed in the race to integrate photovoltaic into the envelope of the buildings (BIPV) without penalizing aesthetics. Faced with luminescent concentrators or dispersive systems, which often color the glass or lose efficiency, Nanjing’s proposal prevents visible dye and reduces the number of necessary cells on the edge (up to 75% less, according to the authors) which, in theory, would reduce the installation and even allow to use higher performance cells such as those of Gallium arseniuro in the song.
In parallel, several companies compete for the same space. The Californian Next Energy Technologies presented this year that qualifies as the largest transparent organic window manufactured to date (101.6 × 152.4 cm), a milestone of industrial scaling although with a different technological approach (transparent OPV deposited by “slot-die”).
The American Ubiquitous Energy, on the other hand, develops transparent coatings based on dyes that “selectively harvest” part of the spectrum to generate electricity without losing transparency, with the declared objective of transforming glazed facades into vertical solar fields.
What does it contribute
The main contribution of Nanjing is conceptual and optical: it demonstrates that it is possible to unidirectionally concentrate the light captured by a window without penalizing clarity and with photometric parameters compatible with high buildings (high transmittance and fidelity). The practical, although promising results are still far from the commercial efficiencies of the conventional photovoltaic modules: the article itself places the conversion of the set into the 3% –4% environment and details the improvement lines to make the leap to products.
In spite of this great advance, you still have to look at several unknowns such as weathering durability in long cycles (UV radiation, thermal shocks and humidity), industrial integration over doubles and triple glazing, the cost per square meter of the coating against BIPV alternatives already available, and the net energy balance when these windows are combined with thermal management of the building (shadow, shadow, shadow, HVAC loads).