A shadow is a dark area where light from a light source is blocked by an object. To date, not much engineering use has been found for them and they are actively avoided in optoelectronic applications. Now, researchers at the National University of Singapore have presented a “shadow-effect energy generator” (SEG) which uses this optical effect to generate electricity.
In a research paper published in the journal Energy & Environmental Science on April 15th, 2020, the NUS researchers describe how when the SEG is placed in a shadowed area, it uses the contrast in illumination between lit and shadowed areas to generate a direct current.
Generating Electricity Using the ‘Shadow-Effect’
The NUS team’s SEG system, which can be fabricated at a lower cost when compared to commercial silicon solar cells, is comprised of a set of SEG cells that are arranged on a flexible and transparent plastic film. Each sell itself is a thin film of gold deposited on a silicon wafer. Tests and experiments were conducted using the SEG to measure its performance in two areas: electricity generation and use as a self-powered proximity sensor.
“When the whole SEG 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 Professor Andrew Wee of the NUS Department of Physics.
Not only is the SEG cheaper to fabricate when compared to commercial silicon solar cells, but it is also twice as efficient. The harvested energy from the SEG in the presence of shadows created under indoor lighting conditions was high enough to power a digital watch. In addition, the team also demonstrated that the SEG is able to serve as a self-powered sensor for monitoring moving objects. When an object passed by the SEG, it cast an intermittent shadow on the device which triggered the sensor to record the presence and movement of the object.
The SEG developed by NUS researchers uses the contrast in illumination between the lit and shadowed areas to generate electricity. Image credited to the Royal Society of Chemistry
Improving the Versatility of Electronic Devices
The team’s novel energy generation concept could open up new approaches for generating green energy under indoor and low-light conditions for the powering of electronics.
Mobile electronic devices require an efficient and continuous supply of power. As they are used both indoors and outdoors, power sources capable of harnessing ambient light could have a huge impact on their versatility. Although current solar cell technology can perform this role outdoors, energy harvesting efficiency drops substantially under indoor conditions where shadows are present, and light is lower.
The NUS team is now looking at developing self-powered sensors with versatile functionalities, as well as wearable SEGs attached to clothing for energy harvesting during normal daily activities. Another promising area, they say, is the development of low-cost SEG panels that can be placed indoors to harvest energy from indoor lighting.
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