Prototype device creates electricity from shadows

NUS research team have created a device called a shadow-effect energy generator (SEG), which plays on the contrast between light and shadow to generate electricity.

According to the research, published in the scientific journal Energy and Environmental Sciences, the device uses contrast in illumination to induce a voltage difference between shadow and illuminated areas, thus generating electricity. Wearable devices like smartwatches and mobile phones can easily use this innovative technology to harness energy for continuous functionality. To allow convenience, the team developed a low=cost, easy-to-fabricate SEG to convert illumination and shadow to generate electricity and to serve as a self-powering proximity sensor to monitor passing objects.

The SEG cells are arranged on a flexible transparent plastic film, where each cell is a thin film of gold placed on a silicon wafer. Professor Andrew Wee, co-team leader says,"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."

Harvested energy from these devices under indoor lighting is enough to power a smartwatch. The object sensor works pretty well on the SEG, recording the presence and movement of the object when it passes by and casting an intermittent shadow on it.

After working for four months on the SEG, the NUS team is determined to make it more cost-effective and is aiming to replace the gold with other materials. They want to make the device more versatile so it can be wearable and harvest energy during normal daily activities.