Abstract:
A wave power converter employing independently staged surge energy capture for converting useful wave surge energy to electric power over a relatively broad range of surf conditions. The wave surge power converter includes an inclined ramp with several openings for receiving wave water into several independent chambers for capturing and retaining surge water in hydraulic isolation, a check valve in each chamber permitting water to flow into a conduit and a generator for producing electrical power from water flow in the conduit. The apparatus is suitable for low-cost manufacture, offers simple robust operation suitable for underdeveloped regions of the world, may be fabricated from commonly-available components, requires few moving parts and no valuable (lootable) components other than a generator, and is self-flushing for low maintenance operation.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to a wave power converter and more particularly to a wave power converter employing a plurality of independent water chambers to capture both vertical and horizontal components of surge energy from overtopping waves. 
   2. Description of the Related Art 
   Wave power as a means of generating electricity has been the focus of low-key study in the US and Europe for over thirty years, but with little public support. Wave energy flux arises primarily from wind friction at the sea surface and is entirely distinct from the diurnal flux of tidal energy arising from the lunar cycle and from the steady flow of the major ocean currents arising primarily from the several solar heating and cooling cycles. Wave power generation is not a widely employed technology. The world&#39;s first commercial wave energy conversion farm, the Aguçadora Wave Park in Portugal, was established in 2006. Public interest in this carbon-free power source is now growing because of recent public concern over the accumulating effects of atmospheric carbon loading on world climate. 
   Ocean waves are generated from a portion of the wind energy coupled to the ocean surface over large areas and the available wave energy in a local region is greater than the solar and wind energies available in the same area. Wave energy available from U.S. coasts alone exceeds the entire U.S. production of coal-fired electrical power, constitutes a perpetual, renewable energy source, and is perhaps the only carbon-free energy source suitable for replacing carbon-based power production on a very large scale without concomitant environmental effects. 
   The prior art is replete with wave power conversion proposals. Wave power conversion devices may be generally categorized by the choice of energy capture method used to capture the wave energy. They may also be categorized by choice of location and by choice of power extractor. Types of energy capture methods well-known in the art include point absorber or buoy; surfacing and following or attenuator; terminator with perpendicular alignment to wave propagation; oscillating water column; and overtopping. Location types well-known in the art include shoreline, near-shore and offshore. Well-known types of power extraction systems include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. 
   For example, in U.S. Pat. No. 4,622,471, Schroeder proposes a terminator system using a plurality of units with unidirectional intake gates disposed horizontally at one elevation to operate independently to capture wave surges upstream from an input penstock. They are adapted to intercept waves and convert their kinetic energy to drive a turbine. Each gate unit includes a horizontally-hinged movable gate adapted to permit the incoming waves to slide over the upper surfaces of the gates and into the penstock. The penstock back pressure operates to push each gate upward to direct the remaining forward moving wave energy to a higher elevation, thereby increasing the water head in the penstock. Schroeder controls the penstock head by applying the same penstock back pressure to every gate unit, which are accordingly hydraulicly coupled to one another (not in hydraulic isolation). Schroeder neither considers nor suggests adapting his wave power converter to an overtopping method that retains the captured water at different head pressures in a plurality of substantially isolated chambers each coupled to a penstock, some by way of a check valve. 
   As another example, in U.S. Pat. No. 7,040,089, Andersen proposes an overtopping wave power station device of the kind where the waves flow up a ramp provided with fixed openings arranged so that little of the water flowing up the ramp flows down through the openings and water flowing down the ramp flows down through the openings and into storage reservoirs positioned below the ramp and extending horizontally at various elevations. Andersen couples each storage reservoirs to an associated penstock and turbine intake. All turbine outlets are coupled together, thereby equalizing the head pressures. Andersen relies on ramp intake closing devices to reduce water and head losses at the ramp openings to the lower storage reservoirs and neither considers nor suggests adapting his overtopping wave power converter to retain the captured water at different head pressures in a plurality of substantially isolated chambers each coupled to a penstock, some by way of a check valve. 
   Normally, the relation between output and investment grows advantageously with the size of the plant. In many cases, it pays to build large plants. However, a large rotating machine, such as a turbine equipped with a generator, costs more than a number of smaller machines with a corresponding total capacity. Complex systems such as hydraulic control systems, are not well suited to incremental implementation (do not scale up well), and have high costs and risks associated with large installations. 
   Traditionally, low head water turbines have been of an open type, as exemplified for example by conventional water wheels, and have had extremely low efficiency. Conventional power generation turbines such as Francis turbines, Kaplan turbines and Peleton turbines traditionally require high heads of water to generate the water pressure and velocity required to move the turbine blades. Such arrangements require large high dams, additional flumes and the like, requiring massive capital expenditures. A more efficient class of turbines, such as the Root Turbine, for example, can be economically constructed to operate at the higher efficiencies suitable for low head electric power generation applications requiring closed turbine systems to maintain siphon. 
   Another well-known challenge is to provide a wave power converter able to tolerate the sometimes volatile conditions of the sea surface. Some practitioners suggest selecting installation sites where the average waves are similar in scope to the extreme waves. Also, the wave power converter must withstand a major storm while also operating with acceptable efficiency during average wave conditions. 
   These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below. 
   SUMMARY OF THE INVENTION 
   This invention solves the above described problems by introducing for the first time a wave power converter having means for the independently staged capture of wave surge energy vertical and horizontal components from a broad range of wave conditions to facilitate a stable supply of hydraulic head pressure for conversion to electrical power. 
   It is a purpose of this invention to provide wave power converter apparatus employing independently staged surge energy capture for converting useful wave surge energy over a relatively broad range of surf conditions, including relatively calm surf conditions and abnormally higher surf conditions. It is an advantage of the independently staged surge energy capture apparatus that some energy may be captured from low surf and more energy may be captured from higher surf without the need for adjusting the apparatus. It is a feature of the converter of this invention that the disposition of the independent chambers are disposed to capture and convert a significant amount of the horizontal surge kinetic energy component into potential energy in the form of elevated hydraulic head. 
   It is another purpose of the invention to provide a wave surge power converter suitable for low-cost manufacture and simple robust operation in underdeveloped regions of the world. It is an advantage of the apparatus of this invention that it is suitable for fabrication from low-cost commonly-available components. It is another advantage of this invention that the power converter apparatus has few moving parts, has no valuable (lootable) components other than a generator, is self-flushing and requires little maintenance. 
   In one aspect, the invention is a wave surge power converter having a ramp with an inclined surface providing several openings for receiving wave surge water when a wave surges up the inclined surface; several independent chambers each located under an associated ramp opening for capturing the received wave surge water and retaining the captured water in substantial hydraulic isolation from the other chambers; a conduit having an exit; a check valve disposed within each of one or more chambers to permit water flow into the conduit from the chamber responsive to a hydraulic pressure difference across the check valve; and a generator for producing electrical power from a flow of water in the conduit arising from a hydraulic pressure difference between the conduit and the exit. 
   The foregoing, together with other objects, features and advantages of this invention, can be better appreciated with reference to the following specification, claims and the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, in which like reference designations represent like features throughout the several views and wherein: 
       FIG. 1  is a diagram illustrating a perspective view of a preferred embodiment of the wave surge power converter apparatus of this invention; 
       FIG. 2  is a diagram illustrating a side cross-sectional view of the apparatus of  FIG. 1 ; 
       FIG. 3  is a diagram illustrating an exploded perspective view of a preferred check valve embodiment suitable for use with the apparatus of  FIG. 1 ; 
       FIG. 4 , including detail  FIG. 4A , is a diagram illustrating a front view of the apparatus of  FIG. 1 ; 
       FIG. 5  is a diagram illustrating a rear view of the apparatus of  FIG. 1  with the tail-wall removed to expose the interior of the rear chamber; 
       FIG. 6A  is a diagram illustrating a side cross-sectional view of an alternative embodiment of the wave surge power converter apparatus of this invention showing exemplary check valve dispositions during normal flow conditions; 
       FIG. 6B  is a diagram illustrating a side cross-sectional view of the wave surge power converter apparatus of  FIG. 6A  showing exemplary check valve dispositions during abnormal back-flow conditions; and 
       FIGS. 7A-B  are schematic diagrams illustrating a top view of an illustrative transmission embodiment suitable for use with the apparatus of  FIGS. 6A-B  under the two exemplary flow conditions illustrated in  FIGS. 6A-B . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1  illustrates a preferred wave surge power converter embodiment  10  of this invention, showing the inclined ramp  12 . During operation, converter  10  is preferably disposed at an ocean surface  14  having episodic wave surges generally oriented in the direction indicated by the arrow  16  such that a typical wave surges vertically generally along the vertical surge component  18  and horizontally generally along the horizontal surge component  20 . Ramp  12  is shown with a slope of about 33% (17-18 degrees) and is preferably oriented generally along surge direction  18  such that the wave surge water moves up ramp  12 , progressing along a series of openings  22 A-D therein. Each of openings  22 A-D that are thereby exposed to the wave surge then receives surge water into the associated one of the plurality of independent chambers  24 A-D. Each of the first independent chambers  24 A-C is substantially isolated hydraulically from its neighbors by means of a single check valve (described below in connection with  FIGS. 2 ,  3  and  6 A-B) disposed in the associated one of the plurality of drain assemblies  26 A-C. No check valve is required in drain assembly  26 D for the final chamber  24 D because the hydraulic head in chamber  24 D is made equal to the hydraulic head in conduit  28  for reasons described in more detail below. As may be readily appreciated from this description, any surge water captured within each chamber  24 A-D flows down by gravity through the associated drain assembly  26 A-D into a plenary conduit  28  and out into the ambient ocean  30  through the draft tube  32 . This flow of captured water from each of one or more chamber(s)  24 A-D through the associated drain assembly  26 A-D into conduit  28  and out draft tube  32  arises from the hydraulic pressure difference between at least one chamber(s)  24 A-D and ambient ocean  30  and may be employed to turn a low-head turbine (not visible, see  FIGS. 2 ,  5  and  6 A-B) within conduit  28  that is coupled by means of, for example, a shaft  34  to a generator  36  for generating electrical power. The substantial hydraulic isolation of chambers  24 A-D is an important feature of converter  10  for reasons that are described in more detail below. Another important feature of converter  10  is the grill  38  or “trash rack” formed from a plurality of slats, exemplified by the slat  40  ( FIG. 4A ), disposed over openings  22 A-D to prevent most floating debris from entering chambers  24 A-D by facilitating the sloughing of debris back into the surf during the relaxation of the wave surges. For clarity, grill  38  is only partially illustrated in  FIG. 1  and actually extends across the entire width of converter  10  to completely cover all of openings  22 A-D. 
     FIG. 2  is a diagram illustrating a side view of converter  10  disposed in an exemplary operating position under a pier  42  by means of, for example, the two structural supports  44 A-B. The disposition of the closed low-head turbine  46  may also be seen in draft tube  32  and the disposition of each of the plurality of check valves  48 A-C may be seen in the associated drain assemblies  26 A-C. For example, check valve  48 A operates to prevent water flow from conduit  28  to chamber  24 A in the following manner.  FIG. 3  illustrates an exploded perspective view of an illustrative embodiment of check valve  48 A, which exemplifies any of the plurality of check valves  48 A-C. During operation check valve  48 A is oriented with respect to gravity as shown by the gravity arrow  50 . A float ball  52 A is retained within a drain pipe  54 A between a lower sieve plate  56 A and an upper valve seat  58 A so that, when hydraulic pressure at the bottom of chamber  24 A exceeds the hydraulic pressure in conduit  28  ( FIGS. 1-2 ), water flow urges float ball  52 A away from valve seat  58 A, thereby permitting water to flow downward through drain pipe  54 A and through sieve plate  56 A into conduit  28  ( FIGS. 1-2 ). Should the hydraulic pressure in conduit  28  equal or exceed the hydraulic pressure at the bottom of chamber  24 A, then check valve  48 A closes to prevent any water flow in the upward direction because float ball  52 A urges against valve seat  58 A, thereby closing off all flow in drain pipe  54 A. These elements of check valve  48 A are suitable for simple and inexpensive manufacture for robust performance. For example, valve seat  58 A and drain pipe  54 A may be embodied as simple sections of PVC pipe, float ball  52 A may be embodied as a simple rubber sphere (e.g., a ball), and sieve plate  56 A may be embodied as a simple plastic drain sieve, for example. 
   Returning to  FIG. 2 , the hydraulic chamber independence feature of converter  10  is now described. From  FIG. 2 , it may be readily appreciated that the hydraulic head within conduit  28  generally approaches but cannot exceed the highest of the independent chamber hydraulic heads  57 A-D within chambers  24 A-D. Hydraulic heads  57 A-D illustrated in  FIG. 2  exemplify a snapshot of the relationship among chambers  24 A-D typically resulting from the cumulative capture of water from various wave surges overtopping ramp  12  and encountering openings  22 A-D ( FIG. 1 ) and an unchecked flow of water from chamber  24 D down and out through drain assembly  26 D to conduit  28 . Accordingly, check valve  48 A is illustrated as operating to check water flow through drain assembly  26 A from chamber  24 A into conduit  28  because hydraulic head  57 A (the water level) in chamber  24 A is illustrated to be less than hydraulic head  57 C (the highest chamber water level) within conduit  28 . Similarly, check valve  48 B is illustrated as operating to restrict water flow through drain assembly  26 B from chamber  24 B into conduit  28  because the water level (hydraulic head) in chamber  24 B is illustrated to be less than the hydraulic head within conduit  28  but greater than the hydraulic head  57 A in chamber  24 A. Finally, check valve  48 C is illustrated as fully open to permit unchecked water flow through drain assembly  26 A from chamber  24 A into conduit  28  because hydraulic head  57 C (the water level) in chamber  24 C is illustrated to be the highest chamber water level, which is equal to the hydraulic head in conduit  28  unless incoming wave surges fill chamber  24 D. No check valve is required in drain assembly  26 D for the final chamber  24 D because the hydraulic head in chamber  24 D is always equal to or less than the hydraulic head in conduit  28  and final chamber  24 D operates as a surge chamber for the remaining chambers  24 A- 24 C to moderate hydraulic head fluctuations and temporarily store water not immediately flowing through conduit  28  to turbine  46 . The relatively large volume of chamber  24 D contributes to the maintenance of a steady useable flow and generation of power therefrom. 
   From the above, it may be readily appreciated that the primary flow through conduit  28  results from the chamber having the highest hydraulic head (water level). As the highest-head chamber drains and approaches the head of neighboring independent chambers, these begin to flow into conduit  28 , thereby maintaining the water flow through turbine  46  necessary for effective power generation. As illustrated in  FIG. 2 , unchecked chamber  24 D is prevented from flowing only by the back-pressure from conduit  28  from the higher hydraulic head  57 C in chamber  24 C. As hydraulic head  57 C falls, hydraulic head  57 B begins to flow, followed by hydraulic head  57 D, and finally by hydraulic head  57 A. This staged capture and flow procedure exemplifies the operation of convertor  10  of this invention. Because chambers  24 A-D are disposed in substantial alignment with horizontal surge component  20  ( FIG. 1 ) and openings  22 A-D are disposed at different elevation along vertical wave surge component  18 , each chamber  24 A-D will capture water from certain wave surges and not from others; but the staged capture and flow operation ensures a steady useable generation of power therefrom. Because turbine power output increases proportionately to the product of hydraulic head and flow rate, converter  10  is suitable for operation at low hydraulic pressure differences and high flow rates. This is advantageous because the mass and velocity of incoming wave surges tends to limit available hydraulic head but flow volume is limited only by the scale of converter  10 , which may be scaled up in either horizontal dimension to any useful size and number of isolated chambers. 
     FIG. 4  illustrates a front view of converter  10 , showing the entire embodiment of grill  38  and detail  FIG. 4A  illustrates a cross-sectional view of a useful embodiment of slat  40 , showing the upper surface  60  to be larger than the lower surface  62 . This trapezoidal cross-section facilitates trash rejection without significant reduction of water capture when slats of this cross-section are arrayed to form grill  38 . Moreover, the narrow separations urge the incoming wave surge water further up ramp  12  before capture, thereby converting a significant amount of the horizontal surge kinetic energy component  20  into potential energy in the form of elevated hydraulic head. This improved conversion of horizontal kinetic energy into stored potential energy is an important feature of the converter of this invention. Although ramp  12  is illustrated as having a single linear slope from end to end, an alternative ramp embodiment (not shown) having a concave or convex curved surface whose elevation varies non-linearly from end to end may be useful for optimizing kinetic to potential energy conversion in various alternative ocean conditions. 
   During operation, as described above, converter  10  continuously captures and converts the surge kinetic energy component into stored hydraulic head. This stored potential energy is then converted to electrical energy by releasing the stored water through closed low-head turbine  46 . The combined storage volume of independent chambers  24 A-D is balanced with the flow rate exiting from draft tube  32  to facilitate continuous stable rotation of closed low-head turbine  46  and the coupled electrical generator  36 , thereby providing a steady supply of electrical power from episodic wave surges. 
   The theoretical relationship between the surge kinetic energy KE in joules and the resulting stored potential energy PE in joules (assuming lossless conversion) is expressed by the following:
 
KE= m·v   2 /2 =m·g·h =PE  [Eqn. 1]
 
wherein:
 
   m=Mass of incoming surge water (kg), 
   v=Surge water velocity (m/sec), 
   g=Gravitational constant (m/sec 2 ), and 
   h=Available hydraulic head (m). 
   Eqn. 1 demonstrates that hydraulic head h varies directly with the square of surge water velocity v, making the faster wave surge a more useful source of energy. During operation of converter  10 , surge kinetic energy is converted to potential energy because surge water rushes up grill  38  before draining down into one or more independent chambers  24 A-D. Water held in each chamber is isolated hydraulicly from the other chambers by check valves check valves  48 A-C, which together facilitate a generally evacuated (entrainment air-free) and continuous supply of seawater to turbine  46 . Independent chambers  24 A-D operate to maintain a full flow in conduit  28  by providing a staged reserve supply during wave surge “dry spells.” Turbine  46  rotates responsive to the flow of water from conduit  28  through draft tube  32  and into ambient ocean  30 . Draft tube  32  extends downward to preserve a siphon (suction) head when ocean surface  14  drops below the base of turbine  46 , which contributes to the aggregated hydraulic head powering turbine  46  and thus to the resulting output power from generator  36 . The exit of draft tube  32  must remain submerged to maintain siphon head. 
   Available converter output power is expressed by the following:
 
 HP=Q·h·g·n/C   [Eqn. 2]
 
where:
 
   HP=Power delivered by the turbine (hp) 
   Q=Mass flow rate through the turbine (kg/sec) 
   h=Available hydraulic head. (m) 
   g=Gravitational constant (m/sec 2 ), 
   n=Turbine efficiency (%), and 
   C=Unit conversion factor=746 W/hp. 
   Eqn. 2 demonstrates that turbine output power HP varies directly with hydraulic head h and mass flow rate Q. Accordingly, converter  10  operates at high mass flow rates to produce useful power from low hydraulic heads. The available hydraulic head h is limited by the mass and velocity of the incoming wave surges and mass flow rate Q is limited by the scale of conduit  28  and chambers  24 A-D; that is, by the scale of the structure of converter  10 . 
     FIG. 5  illustrates a rear view of converter  10 , with the tail-wall removed to show the interior of final chamber  24 D and other elements of converter  10  described above in connection with  FIGS. 1-4 . Note that draft tube  32  has a submerged exit, which should be disposed to ensure that the siphon lock between draft tube  32  and ambient ocean  30  is not lost during normal wave action. 
     FIG. 6A  illustrates a side view of an alternative wave surge power converter apparatus embodiment  100  showing the plurality of drain assemblies  126 A-D and exemplary dispositions of the check valves  148 A-C during normal flow conditions, which occur when ocean surface  14  remains below the highest of the independent chamber hydraulic heads  157 A-D while remaining above the exit of the draft tube  132  to maintain siphon head through the turbine  146 . Converter  100  includes a shaft  134  for coupling turbine  146  to a generator  136  but also provides an additional reversible transmission  166  to facilitate uninterrupted power conversion during backflow conditions that are now described. 
   Backflow conditions may arise whenever the ocean surface  114  rises and remains above one or more of independent chamber hydraulic heads  157 A-D so that water is urged up through the draft tube  132 , backing up through turbine  146 , and into the conduit  128 . Backflow operation should not be necessary for most ocean conditions, but converter embodiment  100  is now described as a useful solution to operations in ocean surf states leading to occasional backflow conditions. 
     FIG. 6B  is a diagram illustrating a side view wave surge power converter  100  showing illustrative dispositions of check valves  148 A-C during abnormal backflow conditions that may arise when ocean surface  114  is elevated above the highest one of independent chamber hydraulic heads  157 A-D. During operation, significant backflow up draft tube  132  and turbine  146  causes turbine  146  to reverse direction and rise up, thereby lifting shaft  134  to effect a gear shift in transmission  166 , thereby preventing a polarity reversal in generator  136 . 
     FIGS. 7A-B  illustrate two top views of transmission  166  suitable for use with converter  100  the two flow conditions illustrated in  FIGS. 6A-B .  FIG. 7A  illustrates the gearing arrangement for normal down-flow operation ( FIG. 6A ) wherein shaft  134  turns clockwise, an idler gear  170  turns counterclockwise, and the generator shaft  172  turns clockwise. A ratchet-type mechanism (not shown) may be provided to limit generator shaft  172  to clockwise rotation, for example.  FIG. 7B  illustrates the gearing arrangement for backflow or up-flow operation ( FIG. 6B ) wherein shaft  134  turns counter-clockwise, a first idler gear  170 A turns clockwise, a second idler gear  170 B turns counter-clockwise, and generator shaft  172  turns clockwise. The backflow also lifts the turbine gear on shaft  134  to facilitate its engagement with idler gear  170 A, which is located above idler gear  170  to form, for example, the two-level transmission  166  illustrated in  FIGS. 6A-B . When turbine gear at shaft  134  rises, it disengages from the normal flow gears in  FIG. 7A  and engages the backflow gears in  FIG. 7B . Using two idler gear levels permits generator gear at shaft  172  to rotate counter-clockwise under all flow conditions. 
   As may be readily appreciated from the above description, the wave surge power converter of this invention offers several advantages. For example, other than the turbine and generator elements all converter elements may be embodied to include only concrete, PVC, rubber and neoprene. Such inexpensive and corrosion-resistant materials are well-adapted for this marine application and even better suited to fresh water applications having significant wave surges, such as the shorelines of the Great Lakes. 
   The preferred vertical orientation of the walls separating each of the horizontal array of independent chambers  24 A-D facilitates the capture of the smaller available increments of potential energy, such as a single foot of hydraulic head. A vertical array of horizontal chambers disadvantageously requires larger hydraulic head differentials and cannot capture the smaller potential energy increments available in many surf conditions. For example, the horizontal chambers disclosed in the above-cited Anderson reference (U.S. Pat. No. 7,040,089) cannot capture significant energy from wave surges of less than two feet. Moreover, instead of the multiple load-bearing floors required for a vertical array of horizontal chambers, a single load-bearing chamber floor is sufficient for the converter of this invention. Similarly, instead of the disadvantageously large amount of air entrainment experienced with a vertical array of horizontal chambers as draining water powers a turbine, the converter of this invention entrains a minimal amount of air in water passing through drain assemblies  26 A-D, plenary conduit  28 , turbine  46  and out draft tube  32  to the ambient ocean  30 . 
   During operation of the converter of this invention, hydraulic head is not lost to backflow as it is in a horizontal chamber array, for example, when a new wave fills a lower horizontal chamber while it is also receiving drainage from an upper chamber. This feature of a vertical array of horizontal chambers causes overtopping of the lower chamber; thereby losing captured potential energy to the surrounding ocean. 
   During operation of the converter of this invention, large volumes of water are reserved in independent chambers and remain available to buffer the continuous flow of water to the conduit and the turbine necessary for stable power output; even during a prolonged intermission (dry spell) between wave surges. 
   Clearly, other embodiments and modifications of this invention may occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawing.