NREL researcher to patent novel wave energy device design

National Renewable Energy Laboratory’s (NREL) researcher Scott Jenne has designed an inflatable wave pump device that could lead the way to affordable wave energy of the future.

An image of Jenne's inflatable wave pump design (Courtesy of Josh Bauer, NREL)
Jenne’s inflatable wave pump design (Courtesy of Josh Bauer, NREL)

Said to be able to withstand large hydrodynamic loads, requiring minimal installation and maintenance to boot, the inflatable wave pump can absorb wave energy through varying pressures at or below the water’s surface, according to NREL.

The device absorbs energy via the pressure distributed around the flexible body and transfers the energy into a single location that is easy to harness – in this case, the diaphragm.

The design employs inexpensive materials, such as rubber or rubber-coated fabrics, to take the place of the more expensive, and hard to transport, rigid materials such as steel and composite structures.

A diaphragm with a spring stiffness is central to the design of wave pump. The system transfers energy, in the form of air pressure, into this diaphragm, which operates as a positive displacement pump. The spring stiffness of the diaphragm provides the restoring force needed to complete the cycle.

When a wave passes over the submerged device, it compresses the air chamber and expands the diaphragm, which pushes water out of the device through a one-way check valve.

When the pressure in the chamber is reduced, the spring on the diaphragm pulls water back into the device through another check valve while simultaneously re-inflating the air chamber so that the process can start again, according to NREL.

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Aside from Jenne, another NREL researcher Yi-Hsiang Yu co-invented the device. Together, the researchers developed the first iteration of the device, which later underwent modeling and validation efforts that helped move the wave energy device concept from prototype toward patent.

The researchers evaluated the design in three different sizes (1 m, 10 m, and 20 m in diameter) and assessed the device on the grounds of potential energy extraction and tuning parameters.

The analysis that followed found that the inflatable wave pump performed similarly to the traditional point absorber wave energy devices, while providing additional tuning parameters, according to NREL.

Specifically, tuning the spring rate and air volume enables additional controllability for different sea states, instead of relying on active power take-off control or adding mass to this system, as would be the case with traditional devices, NREL stated.

The device design was guided by key areas currently impacting the affordability of wave energy: load shedding, manufacturability, and installation.

According to NREL, Jenne’s concept also improves upon current point absorber designs in the context of maintenance and operations.

These added benefits suggest there may be opportunities for this device to satisfy a broad variety of market applications.

The potential applications for this innovative new device are vast – from desalination to small-scale shallow water installation, to near-shore operations and more.

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