A team of researchers from Nanjing University has developed a new solar concentrator that can transform ordinary windows into invisible sources of renewable energy; solar windows
By using advanced cholesteric liquid crystal coatings, the team has created transparent, colourless solar windows that can generate power without affecting the appearance or clarity of the glass.
Using the power of light
Unlike traditional solar concentrators that rely on luminescent or scattering materials, which often introduce visual distortion, reduce transparency, or present challenges in large-scale use. These new solar windows offers a sleek, nearly invisible alternative. This next-generation concentrator, known as a colourless unidirectional solar concentrator (CUSC), utilises a series of cholesteric liquid crystal (CLC) multilayers to manipulate light uniquely.
These multilayer films, with submicron lateral periodicities, are engineered to selectively guide circularly polarised sunlight toward the edges of the window. Photovoltaic (PV) cells placed at the edges then convert the concentrated light into electricity. This means that the central surface of the solar windows remains completely transparent, while energy is quietly harvested at the margins.
High efficiency
A feature that makes CUSC solar windows design so unique is its ability to maintain high optical quality. The system achieves an average visible transmittance of 64.2%, ensuring that indoor spaces remain bright and natural alongside a colour rendering index of 91.3, which preserves the accurate appearance of colours through the glass.
This high-performance combination makes the CUSC particularly well-suited for urban environments, where aesthetics and building codes often limit the use of conventional solar panels.
In tests, a small 1-inch-diameter prototype was able to generate enough electricity to power a 10-milliwatt fan under natural sunlight.
According to simulations, a 2-meter-wide CUSC window could concentrate sunlight by up to 50 times. This dramatically reduces the amount of PV material needed by as much as 75% making the system both cost-effective and resource-efficient.
The design also supports integration with advanced photovoltaic materials such as gallium arsenide, which are known for their high conversion efficiencies.
Ready for urban use
The multilayered CLC films are created using photoalignment and polymerisation techniques. They can be manufactured at scale through roll-to-roll processing, a widely used and cost-efficient method in industrial production.
The films have shown stability under long-term environmental exposure, making solar windows suitable for a wide range of applications, including retrofitting existing windows in commercial and residential buildings.
Because the system can be applied to current infrastructure, it offers a practical path toward widespread adoption in cities aiming to reduce carbon emissions and promote energy independence.
While the initial focus is on architectural glass, the research team envisions wider applications for their technology. Future developments aim to expand broadband efficiency and polarisation control, which could enable the use of CUSC in greenhouses, car windows, and even transparent solar displays.
