Converting the immense power of our oceans into reliable electricity to light our cities, fuel our travels, and make our homes habitable is one of the great engineering challenges of our time.
A beguiling array of wave-energy devices, tidal turbines, and coastal-barrage proposals are in the works to meet this challenge, but the prospect of them competing with wind and solar power is a distant one indeed. That’s because the realities of designing, building, and deploying these devices are incredibly complex.
Tidal and wave equipment falls into these categories:
- Power-conversion devices that use blades, turbines, and other hardware to capture the kinetic energy of moving seawater and flowing rivers and convert it to a stream of usable electricity.
- Cables to transmit power from the devices to the mainland and sometimes are also required to hold these devices in place.
- Cable accessories to connect cable arrays and devices to efficiently transmit the generated power and extend their capabilities.
- Moorings that anchor devices to the sea floor via cables, ropes, or chains.
All this equipment must work together, and failure of any one component can bring the whole system down.
These are the five main equipment complications confronting tidal and wave engineers:
1. Expense of early-stage development
Ocean-energy device costs remain extremely high because there are no benefits of manufacturing at scale. Each device has to be painstakingly designed, constructed, and tested in laboratories, then turned into prototypes to be tested in actual ocean waters.
The long process of trial and error requires funding to survive. Right now, a lot of funding is coming from governments because private companies don’t see much chance of getting a strong return on their investment.
2. Abundance of unproven prototypes
There are at least a dozen or more promising devices for capturing the motion of waves and the rise and fall of tides. With wave energy, devices can move up, down, and side-to-side, generating motion that can be converted into electricity.
But because the motion of waves is affected by surface winds, weather, and local topography, wave action is highly idiosyncratic and difficult to capture reliably. Furthermore, an ocean-energy device that works great in one locale might be terrible in another, making it difficult to develop a standard design.
An example of proposed wave energy devices includes:
- Floats or buoys that move up and down with the waves’ motions. This movement is converted to kinetic energy that powers an electrical generator. (Wired magazine profiles an intriguing buoy design from a Swedish company.)
Tidal power examples:
- One project uses devices that look like wind turbines, except they’re mounted underwater.
- Another project uses a gigantic metal water wheel with blades that spin from the motion of advancing and retreating tides.
Each of these proposed ocean-energy devices is intriguing in its own right, but there’s still a sharp contrast with offshore wind, where there’s a strong consensus on the most viable technology and a track record of which devices work best.
3. Environmental disruption
Any large mechanical device placed into an active ocean ecosystem is going to be problematic. Spinning blades may injure or kill aquatic species. A coastal barrage for tidal energy might upset an entire estuarial ecosystem.
Mechanical devices also can leak lubricants and emit noises that make trouble for fish and aquatic mammals. Engineers can tweak their designs in an attempt to minimize environmental damage, but they really can’t be sure what will happen until they get their prototypes in the water, so it’s difficult to solve these problems on the drawing board before they become much more expensive.
4. Unpredictable weather
Though waves splash endlessly against the coastline, their frequency and amplitude shifts constantly because wind has so much influence on water at the surface. Rough conditions are often a good thing for these devices because it means more motion, thus more energy created. But electricity users require a regular, reliable energy stream — not one that changes every time a low-pressure system moves in. This is why battery storage is being considered in some cases.
Hurricanes, tsunamis, typhoons, and other calamities pose a realistic risk of destroying equipment in an instant, while day-to-day crashing of the seas wears equipment out over months and years. Either way, engineers have to build incredibly robust machinery to survive the whims of weather because these devices are going in high-energy locations that have previously been avoided by subsea cable and construction projects. Even wind power installations still face some of these same demanding issues, as they are not unique to tidal energy.
5. Corrosion and bio-fouling
Devices strong enough to convert waves into energy typically require the strength of metal alloys. The trouble is that saltwater is so corrosive to tough, economical alloys like steel. That requires an extra level of care at the design, construction, and installation phases to fend off the effects of corrosion. Admittedly, there are many metallic alloys that have amazing corrosion resistance, but building entire energy arrays out of these metals will be inherently costly.
And then there are the creatures that attach themselves to anything we put in the ocean. Small animals and plant life can attach to the moving parts of underwater devices, creating potential for costly breakdowns and maintenance.
New technology and development is on the horizon
The challenges of ocean energy equipment are no reason to give up and move on. This is especially true in light of news that a commercial-scale tidal-energy project in Scotland got the green light for development in June 2017.
Obviously, offshore wind will be the most productive marine-energy source for the foreseeable future, but as long as the oceans keep moving, engineers, researchers, inventors, and entrepreneurs will be scouting for ways to bring tidal and wave energy into the mainstream.
One thing’s for sure: The ocean-energy industry will need tough, long-lasting cable accessories to solve the attachment, transmission, and cable repair part of this puzzle. PMI is your premier resource for those cable accessories.
- Pros and Cons of Tidal Energy
- Hurdles in Establishing Practical & Reliable Wave Energy
- Six Obstacles to the Development and Commercialization of Marine Energy Devices
Steel cables have unmatched strength and stability, which is why they’re so common in dry-land uses like elevators, construction cranes, and suspension bridges. But steel cables have troubles in marine environments: they rust, they sink, and they’re just hard to handle easily.
Synthetic cables are showing up these days in a lot of marine engineering projects, from seismic operations to cutting-edge marine-energy projects. They’re lighter, stronger, more flexible, and they float, making them a great choice for towing, lifting, and a host of static and dynamic applications.
Marine energy project managers often find that steel’s weight and susceptibility to corrosion limits their options. To keep things simple, let’s think about a basic floating platform. The weight and buoyancy balance requirements mean that every kilogram of steel cable weight subtracts a similar weight of equipment on the platform.
That means subtracting cable weight adds a lot more options in a wide array of marine applications, including ocean-energy initiatives. A meter of synthetic cable weighs about one-fifth of a similar length of steel cable. Similarly, a kilogram of synthetic cable has about five times the strength-to-weight ratio of a similar weight of steel.
Synthetic Cable Basics: Aramid vs. LCP
Synthetic fibers use advanced polymers that can be engineered to perform specific duties under precise conditions. They all have pros and cons that can make them optimum for some applications and less than ideal for others.
Marine applications typically use two kinds of synthetic fibers:
- Aramid, including the well-known Kevlar® brand. These fibers work great in transmission cables because they have low elongation, which keeps the conductor (fiber optics or copper) from stretching and breaking. They also have high tensile strength and high modulus.
- LCPs (liquid crystal polymers), including the Vectran® brand. Though similar to aramids, they have a different chemical structure. LCP has comparable elongation characteristics to aramids but provides superior abrasion resistance.
There are two potential issues with synthetics that do not affect steel: they’re more vulnerable to abrasion and breakdown from exposure to ultraviolet light. That might not be a problem with a cable that rests at the bottom of the ocean, but it can be a challenge for cables that sit outside and get reeled in and out frequently.
The chemical structure of synthetic cables can be tweaked to suit specific applications. Ropes can be designed to stretch a lot or remain static, depending on how they will be used.
Attachment points for synthetic cables
There’s a lot to like about synthetic cables and ropes in marine energy applications, but there’s one area where steel has an advantage: the method of attachment or termination.
Steel cable terminations can use helical rods to get a firm, trustworthy grip on the end of a length of steel.
Furthermore, the termination has to be designed specifically for the way it will be used—especially in applications like optical and/or electrical transmission. Since all marine energy projects transmit electricity to the mainland grid, this is a key concern.
The incredible strength of synthetic cables can be undermined if you choose the wrong kind of termination. We’ll discuss the fundamentals of synthetic strength member termination in an upcoming blog post.
At PMI, our synthetic strength member terminations have been carefully designed and tested to preserve the strength of the cables they’re attached to. We’ve been building rugged premium accessories for the deep-sea cable industry for decades, so we know what it takes to get the best performance from synthetic cables and their attachment points in marine energy projects.
Gravity from the sun and moon tugs at the surface of our oceans, creating tides that move massive quantities of water across broad expanses of shoreline twice a day. All that moving water produces kinetic energy we can convert into electrical power.
Though all of the earth’s continents have shorelines and tides, we haven’t done much with all that energy. To date, tidal energy technology generally takes two forms:
- Tidal current converters. These devices are typically underwater turbines that look much like a wind turbine and capture energy from water moving past the blades.
- Coastal barrages. A barrage is a kind of dam across the opening of an estuary. It works much like a hydroelectric plant, except that it uses turbines to capture energy from rising tidewater rather than river water.
Current technologies offer only a glimpse at tidal energy’s potential. To get the whole picture, we need to weigh the pros and cons of tidal energy.
Here’s a quick summary: (more…)
Marine energy is a beguiling concept because our oceans have massive energy potential. Oceans can produce kinetic energy and store solar energy, both of which can be converted into electricity to replace fossil fuels that contribute to global warming.
But surface water on our planet also produces significant challenges: it’s turbulent, corrosive and teeming with life. Coastal areas are pivotal to local economies. Developing marine energy devices to tap the energy of the world’s oceans is rife with difficulties that boil down to six pivotal concerns.
Cost of Development
There’s no way to avoid the huge costs of developing first-generation marine energy technologies. For instance:
- Scientists must get funding to develop and test hypotheses.
- Engineers must find practical ways to convert research findings into effective mechanisms.
- Prototypes must be developed using components that can withstand brutal ocean environments.
And all this must happen before moving to the manufacturing process, which imposes a new set of development costs.
Legal and Regulatory Hurdles
Oceans are shipping lanes and fisheries. Coastlines are prime tourist destinations. Waterways play a huge role in economies around the world, and all economies have legal and regulatory challenges.
These are the complications entrepreneurs have to think about before they wade into the uncharted waters of marine energy development. They’re reluctant to pour a lot of time, energy and money into projects that could get mired in litigation and regulation.
It’s one thing to bring a new car factory to town with the potential to create thousands of jobs. Marine energy device developers can’t make those kinds of promises.
Also, marine energy is so new that few people at the political level understand its potential. That makes it difficult to rally voters who can lean on politicians to encourage marine energy development.
Also, public subsidies for renewables development can become extremely controversial if voters decide they haven’t gotten a good return on their investment. Because all politics is public, developers might not want to see their names in the headlines if their projects become a political liability.
The public also has no idea of the potential for marine energy devices, so it’s hard to tap a deep vein of public popularity to encourage investors and entrepreneurs to enter the sector.
Furthermore, devices could be installed in places where the public can see them and object to changes in their favorite scenic ocean views. And they might wonder about what will happen to our oceans if we install these devices in them.
All waterways are delicate ecosystems that are easy to knock out of balance. Installing rigid metal devices on the sea floor will create artificial reefs that could lure invasive species that have a survival advantage over the animals that are already there.
Devices also generate sounds that can affect some subsea species. The spinning blades of subsea turbines can potentially kill or injure fish and aquatic mammals.
Large numbers of devices in the water might also interrupt the migration patterns of fish and mammals, tripping up local fishers that depend on them for their livelihoods.
Levelized Cost of Energy (LCOE)
Levelized cost of energy (LCOE) is a complex calculation that can be used to compare the cost-effectiveness of competing energy sources. For instance, the LCOE of offshore wind installations is about two-and-a-half times higher than land-based wind power, according to the U.S. Energy Information Administration.
Post renewable energy sources have substantially higher LCOE than natural gas or coal, and some estimates say that marine energy devices have a LCOE as much as double that of natural gas or coal.
All of these challenges await anybody who ventures into the marine power device sector. The risks are large, but the rewards of devising technologies that can free us from fossil fuel dependencies could be even bigger — especially to those who come up with the most transformative devices.
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It’s one thing to dream about the immense power residing in our planet’s oceans. It’s quite another to put human ingenuity to work tapping into the ocean’s powers.
That was the backdrop of the International Marine Energies Technologies Course, held in mid-March in The Netherlands. Some of the best minds in marine energy technologies gave presentations covering intriguing innovations in the sector. PMI was the only U.S. company attending the course.
At PMI, we’re fascinated with the potential of marine energy. We supply cable hardware to companies that do business in the deep sea, including seismic exploration firms that tow massive cable arrays to hunt for petroleum deposits below the ocean floor. Since we’re experts in hardware that can survive treacherous undersea environments, we’re eager to contribute to initiatives that tap the energy of our oceans.
Europe has a huge head start on marine renewable energy technologies. Offshore wind farms are now mainstream technologies along the coasts of many European nations. With that technology well understood, European companies are starting to look at other ways to draw energy from the ocean.
The course covered four technologies:
- Ocean thermal energy conversion (OTEC). This technology taps the massive amount of solar energy trapped at the surface of the ocean in the tropics. OTEC uses warm sea water to convert a liquid into steam that drives a turbine, producing electricity. After the steam passes through the turbine, it gets cooled by water pumped up from the ocean depths, condensing it back into fluid form to continue the cycle.
- Salinity gradient power. When fresh water bodies are near salt water bodies, there is a substantial energy potential that can be harvested. Through pressure retarded osmosis or reverse electrodialysis, electricity can be generated. Salinity gradient technologies are being developed in Norway and the Netherlands.
- Tidal power. The ebb and flow of ocean tides can generate substantial kinetic energy that can be converted into electricity by several kinds of technologies. Tidal energy depends on the velocities water moves. (See Massive Tides Invite Wave of Tidal Energy Research for more).
- Wave power. Where tidal relies on the velocity of water, wave power relies on the change in height of waves to harvest energy. (See Scotland’s Sunken Wave Turbines for more).
Each marine energies technology has pros and cons. While all can produce energy without the use of fossil fuels, they also face substantial challenges because of the chaotic and corrosive nature of oceans. Furthermore, they require substantial financial investments and must offer some hope of providing a return to investors.
Moreover, any devices placed in the ocean are entering an active ecosystem that must be protected. The sessions of the International Marine Energies Technologies Course addressed these challenges. The people attending included engineers, researchers and representatives of companies venturing into the emerging ocean-energy field.
So what was PMI doing in Holland for three days? Well, we supply cable hardware to companies that do business in the deep sea, including seismic exploration firms that tow massive cable arrays to hunt for petroleum deposits below the ocean floor. It’s a great business to be in, but we also recognize the necessity to tap into renewable energy sources in the years to come.
Since we’re experts in hardware that can survive treacherous undersea environments, we’re eager to contribute to initiatives that tap the energy of our oceans. Ocean energy technologies are barely off the drawing boards in the United States, but our European colleagues are getting devices in the water and starting to generate energy.
And that’s getting us energized about the power of our oceans.
Related: “Tidal and Wave Energy Industry Struggles With Harsh Ocean Environments”
Want more information about our experience at International Marine Energies Technology Course? Schedule to speak to a representative.
Fundy Bay is famous for pictures of fishing boats tilted on their hulls — run aground by the immense power of the world’s largest tides.
The waters of this scenic coastal inlet along Canada’s Nova Scotia and New Brunswick provinces rise and fall by more than 50 feet twice a day, every day of the year. That predictability is one of the key reasons why green-energy researchers are fascinated with the potential of converting tidal movements into electricity. Solar power goes dark after sunset and wind power rises and falls with moving weather patterns. But tides rise and fall like clockwork, creating the potential for an extremely reliable stream of electric power.
The Trouble with Tidal Energy
Unfortunately, the ocean is one of the worst places on earth to install mechanical equipment. Saltwater is extremely corrosive, and working on machinery underwater is incredibly dangerous and expensive.
Some wave and tidal energy projects are mounting turbines on the sea floor. This keeps the turbines out of sight, which is a boon to coastal views, but it also dramatically increases the costs of upkeep precisely because they are so difficult to access.
Floating Platforms: A Tidal Energy Alternative
Fundy Bay’s epic tides have made it a hub for working out these kinds of challenges in wave and tidal energy research. One alternative researches are exploring is mounting a turbine beneath a floating platform that’s moored to the ocean floor via cables. A turbine connected to a floating platform could have all of its machinery easily accessible from the platform rather than mounted on the sea floor, where the only way to reach it is with scuba divers or remote-operated vehicles (or both).
In March 2016, a Canadian firm called Dynamic Systems Analysis (DSA) helped launch a floating research platform called EcoSPRAY that will document how highly turbulent tides work. This, in turn, will provide clues to the best ways to deploy floating tidal energy platforms that have been moored to the ocean floor.
The platform is operating in the Grand Passage between Freeport and Westport, Nova Scotia, in the Outer Bay of Fundy. Sensors on the EcoSPRAY will track wind speeds, tidal currents and wave actions. A drag plate mounted on the bottom of the platform will simulate the thrust of an underwater turbine, DSA says.
Protecting tidal ecosystems
While floating tidal power platforms would be less visually pleasing than turbines mounted on the sea floor, they have the potential to be less disruptive to underwater environments. Mounting an underwater turbine is a major construction project, whereas placing anchor points on the sea floor for mooring cables could be far less disruptive to the coastal environment.
Protecting that environment is very much on the minds of Fundy Bay researchers. Fundy Ocean Research Center for Energy (FORCE), the Offshore Energy Research Association (OERA) and the Nova Scotia Department of Energy are all working together on a half-million-dollar program to determine the effects of tidal energy turbines this year.
This points to the future of wave and tidal energy, which may well depend on finding the best mix of high energy output, low cost and minimal impact on the subsea environment.
• EcoSPRAY tidal platform inspects moorings in high-tidal flows
• Fundy tidal energy study to look at seabirds, lobster, acoustic environment
The Gulf Stream moves a stupendous volume of water up the Atlantic Coast of the United States and across the North Atlantic to Europe. Could all that movement provide power to coastal communities?
Perhaps, though it’s probably a decade away. A recent article in the Virginian-Pilot of Norfolk, Virginia, explained that scientists are studying the waters off Cape Hatteras, North Carolina, one of the most powerful flow points in the Gulf Stream, to see if there is a way to harness that energy.
Figuring out how to do that would be a triumph of offshore energy engineering. While ocean wave energy is considered a promising source of renewable power, drawing energy from individual currents within our oceans is still mostly an idea on the drawing board.
The Virginian-Pilot article sounds a note of caution: “So far, no commercially connected turbines operate in the Gulf Stream, according to the Bureau of Ocean Energy Management. A few prototypes have been tested off the coast of Florida. Challenges include turbine maintenance in a harsh, salty environment and long distances to run cable connections.”
One expert quoted in the article said the Gulf Stream’s flow is strong enough to power all of North Carolina (population 9.5 million) and more. That’s makes sense, given that the Gulf Stream transports more water per second than all the world’s rivers combined, according to National Oceanic and Atmospheric Administration.
At PMI, we are monitoring all the developments in marine renewable energy. Companies are already proposing turbines for inland rivers, so it stands to reason that ocean current development could follow in that path. As these technologies advance, we’ll be poised to provide tough, durable cable hardware to ensure that power finds its way to land safely.
The coast of Scotland has some of the world’s strongest waves, which makes it a vital testing ground for wave turbines that convert wave movements into electricity.
So it’s no surprise that the Pentland Firth region of the Scottish coast is the site of the $1.5 billion MeyGen turbine project, where offshore cables are being laid in the opening phases of an initiative that aims to install 279 wave turbines below the surface of the ocean. As a recent Quartz.com report noted, the project could provide up to 400 megawatts of electric juice that could power 175,000 homes.
The wave-power turbines look much like wind-power turbines. Moving waves turn the turbine blades, generating electric power. Some observers say wave-power technology is about three decades behind wind power. But the MayGen project could signal the arrival of wave technology power, once it gets up and running.
Wave power technology is taking a wide array of shapes. Some devices look a bit like mechanical eels floating on the surface of the water; others are more like paddles that flow back and forth with the waves, moving a piston that generates power.
The ocean is an alluring power source, because it is so much denser than air and can therefore generate far more movement that can be converted into electricity. But even with 800 times more density than air at the surface, the water in the ocean creates an extremely problematic environment for energy development.
A recent Wall Street Journal article pointed out severity of the challenge:
“People say this is not rocket science,” says Neil Kermode, managing director of the European Marine Energy Centre. “No. You fire a rocket into a nice, cold vacuum. We’re trying to do things in a salty, grit-filled electrolyte that’s got animals in it.”
Indeed, waves flow in multiple directions, unlike the wind, and the undersea environment could potentially be damaged by these kinds of projects. These and other factors vastly complicate wave-power generation.
Right now, cable-laying equipment is installing the offshore cables that will convey power to the people of Scotland after the wave turbines are up (well, down) and running. While power cables may not seem as exciting as subsea turbines, they still represent one of the most vital components of the project.
As wave power advances, PMI will be poised to provide durable ocean cable hardware to help these kinds of projects succeed. We have the experience and knowhow to design and manufacture rugged cable accessories that can last for years in the most difficult ocean environments. As the energy world transitions from fossil fuels to renewables, PMI cable hardware will be there every step of the way.
Elsewhere on the PMI blog: Tidal and Wave Energy Industry Struggles With Harsh Ocean Environments
Related article at Environment360 published by Yale University: Will Tidal and Wave Energy Ever Live Up to Their Potential?
Need some tips on how to extend your subsea power cable life? Check out our guide:
Waves and tides offer some of the most predictable, consistent, and just generally big energy resources available. However, rollouts of actual wave and tidal energy power installations have been slow. Part of the reason for this is that there is no consensus at all on what represents the best device designs to actually harness waves and tides and therefore on what subsea equipment is necessary to use.
Any subsea equipment needed to harness tidal energy is going to be expensive – and will tend to drive building costs to be anywhere between 3 to 15 million dollars and sometimes more. But in the long run, the investment will pay off.
Now the pros and cons of tidal energy always bring debate – but tidal energy has a lot going for it:
Consistent Power – Tides move constantly throughout the day, which provides a consistent stream of electricity generation capacity.
Pollution-Free – By taking advantage of only the tide, tidal power creates no greenhouse gas emissions or water pollutants.
Renewable – No material resources are used or changed in the production of tidal power, making it a truly renewable power form.
Minimal Visual Impact – Tidal power devices are fully or nearly completely submerged in water well offshore. This reduces the “damaging of water views” that has been associated with offshore wind turbines.
Efficient – Tidal Power converts roughly 80% of the kinetic energy into electricity, as opposed to coal and oil which convert only 30% of the energy held within.
Locations – There are numerous locations for tidal power around the world. Other websites online have this number at 40, however the coast of British Columbia, Canada has 89 alone.
And most importantly it offers low operating costs – Once installed, there are few ongoing operating costs or labor costs. By making investments at the forefront and building these systems properly with reliable equipment, tidal energy power plants offer a long lifespan, ultimately reduce costs, and make tidal energy more cost-competitive in the long run.
There are more ways to save big. Download our free guide: Decrease Drag & Optimize Performance, our in-depth hydrodynamic efficiency studies can help companies innovate new systems on existing subsea cable devices and analyze cost saving opportunities.
Offshore wind and solar energy have been getting all the attention in the quickly growing renewable energy industry, but there’s another player that is beginning to grow strength in the energy market – ocean waves and tidal currents, or “marine energy”. There are vast amounts of energy that are produced within the moving waters of oceans and rivers, and companies working to harness this energy are quickly gaining speed.
While not nearly as large as the main competitors in renewables, marine energy has strong advocates and is quickly gaining steam in the renewable market. About 30 tidal and 45 wave energy companies are at an advanced stage of technological development. One of the biggest issues these companies are facing that has impeded forward movement in the market is the harsh ocean environments – the same thing that makes the industry work in the first place.
The intensity of sea waves is greatly unpredictable and can cause damage throughout the process. Installation of the equipment is often difficult – the areas that are best suited to harness wave and tidal energy are often very hazardous and can be difficult to navigate. As we mentioned in our article on subsea cable vulnerability, subsea cables and hardware have to withstand 14.5 psi per every 10.05 meters they are lowered into the ocean. That coupled with the harsh environment that marine energy succeeds in, makes for a harsh environment for equipment.
PMI has many years of experience engineering proven subsea hardware for companies around the globe. We are excited to be part of the quickly growing marine energy market and are ready to create custom and quality solutions that will withstand harsh and hazardous environments.
Read more about the potential of wave and tidal energy.
The outcome of your project will rely on the quality of your subsea terminations. Make sure to download our guide – 7 Questions You Should Be Asking About Your Subsea Terminations – for a through breakdown of what you should be looking for in your subsea terminations.