Ocean Waves & Electrical Energy

Have you ever asked yourself: where can we find more renewable energy? Humankind has found many ways to acquire this type of energy resource. I’m sure you have already heard of wind, hydro, geothermic, and solar energy, but have you ever thought about harnessing the ocean as wave energy? According to the Bureau of Ocean Energy Management, ocean waves have a lot of energy potential. In the measurement of terawatt hours/year (TWh/yr), just one unit of energy could supply approximately 93,850 average U.S. homes annually—the potential recoverable amount of resource that could be obtained from along the U.S. coastal shelf edge is close to 1,170 TWh/yr. Potential recoverable energy refers to the energy gathered from regions that aren’t sensitive due to naval operations or environmental concerns and therefore can provide energy with little to no ecological distress [1]. This is still about one-third of the electricity used in the United States each year [1].

Devices that harness this energy have many wires and cables to transport the electrical power from the device to a storage facility on land. Some of the wires run along the sea floor and must be connected with other wires by a waterproof container, such as a submersible enclosure. Nemaco has many specialty casings for this purpose, such as the IP68 and the NEMA 6P enclosures . These enclosures provide ingress protection—which is a defense against foreign bodies (such as fingers or water) contacting wiring. Nemaco provides custom-design enclosures to maximize the durability of the casings; using materials such as aluminum, stainless steel, and other corrosion-resistant constituents, Nemaco will provide customers the enclosures that will fit their needs.

Types of wave harnessing devices

There are a few types of these “wave harnessing devices” in use or in the process of being made today, four of them suitable to be used on the Outer Continental Shelf, where the most energy can be harnessed. The first device is a Terminator. This contraption is angled perpendicular to the direction of the waves to capture or reflect its energy. Terminators can be on the shore, near shore, or even floating devices. These types of devices work because the water moves a column inside it to force air through an opening connected to a turbine, which generates power [1]. The power then is transported to the shore to be stored in a special type of facility.

The second type of device is what is called an Attenuator. These are long, floating structures that are parallel to wave direction. Waves flex the joints between the segments, which are, in turn, connected to hydraulic pumps to generate power as the waves move across. A transformer then connects a power line to the Attenuator that runs to a junction box on the seafloor. Finally, a subsea cable runs the electricity to shore where it can be stored in a power station, waiting to be used by homes, businesses, or facilities [1]. There has been a recent example of an attenuator in the United Kingdom; there are 10 floating flexible mooring devices in Lewis, Scotland in development by Pelamis Wave Power Limited. Pelamis Wave Power Limited is planning on connecting their device to the grid to supply energy to buildings in Scotland [4].

Another type

Another type of wave energy device is the Point Absorber. This type of device is a floating structure—like a buoy—inside of a fixed cylinder. It generates energy from the bobbing motion of the buoy-like structure in the cylinder caused by waves. This creates either electromechanical or hydraulic energy, which is converted to power stored on the coast. The last type of device is called an Overtopping Device. These contraptions are reservoirs that are filled by waves as they come, giving the holding unit a slight build-up of water pressure—somewhat like a dam. When the water buildup is released from the reservoir, it falls and turns hydro turbines and generates power [1].

There has been a more recent style of wave energy-harnessing device, which is being constructed at the School of Berkeley Engineering. An assistant professor, Reza Alam, worked with graduate student Marcus Lehmann to build a device called the Wave Carpet. The goal is to have a device that could lay on the bottom of the seafloor where it would absorb the energy of the waves—just as a natural seafloor would. The device would have a flexible membrane that moves in response to passing waves, collecting the energy (which is usually passed into the mud that covers the seafloor). To convert that motion into usable power, Alam and Lehmann devised vertical double-action pumps fastened to the membrane. These pumps use the membrane’s motion to power a shore-based turbine that generates electricity [1].

More problem

Another problem that Alam and Lehmann faced was that salt water is highly corrosive. They solved this by building the Wave Carpet of corrosion-resistant materials and operating it far enough below the waterline to avoid destructive surface storms. The Wave Carpet is about 30″ long by 30″ wide by 3–10″ high, making it strong enough to withstand regular and storm waves [1]. Nemaco offers specialty marine epoxy coatings for electrical casings to ensure quality and durability so that devices like these can last as long as the transmission cables they connect to.

The Wave Carpet is only one example among many machines being designed and implemented to obtain clean energy as alternatives to non-renewable sources such as coal and gasoline. These machines can be located near “load centers” (storage facilities for energy and power) to reduce transmission losses [2]. Such devices could help power desalination plants, sewage treatment facilities, and many other systems—reducing the impact humans have on the environment and paving the way for a cleaner, healthier future.

References

[1] Bureau of Ocean Energy Management (BOEM). “Ocean Wave Energy.” <https://www.boem.gov/Renewable-Energy-Program/Renewable-Energy-Guide/Ocean-Wave-Energy.aspx>. March 29, 2019.

[2] Office of Energy Efficiency & Renewable Energy. “How Are Ocean Waves Converted to Electricity?” <https://www.energy.gov/eere/articles/how-are-ocean-waves-converted-electricity>. April 19, 2017.

[3] Levy, Tomas W. Berkeley Engineering. “Making Waves: Turning Ocean Power into Electricity.” <https://engineering.berkeley.edu/2016/03/making-waves-turning-ocean-power-electricity>. March 15, 2016.

[4] The European Marine Energy Center LTD (EMEC). “Wave and Tidal Projects.” <http://www.emec.org.uk/marine-energy/wave-and-tidal-projects/>. 2019.