POWER August 2015 - 13

4. An evaporation-driven piston. A device created by researchers at Columbia University
uses bacteria spores that swell with humidity to drive a piston and cause a light to flash.
Courtesy: Columbia University
5. Second powerhouse. The Waneta
Expansion Limited Partnership this June connected
the Waneta Expansion Project near
Trail, British Columbia, to the BC Hydro grid.
Courtesy: Voith Hydro
engine, they created a rotary engine that
drives a miniature car.
The piston-driven engine consists
of thin, double-sided plastic tape onto
which spores are glued on both sides.
On one side of the tape, the spores are
glued in a dashed line, and on the other
sides, the line is offset so that it overlaps
with the gaps on the other side. When dry
air shrinks the spores, the spore-covered
dashes curve, transforming the tape from
straight to wavy, shortening the tape, and
pulling whatever it might be attached to,
the researchers explained. When the humidity
expands the spores, the tape extends,
releasing force. It works akin to an
artificial muscle that is dependent on the
changing humidity.
Dozens of these tapes placed side by
side make up a stronger artificial muscle
that can then be placed inside a floating
plastic case topped with shutters (Figure
4). Inside the case, evaporating water
makes the air humid, and the humidity
causes the muscle to elongate, opening
the shutters and allowing the air to
dry out. When the humidity escapes, the
spores shrink and the tape contracts, pulling
the shutters closed and allowing humidity
to build again. The spore-covered
artificial muscles function as an evaporation-driven
piston, and coupling that
piston to a generator produced enough
electricity to cause a small light to flash.
" When we placed water beneath the device,
it suddenly came to life, moving on
its own, " Xi Chen, a postdoctoral fellow
working on the project, said.
The researchers say that with its current
power output, the floating evaporaAugust
2015 | POWER
tion engine could supply small floating
lights or sensors at the ocean floor that
monitor the environment. With evaporation
energy scaled up, however, they predict
that it could one day produce power
from a giant plant that floats on a bay or
a reservoir.
WELP Connects 335-MW
Hydro Expansion in British
Columbia
The 335-MW Waneta expansion completed
this June near Trail, British Columbia,
adds a second powerhouse downstream
of the Waneta Dam on the Pend-d'Oreille
River, near the border between Canada and
the U.S. (Figure 5).
The project is owned by the Waneta
Expansion Limited Partnership (WELP)-a
joint venture between Columbia Power
Corp. and Columbia Basin Trust. The expansion
also included construction of a
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POWER August 2015

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