A team of scientists at the National University of Singapore have developed a new kind of solar cell that uses the contrast of both light and shade to generate electricity.
It works by placing a super-thin coating of gold on silicon, a typical solar cell material; and just like a solar cell, light shining on silicon energizes its electrons. However, with the addition of a gold layer, the shadow-effect energy generator produces an electric current when part of the device lies in shadow.
The team, led by Dr. Swee Ching Tan, call the device a shadow-effect energy generator (SEG) and the paper that explains the principle in detail appears in the journal Energy & Environmental Science.
The new cell uses the contrast between light and shade to produce an electrical current
The excited electrons jump from the silicon to the gold. With part of the device shaded, the voltage of the illuminated metal increases relative to the dark area and electrons in the generator flow from high to low voltage. Sending them through an external circuit creates an electrical current.
The SEG must be in both light and shade in order to work; if it is entirely in light or entirely in shade, it will not work. However, when you imagine somewhere like Manhattan, where skyscrapers create a constantly shifting light-shade environment, the usefulness of this becomes clear. And as an added bonus, the SEG solar cell is also easier to produce than commercial silicon solar cells.
“The manufacturing process is much simpler, it’s just one step,” Swee Ching Tan, a materials scientist at the National University of Singapore and lead author of the paper, told Forbes. “We can generate energy anywhere on Earth, not just in open spaces.”
Optimum energy output is achieved when half of the device is in shade and half is in light
“With conventional photovoltaic panels, where a constant source of light is used to power devices, shadows have a negative effect, since it [sic] reduces the performance of devices. With this work, we capitalized on the illumination contrast caused by shadows as an indirect source of energy. The contrast in illumination induces a voltage difference between the shadow and illuminated sections and we get an electrical current as a result,” Tan said.
The panel comprises a set of SEG cells arranged on a flexible and transparent plastic film. Each SEG cell is a thin film of gold deposited on a silicon wafer. The team then conducted experiments to test the performance of the SEG in generating electricity and as a self-powered sensor.
Based on laboratory experiments, the team’s four-cell SEG is twice as efficient when compared with commercial silicon solar cells, under the effect of shifting shadows. The harvested energy from the SEG in the presence of shadows created under indoor lighting conditions is sufficient to power a digital watch (i.e. 1.2 V).
“The paper from the National University of Singapore provides an innovative and promising method for harnessing energy from an unusual source – the contrast between light and shadows. This combination of creativity and rigorous technical understanding is a great example of how scientists around the world are addressing the urgent problem of renewable energy,” Dr Sam Keltie, Executive Editor of Energy & Environmental Science at the Royal Society of Chemistry, told Forbes.
For the time being, Tan and his team have small scale applications in mind, charging mobile phones for instance, but the potential to upscale is significant. Despite the research only just being published, Tan has already had industry representatives expressing an interest.
“This will take number of years for mature. So this is just the first prototype. So you there's still plenty of work that can be done to further improve the efficiency,” said Tan.
