ON/OFF - Offshore Center Danmark

The story about Wave Star
Energy
Wave Star Energy was established in October
2003 with the purpose of commercialising
wave energy based on the Wave Star
concept. Since then extensive wave tank
testing in scale 1:40 was carried out during
2004, to optimize the basic configuration of
the wave energy device and verify hydrodynamic
modelling.
In 2005 a scale 1:10 converter was designed
and built with a hydraulic transmission
system and built to the same standard as a
full scale converter with the same instrumentation,
electronic control system and
grid connection.
It was installed 6th of April 2006 in the
sea at Nissum Bredning, close to Thyborøn
in the North Western part of Jutland, in a
wave climate, which is approximately 1/10
of the North Sea. After extensive testing of
all control systems, the system was put into
daily operation on the 24th of July 2006.
Since then the system has logged almost
4.000 working hours by the end of December
2006, without any major problems. The
intention is to optimize the power output
and gather information on reliability over
the next two years. The site can be visited
by appointment only and is connected to
land with a pier.
Funding
Wave Star Energy is mainly privately founded.
The family Clausen, behind Danfoss,
is among the main investors in Wave Star
Energy. In addition Wave Star Energy has
received substantial PSO (Private Service
Obligation) funding for renewable energy.
How does the wave energy
device work?
The converter consists of two rows of each
twenty floats. Forty floats in all. The floats
are attached to a structure, which sits on
piles. All moving parts are above water.
The converter is normally installed so it is
oriented towards the dominant wave direction.
When the wave passes, the floats pump
hydraulic energy into a common transmission
system. Because the converter is oriented
towards the dominant wave direction
the floats pump energy into the transmission
system distributed over time, which produces
an even output to a hydraulic motor
which drives a generator directly.
A frequency converter locks the generator
onto the grid.
In a specific water depth, the highest possible
wave, before it breaks, is 75% of the
water depth. The lower part of the structure
is at least the water depth above the water
line. The wind load even in very high winds
is negligible compared to the wave loads on
the floats in normal operation.
Practical tests have shown the Wave Star
can accept waves from all directions. Crossing
waves only produces a more uneven
output to the grid, which is not a problem.
Scaling of the Wave Star
concept
The ability to scale, in size and power, is
very important to meet commercial kWh
prices in the future. The current scale 1:10
device installed in the sea is 24 m long with
Ø 1 m floats. In 0,5 m waves it produces
1.800 Watts.
The scale 1:10 installation in
the sea in Nissum Bredning
in the North West of Jutland.
The next scale 1:2 device for 10 m water
depth in the North Sea is 120 m long and
with Ø 5 m floats. In 2,5 m waves it will
produce 500 kW.
Full scale 1:1 device for 20 m water depth
in the North Sea / Atlantic Ocean is 240 m
long and with Ø 10 m floats. In 5,0 m waves
it will produce 6 MW.
Every time the Wave Star is doubled in size
and the waves are doubled, the power goes
up with a factor of 11!
The Wave Star gets more cost efficient with
greater depth and size.
For the Wave Star an optimal water depth
is between 10 to 40 m, as the converters are
gradually scaled up in size. When organised
in wave farms, the Wave Star is space
efficient because it sits on piles and does
not sway around in moorings. It is expected
that 16 to 24 MW power capacity can be installed
per km2, which is 2 to 3 times more
space efficient than wind turbines.
What are the future plans?
In parallel with the testing over the next two
years of the scale 1:10 converter, the design
of the scale 1:2 500 kW device for the North
Sea is already in progress.
Main components like arms, floats and
sections of the structure will be tested in
the North Sea during 2007. A test site is currently
under construction and will be ready
by March 2007. In 2008 the scale 1:2 500
kW device will be built and dry tested. In
2009 it will be installed at Horns Rev 15 km
West of Esbjerg and grid connected to the
160 MW offshore wind turbine site. After a
test period of 1 year the first 500 kW series
production device will be released for sales
and commercialisation begins.
Offshore Center Denmark 7
Newsletter ON/OFF 10 - May 2007