Scientists from the National University of Singapore has sought to investigate how electricity may be produced from shadow under indoor lighting conditions. They created a special device called shadow-effect energy generator (SEG) which they claim is able to harvest electricity from the contrast in illumination between lit and shadowed areas under weak ambient light. “Without any optimization, our generator has a power density of 0.14 microwatt cm−2 under indoor conditions 0.001 sun, where shadows are persistent,” the team said.
According to the research findings, published in the paper Energy harvesting from shadow-effect, the new device can perform 200% better than commercial silicon solar cells under the effects of shadows.
The group also explained that the SEG is able to power an electronic watch and may be used to serve self-powered sensor for monitoring moving objects by tracking the movement of shadows. The device is based on a set of SEG cells placed on a flexible and transparent plastic film, with each SEG cell being a thin film of gold deposited on a silicon wafer.
“When the whole SEG cell is under illumination or in shadow, the amount of electricity generated is very low or none at all,” said research co-author, Andrew Wee. “When a part of the SEG cell is illuminated, a significant electrical output is detected.” According to the group, 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.
The NUS team is now seeking to experiment with other materials, besides gold, to reduce the cost of the SEG. Although not directly related to solar, this new technology opens up new horizons for producing clean energy under indoor lighting conditions.