Ocean energy could be the wave of the future | Science News for Students

Ocean energy could be the wave of the future

Wave-power systems are the latest in clean, renewable energy
May 30, 2019 — 6:45 am EST
a surfer surving on a blue wave

Not just great for surfing, waves may be the next big thing in renewable energy.

EpicStockMedia/iStock/Getty Images Plus

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 and wind. 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. That greenhouse 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 only shines during the day. Wind comes and goes. There are very few places where wind is constant enough to generate electricity all the time. And as easy as it sounds, storing energy for later use has proven a major challenge.

But ocean waves? As anyone who’s stayed near a beach can tell you, waves crash onto shore morning, 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 caps on an ocean or some lake on a windy day, you’ve seen this in action. The wind causes water at the surface to bob up and down. Even though it seems as though the water is traveling from one place to another, it doesn’t actually go very far. Rather, it moves in circles — up, up, up to the 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 gently bobbing 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.  The water bumps up against the ocean floor, squashing the circle into an oval. Much like a person tripping over something, the water “trips” over the ground. The top part lurches past the bottom. The wave “breaks,” crashing closer to the beach.

Wave energy systems use the water’s movement to make electricity. Some types of these devices harness the power of breaking waves. Others make use of swells. Still others use the pressure of waves near the ocean floor. Yet all have the same goal: Convert wave energy into electrical energy. That electricity can be used to power the electric grid. That’s the network of cables that transmits electricity to homes and buildings so we can use it.

Wave power is restricted to areas near the ocean. After all, the cables that carry electricity can only 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.

With all that promise for wave power, researchers are testing how well different types of generators convert ocean energy to electricity. Along the way, they’re trying to make sure that sea 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 energy converters.

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

To figure out the best sites, scientists turn to computer models. Joao Morim Nascimento and Nick Cartwright are environmental engineers in Australia. Both work at Griffith University in Southport, Queensland. An environmental engineer works to reduce pollution and waste. The pair wanted to find good places for wave-energy converters along their country’s southeast coast. It’s home to several large Australian cities. Since so many people live near the coast, this area could be great for wave power.

The researchers started out with an existing computer model called SWAN. (That name stands for Simulating WAves Nearshore.) SWAN was developed by researchers at the University of Delft 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 multiple waves.

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

a global map showing the distribution of wave power in oceans around the world
This map shows where wave energy is most available in oceans around the world. Red areas have the most wave energy and purple the least. Much of wave-rich area is too far from land to be useful for energy converters. Engineers use computer models to find wave “hotspots” closer to shore.
Andrew Cornett/Univ. of Ottawa

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 no more than 22 meters (72 feet) deep. These are ideal, he explains, because it is easier and cheaper 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 to harness and convert enough of it into power” that people can use. Part of that challenge is the ocean itself. Waves constantly pound at the equipment. The hardware also can experience some extreme weather. Very large storm waves can damage the converters, Cartwright says. And, he adds, salty seawater corrodes, or breaks down, any metal parts.

a diagram showing different kinds of wave energy generators
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). Still others sit near the sea bottom (6).
Ingvald Straume/Wikimedia Commons (CC0)

Sea carpet

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

a computer illustration of a wave carpet
The wave carpet lies off the coast in water about 18 meters (60 feet) deep. As waves pass over the top, the carpet moves with them and absorbs their energy.
TAF Lab/UC Berkeley

One of the newest systems looks a bit like a flat carpet. Mohammad-Reza Alam and his team at the University of California, Berkeley designed the converter to mimic a muddy seafloor. Places with lots of mud are good at absorbing incoming waves, Alam explains. Fishermen in shallow seas often head for muddy areas when rough weather hits. Boats hanging out there are protected from big waves as they ride out a storm.

If mud can absorb that much energy, Alam reasoned, then an energy converter that acts 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 the seafloor, where it can bend and flex right along with the waves. As it moves up and down, it pushes posts in and out of a piston pump. The pump converts the piston’s movement into electricity, 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 would be able to power lots of homes. Each hour, he says, “every square meter of the carpet can get about 2.5 kilowatts [of electricity] out of water near the coast of California.” That’s twice the amount 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 that harnesses 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 [151 square feet] of solar panels.” That’s 14 times as much! He says a full-size wave carpet would probably be about 10 meters (33 feet) wide by 20 meters (66 feet) long. So it should be able to generate 500 kilowatts of electricity per hour — enough to power more than 400 homes — around the clock.

Other locations, such as northern Europe, have more energetic waves. So a wave carpet there could generate more electricity, Alam notes. On the flip side, weaker waves in places like the Gulf 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 out of sight. That’s important to many people who spend time at the beach. They don’t like to see big energy-generating structures (like wind turbines) when they’re out for a swim or sail. In fact, many wind farms are located far from shore, so that people enjoying the beach don’t see them. The wave carpet, however, can be close to shore. That means the cables that carry electricity to the grid can be much shorter. And the electricity generated by the carpet should therefore 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 clean energy sources can still cause problems.

Wind turbines can get in the way of migrating birds and bats, for example. (Some estimates say hundreds of thousands of these animals may die each year from collisions with the massive spinning blades.) The lower height of wave-energy converters means they probably wouldn’t interfere with migrating animals. But “we do need to consider their interaction with the marine environment carefully,” says Deborah Greaves. She is an ocean engineer at the University of Plymouth in England.

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

a wave convertor
This type of wave converter uses pressure from the waves as they press against large panels to generate electricity.
JamesMCP/Wikimedia Commons (CC BY-SA 4.0)

The electric generators also could affect how wildlife interact. Many birds and marine mammals hunt for fish in areas that might be ideal sites for wave converters. It’s possible that converters 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. But fish, 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 these converters to make sure they won’t harm local ecosystems.

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

On the plus side, converters might become the base for an artificial reef if algae, mussels, barnacles or corals take hold of the structure and begin to grow. Such reefs provide protection for fish and other marine life. That could increase the diversity of marine life in the area. They could be helpful, as long as those critters don’t interfere with the wave converter’s movement.

“From the vast resources of the ocean, wave energy has the potential to make a huge contribution 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.”

an underwater wreck which has started to become an artificial reef
Human-built structures, such as this underwater wreck, can become the basis for artificial reefs, which help boost marine life. This is one potential benefit of wave-energy converters.
WhitcombeRD/iStockphoto

Power Words

(more about Power Words)

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

atmosphere     The envelope of gases surrounding Earth or another planet.

bat     A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.

buoy     A floating device anchored to the bottom of a body of water. A buoy may mark channels, warn of dangers or carry instruments to measure the environment.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

constant     Continuous or uninterrupted.

coral     Marine animals that often produce a hard and stony exoskeleton and tend to live on reefs (the exoskeletons of dead ancestor corals).

corrode     (adj. corrosive) A chemical process that weakens or destroys normally robust materials, such as metals or rock.

diversity     A broad spectrum of similar items, ideas or people. In a social context, it may refer to a diversity of experiences and cultural backgrounds. (in biology) A range of different life forms.

dolphins     A highly intelligent group of marine mammals that belong to the toothed-whale family. Members of this group include orcas (killer whales), pilot whales and bottlenose dolphins.

ecology     (adj. ecological)  A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

environmental engineer     A person who uses science to study and solve problems in ecosystems — from forests to the human body.

erosion     (v. erode) The process that removes rock and soil from one spot on Earth’s surface, depositing it elsewhere. Erosion can be exceptionally fast or exceedingly slow. Causes of erosion include wind, water (including rainfall and floods), the scouring action of glaciers and the repeated cycles of freezing and thawing that occur in many areas of the world.

factor     Something that plays a role in a particular condition or event; a contributor.

flex     To bend without breaking. A material with this property is described as flexible.

generator     A device used to convert mechanical energy into electrical energy.

greenhouse gas     A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

grid      (in electricity) The interconnected system of electricity lines that transport electrical power over long distances. In North America, this grid connects electrical generating stations and local communities throughout most of the continent.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

marine mammal     Any of many types of mammals that spend most of its life in the ocean environment. These include whales and dolphins, walruses and sea lions, seals and sea otters, manatees and dugongs — even polar bears.

metal     Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure). 

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

network     A group of interconnected people or things. (v.) The act of connecting with other people who work in a given area or do similar thing (such as artists, business leaders or medical-support groups), often by going to gatherings where such people would be expected, and then chatting them up. (n. networking)

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

population     (in biology) A group of individuals from the same species that lives in the same area.

predator     (adjective: predatory) A creature that preys on other animals for most or all of its food.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

reef     A ridge of rock, coral or sand. It rises up from the seafloor and may come to just above or just under the water’s surface.

renewable energy     Energy from a source that is not depleted by use, such as hydropower (water), wind power or solar power.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sonar     A system for the detection of objects and for measuring the depth of water. It works by emitting sound pulses and measuring how long it takes the echoes to return.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

sustainable     An adjective to describe the use of resources in a such a way that they will continue to be available long into the future.

tablets     (in computing) A small, hand-held computer that can connect to the Internet and that users can control using a touch screen. An Apple iPad, Samsung Galaxy and Amazon Kindle Fire are all examples of tablets.

transmit     (n. transmission) To send or pass along.

turbine     A device with extended arm-like blades (often curved) to catch a moving fluid — anything from a gas or steam to water — and then convert the energy in that movement into rotary motion. Often that rotary motion will drive a system to generate electricity.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed.

wind turbine     A wind-powered device — similar to the type used to mill grain (windmills) long ago — used to generate electricity.

Citation

Journal:​ ​​J.​ Morim et​ ​al.​ Wave energy resource assessment along the Southeast coast of Australia on the basis 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 test centres in Europe. International Journal of Marine Energy. Vol. 14, June 2016, p. 68. doi: 10.1016/j.ijome.2016.02.003.

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

Further Reading