Healy Wave Energy, LLC

Technology

 

Overview

The Healy wave energy converter (HWEC) is under development using a scale-up approach incorporating numerical modeling, wave tank testing, and open-ocean testing of a full-scale prototype designed for maximum reliability. It is based on a two-body structure and consists of a flotation buoy (A) rigidly connected to a long vertical inertial tube (B) which is open at the top and the bottom. A piston-rod assembly (C) is enclosed and connected to a PTO mechanism which is driven by the relative motion between the piston and the buoy–inertia tube structure due to the inertia of water within the tube. The PTO consists of an air compressor (D), a dynamic pressure regulator (E), and an air turbine (F) connected to an induction generator supported by a power electronic conversion system. Low operating pressures eliminate the need for traditional seals, allowing instead the use of rolling diaphragms to separate the high- and low-pressure sides of the compressor, and a near frictionless oil-over-water seal on the center shaft. A series of one-way valves rectifies airflow from the compressor and between the regulator and the turbine. The induction generator is operated in either self-excitation mode (using switched capacitors) or external excitation mode (using an inverter) to generate flexible power forms and to maximize the energy yield over a wide range of operating conditions. Hydrodynamic end-stop features (G) significantly reduce end-stop forces, reducing structural costs.

 
 

Wave energy extraction

The Healy device is a two-body heaving point absorber. Wave forces drive the flotation buoy and inertia tube to oscillate in the vertical direction. This results in relative motion between the buoy and the piston. That relative motion drives the pneumatic Power Take-off unit (PTO).

Point absorbers typically achieve a high power-to-weight ratio. However, practical challenges have historically stymied WEC developers. The Healy WEC overcomes traditional challenges in WEC design by combining a number of novel technologies with proven, off-the-shelf solutions borrowed from other industries.

 

Low pressure double-acting piston compressor with rolling diaphragms

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Low pressure double-acting piston compressor with rolling diaphragms

1. Air supply from compressor piston.

2. Turbine / generator.

3. Upper & lower guide Rollers

4. Upper & lower hydraulic shocks

5. Pressure regulator piston

6. Rolling diaphragms

7. Vacuum chambers (4)

One-way valves rectify airflow from a double-acting pneumatic piston. Low operating pressures eliminate the need for traditional seals, allowing instead the use of rolling diaphragms to separate the high- and low-pressure sides of the compressor, and a near frictionless oil-over-water seal on the center shaft.

  • Rolling diaphragms were tested at 34 inches WC 24 hours a day for 2-1/2 years. This is equivalent to 15 years of operation with a 6 second wave frequency. No failure was experienced.

  • The spherical roller bearings supporting the 8” x 8” square piston rod employed for the compressor and the pressure regulator are automatically lubricated to provide 25 years of service in our prototype application per the bearing manufacturer’s review of our application. The same holds true for the turbine generator design per the motor manufacturer.

 

Pressure regulator and high-efficiency turbine

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Pressure regulator and high-efficiency turbine

1. Air supply from compressor piston

2. Turbine.

3. Upper & lower Guide Rollers

4. Upper & lower hydraulic shocks

5. Pressure regulator piston

6. Generator

7. Turbine air flow

8. Turbine cross-section

  • Dynamic pressure regulator helps smooth peaks and troughs in the pressure differential

  • Spherical roller bearings supporting the square piston rod are automatically lubricated to provide 25 years of service

  • Rectified airflow enables the use of a high-efficiency unidirectional air turbine generator automatically lubricated for 25 years service.

 

Variable-ballasted piston with inertia tube

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Upper & lower inertia tubes

1. Flotation buoy base

2. Upper inertia tube

3. Lower inertia tube

4. Neutral buoyancy tank

5. Upper and Lower snubber assemblies

6. Water exit ports

7 . Diver access doors

8. Compressor Piston Rod Assembly

  • Inertia tube encloses a large virtual reaction mass around the piston head

  • Submerged piston head is an adjustable ballast tank.

 

Hydrodynamic end-stop features

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TOP & BOTTOM HYDRODYNAMIC END STOPS.

1. Neutral buoyancy tank

2. Long life, field replaceable polyamide bushings

3. Neutral buoyancy tank air supply pipe

4. Field replaceable polyurethane shocks

5. Flow restrictor holes

  • Shape of inertia tube and piston allows fluid flow around piston when the piston is near its end stops. This reduces fluid loading on piston when approaching end stops and in survival conditions.

 
 

Reliability and serviceability

The Healy WEC is designed with a keen focus on reliability and survivability.

  • Components have proven track record either in industry use or in fatigue testing

  • The system is fully serviceable at sea.