SUBSURFACE DIRECT-DRIVE POWER BUOY
Described herein is a utility-grade power buoy. The device is submerged below the ocean surface and attached to the sea floor. The device is out of view from shore and is able to operate within the Neritic or Sublittoral Zone, i.e., relatively shallow depths from 80 feet to the edge of the continental shelf. The device has an advantage over floating OWC (Oscillating Water Column) point absorbers which are visible and generally use self-rectifying turbines for a power take-off (PTO). In a floating turbine-type buoy, one half of its reciprocating cycle forcefully exhausts compressed air into the atmosphere. The other half cycle draws in a reduced volume of air which is weaker and less efficient. In contrast, a subsurface buoy has a closed air system where the bi-directional air flows are always contained within the buoy. The closed system produces balanced air flows in both directions and eliminates the cyclical atmospheric intake losses seen in floating OWC buoys.
An internal float and vertical shaft within the submerged buoy allows a direct, one-to-one energy transfer from incident waves to the PTO. The direct-drive PTO reacts in real time synchronicity within variable ranges of oceanic wave periods and amplitude. Floating buoys are able to extract a wider range of power within irregular wave domains by using complex reactive phase control or latching methods. With the direct-drive subsurface buoy, a simpler means of getting optimal power capture over a wide bandwidth is achieved by having one of its main components, the Acceleration Tube, made up of conjoined tubes of different diameters and lengths as shown in Figure 1.
The subsurface direct-drive buoy operates on long-established laws of fluid dynamics and the effects of pressure on floating or submerged objects. The buoy's excitation force comes from the pressure differentials between the top and bottom extremities of the buoy. A reciprocating volume of water is vertically displaced by the pressure of passing waves as they crest above the buoy's upper mantle which contains a fixed volume of trapped air. As waves pass over the buoy, the pressure increases at the buoy's upper portion but the pressure at the buoy's lowest point is less effected by passing waves. The differential pressures caused by passing waves creates a cyclic up and down movement of water inside the buoy's Mantle and Acceleration Tubes. The oscillating free surface of water inside the Acceleration Tube causes the Float and Shaft to move up and down. The up and down linear movement is translated to a continuous one way rotational movement of the PTO.
The buoy is a circular, hollow, structure comprised of two vertical axis components. One component, the Mantle, has an opening at its underside. The second component, the Acceleration Tube, has multiple openings at its top and bottom allowing a wide range of response to variable wave spectra. A pocket of air is contained between both components (see FIGURE 1). A precise volume of air is pumped into the Mantle during launch and deployment operations. The set volume of air remains trapped within the structure. When there are no waves, the free surface of water inside the Mantle and Acceleration Tubes are at the same level. When a passing wave crests above the buoy, the pressure differentials between the upper and lower portions of the buoy are altered and this creates a downward force that pushes out the water from the lower openings in the Acceleration Tubes while, simultaneously, water is drawn into the opening at the Mantle. This causes the free surface air/water interface to rise inside the Mantle and lower inside the Acceleration Tubes. When the wave crest lowers, an inverse action takes place which draws water into the Acceleration Tubes and is pushed out at the Mantle opening. This reciprocating cycle causes an internal Float within the main Acceleration Tube to rise and fall in sync with the combined free surface of water inside the interconnected tubes. A Shaft is affixed to the internal Float which extends upward into a sealed PTO and Generator Pod. The sealed PTO and Generator Pod can be removed independently from the main buoy for routine maintenance operations while the buoy itself remains in place.
The direct-drive PTO (see FIGURE 2) mechanically converts the up and down linear action of the internal Float and Shaft into a continuous one way rotary movement. The rotary force spins a flywheel which in turn spins generators or sea water pumps. Alternatively, the PTO can also spin two back-to-back flywheels which can function as stand-alone radial-flux, permanent magnet generators. The PTO was granted US patent 8,745,981. Click HERE to view more details and videos of the PTO.
BACKGROUND OF THE INVENTION:
The current invention is a continuation of the aforementioned patent. In this new iteration (U.S. patent application 62/606,589), the buoy is now disposed below the ocean surface and the turbine is now omitted, using only the mechanical direct-drive PTO. The primary excitation force is now the pressure differentials which act upon the upper and lower extremities of the buoy.
The use of pressure differentials has been employed in various wave energy converter (WEC) designs. A prior art search for subsurface WEC's did find examples that use pressure differential excitation to drive an internal float and shaft. However, none of these early designs specify or claim the type of PTO as disclosed in the present invention.
Examples of prior art subsurface WEC's are: M3 Wave; CalWave Power Technologies; 40South Energy; Bombora Wave Power; an air turbine invention by Seung Kwan Song called SPA-OWC: US 9,518,556 B2; an invention by W.W. Hirsch: US 7,199,481 B2; an invention by Dr. Gareth Stockman called WaveSub: WO2010007418A2 and patents held by Ocean Power Technologies: US 6,768,217 B2, 6,933,623 B2 and 6,768,216 B1.
An example of a prior art surface WEC is the WaveEL developed by the Norwegian company Waves4Power. Like the subsurface design described herein, Waves4Power uses a float and shaft inside an Acceleration Tube to power their direct-drive PTO. But, unlike the present device, their direct-drive is an hydraulic PTO. The use of hydraulic fluids at sea gives rise to the possibility of spills or leaks that would pose a threat to the marine environment!
The submerged structure is hidden from view from shore. The primary driving forces are wave-activated pressure differentials between the upper and lower extremities of the submerged buoy. By integrating the patented PTO with a proven subsurface buoy design, a new, greatly improved point absorber has been created. The submerged buoy is protected from heavy seas and, consequently, there is little stress placed on its single-point mooring. The buoy is less expensive to build because the structure can be much lighter than surface-type power buoys. The buoy is vertical and stable with no pitch and surge motions. Being stationary, the device does not require complex and expensive phase-control or latching mechanisms. This is a significant cost saving over surface buoys. The buoy’s internal drive float rises and falls in direct synchronicity to all types of incident wave spectra for optimum one to one power capture. Travel limits of the internal float and shaft, have no abrupt 'end stops' and shock loads due to the measured amount of air contained within the closed system. The design uses multi-length and varied diameter Acceleration Tubes for sensitive energy capture over a wide bandwidth. The direct-drive PTO and its PM, air-cored generators are housed within a sealed pod. The modular pod can be easily removed at sea for servicing. The buoy will scale from a micro grid to utility-grade sizes. The direct-drive PTO is versatile: it can also spin centrifugal pumps to deliver water to onshore storage tanks. The stored water will drive generators to power desalination plants. The PTO’s one way flywheel(s) maintains momentum at the top and bottom of each wave cycle for a smooth and sustained power output.
About John Hanna, (DBA WETGEN): Navy veteran. Coast Guard documented mariner. Former skipper of the research vessel 'Ed Ricketts' for California State University's Moss Landing Marine Laboratory. Mr. Hanna has twenty eight years experience in QA/QC management on multi-million dollar government and private sector projects for structural steel and welding. WETGEN has been a licensed business in the City of Coos Bay, Oregon since 2010 (No. 9098). WETGEN is registered with Dun & Bradstreet. Contact via LinkedIn.