BY CARLOS COSSIO
As incredible as it may sound,
the purpose of this project is to
power a device from a set of
potted plants. A ‘bio-energy
battery’ of this sort may remind
you of the well-known potato
and lemon batteries where two
electrodes made from different
metals (typically copper and zinc)
are stuck into a piece of fruit to form
a sort-of simple galvanic cell. However, in this case the cells
of the battery draw their energy directly from the plants,
rather than from an electrochemical process.
■ FIGURE 1. Block diagram showing the serial connection
procedure among several plants. Like any standard battery,
every plant has a positive and negative terminal.
There is no question that our plant battery supplies free nergy. It may not be a lot, but it is still energy. As
stated, this energy is generated directly by the plants and
will continue to supply energy as long as they remain
alive. The operating principle of our potted plant battery is
currently the subject of study at several research centers.
These voltages have recently been attributed to a pH
difference between xylem tissue and soil content.
A potential difference of approximately 400 mV can
be measured between the plant and the soil it grows in.
This voltage source can supply a power of approximately
0.8 microwatts, regardless of whether it’s a small
houseplant or a large bush.
■ PHOTO 1. A needle stuck into a plant branch works as
the positive terminal of the potted plant battery.
Certainly, this is far too little power for most
applications, but it is enough to operate a simple LCD
Five plants are enough to power an
ultra-low power MSP430F2013 available
from Texas Instruments. Just like a
standard battery cell, each plant has two
terminals. The first terminal is located on
a branch of the plant and is formed by
sticking a needle or small pin through
the branch, then connecting an alligator
clip to it. (See Photo 1.) The other
■ PHOTO 2. A closer view of the ground
terminal. A long metal rod inserted in
the soil of the plant, then connected with
an alligator clip works as the negative
terminal of the battery.