NZ749891B2 - Apparatus for harvesting energy from waves - Google Patents
Apparatus for harvesting energy from waves Download PDFInfo
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- NZ749891B2 NZ749891B2 NZ749891A NZ74989117A NZ749891B2 NZ 749891 B2 NZ749891 B2 NZ 749891B2 NZ 749891 A NZ749891 A NZ 749891A NZ 74989117 A NZ74989117 A NZ 74989117A NZ 749891 B2 NZ749891 B2 NZ 749891B2
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Abstract
wave energy harvesting apparatus comprising a floating platform (2), a cylinder (1), and a piston (5) having a piston rod (6) connected to a mooring (10) at the sea floor. At least one penstock tube (13) is in fluid connection at its lower end with a lower portion of the cylinder, below the piston. The penstock tube being provided along the cylinder and has an opening at the upper end so that water pumped upwards in the tube will hit a water turbine (4) arranged above the cylinder. The water turbine is connected to a generator (15). The cylinder has an opening in an upper portion and in the lower portion thereof, provided with a one-way valve (22) allowing water into the lower portion of the cylinder while the cylinder moves downwards. When the platform rises, water will be refilled in the upper section through the upper opening. The upper opening of the penstock tube further comprises one or more adjustable nozzles arranged to regulate the pressure and the speed of water exiting the penstock tube. The invention provides a power take-off system to be used in a Wave Energy Converter of point absorber type, with improved efficiency and lower cost compared to prior wave power systems. . The penstock tube being provided along the cylinder and has an opening at the upper end so that water pumped upwards in the tube will hit a water turbine (4) arranged above the cylinder. The water turbine is connected to a generator (15). The cylinder has an opening in an upper portion and in the lower portion thereof, provided with a one-way valve (22) allowing water into the lower portion of the cylinder while the cylinder moves downwards. When the platform rises, water will be refilled in the upper section through the upper opening. The upper opening of the penstock tube further comprises one or more adjustable nozzles arranged to regulate the pressure and the speed of water exiting the penstock tube. The invention provides a power take-off system to be used in a Wave Energy Converter of point absorber type, with improved efficiency and lower cost compared to prior wave power systems.
Description
SUMMARY OF INVENTION
According to a first aspect of the present invention, an apparatus for harvesting energy
from waves, of the wave energy converter of the point absorber type, is provided. The
apparatus comprises a floating platform, a cylinder connected thereto and arranged
underneath the floating platform, and a piston having a piston rod arranged to be
connected to a mooring at the sea floor, wherein at least one penstock tube is in fluid
connection at a lower end thereof with a lower portion of the cylinder , below the piston,
the at least one penstock tube being provided along the cylinder and having an opening
at an upper end thereof facing a water turbine arranged above the cylinder, the water
turbine being in connection with a generator , wherein the cylinder has at least one
opening in the lower portion thereof and provided with a one-way valve arranged to allow
water into the lower portion of the cylinder when the cylinder moves downwards and thus
the piston moves upwards relative the cylinder, wherein the cylinder has at least one
opening in an upper portion of the cylinder arranged to allow water into the upper portion
of the cylinder when the cylinder moves upwards and thus the piston moves downwards
relative the cylinder, and wherein the upper opening of the at least one penstock tube
further comprises one or more adjustable nozzles arranged to regulate the pressure and
the speed of water exiting the at least one penstock tube. The penstock will preferably be
relatively straight and alongside the cylinder as a tube or large pipe, but may as well have
other shapes, for example winded around the cylinder.
According to an embodiment the cylinder is connected via a swivel coupling to the floating
platform. The swivel may be able to rotate around one or more axes. According to an
embodiment the piston is movable up and down from a middle position in the cylinder.
Preferably, the cylinder has at least one opening in fluid connection with the surrounding
water in an upper portion and in the lower portion thereof, respectively.
According to an embodiment the at least one opening in fluid connection with the
surrounding water is provided with a one-way valve allowing water into the lower portion
of the cylinder while the cylinder moves downwards and thus the piston moves upwards
relative the cylinder.
According to an embodiment the at least one opening in fluid connection with the
surrounding water is provided with a screen or filter.
According to an embodiment the fluid connection between the cylinder and the at
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least one penstock tube comprises at least one one-way valve allowing water to flow
from the cylinder to the penstock tube.
According to an embodiment at least two penstock tubes are provided on opposite
sides of the cylinder. Preferably, the upper openings of the at least two penstock tubes
are provided at different levels so that water from at least one first opening at a first
side of the water turbine will hit buckets at the top of the water turbine and water
from at least one second opening at a second side of the water turbine will hit buckets
at the bottom of the water turbine, or vice versa. According to an embodiment one or
more penstock tubes are connected to a vertical axis hydro turbine (the runner wheel
positioned flat), the turbine laying directly on top of the cylinder, although with room
for water escape. The hydro turbine may have from one to several nozzles, as well as
from one to several runners. In this embodiment, the generator may be positioned
directly on top of the hydro turbine.
According to an embodiment the at least one penstock tube has a spear valve in its
upper opening. Thus, it is possible to regulate the water flow and pressure out of the
upper opening of the penstock. Other adjustable nozzles than a spear vale is also
possible. A fixed size nozzle or orifice is also an option, especially for smaller and
cheaper installations, although resulting in lower efficiency.
According to an embodiment the at least one penstock tube has a pressure valve in its
upper opening. Preferably, the valve will open at a determined pressure letting water
in the penstock out. It is preferred to have a pressure valve that is of a one-way type.
According to an embodiment the water turbine is a Pelton turbine. According to an
embodiment a coupling is provided between the water turbine and the generator.
Preferably, a flywheel is provided between the water turbine and the generator. In
case of a vertical axis hydro turbine with the generator mounted on top, one
embodiment would be to have one flywheel directly below the lower runner wheel, as
well as one on top of the generator.
According to an embodiment the floating platform is at least 1 meter x 20 cm for
private use. For commercial deployment, sizes up to 140 meters length and a lifting
force of more than 4000 tons is possible with today's materials. This will be increased
with time.
In short one might describe the invention as a cylinder pump where the piston rod is
attached to a weight standing on the sea floor, the cylinder is attached to the floating
platform, the pressurized water being streamed upwards to a turbine, driving a
generator. The water flow is being regulated via one way valves on the cylinder, as well
as one or more nozzles facing the turbine, regulating the pressure and subsequently
the speed of the water hitting the turbine. The pressure may range from 0 to 200 bar,
ideally from 20-100 bar in the lifting phase, being reduced to about zero in the
descending phase. It is possible to think of it as an inverted waterfall, since it
pressurizes water in a penstock/tube, on a scale similar to Hydro Power stations having
a fall ranging from 50 to several hundred meters, thereafter running a water turbine.
(10 bars being about equal to 100 meters water fall).
As the principle will work in any size, this invention is relevant from half a meter
cylinder’s length and can actually be used in a bay outside a summer cabin. Like ways,
cylinder lengths of 40 meters at 60 meters' depth or more, lifting 4000 tons, will be
conceivable, too, since the principle is the same. The attachment to the sea floor may
be a weight or an arrangement drilled into the sea floor structure. The material in the
cylinder, penstock as well as the piston, may be of several materials, composites
though being of preference. One or more cylinders may be used for each floating
platform. The cylinder may be attached to the platform either fixed or with a flexible
joint, the latter being of preference, to be able to adjust to the rolling wave
movement. The one way valves and nozzle(s) may be opened or closed with the
direction of water flow and/or fixed pressure settings, but may also be controlled
electrically through sensors as well as computer controlled.
The water turbine is ideally a Pelton turbine, but the concept will also work with other
water turbines. The size of the turbine wheel as well as the number of runner wheels,
buckets, nozzles/spear valves as well as control systems, may vary. A flywheel is
desirable but not required. This, as well as the size of the flywheel, depends on the
generator type, grid voltage and size plus number of units installed in the same area.
The generator and control systems will vary, depending upon the size of the system,
the user, as well as the grid connection. A variable speed induction generator with
power converter is one relevant option. The piston rod is connected to the mooring
weight, inside a hollow strut, by thread or a clamshell solution, for example, which is
favourable both for installation and decoupling due larger maintenance/service. There
will be filters or screens around various water openings to avoid contamination of the
system.
Depending on the floating platform layout, size and whether the cylinder is flexibly or
fixedly attached to it, a prop shaft between the water turbine and the generator (via
the flywheel if present), is desirable, but not a must. The prop shaft may have a spline
coupling, too.
The platform should preferably be held in an approximate position by mooring lines
and anchors on the sea floor, but will also function with the cylinder and piston rod as
the only attachment. In contrast to other existing systems, the present invention
concept, combined with larger floating platforms, can with today's newer composite
materials, give incredible average performance figures up to 9 MW per unit, 90 times
more than the more common systems and many times more than the best performing
competition.
The world's largest offshore wind power units, being the most economical, rages 220
meter-high and has a turbine diameter of 165 meter, giving at most an average of 3.3
MW output. The total weight is about 6000 tons whereof 1900 tons is based 140
meters above sea. A system according to the present invention having similar
performance, weighs about 1700 tons, whereof 1500 tons consist of a simple sea floor
weight, chains and anchors. Only 220 tons comes from the platform and machinery, a
fraction of a wind power plant. Installing the wind power unit is extremely more
complex than the present inventive system. Since the height is so much lower than
wind power, the concept will be invisible from shore at a distance of 7 km, much
shorter than the 52 km needed for wind power to be the earth's curvature. This
explains the often 30-50 km distance from land they are normally located. Combined
with the fact that the concept is so much simpler to install and remove in the future,
the number of permissible locations are of a far better magnitude. To make the
platform more visible for other vessels, a spray fountain may be arranged on top,
needing only a very minor portion of the pressurized water to operate. As the concept
may be close to shore, it is quite possible this addition will make it more popular
amongst neighbours. A sight-able gage on deck showing the output would also add to
the popularity. The cost for a wind power unit this size, installed, is roughly 200 M SEK.
The cost for the present inventive system combined with a larger floating platform is
estimated to be 60-35% of above mentioned wind power units, calculated in relation
to cost per produced MW. The percentage cost drops with increasing size. The
numbers are even more favourable when compared to rated power. Running cost
should at most be similar to wind power per produced MW.
The above statements are made to show the importance of getting this under-way, as
well as to show differences as to what else is available today.
SHORT DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail by means of exemplifying
embodiments under referral to the drawings, in which:
Fig. 1 shows an embodiment of the inventive apparatus, combined with a
floating platform, in a view showing the platform’s long side, the one facing the
waves.
Fig. 2 shows the inventive apparatus of Fig. 1, combined with the platform,
in a view showing the platform’s short side.
Fig. 3 shows an embodiment of a swivel arrangement from above.
Fig. 4 shows an embodiment of a lower portion of a piston rod and its
connection to a mooring weight.
Fig. 5 shows an embodiment of a lower portion of a piston rod and its
connection to a mooring weight, with the addition of a strut between the piston rod
and the U-joint.
Fig. 6 shows a connection to the mooring as well as the installation principle
with a wire rope winch. This view is turned 90 degrees from the view of Fig. 4.
Fig. 7 shows an embodiment of the present invention from a short side of a
combined platform.
Fig. 8 shows an embodiment of a lower portion of a piston rod and its
connection to a mooring of another type.
Fig. 9 shows another embodiment of mooring of the embodiment of the
present invention in Fig. 7, seen from a long side.
DETAILED DESCRIPTION OF THE INVENTION
All illustrations of the drawings are for the purpose of describing selected
embodiments of the present invention and are not intended to limit the scope of the
present invention. The present invention concerns a power take-off apparatus to be
used in a Wave Energy Converter (WEC) of the point absorber type. In Fig. 1 and 2 an
embodiment is shown having a cylinder 1 which is attached to a floating platform 2,
either fixed, or preferably, hanging in a free swivel arrangement 3, see also Fig 3. The
swivel 3 may operate in one or more axis. The length of the cylinder 1 can be from 1⁄2
meter, up to more than 40 meters for areas with high waves and occasional monster
waves. The diameter of the cylinder 1 should preferably be around 1/10-1/15 of the
length, if the very occasional monster waves are to be accounted for, but will work
perfectly with other ratios as well. The latter depending on the float area. As a general
rule, monster waves can be up to ten times the normal wave height, meaning in
practical life that on the Atlantic coastline, the available stroke length should be 15
meters in each direction, 30 meters in total. Cylinder total length should then be 35-40
meters. The piston rod length will be of similar length, or more in deeper water. As can
be seen in the figures the float area is many times the cylinder area in order to
increase the pressure in the water pumped to a water turbine 4. Thus, the larger ratio
the more pressure may be achieved. This ratio will depend on the optimum
combination of flow and pressure to the specific tubine(s) selected for the specific
installation, as well as the wave heights in the specific location.
The material of the cylinder 1, piston 5, piston rod 6 and strut 8, can be of several
options, such as metal or polymer composite material comprising reinforcing fibres, for
example. Sandwich composites are one good alternative, since it is extremely strong
and thin in relation to weight, does not corrode or break down in salt water, is easy to
produce in various shapes and strengths, as well as being price-worthy. Installation is
also easier due to the lower weight. Above the cylinder 1, a water turbine 4 is
mounted, preferably of the Pelton type or similar principle. The Pelton Turbine has the
advantage of being able to work out of water, as well as giving excellent performance
under a relatively wide range of pressure and flow rate. The lifetime in regular hydro
power stations are more than thirty years. For salt water use, a slightly different grade
of stainless steel should be used, to avoid pitting of the buckets and other parts of the
turbine 4. Adding 2% molybdenum is a common method. Otherwise an off the shelf
turbine concept may be used. The reason for mounting the turbine 4 directly above of
the cylinder 1, is to avoid having any flexible tubes with a more limited lifetime and to
directly use the power of the water pressure in order to decrease power losses. Thus,
the penstocks are hard. Inside the cylinder 1, a piston 5 is present, preferably having
piston rings suitable to work with the chosen cylinder material. As the up and down
strokes mostly will shift direction every 2-4 seconds, plus the speed being 0,5-1,5
meters per second, the piston rings do not have to seal perfectly. This because the
volume and speed of the water will be little affected by a minor compression leakage.
The piston 5 is connected to a piston rod 6, which slides in a bushing 7, at the lower
end of the cylinder 1. The purpose of this bushing 7 is to keep the piston rod steady in
the centre of the cylinder 1. The piston rod 6 is connected at the lower end to a hollow
strut 8 or directly to the upper portion of a U-joint 29. The piston rod 6 is locked to the
strut 8 or U-joint 29 with treads 31 and a locking nut 30, as in figure 4 and 5, or by a
clamshell concept, indicated in figure 1 and 2. Flanges that meet and are tightened by
large bolts, are another option. If a strut 8 and treads 31 is used, it goes inside the
upper portion of the U-joint 29 as depicted in figure 5, see more in below description.
Other solutions, as long as they can be adjusted to relevant location depths and to a U-
joint, are also possible.
The piston rod 6 or strut 8 is in turn connected to a mooring weight 10 standing on the
sea floor, alternatively a screw or rod may be drilled and cemented into the sea floor
rock. A flexible U-joint 23 is mounted between the weight 10 and the strut 8. The
principle of the U-joint being the same as in any socket wrench set or auto-mobile
prop shaft.
As the platform 1 moves upwards with a wave, the cylinder 1 moves with it, while the
piston 5 stands still. The water mass around the piston 5 also stands still. The only
water that moves is the water being compressed and squeezed out of at least one one-
way valve 11 in the lower portion of the cylinder 1, as well as mainly horizontal refill in
the upper portion of the cylinder 1 through at least one opening 19. In other words,
the overwhelming majority of the water is standing still in relation to the surrounding
water, meaning that there will only be minor energy drawn for this work. There can be
one or more one-way valves 11. The pressurized water will flow through the at least
one one-way valve 11 into and upwards in at least one penstock tube 13, in the shown
embodiment two penstock tubes arranged on opposite sides outside the cylinder 1,
parallel with the cylinder 1. It is conceivable to arrange at least one penstock tube 13
inside the cylinder, too, although the piston 5 must be redesigned. At least one spear
valve 12 or another valve with similar cut off/on function, is arranged in an upper
opening of the penstock tube 13, possibly in combination with a separate pressure
valve, and they will open when a specific pressure is obtained. Thus, the water will
flow out of the spear valves 13 at high speed, hitting the buckets of the water turbine
4, driving the turbine at an optimum speed. The spear valve, which controls the
pressure and flow of water hitting the buckets, might have to be slightly strengthened,
as the number of movements will be higher than in regular use. A separate pressure
valve just before the spear valve might be an option to relieve a standard spear valve
of wear and tear. A turbine may operate with fixed nozzles instead of spear valves,
especially if having multiple nozzles, and will therefore use the separate pressure valve
to let pressurized water into an inlet ducting provided around the turbine.
According to a specific embodiment a small electrical water pump 26, combined with a
one way valve, may supply constant water supply at the highest points on the
penstock(s). A supply line 27 may run along the penstock down to below sea level. As
the spear valve and/or pressure valve at the upper opening towards the water turbine
does not close completely airtight, the electrical water pump will avoid air pockets to
form during return stroke. The water turbine 4 is connected to a generator 15. The
connection may preferably be a prop shaft 16. An optional flywheel 14 may be
arranged between the water turbine 4 and the generator 15. The optimum pressure of
the water coming from the penstock 13 will depend upon the size and lifting force of
the floating platform 2, the wave height and wave speed, the cylinder diameter as well
as the resistance in the flywheel 14 and the generator 15. As the pressure will come
onto the turbine 4 with high force during each heave motion, the generator 15 will
experience a rather rapid acceleration force, even if dampened by the flywheel 14.
This may be dampened by a torsion or torque coupling between the turbine 4 and the
generator 15, similar to solutions in wind power applications. As the platform 2 might
be moving in a different pattern than the cylinder 1, a flexible connection to the
generator 15 is needed. This is done by the prop shaft 16, having U-joints 17 in both
ends or near the ends. Preferably a spline 18 is provided in the middle area. In this
way, the U-joints 17 will take care of the frequent and larger movements of the waves
hitting the long side of a rectangular platform 2, while the spline 18 will handle the
smaller movements when waves move the platform from the short side. When the
angle of the U-joints 17 increases, this will have as an effect that the rotation speed
will vary slightly with each revolution. The generator 15 might be prematurely worn by
this, whereby a torsion or torque coupling in connection with the prop shaft, similar to
concepts used in wind power applications. The generator 15 should preferably be
placed in a lower section of the platform 2. It is also possible to mount the generator
15 directly attached to the turbine, given enough room and the extra weight
accounted for. As the strain on the swivel arrangement 3 is so large due to the lift
resistance, the extra weight of a generator will make a small impact.
One option with this solution is to use a vertical axis hydro turbine 4’(the runner wheel
positioned flat), the turbine laying directly on top of the cylinder 1, although with room
for water escape, ref figure 7. The hydro turbine 4' may have from one to several
nozzles, as well as from one to several runners. In this embodiment, the generator 15
may be positioned directly on top of the hydro turbine 4'. In this set up, a flywheel 14
directly below the lower runner wheel, as well as one on top of the generator 15, may
be a practical solution.
When the platform rises, water will need to be refilled in the upper section of the
cylinder 1. This is done through large openings 19 in the upper portion. To avoid fish
and other sea organisms, as well as debris floating in the ocean, filters or screens 20
are installed outside these openings. The size of the filters masking 20 will depend on
the local area. Most likely the filter 20 will be larger than depicted, as the depicted
filter area will slow the water speed. A more cage-like device provided outside the
openings would thereby allow smaller holes, but still allow sufficient flow of water due
to the increased surface size, which again will allow less fragments into the cylinder. A
one-way flapper valve is an additional option, so that there is no filter when blowing
outwards. The position of the holes 19 are relatively high up in the cylinder 1. The
position should be so that more than 95% or so of the wave heights are not affected by
the holes 19. When the waves at seldom time cause the piston to go past these,
efficiency is lost only in this area, while normal performance will be available below.
When the platform 2 sinks down towards the wave trough, water must be refilled in
the lower portion of the cylinder 1. This is done by water first passing at least one filter
or screen 21, then passing at least one one-way valve 22. There can be one or more
one way valves 22. The direction of flow is shown by small arrows in all one way
valves. Also here the filters 21 may be larger in size than depicted, i.e. the total area of
the screen being larger, not to slow down the water and thereby allowing smaller size
masking. This means basically that as long as the masking is of less size than the spear
valve opening, any debris coming into the cylinder, will be blown out through the spear
valve orifice. Most non organic pollutant of any size is normally floating on the surface
or sinking to the bottom, meaning that at typically 20-40 meters' depth, there will be
mostly organic substances, which not will be trapped for long inside the cylinder 1 or
penstock 13. The outside of the cylinder 1 and platform 2 may be coated by antifouling
paint. The dark inside of the cylinder will not attract much organic life to grow.
Competent consultant in this field states that this will be of Pte little or moderate
problem, as the organic life is attracted to lighter areas. Treatment with ceramic
coatings will further contribute positively in favour of less organisms being attracted to
the cylinder walls. The piston may nevertheless have upper and lower scrape rings to
remove residuals that will grow on the cylinder wall. As the stroke length in normal
operation will be much lower than maximum length, residuals in the upper and lower
area may need to be cleaned away at intervals. This might be done by releasing the
joint 23 and move the piston for the whole distance up and down. Having divers doing
it manually is one option as well, for instance with high pressure water. A third option
is to mount an extra scrape piston of small height but the same diameter, in the lower
and upper area, and from time to time move them towards centre. A fourth option
would be movable high pressure water nozzles or robots, steered from the outside by
divers or from remote controls on board.
When the platform 2 sinks downwards, water above the piston will escape through the
large openings 19, with relatively small resistance. This outward blow will contribute to
keeping filters 19/20 clean from debris and residuals.
It is possible to provide overpressure relief valves 24 both in the lower section of the
cylinder 1, as well as in the top section of the penstock 13. The swivel arrangement 3,
as depicted in Fig. 3, is of the same principle as in a boat compass or a gyro. In the
platform 2, there is a wet room with walls 25 depicted in Fig 1. Large bolts with
bearings will be installed in the walls of the wet room 25. These will be bolted to the
frame 3A which then is free to swivel in one direction. Bolts and bearing 3C will be
mounted between the frame 3A and the cylinder 1 as well. The bearings can be on
both sides or either side of the bolt, the principle is the same. In this way, the cylinder
1 is free to move both back and forth plus sideways. The swivel 3 may be provided
according to the solution depicted in the drawing but may also function well with one
bearing on each side of the cylinder, connected to the platform 2, giving freedom of
movement only in one axis.
The wet room will have drainage from the water flow hitting the buckets, by an open
area outside the cylinder 1. As some water might leak into the platform 2 from where
the prop shaft goes through the wet room wall 25, a drainage and possibly a bilge
pump is preferred in this area. A circular deflector plate/disc 40 mounted directly on
the prop shaft, between the pump and the wall 25, will stop most of the water splash
initially. Three walls 28 in sequence with a common lower outlet, behind the plate/disc
29, will further minimise water coming into the inside of the platform 2. Due to gravity
and the consequent curve of the water spray, water splash will often hit one of the
three walls.
As the water depths in the areas relevant for installation will vary, the length of the
piston rod or strut or both needs to be variable. The location depth should preferably
be more than 1.3 times the highest probable monster wave in the relevant area, as
one then will avoid damaging breaking waves, and the water instead will have so called
deep water wave character, at the location. 50 meters or more will be a conservative
figure for the Atlantic coastline.
It is preferred to have a flexible system for adjusting the length of the piston rod 6, the
target being to have the piston 5 approximately in the centre position in low
waves/average wave height. This can be done in several ways. One is by having a
selection of different piston rod 6 lengths available, and mounting the piston rod
directly into an upper portion 29 of a U-joint 23, see Fig. 4. With this concept, the
threaded 31 lower end of the piston rod 6, goes into the upper portion 29 of the U-
joint. A locknut 30 keeps the position static so as not to wear out the treads. A
different option is to have a strut 8, as in Fig. 1, 2 and 5, in between the piston rod 6,
and the upper portion 29 of the U-joint 23. With this solution one will have for
instance only one or two lengths of piston rods 6, but a selection of different lengths of
the strut 8. The threads 31 on the piston rod 6 as well as in the strut 8, may be of
several meters, to further adjust exactly to the desired length. In this option, the piston
rod 6 is screwed to desired position in the strut 8, and tightened with the locknut 30.
The same principle apply applies to the strut 8 and the upper portion 29 of the U-joint
23. The U-joint 23 will as a consequence be of a larger diameter in Fig. 5 than in Fig. 4.
In both options, a lower portion 32 of the U-joint 23, will be attached to the mooring
weight 10 in a practical manner. All above mentioned parts will preferably be installed
before being towed to the final location. At location there will some small movements
due to waves, but being largely helped by placing the platform 2 with the short end
towards the waves. Divers will be in contact with deck crew to position the lower
portion 32 of the U-joint 23, into a block 33, see Fig 6. A wire 34 may run through the
lower portion 29, with a locking nut 35 on the end. (The nut 35 may instead be two
coned halves pressed together around the wire, then positioned in a fitting cone in the
block 33). The nut 35 as well as the wire 34 will be removed after installation. A guiding
bracket 36, with a wire hole in it, will guide the lower portion 29 towards its final
position. A manual wire rope winch 37 will be used to pull the wire. The slight
movement up and down in the waves will further help to position the parts together.
The fitting between the lower portion 29 and block 33 will be tight. When in
approximate position a bolt 38, which is cone shaped, will be hammered in position for
the final fixed setting. A locknut 39 will ensure that the bolt 38 stays in position. Figure
4 and 6 are respectively 90 degrees in relation to the other.
The above are two options for connecting and installing the system in a practical
manner. Other solutions are possible, for instance clamshell, flexible joints and pulleys,
as well as the abovementioned solution with a vertical tower like strut from the sea
floor mooring. One may also omit the strut 8 and the U-joint 23 as depicted, and
instead directly integrate the upper portion 29 of the U-joint 23 in the lower part of
the piston rod. The lower part 32 of the U-joint 23 may also be directly integrated in
the block 33, so as to have less parts. The principle of the patent remains the same.
One option is as well to make the sea floor mooring shaped like a round ball 29
underneath, omitting the joint 23 and instead having the slight rotation forth and back
happen towards the sea floor itself. Instead of using only the sea floor as the ground
for this, susceptible to creating a hole, a concrete or metal floor 30, on which the
round mooring rolls forth and back, would be a possible solution.
At deeper water depths, buckling of the piston rod 6 will be a concern, even with use
of the strut 8 for extension. This may be avoided by having a separate thicker and
more solid rod, extending up from the mooring 10’, thereby heightening the joint 23 to
a more suitable level. This lower rod may have various shape, like for instance a tripod
28, see figure 8. The effect will be of simulating a raising of the seafloor to a lower
depth, using a tower like construction up from the bottom. In this way, one can use
the same length and width of the piston rod 6 for all installation depths, if so wanted.
The main advantage is though that the concept may be installed outside countries
where the waters are very deep, like Japan. In figure 8 the three legs are depicted as
28A, 28B and 28C. They are provided in a triangle position when seen from above. The
moorings 10’will be placed on the seafloor. For towing from construction site to final
location, depth and drag is a consideration. One option is to transport the cylinder 1
and systems lying flat on top of the platform, then having a crane equipped ship lift it
into place.
Another option is to lift the cylinder for instance halfway up for transport, and then,
possible with an on-board crane, lower it into position.
A third option is to have the cylinder 1 floating in the water, at location have it
installed from below. The Pelton Turbine may or may not be in the water as well,
depending of practicality regarding connections for hydraulics and electrics.
Electricity to run the systems can be tapped from the generator and via a converter be
led to a battery, supplying the systems. Alternatively, a small simple wind power unit
may as well supply the battery with sufficient power, as the periods with zero winds at
sea are quite short.
In any technical system, there are risks of parts failing or shearing. Besides the
overpressure valves 24 mentioned above, more safety components may or should be
installed. These may include explosive cartridges or weaker points to break off the
piston rod 6 or the swivel arrangement 3 in case of piston seizing. Similar solutions
could be applied to some of the mooring chains so as to move the platform laterally
from the location, thereby avoiding parts colliding more than necessary in the event of
a shear or parts being stuck. Likewise control features that dumps the pressure via the
overpressure valves 24, either to avoid the maximum bar pressure to be exceeded, or
to totally dump the pressure in case of some defined malfunctions. Warning sensors
connected to fire suppressant systems as well as bilge pumps will be of relevance as
well. Without listing all options, similar conservative set- ups as in shipping and
aviation is what will be needed, especially in the larger and costlier versions of this
platform and power take-off concept.
Claims (13)
1. An apparatus for harvesting energy from waves, of the wave energy converter type being a point absorber, comprising a floating platform, a cylinder connected thereto and arranged underneath the floating platform, and a piston having a piston rod arranged to be connected to a mooring at the sea floor, 5 wherein at least one penstock tube is in fluid connection at a lower end thereof with a lower portion of the cylinder, below the piston, the at least one penstock tube being provided along the cylinder and having an opening at an upper end thereof facing a water turbine arranged above the cylinder, the water turbine being in connection with a generator, wherein the cylinder has at least one opening in the 10 lower portion thereof and provided with a one-way valve arranged to allow water into the lower portion of the cylinder when the cylinder moves downwards and thus the piston moves upwards relative the cylinder, wherein the cylinder has at least one opening in an upper portion of the cylinder arranged to allow water into the upper portion of the cylinder when the cylinder moves upwards and thus the piston 15 moves downwards relative the cylinder, and wherein the upper opening of the at least one penstock tube further comprises one or more adjustable nozzles arranged to regulate the pressure and the speed of water exiting the at least one penstock tube.
2. The apparatus according to claim 1, wherein the cylinder is connected via a 20 swivel coupling to the floating platform.
3. The apparatus according to any one of the preceding claims, wherein a screen is provided in the at least one opening in the upper portion of the cylinder and/or in the at least one opening in the lower portion of the cylinder, respectively.
4. The apparatus according to any one of the preceding claims, wherein the 25 fluid connection between the cylinder and the at least one penstock tube comprises at least one one-way valve arranged to allow water to flow from the cylinder to the at least one penstock tube.
5. The apparatus according to any one of the preceding claims, wherein at least two penstock tubes are provided on opposite sides of the cylinder. <filename>
6. The apparatus according to claim 5, wherein the water turbine is arranged with a horizontal axis of rotation, and wherein the upper openings of the at least two penstock tubes are provided at different levels so that at least one first opening at a first side of the water turbine faces buckets at the top of the water turbine and 5 at least one second opening at a second side of the water turbine faces buckets at the bottom of the water turbine, or vice versa.
7. The apparatus according to any one of claims 1-5, wherein the water turbine is arranged with a vertical axis of rotation.
8. The apparatus according to any one of the preceding claims, wherein a 10 valve with a cut off /on function, such as a spear valve is arranged in the upper opening of the at least one penstock tube.
9. The apparatus according to any one of the preceding claims, wherein a pressure valve is arranged in the upper opening of the at least one penstock tube.
10. The apparatus according to claim 9, wherein the pressure valve is adapted 15 to open when a predetermined pressure is obtained.
11. The apparatus according to any one of the preceding claims, wherein the water turbine is a Pelton turbine.
12. The apparatus according to any one of the preceding claims, wherein a coupling is provided between the water turbine and the generator. 20
13. The apparatus according to any one of the preceding claims, wherein a flywheel is provided between the water turbine and the generator. <filename>
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE1650826-9 | 2016-06-13 | ||
SE1650826A SE540263C2 (en) | 2016-06-13 | 2016-06-13 | Apparatus for harvesting energy from waves |
PCT/SE2017/050623 WO2017217919A1 (en) | 2016-06-13 | 2017-06-12 | Apparatus for harvesting energy from waves |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ749891A NZ749891A (en) | 2021-09-24 |
NZ749891B2 true NZ749891B2 (en) | 2022-01-06 |
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