New Wave of Interest: Harvesting Energy from the Ocean
Stevens researchers design improved wave-energy generators, potentially the most efficient ever developed
As global interest in clean, renewable energy sources increases, a new Stevens research effort is gaining rapid momentum: the generation of electric power from a familiar — and carbon-free —source.
"We are aiming to design a floating, oscillating surge wave-energy converter that generates 100 kilowatts," says Stevens professor and Davidson Lab director Muhammad Hajj, who has been awarded $1.8 million by the U.S. Department of Energy in support of his designs for a prototype that can generate energy from wave motion.
"This sytem could power marine observatories; coastal industrial facilities, schools and hospitals; or be tapped during blackouts or other emergencies for reserve power," continues Hajj, who is collaborating with Virginia Tech and the private company Resolute Marine Energy (RME) in the research. "Arrayed in a wave-energy farm, the devices could also be used for utility-scale power generation."
Hajj recently testified before the New Jersey Legislature that just one meter of wave height, harvested continuously for energy, could power a single home for a full year. He believes improved technologies to do so will be ready for use in off-grid applications within in as little as five years.
"The right device could be a huge game-changer for renewable energy," says Hajj.
Novel design, electronics, hardware
Ocean waves have been studied since the 18th century for their potential to sustainably produce energy. Unlike wind or solar power, waves are produced continually, 365 days a year, and they contain high power density. They also don't require the use or clearing of land, and by some estimates wave power could supply up to half of the United States' electricity needs if it were fully deployed.
Yet a dominant, scalable technology that can ride waves and generate power with high efficiency and consistency over time has never emerged.
Now Hajj's team is experimenting with several innovations to existing technologies.
One prototype device in development consists of a large platform, moored to the sea bottom, which rides 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 is developing an enhanced design in which the flaps are designed and controlled to operate out of sync with one another — increasing the amount of energy generated, he has found, while also enhancing the platform's stability.
Another innovation involves improvements in so-called power takeoff (PTO) systems, which convert the kinetic energy of waves into actual 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 develop new mooring platform designs and new electronic controls for the system. Flaps will be automatically controlled by algorithms that operate specially designed mechanical components, continually reorienting their direction and position to maximize the power harvested. The DOE has provided an additional $400,000 to the National Renewable Energy Lab and Sandia National Lab to support Hajj's team in system design and control for these aspects.
Safety mechanisms — such as the ability to lock down flaps in high seas — are also being considered in the designs in order to extend the platform's life at sea to up to 20 years.
Testing on the Stevens campus
Once assembled, the Stevens prototype will be about half the size of the envisioned commercial design. Yet it will still be quite large, roughly 150 feet long by 40 feet wide. Each individual flap, alone, will be 35 feet long by 25 feet wide. Preliminary calculations indicate this new design could double the energy-capturing surface area of each unit, while reducing a unit's energy generation cost — known as its LCOE — by 40% while significantly reducing the variability of power generated between high and average periods.
"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 stability.
"This means 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,” says Hajj.
During initial phases of the project, 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," notes Hajj. "It's exciting to continue this important tradition and support renewable energy generation."