Power Plant

"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


Tim Entwisle said…
Subject: power plant?

I had a look...

Bit Hard to know what they are doing... And from what is given in the news paper article, its not clear the power comes from the tree - but I assume it does, because they would have checked that...

I mean you could get 10s of millivolts from hanging wires froms your clothes lines (just from stray fields and the like) - but I am guess this is not what they are picking up. It's kind of funny that they brush over the most interesting bit - which is why the tree has that potential there... and what purpose it serves -- and then I would be worried about what effect drawing the power from it would cause on its health, given that it is presumably meant to do something....

But the rest of it sounded more like just engineering. Once you had lots of little pontential differences (voltages in electrician speak) (at very powers - so with not much possibility to drive anything - in battery terms they would go flat fast), there are alot of ways of "adding" them together to give you a significant voltage and power (or stepping them up), using conventional ideas. Like how we add all our batteries together in devices that require a higher voltage (if you remember the early 'ghetto blasters' - they took about 12 D batteries so they had 18V our of just 1.5V batteries.... Or how in the flash we use time to allow a capacitor to 'charge' up from a normal battery over a time, and give us a very short burst of very high power - high current output for an short lived bright burst of light.

Those guys on this project happen to be 'nano' freaks - so they have lots of solid state 'nano' circuits, which means they create some really low powered micro circuits (which of course they call nano circuits) - just means they are very small, and have very small currents....

Basically its i like having your video recorder in standby mode, and even though Al gore is troubled by how much power it uses - it really isnt very much - but in their case, it is another order of magnitude less, because the circuits are so tiny, they used nothing.... and the recorder is set to record something (say)... so it sits in stand by using nothing for most of the time using so little that even al gore might find it convinient; then it switches on for a second to record (in this case presumably a tempature or soil mositure or something).

I am not really sure what you werent sure of... and besides i am really admin not physics....

Colin Entwisle