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Experimenting with Tree Energy
When Christopher Love takes a walk in the woods, he finds giant batteries. These batteries aren't typical Duracells or Energizers, though. They are tens of meters tall, with trunks, branches, twigs, and leaves. They are trees.
A recent experiment by Love and his colleagues at MIT reveals that pH differences between tree trunks and the surrounding soil create voltage differentials, just like those found in household rechargeable batteries. Energy flow across these differentials can power tiny electrical devices.
According to Love, "it has long been known that there is a voltage difference between the xylem of many plants and the surrounding soil, but the mechanism behind this voltage has remained controversial". The MIT team's paper discusses both the mechanism (the pH differences) and, more importantly, the applications of this critical discovery.
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Using Energy to Power Sensors
Because the trees can only produce about 200 mV of electricity, they cannot power large-scale lighting, heating, or industrial systems. But the trees can power small sensors- sensors that can save thousands of acres of forested land from deadly wildfires.
Wildfire detection is notoriously tricky. Traditional, battery-operated sensors are placed high on trees in remote wilderness. As the batteries need constant replacement, millions of dollars are spent on sensor network maintenance every year. Tree-powered sensors could eliminate most of that cost.
In addition, the tree sensors can collect real-time information on air, soil, and water conditions in remote areas. Ecological and environmental researchers usually travel to the locations that they study. The sensors would allow them to collect data from the safety of a lab. It's the difference between driving fifty miles on dirt tracks to collect a temperature reading and having that reading fed into your computer as you lounge in an armchair at home.
However, the new technology raises some important questions. Trees are a novel source of renewable energy, but they are also essential parts of forest ecosystems. If thousands of trees are "plugged in", will there be any effect on soil and water conditions? If trees are used to power remote sensors, how will animals be affected by the thousands of wires strewn across the forest?
Now, though, tree bioenergy converters (produced by VoltTree, a subsidiary of a major electronics manufacturer) are just being developed for fire sensors. According to Victoria Henderson, VoltTree's devices "truly have potential". If they work well, the power units could be used for nationwide infrastructure.
These generators are still in the early stages of development. Even in the nascent stages, though, they still represent an extraordinary leap in renewable energy research. Trees are no longer just landscaping features and sidewalk liners, but natural generators bristling, bubbling, and popping with energy.
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Love CJ, Zhang S, Mershin A (2008) Source of Sustained Voltage Difference between the Xylem of a Potted Ficus benjamina Tree and Its Soil. PLoS
ONE 3(8): e2963. doi:10.1371/journal.pone.0002963
VoltTree Power. http://voltreepower.com/index.php
Power From Trees. http://www.alternative-energy-news.info/power-from-trees/