Published on August 3rd, 2009 | by Mariella Moon2
Scavenging Energy from Evaporation
August 3rd, 2009 by Mariella Moon
A group of American scientists headed by Michel Maharbiz believe they have devised a way to produce energy using evaporation.
Hailing from the University of California in Berkeley, the University of Michigan and MIT, these electrical engineers devised a process that mimics the natural occurrence of evaporation in plants. In a process called transpiration, water absorbed by the plant roots travel upwards to be excreted by the leaves. The scientists recreated leaves in the laboratory out of glass wafers etched with tiny water-filled channels that resemble veins. The glass leaves allow the water to evaporate through the open-ended veins, causing a continuous draw of fluid at the rate of 1.5 centimeters per second.
According to NewScientist: “The researchers added metal plates to the walls of the central stem and connected them to a circuit. The charged plates and the water within the stem create a sandwich of two conducting layers separated by an insulating layer – in effect, a capacitor.”
Along with water, air bubbles are pumped into the leaves causing changes in capacitance and generating electricity brought about by the difference in electrical properties between water and air. The energy harvested is then stored into a storage capacitor. Each bubble produces 2 to 5 microvolts power, and the power density of the whole device is 2 microwatts per cubic centimeters. Maharbiz believes that following modifications, power density could reach hundreds of microwatts per cubic centimeters. Admittedly, the output of the synthetic leaves is a far cry from various portable power sources such as fuel cells. Nevertheless, when it comes to energy scavenging sources (including devices that harness energy from body movement and the like), Maharbiz claims their system has a respectable output.