Trees could be the ultimate in green power - tech - 10 September 2009 - New Scientist
Shoving electrodes into tree trunks to harvest electricity may sound like the stuff of dreams, but the idea is increasingly attracting interest. If we can make it work, forests could power their own sensor networks to monitor the health of the ecosystem or provide early warning of forest fires.
Children the world over who have tried the potato battery experiment know that plant material can be a source of electricity. In this case, the energy comes from reduction and oxidation reactions eating into the electrodes, which are made of two different metals – usually copper and zinc.
The same effect was thought to lie behind claims that connecting electrodes driven into a tree trunk and the ground nearby can provide a current. But last year Andreas Mershin's team at MIT showed that using electrodes made of the same metal also gives a current, meaning another effect must be at work. Mershin thinks the electricity derives from a difference in pH between the tree and the soil, a chemical imbalance maintained by the tree's metabolic processes.