Ocean currents can power the world,
Nov 29, 2008 - Jasper Copping - telegraph.co.uk
| Existing technologies require
an average current of five or six knots to operate
efficiently, while most of the earth's currents
are slower than three knots. Photo: AP
The technology can generate electricity in water
flowing at a rate of less than one knot - about one
mile an hour - meaning it could operate on most waterways
and sea beds around the globe.
Existing technologies which use water power, relying
on the action of waves, tides or faster currents created
by dams, are far more limited in where they can be
used, and also cause greater obstructions when they
are built in rivers or the sea. Turbines and water
mills need an average current of five or six knots
to operate efficiently, while most of the earth's
currents are slower than three knots.
The new device, which has been inspired by the way
fish swim, consists of a system of cylinders positioned
horizontal to the water flow and attached to springs.
As water flows past, the cylinder creates vortices,
which push and pull the cylinder up and down. The
mechanical energy in the vibrations is then converted
Cylinders arranged over a cubic metre of the sea
or river bed in a flow of three knots can produce
51 watts. This is more efficient than similar-sized
turbines or wave generators, and the amount of power
produced can increase sharply if the flow is faster
or if more cylinders are added.
A "field" of cylinders built on the sea bed over
a 1km by 1.5km area, and the height of a two-storey
house, with a flow of just three knots, could generate
enough power for around 100,000 homes. Just a few
of the cylinders, stacked in a short ladder, could
power an anchored ship or a lighthouse.
Systems could be sited on river beds or suspended
in the ocean. The scientists behind the technology,
which has been developed in research funded by the
US government, say that generating power in this way
would potentially cost only around 3.5p per kilowatt
hour, compared to about 4.5p for wind energy and between
10p and 31p for solar power. They say the technology
would require up to 50 times less ocean acreage than
wave power generation.
The system, conceived by scientists at the University
of Michigan, is called Vivace, or "vortex-induced
vibrations for aquatic clean energy".
Michael Bernitsas, a professor of naval architecture
at the university, said it was based on the changes
in water speed that are caused when a current flows
past an obstruction. Eddies or vortices, formed in
the water flow, can move objects up and down or left
"This is a totally new method of extracting energy
from water flow," said Mr Bernitsas. "Fish curve their
bodies to glide between the vortices shed by the bodies
of the fish in front of them. Their muscle power alone
could not propel them through the water at the speed
they go, so they ride in each other's wake."
Such vibrations, which were first observed 500 years
ago by Leonardo DaVinci in the form of "Aeolian Tones",
can cause damage to structures built in water, like
docks and oil rigs. But Mr Bernitsas added: "We enhance
the vibrations and harness this powerful and destructive
force in nature.
"If we could harness 0.1 per cent of the energy
in the ocean, we could support the energy needs of
15 billion people. In the English Channel, for example,
there is a very strong current, so you produce a lot
Because the parts only oscillate slowly, the technology
is likely to be less harmful to aquatic wildlife than
dams or water turbines. And as the installations can
be positioned far below the surface of the sea, there
would be less interference with shipping, recreational
boat users, fishing and tourism.
The engineers are now deploying a prototype device
in the Detroit River, which has a flow of less than
two knots. Their work, funded by the US Department
of Energy and the US Office of Naval Research, is
published in the current issue of the quarterly Journal
of Offshore Mechanics and Arctic Engineering.