A new Stevens effort, supported by the U.S. Department of Energy, will leverage innovative engineering and design ideas that could finally produce a breakthrough technology for generating electric power from waves.
"We are aiming to design a floating, oscillating surge wave-energy converter that generates 100 kilowatts," explains Stevens professor and Davidson Lab director Muhammad Hajj, who was recently awarded $1.8 million by the DOE to design a prototype to generate energy from wave motion, in collaboration with Virginia Tech and private firm Resolute Marine Energy (RME).
"Deploying a device such as the one we propose could power floating marine observatories; nearby coastal industrial facilities, schools or hospitals; or be tapped during blackouts or other emergencies for reserve power," says Hajj. "Arrayed in a wave energy farm, the devices could also be used for utility-scale power generation."
He believes the updated technology will be ready for use in off-grid applications within five years.
"The right device could be a huge game-changer for renewable energy," he says.
Novel designs, energy converters, electronics and moorings
Ocean waves have been studied since the 18th century for their potential to cleanly, sustainably produce energy. It has been estimated that wave power could supply up to one-half the United States' electricity needs if fully deployed. Unlike wind or solar power, waves are produced continually, 365 days a year, and they contain high power density.
Still, a specific scalable technology that can ride constantly changing waves and generate power with high efficiency and consistency has not yet emerged.
But now Hajj's team is bringing several innovative innovations to existing wave-harvesting technology.
The device consists of a large flat platform, moored to the sea bottom, riding passing waves. A pair of flaps atop the platform are pushed and oscillated by each successive wave, turning a generator and producing energy that can be stored, used on site or transmitted ashore via undersea cables.
Hajj's team proposes an enhanced design whereby the flaps on each platform are spaced, designed and controlled to operate out of sync with one another — increasing the amount of energy generated, while also enhancing the platform's stability.
Another innovation involves an improved design of the generator's power takeoff (PTO) system, which converts the kinetic energy of waves into electric power.
The oscillatory motion must be converted to unidirectional rotation to obtain maximum efficiency," explains Hajj. "We are working with Dr. Lei Zuo at Virginia Tech to design and test an innovative, controllable motion rectifier that will effectively convert the irregular oscillatory motion of the plate into a steady unidirectional rotation.”
The team will also redesign the mooring platform and create new electronic controls for the system; flaps will be automatically controlled by algorithms that operate specially designed mechanical components, continually reorienting direction and position for maximal power capture. (DOE provided an additional $400,000 to the National Renewable Energy Lab and Sandia National Lab to support Hajj's team in the system design and control.)
Safety mechanisms — such as the ability to lock down flaps in high seas — are being considered in the designs, as well, to extend the platform's life at sea to up to 20 years.
Testing on the Stevens campus
Once assembled, the Stevens-developed prototype will be half the size of the final, envisioned commercial design — yet still quite large: even at half-size, the platform will be roughly 150 feet long and 40 feet wide; each flap will be 35 feet long and 25 feet wide.
Preliminary calculations indicate the new design could double the energy-capturing surface area of each unit, while reducing a unit's energy generation cost — known as LCOE — by 40% and also shrink the variability of power generated between high and average periods by 50%.
"Reducing LCOE in particular is very important if we are going to see wave-energy converters commercialized and going mainstream," points out Hajj. "We believe we can accomplish this, and we will find out soon."
The team will also optimize the spacing and geometry of the two flaps on the device for maximum efficiency and platform stability.
"This means that individual platforms are designed, built and tuned for optimal energy generation depending on the location. That's important because coastal Pacific waves, coastal Atlantic waves, North Atlantic waves and open-ocean waves all have different characteristics,” notes Hajj.
During the initial phases of the project, as Virginia Tech and RME continue refining power generation, control and other electrical components of the system, Stevens' historic Davidson Lab will be used to analyze a scaled-down version of the prototype and test hydrodynamic designs in the lab's leading-edge wave tank.
"We already have a history of testing wave-power generators among other marine systems in the Davidson Lab," concludes Hajj. "It's exciting to continue this important tradition and support renewable energy generation."