Scientists tap into tree power
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Scientists have solved a long-standing mystery behind the source of a faint electrical current in trees - and it wasn't as hard as they thought.
For years, inventors and scientists have driven nails into trees, wired those nails to nearby metal spikes, and wondered at the faint but predictable electrical current that resulted.
Explanations for the power source ranged from a static energy field in the earth's crust, to the possibility it was generated through rust and corrosion, similar to the old do-it-yourself potato clock experiments.
Now, a team of MIT scientists, using platinum electrodes and everyday ficus house plants, have found that the faint current actually comes from an imbalance in pH between the soil and a living tree. And that discovery is already sparking discussions about novel ways to use that electricity - including as a power source for a tree's own fire alarm.
"All the exotic theories have to be rethought," said Andreas Mershin, the lead scientist in a study published in August in the peer-reviewed on-line science journal "PLoS One." "The energy potential is simply due to pH difference."
"When we started this project, we thought it was going to be very complicated and in the end it ended up being very simple," Mershin added.
Mershin - who began his research in 2006 at the behest of Canton-based MagCap Engineering and then persuaded his skeptical bosses at MIT to let him spend a year developing it - found that five to 300 nanowatts of current can be reliably tapped from every tree every time. The greater the pH difference between tree and soil, the more energy was produced, he found.
The discovery has, in turn, posed a question. "Now the question is: What do you do with it?" said Mershin.
One proposal getting serious attention from the US Forest Service is the fire alarm option. A tree's electricity would be used to charge a battery connected to a small sensor that, after a few minutes, would power a brief radio transmission. That radio signal would carry daily soil and air condition measurements to an existing network of much larger, solar powered Forest Service environmental monitoring stations distributed dozens of miles apart across the country. Those sensors would also send out an emergency signal in the event of a sudden spike in air temperature that might indicate the outbreak of a forest fire.
The device is being designed and marketed by Voltree Power, a recently formed subsidiary of MagCap, an electronic components maker. Mershin joined Voltree after the "PLoS One" study came out and is serving the firm as an unpaid adviser while the sensor device is fine-tuned in preparation for Forest Service tests. Those tests are scheduled for this spring.
"I truly believe it has potential," said Victoria Henderson, branch chief for equipment and chemicals at the Forest Service's National Interagency Fire Center. "If this can enhance our existing technology to a degree that would gain us a lot more fire protection, then we'd look at a plan to purchase it for our nationwide infrastructure, which is huge."
The Voltree sensors are much smaller than the Forests Service's monitoring stations and can be buried out of harm's way so many more of them can be used. That will provide badly needed, very localized measurements of soil and air conditions that will help the Forest Service better anticipate where a fire could break out, as well as quickly pinpoint one when it does start. "It's not just for fire alerts," said Voltree CEO Stella Karavas. "What's really important to the Forest Service is the predictive value of anticipating forest fires before they happen through the soil and weather monitoring services."
Voltree is working with Netherlands-based GreenPeak Technologies, which has installed similar low power wireless sensors for firms such as
If the tests this spring are successful, the Forest Service could eventually plant four Voltree sensors per-acre in the more fire prone areas of the country, Mershin said.
Prospects for the tree-powered sensors could one day range well beyond environmental monitoring and fire detection to include border crossing motion detectors, as well as radiation sensors that could signal movement of smuggled radioactive materials. While those prospects are still far from realization, Karavas said, there is no lack of trees to tap in to.
"Three years ago when we first did this, it was such a low power source we weren't sure what we could do with it," Karavas said.
"But the definition of what low power is keeps dropping every day."
Tim Wacker can be reached at tiwack@comcast.net 
