The SeaTwirl's vertical wind turbine (1), torus ring (2),
float assembly (3) and generator (4)
One of the main drawbacks of wind turbines is the fact that
for maximum efficiency, the power that they generate must be fed
into the grid right as the wind is blowing and their blades are
spinning. While that power can be stored in batteries
for later use, some of it will always be lost in the process.
Sweden's experimental new SeaTwirl system, however, is designed
to kinetically store wind energy until it's required - it's
basically a seagoing flywheel.
The top of a SeaTwirl system consists of a vertical wind
turbine, with a hollow torus ring attached to the bottom. This
is the only part of the system that is located above the surface
of the water.
An axle runs vertically through the center of the turbine and
proceeds into the water. Mounted on that axle, just below the
surface, is a hollow cylindrical float body. At the bottom of
the axle is a generator. The whole system is held in place by
anchoring lines attached to the bottom of the generator.
The wind causes the turbine to spin, regardless of the
direction from which that wind is blowing. Because it's attached
to the turbine, the axle also spins. The water itself acts as a
sort of ultra-low-friction roller bearing, allowing the turbine
and shaft to keep spinning even once the wind has lessened.
Electricity is generated where the rotating axle meets the
non-rotating generator axis. That electricity is fed to the
shore via seabed cables.
When the wind is high, the turbine's vigorous spinning action
causes water to be drawn up from the float, and into the torus
ring. This added weight around the outside of the circular
turbine adds to the centrifugal force, keeping it spinning
longer. As the turbine slows, it folds down, and the water runs
back down into the float. This drawing-in of mass is said to
also help keep the turbine moving, in the same way that
figure skaters start to spin faster when they draw in their arms
and legs.
A one-fiftieth-scale prototype SeaTwirl was tested off the
coast of Sweden in August, and it reportedly performed well. The
designers claim that in its proposed 430-meter (1,411-foot)-long
full-scale incarnation, a commercial SeaTwirl should be able to
generate 4.5 megawatts of mean power, or 39,000 megawatt-hours
per year. It could reportedly store 25,000 kilowatt-hours worth
of power, which they say would be enough to support 8,000 homes
for one hour.
Because much of the
SeaTwirl
system's weight would be supported by the water, it is also
claimed that production costs would be lower than those of
present offshore wind turbines, as heavier, less expensive
materials could be used.
The video below contains some animation that illustrates how
the technology would work.