Common belief is anything that harvests solar energy must be non-transparent. Popular logic is if sunlight is allowed to pass freely through the collector, it cannot lead to energy production. Although this may be partly true for the visible spectrum of light from the sun, it must also be considered that the sun gives out radiations beyond the band of light visible to the human eye.
Therefore, even see-through solar concentrators can successfully harvest energy from sunlight. Now, a team of Michigan State University researchers has proven this by creating a transparent solar concentrator. They claim to be able to turn any window into a photovoltaic solar cell. Not only windows, any sheet of glass, including the screen of a smartphone, can be turned into a harvester of solar energy. All the while, the panel remains truly transparent.
Earlier, transparent solar cells were restricted to tinted glass or compromised the visibility. This did not become popular, as people felt rather uncomfortable sitting behind colored glass making for colorful environments. In contrast, the new solar cell from the Michigan State University is completed transparent.
At MSU, researchers used TSLC or Transparent Luminescent Solar Concentrators. These employ organic salts for absorbing wavelengths of light normally invisible to the human eye, such as the infrared and the ultraviolet light. The researchers can tune the amount and composition of the organic salts to pick up only the near-infrared and the ultraviolet wavelengths leaving the visible spectrum untouched. The organic salts make the captured wavelengths glow at another wavelength – the infrared.
The TSLC then guides the infrared light to the edge of the panel, where it encounters thin strips of photovoltaic cells, which converts it to electricity. The organic salts do not absorb or emit any light in the visible spectrum and the panel looks extraordinarily transparent to the human eye.
The process is non-intrusive and opens doors to several opportunities of deploying solar energy creatively. Tall buildings with lots of windows can benefit tremendously with this technology, as can any mobile device demanding high aesthetic quality. The biggest benefit is you can have a solar harvesting surface and need not even know that it is present.
At present, the energy producing efficiency of TSLC is rather low, of the order of 1 percent, and additional work is needed to improve its performance. However, researchers are confident they will eventually increase the efficiency to above 5 percent. In comparison, non-transparent luminescent concentrators offer efficiencies of up to 7 percent.
In July 2014, the journal of Advanced Optical Materials carried an article describing the transparent solar cells. Apart from the lead researcher Richard Lunt, Yimu Zhao, Benjamin Levine and Garrett Meek are other members of the research team working on transparent solar cells at MSU.
Lunt has cofounded a Silicon Valley start-up – Ubiquitous Energy – for commercializing the transparent solar cell. The researchers have named the technology ClearView Power. They plan to integrate it directly on surfaces of mobiles, creating an auxiliary power source. They also want to promote this as a power-producing invisible coating for windows.
