TECH

Ocean energy could be the wave of the futureWave-power systems are the latest in clean, renewable energy

Not just great for surfing, waves may be the next big thing in renewable energy.EPICSTOCKMEDIA/ISTOCK/GETTY IMAGES PLUS

By Alison Pearce StevensMay 30, 2019 at 5:45 am

If the term “renewable energy” brings to mind a sea of solar panels or towering wind turbines,you’re not alone. It’s becoming more and more common to capture energy from the sun andwind. That’s because these “clean” energy sources generate electricity without polluting our air.Just as important is that they don’t release carbon dioxide into the atmosphere. Thatgreenhouse gas traps the sun’s heat and contributes to our changing climate.

But solar and wind power have one big downfall: They’re not always available. The sun onlyshines during the day. Wind comes and goes. There are very few places where wind is constant

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Explainer: What is the electricgrid?

enough to generate electricity all the time. And as easy as it sounds, storing energy for lateruse has proven a major challenge.

But ocean waves? As anyone who’s stayed near a beach can tell you, waves crash onto shoremorning, noon and night. And that makes them ideal for generating energy around the clock.Now scientists are figuring out just how much energy waves could offer.

When wind blows across the surface of water, it creates waves. If you’ve ever seen white capson an ocean or some lake on a windy day, you’ve seen this in action. The wind causes water atthe surface to bob up and down. Even though it seems as though the water is traveling fromone place to another, it doesn’t actually go very far. Rather, it moves in circles — up, up, up tothe top of the wave, then down, down, down the other side.

That’s true, at least, when the water is very deep, such as out in the ocean. Those gentlybobbing waves are called “swells.” But waves change when they get close to shore.

As the water gets shallower, it can’t travel in circles anymore. The ground gets in the way.  Thewater bumps up against the ocean floor, squashing the circle into an oval. Much like a persontripping over something, the water “trips” over the ground. The top part lurches past thebottom. The wave “breaks,” crashing closer to the beach.

Wave energy systems use the water’smovement to make electricity. Some types ofthese devices harness the power of breakingwaves. Others make use of swells. Still othersuse the pressure of waves near the oceanfloor. Yet all have the same goal: Convert wave energy into electrical energy. That electricity canbe used to power the electric grid. That’s the network of cables that transmits electricity tohomes and buildings so we can use it.

Wave power is restricted to areas near the ocean. After all, the cables that carry electricity canonly be so long. But 40 percent of the world’s population lives within 100 kilometers (60 miles)of the ocean. That means a whole lot of lights, TVs and tablets could be powered by waves.

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Explainer: What is a computermodel?

With all that promise for wave power, researchers are testing how well different types ofgenerators convert ocean energy to electricity. Along the way, they’re trying to make sure thatsea life won’t be harmed in the process.

Power where it’s needed

The first step to creating wave power? Figuring out the best place to put those energyconverters.

Not all coastal areas work for generating wave power. The shape of the land beneath the seachanges the size and shape of waves. Wave-energy converters also are costly. The best spotsshould have plenty of wave action, but not so much that converters might be damaged in astorm.

To figure out the best sites, scientists turn tocomputer models. Joao Morim Nascimentoand Nick Cartwright are environmentalengineers in Australia. Both work at GriffithUniversity in Southport, Queensland. Anenvironmental engineer works to reduce pollution and waste. The pair wanted to find goodplaces for wave-energy converters along their country’s southeast coast. It’s home to severallarge Australian cities. Since so many people live near the coast, this area could be great forwave power.

The researchers started out with an existing computer model called SWAN. (That name standsfor Simulating WAves Nearshore.) SWAN was developed by researchers at the University ofDelft in The Netherlands. It predicts the strength and location of ocean-wave energy. To do so,it factors in things like wind, features on the ocean floor and interactions among multiplewaves.

Morim Nascimento and Cartwright adapted SWAN to apply to southeast Australia. They addeddetails about the water’s depth out to within 50 kilometers (31 miles) from shore. They also putin data on the region’s winds and waves. Then they tested the model using data from buoys inthe ocean. The engineers tweaked the model until it closely predicted the amount of waveenergy being recorded by the buoys.

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ANDREW CORNETT/UNIV. OF OTTAWA

This map shows where wave energy is most available in oceans around the world. Red areas have the mostwave energy and purple the least. Much of wave-rich area is too far from land to be useful for energyconverters. Engineers use computer models to find wave “hotspots” closer to shore.

The model helped the team find “hotspots” — places with what Cartwright describes as an“abundance of wave energy.” Each site is within 5 kilometers (3 miles) of shore in water nomore than 22 meters (72 feet) deep. These are ideal, he explains, because it is easier andcheaper to get the power to shore from these sites than it would be from farther out.

“There is more than enough natural energy there in the ocean,” he says. “The challenge is toharness and convert enough of it into power” that people can use. Part of that challenge is theocean itself. Waves constantly pound at the equipment. The hardware also can experiencesome extreme weather. Very large storm waves can damage the converters, Cartwright says.And, he adds, salty seawater corrodes, or breaks down, any metal parts.

TAF LAB/UC BERKELEY

The wave carpet lies off the coast in water about 18meters (60 feet) deep. As waves pass over the top, thecarpet moves with them and absorbs their energy.

INGVALD STRAUME/WIKIMEDIA COMMONS (CC0)

Wave energy generators come in many shapes and sizes. Some designs bob or float on the surface (1, 2, 4)or flip from side to side (3). Another type harnesses energy from waves as they crash onto shore (5). Stillothers sit near the sea bottom (6).

Sea carpet

Scientists and engineers are trying lots of different ways to overcome these challenges. Theirideas have led to many types of designs. Some converters float on the surface, tethered towave-generators on the ocean floor. Others have one end anchored to the sea bottom with theother free to flip from side to side as waves wash over it. Still others use air or water pressureto generate electricity.

One of the newest systems looks a bit like aflat carpet. Mohammad-Reza Alam and histeam at the University of California, Berkeleydesigned the converter to mimic a muddyseafloor. Places with lots of mud are good atabsorbing incoming waves, Alam explains.Fishermen in shallow seas often head formuddy areas when rough weather hits. Boatshanging out there are protected from bigwaves as they ride out a storm.

If mud can absorb that much energy, Alamreasoned, then an energy converter that acts

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like mud should do the same. That would make it extremely efficient at harvesting wave power.

The “carpet” part of his converter is made from a smooth sheet of rubber. It rests near theseafloor, where it can bend and flex right along with the waves. As it moves up and down, itpushes posts in and out of a piston pump. The pump converts the piston’s movement intoelectricity, which then travels along a cable to the electric grid.

The carpet is able to remove almost all of the energy from the waves, Alam says. And it wouldbe able to power lots of homes. Each hour, he says, “every square meter of the carpet can getabout 2.5 kilowatts [of electricity] out of water near the coast of California.” That’s twice theamount of electricity used each hour by a typical American home

Mohammed-Reza Alam and his team at the University of California, Berkeley discuss their wave carpet thatharnesses energy from ocean waves to generate electricity.

UC BERKELEY/YOUTUBE

“If we want to get the same power from solar,” Alam says, “we need 14 square meters [151square feet] of solar panels.” That’s 14 times as much! He says a full-size wave carpet wouldprobably be about 10 meters (33 feet) wide by 20 meters (66 feet) long. So it should be able togenerate 500 kilowatts of electricity per hour — enough to power more than 400 homes —around the clock.

Berkeley Team Producing Energy from Ocean WavesBerkeley Team Producing Energy from Ocean Waves

https://www.youtube.com/watch?v=INEGcJ7AGGQ

Other locations, such as northern Europe, have more energetic waves. So a wave carpet therecould generate more electricity, Alam notes. On the flip side, weaker waves in places like theGulf of Mexico couldn’t pump as much electricity into the electric-power grid.

Anchored to the sea floor, the whole structure lies just above the seabed. So it’s completely outof sight. That’s important to many people who spend time at the beach. They don’t like to seebig energy-generating structures (like wind turbines) when they’re out for a swim or sail. Infact, many wind farms are located far from shore, so that people enjoying the beach don’t seethem. The wave carpet, however, can be close to shore. That means the cables that carryelectricity to the grid can be much shorter. And the electricity generated by the carpet shouldtherefore cost less.

Good for the environment?

There’s no question that finding new sources of renewable energy is good for the environment.Less pollution and fewer greenhouse gases are good for people, plants and animals. But cleanenergy sources can still cause problems.

Wind turbines can get in the way of migrating birds and bats, for example. (Some estimates sayhundreds of thousands of these animals may die each year from collisions with the massivespinning blades.) The lower height of wave-energy converters means they probably wouldn’tinterfere with migrating animals. But “we do need to consider their interaction with the marineenvironment carefully,” says Deborah Greaves. She is an ocean engineer at the University ofPlymouth in England.

One concern is about any ecological impacts of absorbing all of that energy from incomingwaves. (After all, that’s how they generate electricity — by converting wave energy intoelectrical energy.) Energy tapped from the waves will reduce how much energy will remain asthe waves continue in toward shore. They will be smaller, at least for some distance. Smallerwaves could lead to less mixing of nutrients within the water column (that’s the water betweena particular bit of ocean bottom and the surface above it). And that could impact with speciesthat live there, Greaves says. “But it can also be a benefit,” she adds. After all, “wave-energyconverters can help provide some coastal protection” by reducing erosion.

Classroom questions

JAMESMCP/WIKIMEDIA COMMONS (CC BY-SA 4.0)

This type of wave converter uses pressure from the waves as they press against large panels to generateelectricity.

The electric generators also could affect how wildlife interact. Many birds and marinemammals hunt for fish in areas that might be ideal sites for wave converters. It’s possible thatconverters could even attract fish to them if the smaller critters they eat seek refuge there.That could, in turn, attract hungry predators. This might help boost marine life in the area. Butfish, seals and other animals might also get tangled up in long cables that anchor surface-floating energy converters. So researchers must study where they want to install theseconverters to make sure they won’t harm local ecosystems.

Another concern: The converters will make noise. This can be a problem for fish, dolphins andother animals that rely on sound to find food or to communicate. The deep rumble of a boatand the loud ping of sonar cause all kinds of problems for ocean animals. These critters maystruggle to find food or become disoriented. However, Greaves says, wave converters areunlikely to create high levels of noise. The noisiest part would happen when the converters areinitially installed at some site. Once they start running, they should be fairly quiet.

On the plus side, converters might become the base for anartificial reef if algae, mussels, barnacles or corals takehold of the structure and begin to grow. Such reefsprovide protection for fish and other marine life. That

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could increase the diversity of marine life in the area. They could be helpful, as long as thosecritters don’t interfere with the wave converter’s movement.

“From the vast resources of the ocean, wave energy has the potential to make a hugecontribution towards our clean energy needs of the future,” Greaves says. But, she cautions, it“needs to be done in a sustainable way, in harmony with the marine environment.”

WHITCOMBERD/ISTOCKPHOTO

Human-built structures, such as this underwater wreck, can become the basis for artificial reefs, which helpboost marine life. This is one potential benefit of wave-energy converters.

CITATIONSJournal: J. Morim et al. Wave energy resource assessment along the Southeast coast of Australia on thebasis of a 31-year hindcast. Applied Energy. Vol. 184, December 15, 2016, p. 276. doi: 10.1016/j.apenergy/2016.09.064.

Journal: D. Greaves et al. Environmental impact assessment: Gathering experiences from wave energy testcentres in Europe. International Journal of Marine Energy. Vol. 14, June 2016, p. 68. doi:

https://www.sciencedirect.com/science/article/pii/S0306261916313666https://www.sciencedirect.com/science/article/pii/S2214166916300091

10.1016/j.ijome.2016.02.003.

Meeting: M. Lehmann et al. An artificial seabed carpet for multidirectional and broadband wave energyextraction: Theory and Experiment. Proceedings of 10th European Wave and Tidal Energy Conference(EWTEC2013). September 2-5, 2013. Aalborg, Denmark.

Wordfind

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