"As far as we know this is the first peer-reviewed paper of someone powering something entirely by sticking electrodes into a tree."
So says one of the authors of a paper about to be published in Institute of Electrical and Electronics Engineers' Transactions on Nanotechnology, as reported in the University of Washington News.
Apparently up to 200 millivolts can be generated by sticking one electrode in a tree and the other in nearby soil. The pioneering researchers (Babak Parviz, Carlton Himes, Brian Otis, Eric Carlson and Ryan Ricchiuti) from Massachusetts Institute of Technology powered an electrical circuit entirely from this power source.
Their undergrad student spent summer hooking nails to trees on the university campus, discovering that larger leaved maples were the real power plants.
Others in the team built a ‘boost converter’, which turns the measly 20 millivolts into 1.1 volts – don’t ask me how, I’m a botanist!
Apparently one of the problems with this technology is that the boost converter and related electronics would “spend most of their time in sleep mode in order to conserve energy”, succinctly described as “creating a complication”.
To avoid the system going to sleep and never waking up, a clock was built that runs on 1 nanowatt, producing an electrical pulse every few seconds to wake up the system. I love this kind of physics talk - perhaps my physicist brother Colin can tell me this actually means!
The researchers are keen to point out that this tree-power is quite different to potato or lemon systems where two different metals react to create a potential difference across the tuber/fruit creating a current. To avoid confusion with the ‘potato effect’ (as they call it), the researchers used the same metal for both electrodes.
They are also quick to point out that tree-power is not going to be a substitute for solar-power. Rather, it could provide a cheap way to run tree sensors measuring e.g. environmental changes in forests. Or perhaps the electronic output could be used as a measure of tree health – a kind of pulse for a plant.
The researchers don’t know where these voltages come from or why, but they wonder if they have some kind of signalling role.
All very stimulating…and quite odd.
Image: An installation from Future Gardens, held in the Royal Botanic Gardens Sydney in October 2004