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Source: US National Renewable Energy Laboratory

Nov. 18, 2020

Simple solutions: Jenne’s inflatable wave pump design could lead the way to affordable wave energy of the future. Image by Josh Bauer, NREL

Sometimes innovation comes from unlikely places—and tomorrow’s game-changing wave energy device may have just been born out of a Colorado garage.

As a potential renewable energy source, wave energy holds promise nearly as immense as the sea itself. For this exciting new technology to make waves in our future energy generation mix, though, the math must add up.

National Renewable Energy Laboratory (NREL) researcher Scott Jenne may have inched the industry a bit closer to the affordable wave energy of the future with his design for a reliable, easily transportable, inflatable wave pump that can withstand large hydrodynamic loads and requires minimal installation and maintenance to boot.

From Prototype To Patent

Jenne’s journey began around a whiteboard with NREL researcher and co-inventor Yi-Hsiang Yu. Together, they brainstormed initial configurations and modeling techniques. Jenne then set to work in his own garage, where he built the first iteration of the device in his free time to verify some of their early assumptions.

The resulting prototype allowed Jenne to secure an Accelerating Inventions to Market (AIM) award from NREL’s Technology Transfer Office. The grant funded the initial modeling and validation efforts that helped move his wave energy device concept from prototype toward patent.

Yu’s expertise in numerical modeling was crucial in developing an initial frequency domain model that the team used to appraise this specific technology. They evaluated the design in three different sizes (1 meter [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. 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. These added benefits suggest there may be opportunities for this device to satisfy a broad variety of market applications.

Ordinary Materials; Extraordinary Potential

NREL is investigating the use of an array of materials for marine energy, including recyclable composites and flexible material distributed energy converters.

Built from low-cost, flexible materials, the inflatable wave pump can absorb wave energy through varying pressures at or below the water’s surface. This 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 this unique design. 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.

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The above animation video demonstrates the inflatable wave pump in action. Credit: Josh Bauer, NREL

Designed for Affordability

The device design was guided by key areas currently impacting the affordability of wave energy: load shedding, manufacturability, and installation. Jenne’s design differs from other point absorber wave energy devices in several regards:

  • Easily transportable and installable: The pumps can be deflated and transported via land or ship, reducing risks associated with more traditional installations, as is the case with current wave energy converters (WECs). Moreover, because the inflatable pump is both lighter in weight and volume than many other WECs, transportation and maintenance costs can be drastically reduced. Because of their ease of movement, the inflatable pump can be manufactured anywhere and shipped, as opposed to massive WECs, which are oftentimes so large and difficult to move that they must be built at select shipyards that are able to handle the large structures.
  • Improved manufacturability: Jenne’s design takes advantage of current manufacturing expertise, exploiting the substantial knowledge base around the development of products such as rigid inflatable boats, as well as water- and airtight materials. He also ensured that every part of the device could be produced using existing technology and expertise without the need for fabrication at specialty shipyards—a huge benefit of this design—which has the potential to drastically reduce manufacturing time and costs.

Jenne’s concept also improves upon current point absorber designs in the context of maintenance and operations:

  • Ability for load shedding: Load shedding is an essential feature to regulate damaging forces against a wave energy device, and it is key to preventing damage or system failure, as well as keeping material costs low. NREL Researcher Nathan Tom and the NREL wave energy team have carried out seminal research on the topic, creating a Venetian blinds-like concept to aid WECs in load shedding.
    The inflatable wave pump structure can enable load shedding techniques that are otherwise impossible with rigid body WECs, such as the use of pressure relief valves to dissipate energy during extreme wave conditions. This, in turn, can reduce required design loads (the maximum amount of forces a device must withstand), translating to less expensive structures.
  • Minimized points of failure: The inflatable pump design eliminates the need for mechanical seals, which are a common point of failure in fluid power systems, replacing them with longer-lasting static seals.
  • Increased reliability: By eliminating the many moving parts that could be required in other types of wave energy devices, the inflatable wave pump has the opportunity to improve overall system durability and reliability.

Shaping Up To Ship Out

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

In the future, Jenne’s team aims to secure additional funds for further device modeling and testing. The team would like to focus on fine-tuning the spring mechanism, producing concepts that can perform well in compact configurations. The team would also like to move their work from the lab to a few steps closer to the sea with a tank validation of the inflatable wave pump.

The NREL team hopes that the advancement of this device can help future marine energy developers, allowing them to build off the resulting data and use the device and lessons learned from its development as a baseline to advance future wave energy concepts.

Learn more about the groundbreaking inflatable wave pump and NREL’s marine energy research.