Don't look now, but there's a giant rechargeable battery growing on your lawn. It's called a tree.
Scientists have long known that trees generate a faint electrical current. But only recently have they explained why: according to a team of MIT researchers, the current arises from a pH imbalance between the soil and the tree. The voltage is small -- the average tree generates a mere 100 to 200 millivolts. But the potential is huge. Already a company called Voltree has developed a tree-powered sensor that monitors local air temperature and humidity, tapping enough energy to radio the data to a central hub. One can readily imagine a far-flung network of "tree guards" joined to detect, say, forest fires. In March, Voltree teamed up with the U.S. Forest Service to test precisely that concept in Boise National Forest in Idaho. It was, in effect, the world's first living fire alarm.
Stella Karavas, CEO of Voltree, sees extending the model to such things as radiation detection and maybe even border security. Does tree power have a bright future? Hard to know -- but there are billions of trees out there, standing around idle. As the saying goes, many limbs make light work.