by Achini Samararatne
In simple terms energy harvesting is capturing small amounts of energy and converting it into electrical energy to power up low-power devices. With the rapid growth of IoT technology, powering up IoT devices such as sensors has been a challenge and batteries are widely used for powering these devices. More often, the batteries used in IoT devices are non-rechargeable and small in capacity. One disadvantage of batteries is that they are not long lasting for applications such as medical devices where continuous power supply is critical. In some cases, these batteries are not replaceable and consequently the device has to be disposed with the battery. It is reported that over 52 million metric tons of e-waste has been generated so far due to the short lifetime of IoT devices. Moreover, device maintenance and device replacement consume time and money. Incorporating energy harvesting methods to power up IoT devices is an environmentally and economically sound approach. Many countries are heavily invested in energy harvesting research areas due to the multitude of advantages these technologies provide.
Utilization of energy harvesting technologies is the most feasible way to power IoT devices since the power requirement for these devices is small. An electrical engineer and microbiologist at University of Massachusetts Amherst created a technology which can generate energy from moisture in air. This device is called ‘Air-gen’. It consists of two electrodes and a thin film of electrically conductive protein nanowires which are produced by the Geobacter microbe. When the film absorbs water vapour from the atmosphere, surface chemistry and porosity of the film create an electrical current between the two electrodes. Scientists claim that it can generate energy even in extreme low humidity conditions. Renewable energy generated from sources such as solar and wind does not have the advantage of generating energy anywhere at any time, but Air-gen mitigates this problem. Moreover, it is a cost effective and an environmentally benign technology to power small electronics.
Researchers at National University of Singapore have developed a technology that generates electricity from the contrast between shadows and illuminated areas. This device is called shadow-effect energy generator (SEG). Electric current is generated by the induced voltage between illuminated and shadowed area. A SEG cell is an ultra-thin gold strip with the thickness of 15 nanometers, layered on a silicon wafer. The energy harvesting device consists of multiple SEG cells attached to a flexible, transparent plastic film. Traditional solar panels work efficiently only in direct sunlight and efficiency drops significantly in the indirect sunlight. Scientists were able to power 1.2-volt electronic watch with 8 SEGs in ambient light. As such, SEG is another technology which has the potential to power up low power electronic devices.
Collaborative research conducted by Southern University of Science and Technology and Massachusetts Institute of Technology has developed a proof-of-concept prototype which is powered by human body temperature and gelatin. They were able to harvest 2.2V and 5µW of maximum power which is enough to power up IoT sensors. The environment is full of harvestable energy sources, innovative thinking will allow you to identify and utilize them.