Scientists have known that trees can produce extremely small amounts of electricity, but did not know how the energy was produced or how to take advantage of the power. In a recent issue of the Public Library of Science ONE, Zhang and MIT colleagues report the answer. "It's really a fairly simple phenomenon: An imbalance in pH between a tree and the soil it grows in."
The new sensor system taps into trees as a self-sustaining power supply. Each sensor is equipped with an off-the-shelf battery that can be slowly recharged using electricity generated by the tree.
A single tree doesn't generate a lot of power, but over time the “trickle charge” adds up, “just like a dripping faucet can fill a bucket over time,” said Shuguang Zhang, one of the researchers on the project. The system produces enough electricity to allow the temperature and humidity sensors to wirelessly transmit signals four times a day, or immediately if there's a fire. Each signal hops from one sensor to another, until it reaches an existing weather station that beams the data by satellite to a forestry command center in Boise, Idaho.