Tree power might sound like a hippie battle cry, but scientists at the Massachusetts Institute of Technology have literally tapped into the tiny electrical current carried in trees and created a company, Voltree, to capitalize on it as a power source.
"People have known about this phenomena for many years and have tried to explain it by various exotic mechanisms," said Andreas Mershin, a postdoctoral researcher at MIT who is involved in the research.
"But the cause of it is a simple pH difference between the tree and the soil," said Chris Love, a senior in chemistry at MIT and Vice President of Voltree.
Working with the U.S. Forest Service, Voltree has created cheap sensors that use tree power to monitor temperature and humidity conditions inside forests. The goal is to give forest managers and firefighters better tools to predict and monitor fires.
Mershin and Love were initially skeptical of tree power but investigated it anyway. To debunk alternative explanations for the observed electrical charges, Mershin and Love put a potted, four-foot-tall ficus tree into MIT's copper Faraday cage (which blocks out external static electrical fields), stuck platinum electrodes into the soil and into the tree's tissue, and turned off the lights.
Their instruments recorded a slight electrical charge.
To prove their own theory, that the charge was generated by the pH difference between the tree and the soil, the scientists created a range of soil pHs, from an acidic two to a basic 12, by adding hydrochloric acid and potassium hydroxide.
For each unit change in pH, the electrical current changed by 59 millivolts. The greater the difference between the soil pH and the tree's pH, the greater the energy, as Mershin and Love predicted.
Still, it's not much of a current. The batteries that likely power your TV remote are about 1.5 volts. A tree living in harsh soil conditions can generate a few hundred millivolts at best.
But through some proprietary hardware and software tricks, Love and his colleagues amplified that tiny tree current up to 2.4 volts, enough energy to power small sensors. But initially, they didn't know what kind of sensors they should power.
"We had a solution that was looking for a problem," said Mershin.
After considering several possibilities, the team, now incorporated as Voltree, created a cheap, tree-powered sensor that would monitor temperature and humidity inside a forest and approached Tory Henderson of the U.S. Forest Service at the National Interagency Fire Center in Boise, Idaho.
Each sensor package should last approximately 15 years, said Love, and would be placed in a grid with sensors spaced about 65 feet apart. Depending on the programming, data would bounce from one sensor to another until it reached a more permanent weather station, which would send the data to NIFC.