How to generate electricity from a tree?

WASHINGTON - There’s enough power in trees to run an electronic circuit, says a new study.

A study last year led by the Massachusetts Institute of Technology (MIT) found that plants generate up to 200 millivolts when one electrode is placed in a plant and the other in the surrounding soil.

“As far as we know this is the first peer-reviewed paper of someone powering something entirely by sticking electrodes into a tree,” University of Washington (UW) associate professor of electrical engineering and study co-author Babak Parviz said.

The researchers have since started a company developing forest sensors that exploit this new power source. The UW team sought to do further academic research in the field of tree power by building circuits to run off that energy. They successfully ran a circuit solely off tree power for the first time.

Co-author Carlton Himes, UW undergraduate student, spent last summer exploring likely sites. Hooking nails to trees and connecting a voltmeter, he found that bigleaf maples, common on the UW campus, generate a steady voltage of up to a few hundred millivolts.

The UW team next built a device that could run on available power. Co-author Brian Otis, UW assistant professor of electrical engineering, led the development of a boost converter, a device that takes a low incoming voltage and stores it to produce a greater output.

His team’s custom boost converter works for input voltages of as little as 20 millivolts (a millivolt is a thousandth of a volt), an input voltage lower than any existing such device. It produces an output voltage of 1.1 volts, enough to run low-power sensors.

The UW circuit is built from parts measuring 130 nanometres and it consumes on average just 10 nanowatts of power during operation (a nanowatt is one billionth of a watt).

“Normal electronics are not going to run on the types of voltages and currents that we get out of a tree. But the nanoscale is not just in size, but also in the energy and power consumption,” Parviz said, according to an UW release.

Tree power is unlikely to replace solar power for most applications, Parviz admits. But the system could provide a low-cost option for powering tree sensors that might be used to detect environmental conditions or forest fires. The electronic output could also be used to gauge a tree’s health.

These results are slated for publication in the Institute of Electrical and Electronics Engineers’ Transactions on Nanotechnology.