As every middle-school child knows, in the
process of photosynthesis, plants take the sun’s energy and convert it to
electrical energy. Now a Tel Aviv Univ. team has demonstrated how a member of
the animal kingdom, the Oriental hornet, takes the sun’s energy and converts it
into electric power—in the brown and yellow parts of its body—as well.
“The interesting thing here is that a living
biological creature does a thing like that,” says physicist Prof. David
Bergman of Tel Aviv Univ.’s School
of Physics and Astronomy,
who was part of the team that made discovery. “The hornet may have
discovered things we do not yet know.” In partnership with the late Prof.
Jacob Ishay of the university’s Sackler Faculty of Medicine, Prof. Bergman and
his doctoral candidate Marian Plotkin engaged in a truly interdisciplinary
research project to explain the biological processes that turn a hornet’s
abdomen into solar cells.
The
research team made the discovery several years ago, and recently tried to mimic
it. The results show that the hornet’s body shell, or exoskeleton, is able to
harvest solar energy. They were recently published in the German journal Naturwissenschaften.
Discovering a new system for renewable energy?
Previously, entomologists noted that Oriental wasps, unlike other wasps and
bees, are active in the afternoon rather than the morning when the sun is just
rising. They also noticed that the hornet digs more intensely as the sun’s
intensity increases.
Taking
this information to the lab, the Tel Aviv Univ. team studied weather conditions
like temperature, humidity and solar radiation to determine if and how these
factors also affected the hornet’s behavior, but found that UVB radiation alone
dictated the change.
In the
course of their research, the Tel Aviv Univ. team also found that the yellow
and brown stripes on the hornet abdomen enable a photo-voltaic effect: the
brown and yellow stripes on the hornet abdomen can absorb solar radiation, and
the yellow pigment transforms that into electric power.
The team
determined that the brown shell of the hornet was made from grooves that split
light into diverging beams. The yellow stripe on the abdomen is made from
pinhole depressions, and contains a pigment called xanthopterin. Together, the
light diverging grooves, pinhole depressions, and xanthopterin change light
into electrical energy. The shell traps the light and the pigment does the
conversion.
A biological heat pump
The researchers also found a number of energy processes unique to the insect.
Like air conditioners and refrigerators, the hornet has a well-developed heat
pump system in its body which keeps it cooler than the outside temperature
while it forages in the sun. This is something that’s not easy to do, says
Prof. Bergman.
To see
if the solar collecting prowess of the hornet could be duplicated, the team
imitated the structure of the hornet’s body but had poor results in achieving
the same high efficiency rates of energy collection. In the future, they plan
to refine the model to see if this “bio-mimicry” can give clues to
novel renewable energy solutions.
The research team also discovered that hornets
use finely honed acoustic signals to guide them so they can build their combs with
extraordinary precision in total darkness. Bees can at least see what they are
doing, explains Prof. Bergman, but hornets cannot—it’s totally dark inside a
hornet nest.
