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Chinese scientists develop colorless solar concentrator for PV windows

Source：pv magazine


 

A research team based at China’s Nanjing University has developed a transparent, colorless and unidirectional solar concentrator compatible with existing windows.

Solar concentrators are designed to converge solar energy onto the side of architectural glass. Useful in building-integrated photovoltaics, existing solar concentrators often suffer from setbacks, including low efficiencies, coloring, or a lack of compatibility with existing windows.

The research team's newly developed diffractive-type solar concentrator (CUSC) utilizes cholesteric liquid crystal (CLC) multilayers with submicron lateral periodicities to selectively guide sunlight toward the edge of the window where photovoltaic cells are installed. The team fabricated the multilayered CLC films via photoalignment and polymerization techniques, which are scalable via roll-to-roll manufacturing.

Under testing, the CUSC device maintained an average visible transmittance of 64.2% and colour rendering index of 91.3, enabling energy generation without altering the appearance of the window.

“By engineering the structure of cholesteric liquid crystal films, we create a system that selectively diffracts circularly polarized light, guiding it into the glass waveguide at steep angles,” said Dewei Zhang, co-first author of the research. “This allows up to 38.1% of incident green light energy to be collected at the edge.”

The research paper “Colorless and Unidirectional Diffractive-type Solar Concentrators Compatible with Existing Windows,” available in the journal PhotoniX, details how a 1-inch diameter prototype was found capable of directly powering a 10 mW fan under sunlight.

Further modeling found that a typical 2-meter-wide CUSC window could concentrate sunlight by 50 times, reducing the number of photovoltaic cells required by up to 75%. The design also remained stable under long-term exposure and was found suitable for retrofitting onto existing windows, allowing sustainable urban upgrades.

Professor Wei Hu commented that the CUSC design is a step forward in integrating solar technology into the built environment without sacrificing aesthetics. “It represents a practical and scalable strategy for carbon reduction and energy self-sufficiency,” Hu added.

In the research paper's conclusion, the authors write that the CUSC design would be widely adopted in green buildings, agricultural photovoltaics and other emerging areas. “It is expected to contribute to a global terawatt-scale green energy supply and reduce annual carbon emissions by billions of tons,” the paper concludes.

The research team says it is planning to focus future work on enhancing broadband efficiency, polarization control and adapting the technology for agricultural greenhouses and transparent solar displays.