What is ocean energy? When you think of solar power you can picture a photovoltaic panel; when you think of wind energy you can picture a giant windmill on the horizon; but what contraption do you imagine with ocean energy? It’s clear that the ocean is an enormous source of power, as anyone who has been knocked over by a wave, seen them crash on the shore, or been rolled about in a ship can attest. Water is some 832 times denser than air; and ocean energy incorporates the forces of many resources: the sun, the wind, the movements of the earth, and the gravitational pull of the moon.
Ocean Energy Europe says wave energy could be the largest renewable, theoretically providing up to 125% of the world’s current electrical consumption. Experts from the International Renewable Energy Agency (IRENA) say if you included the other technologies - energy made by tides, from the chemical exchange of salty and fresh water, and geothermal exchange - ocean energy could provide 400% of the world’s electrical energy consumption. Since 1799, people have been working out how to turn the energy of the waves into electricity. A little over 200 years later, we’re finally arriving.
It’s reasonable to ask, what’s taking so long? Ocean energy faces some challenges the others didn’t. While solar panels and windmills weren’t easy to figure out, at least they could be developed on dry land where you could test and fix things relatively easily. It’s a lot tougher when the part you want to recalibrate is more than a dozen meters under the surface of the ocean.
And while solar panels and windmills have to withstand storms, they’re not also contending with tons of churning saltwater. Saltwater is highly corrosive and the water in the ocean may oscillate as aggressively as the water in a washing machine, so anything built to sit in it for decades has to be impervious. It can’t break down or expose the environment to toxins. In Seabased’s opinion it also has to be benign or beneficial to the ecosystem.
As Simon Stark, project manager of the Ocean Energy Scale-up Alliance pointed out: “Putting something in the ocean is as difficult as putting it out in space.”
Because it’s cutting edge technology, ocean energy is generally more expensive than solar or wind. But both solar and wind were much more costly when they were emerging technologies. According to IRENA the price of solar dropped 80% between 2010 and 2017, and the price of wind dropped 38%. The same low rates are expected of some ocean energy technologies as they are commercially deployed.
How much power each of these technologies could theoretically generate is calculated by the type of technology and the abundance and type of resource. The calculations do not take into account the cost of any of these technologies.
To give a sense of the promise of ocean energy, the world consumed 22,315 TWh in 2018. Some of these technologies could conceivably provide more power than the world consumed.
In the ocean, there is not one technology for harnessing power; there are many. What follows is an overview from 10,000 feet of what many of these technologies look like and how they work, although there are far too many particulars to cover in this space.
Earlier rendition of Seabased wave energy park
Tidal Energy
The ocean energy technology with the most commercial projects in the water as of 2020 is tidal energy. Imagine the tide is coming in, the water’s getting higher, but there’s a barrier. The water will exert pressure on this barrier, but to pass through it must push through turbines – devices that rotate. The water causes the turbines to spin and the spinning of the turbines creates electricity. When the tide goes out, it happens again. There are many different kinds of turbines designed for this purpose.
Tides aren’t affected by weather conditions but only by the cycles of moon, sun, and earth, so tidal power is entirely predictable. And this technology is proven: EDF has operated a 240-megawatt tidal barrage since 1966. Tidal lagoons are a newer technology and can be entirely land-based. Their turbines include a ring-shaped harbor wall with a section of hydro turbines.
There are also tidal currents that harness the lateral motion of ocean currents.
Scientists estimate tidal energy has the global potential to produce 500–1000 TWh/yr
Wave Energy
After tidal, wave energy is the most developed ocean energy technology. Actually, the most developed technologies, since there are several. Some of them lie on top of the waves like a raft, others sit under the waves with something like a fan sticking up that is slapped around by the moving water, some use turbines. They may be onshore, nearshore, or offshore and can be matched with other technologies like solar panels or offshore wind.
Seabased wave technology is based on a patented direct-drive linear generator that captures this dense resource. A buoy riding the waves is tethered by cable to a generator resembling an 8 meter high spark plug that sits on the sea floor. The waves move the buoy, the buoy pulls the cable, the cable raises and lowers translator (mostly made of magnets) inside the generator. This mechanical energy is converted to electrical energy. This kind of generator is part of an array of generators, each collecting energy from the waves they’re riding. Each generator sends the power to a subsea substation that converts it to electricity that can go directly to the electrical distribution grid. Electrical grids can only incorporate electricity that meets quality requirements and very few renewable technologies can meet those requirements. Seabased wave power parks are designed to be plug-and-play, modular systems that can be expanded as needed. They require little maintenance, so it’s okay if sea flora and sea fauna move in and make the place home, since they’re safe from fishing or recreation in there.
Among the European countries with attractive wave climates are the UK, Ireland, Portugal, France, Spain, and Denmark. But there are also thousands of islands with waves that currently depend entirely on imported fossil fuels. Seabased has designed its system to work not only with big waves, but also with moderate ones.
Wave energy is believed to be one of the most powerful forms of ocean energy with a theoretical potential of 29,500 TWh/yr of high density power.
Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion (OTEC) works in tropical places where the water at the surface is at least 28 Celsius. Some places where it is expected to be effective are parts of India and Africa. OTEC generators draw warm water in from the ocean’s surface. They may operate on seawater alone or they may incorporate a substance like ammonia, which boils at a low -33.34 Celsius. The ammonia becomes vapor which, like any other steam, can turn a turbine when forced into a small space. On the other side of the turbine, cold ocean water, drawn from about 900 meters below the surface, is used to cool the ammonia and it begins its journey again.
OTEC could theoretically produce 44,000 TWh/yr to 88,000 TWh/yr though the power it produces is very low density.
Salinity Gradient
Salinity gradient is a way of using water’s chemistry to make power. When you mix saltwater and fresh water, positive and negative ions will naturally flow from the water with the highest concentration (the saltwater) to that with the lowest (the fresh). This is energy moving around. But if you use special membranes that only let one or another kind of ion through, the water can be made to move in specific ways that creates power. OEE said, “The energy released from 1 m3 fresh water is comparable to the energy released by the same m3 falling over a height of 260 m. The availability and predictability of salinity gradient energy is very high, and therefore makes it a solid baseload energy source.”
Salinity gradient is estimated to have a potential output of 2,000 TWh/yr.
This is a highly condensed look at decades of research with possibly thousands of studies produced on different mechanical designs, materials incorporated, results from different climates, and so forth. What is certain is that the sources of ocean energy – waves, tides, temperatures, and salinity - tend to be predictable and reliable compared to some other renewables. They draw power from the rest of nature to create a formidable source of energy.
The ocean is very different in different places—the Atlantic is not the Caribbean is not the North Sea. All of these ocean energy types may find their optimal technology or combination of ocean technologies to help make the renewable transition. Already the cumulative energy produced from wave and tidal energy has increased from less than 5 GWh in 2009 to approximately 45 GWh in 2019.
“Implementing this wide array of ocean-based opportunities could reduce global GHG emissions by nearly 4 billion metric tonnes of carbon dioxide equivalent in 2030 and by more than 11 billion tonnes in 2050, compared to projected business-as-usual emissions,” according to an article in the World Resources Institute.
There is a tremendous need for the world’s governments to establish policies that would quickly bring these ocean energies to commercialization, just as they did for other emerging technologies. Hopefully one day soon no one will have to ask, What is ocean energy? We’ll all be experiencing a cleaner planet because of it.