Generating electricity from shadows

June 05, 2020 //By Julien Happich
Energy harvester
Researchers from the National University of Singapore (NUS) have demonstrated a way to harness the so-called shadow effect, an optical-driven charge generation effect taking place across an unevenly lit material.

The shadow-effect energy generator (SEG) created by the researchers consists of a set of SEG cells arranged on a flexible and transparent plastic film. Each SEG cell is made of a thin film of gold deposited on a silicon wafer and can be fabricated at a much lower cost compared to commercial silicon solar cells. The contrast in illumination induces a voltage difference between the shadow and illuminated sections, resulting in an electric current.


Conceptual image of the shadow-effect energy generator
(SEG) developed by NUS researchers. Source: National
University of Singapore.

The research breakthrough, published in the Energy & Environmental Science journal under the title “ Energy harvesting from shadow-effect ”, reports that such a SEG is capable of harvesting energy from illumination contrasts arising even under weak ambient light. Without any optimization, the proof-of-concept generator exhibited a power density of 0.14μW cm −2 under indoor conditions (0.001 sun) where shadows are persistent. The authors also claim that the SEG performed at twice the efficiency of commercial silicon solar cells under the effects of shadows.

“The harvested energy from our generator in the presence of shadows arising at a very low intensity (0.0025 sun) can drive an electronic watch (1.2 V)” the authors wrote. What’s more, the SEG could also be used as a self-powered sensor for monitoring moving objects by tracking the movement of shadows. The researchers envisage that shadow-effect generators could be integrated in buildings to generate green energy from ambient conditions.

"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. This novel concept of harvesting energy in the presence of shadows is unprecedented," explained research team leader Assistant


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