Leaf-shaped solar concentrators promise major improvement in solar efficiency

Since its invention in the 1970s, the luminescent solar concentrator (LSC) has aimed to improve solar energy capture by using luminescent materials to convert and concentrate sunlight onto photovoltaic (PV) cells. Unlike traditional concentrators that rely on mirrors and lenses, LSCs can capture diffuse light and have been used in applications such as building-integrated photovoltaics, where their semi-transparent and colored nature offers aesthetic benefits.

However, scaling LSCs to cover large areas has proven challenging due to issues such as self-absorption of photoluminescent (PL) photons in the waveguide. Researchers at Ritsumeikan University (Japan) have proposed an innovative “sheet LSC” design that promises to overcome these limitations by improving light collection and transfer to photovoltaic cells. The sheet LSC design addresses the scalability issue by using smaller, interconnected luminescent components that function like leaves on a tree.

As stated in the Journal of Photonics for Energy (JPE), this innovative device consists of placing luminescent plates around a central luminescent fiber, with the sides of the plates facing the fiber.

This arrangement allows incident photons to be converted into PL photons by the plates, which then pass through the fiber and are collected at its end by a PV cell. To improve efficiency, transparent light guides connect multiple fibers to a single PV cell, effectively increasing the incident area of ​​the LSC while reducing photon losses due to self-absorption and scattering.

This modular approach to LSC design offers several advantages. By reducing the lateral size of individual modules, the researchers found that photon collection efficiency improved. For example, reducing the lateral length of a square sheet LSC from 50 mm to 10 mm significantly increased photon collection efficiency. The modular design also allows for easy replacement of damaged units and the integration of advanced luminescent materials as they become available.

To further improve the system efficiency, the researchers integrated techniques from traditional planar LSCs, such as edge mirrors and tandem structures, into the design of sheet LSCs. Their experiments demonstrated that the optical efficiency of these sheet-like structures can be calculated analytically based on the spectrum and intensity of the incident light, using a single-point excitation technique.

According to JPE Sean Shaheen, editor-in-chief, professor of engineering and physics at the University of Colorado Boulder and member of the Renewable and Sustainable Energy Institute, said: “These results demonstrate a creative approach that advances the concept of luminescent solar concentrators to efficiently guide sunlight to adjacent photovoltaic devices. By combining scalable, bio-inspired designs with improvements in optical engineering, the authors have increased the efficiency of their devices to what is needed for practical use.”

Optimizing photon harvesting in LSCs could pave the way for more flexible and scalable solar energy solutions. This approach to energy harvesting could revolutionize the application of solar concentrators, making them more efficient and adaptable to a variety of uses, from large-scale installations to building-integrated systems. As the technology advances, it promises to significantly improve the performance of solar energy systems and contribute to more sustainable energy solutions.