Scientists develop a method of using shadows to generate electricity

Researchers have developed a way of using shadows to generate electricity, offering a potentially sustainable alternative to fossil fuel powered electricity.

This novel concept developed by National University of Singapore (NUS), offers a new approach to sustainably generating electricity.

The NUS team created a device called a shadow-effect energy generator, which utilises the contrast in illumination between lit and shadowed areas to generate electricity.

The shadow-effect energy generator

This new breakthrough was reported in scientific journal Energy & Environmental Science on 15 April 2020. “Shadows are omnipresent, and we often take them for granted. In conventional photovoltaic or optoelectronic applications where a steady source of light is used to power devices, the presence of shadows is undesirable, since it degrades the performance of devices.

“In this work, we capitalised on the illumination contrast caused by shadows as an indirect source of power. The contrast in illumination induces a voltage difference between the shadowed and illuminated sections, resulting in an electric current. This novel concept of harvesting energy in the presence of shadows is unprecedented,” explained research team leader Assistant Professor Tan Swee Ching, who is from the NUS Department of Materials Science and Engineering.

While commercially available solar cells can perform the role of this device in an outdoor environment, their energy harvesting efficiency drops significantly under indoor conditions where shadows are persistent.

Harnessing the ‘shadow-effect’

The shadow-effect energy generator cells are arranged on a flexible and transparent plastic film. Each cell is comprised of a thin film of gold deposited on a silicon wafer. Carefully designed, the shadow-effect energy generator can be fabricated at a lower cost compared to commercial silicon solar cells. The team then conducted experiments to test the performance of this device in generating electricity and as a self-powered sensor.

“When the whole shadow-effect energy generator cell is under illumination or in shadow, the amount of electricity generated is very low or none at all. When a part of the SEG cell is illuminated, a significant electrical output is detected.

“We also found that the optimum surface area for electricity generation is when half of the SEG cell is illuminated and the other half in shadow, as this gives enough area for charge generation and collection respectively,” said co-team leader Professor Andrew Wee, who is from the NUS Department of Physics.

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