Floating wave power plant,paper,

1. FLOATING WAVE
POWER PLANT
INTRODUCTION:
The oscillating water column (OWC)
principle is an attractive approach to convert
wave energy into electrical energy as
exemplified by operational plants in several
countries [1]. As of today it is reasonable to
expect a wave to wire efficiency of about 24
% with a fixed OWC device [2]. Of this, the
OWC efficiency would be about 60 %, and
the power module (comprising bidirectional
turbine and generator) would be about 40 %.
One aspect of the fixed OWC is that the
structural cost could lie between 70 to 85 %
of the overall cost [3]. This has motivated
the development of floating OWCs which
promise reduced cost with an accompanying
reduction in efficiency in the hydrodynamic
stage. The largest of such structures was the
Japanese Mighty Whale [4]. While
laboratory results predicted a best efficiency
of 50 % in the hydrodynamic stage, practical
measurements showed that the best
efficiency was about 30 %. Hence the
overall wave to wire efficiency was closer to
15 %. There have been continuous attempts
to improve the efficiency of floating OWCs
and the backward bent ducted buoy (BBDB)
is one such attempt [5]. In this work we
show that an improved power module for
the BBDB with variable speed twin
unidirectional turbines can achieve 65 %
efficiency and thus make the floating
structure attractive in spite of the lower
hydrodynamic efficiency.
PLANS FOR IT`S FUTURE
PRODUCTION:
A new Oregon company will announce
Thursday plans to commercialize and
manufacture floating power plant
technology that generates electricity from
waves and wind.
Floating Power Inc. is a joint venture
between Lake Oswego-based boutique
merchant bank BridgeWorks Capital and
Floating Power Plant Inc., a Danish
company that spent the last 12 years
developing and testing the power-generating
platform called "Poseidon."
The Poseidon generates hydraulic power
from waves that interact with floats, as well
as electricity from wind turbines mounted
atop the platform. The electricity it
generates is transported to the grid via
underwater cables. Waller said the
technology thus far is capable of producing
enough electricity to power 15,000 homes
from a single platform.

2. The company will likely have an initial test
module working in conjunction with Oregon
State University-based Northwest National
Marine Renewable Energy Center,
POSEIDON 37:
It is both a floating support structureforwind
turbines and a wave energy device. The
concept of the Floating Power Plant is so far
the only one known in the world that has
combined the two energy forms and has an
operating prototype.
This article will describe the design of a
floating support structure that combines the
energy forms, but since the Floating Power
Plant is the only one using it, the article will
mostly refer to and describe the Floating
Power Plant. The current prototype is called
Poseidon 37 – the number refers to the width
of the structure.
Definitions
When combining wind and wave energy
devices, the support structure acts as a semi-
submerged structure. For Poseidon, the
structure is three-quarters submerged. Semi-
submerged structures are sometimes referred
to as barge floaters, but to avoid confusion
this term will not be used.
The wave energy device could in theory be
of various designs such as the point absorber
or overtopping terminator. But in the case of
the Floating Power Plant the wave energy
device is the so-called Front Pivot Hinged
Wave Absorber.
The wind turbines are defined by the height
of the tower. This height is determined by
the dimensions of the support structure. To
put it in another way: the larger the
platform, the higher the tower. The turbines
can be either of the upwind or downwind
type carrying one, two or three blades on the
rotor. Depending on customer needs, there
can be from 1 to 3 turbines on the platform.
Why combine wind and wave?
Whether one has a starting point in the wind
industry or in wave energy, the logic behind
a combination of the two energy forms is
that it increases the return.
The benefits of adding a wave energy device
to a floating support structure for a wind
turbine is stability and the boat landing.

3. The wave energy device absorbs the wave
motions, and thereby makes the structure
even more stable. According to FPP, 70-90
percent of the energy in the wave motion is
absorbed into a controlled system. This
provides stability compared to a normal
floating structure without any absorption.
And because of the absorption of the motion
energy of the waves, there will always be
calm waters at the rear of the structure – a
lee side, where boat landing on the structure
is possible in harsh weather. See the second
picture below for an illustration of this.
From the other point of view, the benefits of
adding one or several wind turbines to a
floating wave energy device are stability and
increased production. Measurements from
the prototype Poseidon have shown that the
pressure from wind on the turbines stabilizes
the structure in the water, and this stability
increases the power output of the wave
device by 1-2 percentage points.
And since the wave energy device provides
a floating support structure anyway, the cost
of establishing wind turbines offshore in this
system corresponds to the expense of
establishing the turbines onshore.
STRUCTURE:
When using a semi-submerged structure for
a wave energy device, the structure is
modified radically compared to a standard
barge. On the Poseidon 37, three sections
constitute the barge:
The front section, which contains the
turret mooring,
the middle section carrying the wave
absorbers, and
the rear section.
The whole structure is 37 meters wide and
25 meters long (excluding the buoy). The
middle section can be disconnected from the
front, and the energy device can thus be
sailed to port without interfering with the
mooring. This is needed since the P 37 is a
prototype and a test facility. The front and
rear sections ensure that the Floating Power
Plant always turns against the wave front –
and that it does so in a passive way without
consuming energy.

4. The wave absorbers (floaters) are hinged at
the front. The floaters absorb the pressure
motion of the wave both forwards and
upwards. Up to 34 percent of the incoming
wave energy is converted to electricity in the
Floating Power Plant. According to FPP,
this has been confirmed by the research and
consultancy organization DHI (Danish
Hydraulic Institute) in the latest wave flume
test series.
Each absorber on Poseidon 37 weighs 4.7
tonnes without ballast and 24 tonnes fully
ballasted. The ballast system is an active
control system. Along with trimming of the
submerged depth, these are the only two
active controls in the whole structure, thus
the only part where energy is consumed.
Ballast is used to secure the optimum floater
movement: in this way the floaters have
high efficiency in small as well as large
waves.
NEXT STEPS:
The next step is the construction of a power
plant of 110 meters width to be installed in
Oregon, USA. A collaboration between
Floating Power Plant and American venture
capitalists was announced in April 2011, and
the new prototype will be installed between
2014 and 2015.
The largest scale of the Floating Power Plant
will be 230 meters wide and mounted with
three 2 MW turbines. The wave energy
device will have a rated power of
approximately 5-6 MW. The yearly
production will be 50 GWh – of this 60-70
percent will be produced from wave energy,
because the waves represent a more stable
energy source, says Floating Power Plant.