Wave Energy Converters have been making a lot of, um, waves in the energy sector lately thanks in part to China’s brand new, megawatt-scale, wave energy device. This device isn’t the first of its kind, but its sheer size represents a breakthrough for this underutilized but potent branch of the clean energy family tree. What is wave energy generation, and how does it compare to other renewables? And if wave energy is so great, then why is it lagging behind solar, wind and others? Let’s dive into the ocean of renewable energy, where the waves may hold more untapped potential than the sun. Maybe the surfers were right all along.
Wave energy is kind of a branch of the hydropower family tree. Instead of using dams and gravity to capture the potential energy of water as it falls, it’s translating the motion of the ocean into nearly limitless energy. In other words, wave energy uses the kinetic energy stored in the waves and is mechanically similar to wind energy. Technically, they’re both trying to capture waves, but the waves are rippling through different states of matter. There are a couple of important differences though. First, unlike wind, oceanic waves are not intermittent. The surf’s always up, dude! And second, water has more mass than air. Because potential energy is calculated using mass and velocity, it has potential to transfer more energy. That means there’s a lot more potential energy in the sea available for capture. In theory, the U.S. coasts alone could generate up to 2.64 trillion kilowatt hours of energy. That’s roughly 64% of total U.S. utility-scale electricity generation in 2021.1 And waves tend to increase in the winter. So, when shorter days start to negatively affect solar energy, wave energy only gets stronger! 2
Sounds great, but what’s the catch? A lot like solar, the trick is efficiently and effectively converting all that wave energy into usable electricity.2 At the heart of this problem is developing an optimized Wave Energy Converter (WEC) that can generate electricity while surviving the harsh conditions of the ocean.
The oldest record of humanity harnessing hydropower comes from 202 BCE in China. Back then they used trip hammers and a vertical-set water wheel to pound and hull grain, as well as break ore. So, it’s appropriate that we return to China for the latest hydropower innovation.3 This is a massive WEC called the Nankun mobile power bank. And when I say massive, I mean it! The Nankun weighs in at 6,000 metric tons, and can generate up to 24,000 kilowatt-hours of electricity per day. This is equal to the daily electricity consumption of 3,500 households.4 The sheer size and megawatt-scale generation of the Nankun represents a big leap forward over older, smaller kilowatt-scale wave energy devices.4
But the Nankun isn’t the only WEC. From serpentine point absorbers buoys to Oscillating Water Columns that use waves to move air to move turbines,5 to even weirder stuff, there’s a vast array of different designs all competing to be the one to efficiently and commercially crack wave energy. Why is this? It’s not like we see a ton of different ways to turn the wind into energy, and there’s not a huge variety of different solar panel shapes. What makes wave energy so weird?
Well, unlike solar or wind, we haven’t found the best-in-class tools, techniques and materials yet. When it comes to WECs there’s a lot of different ways to skin a cat, and the field is simply less researched than other renewables. According to Robert Thresher of the National Renewable Energy Laboratory (NREL), even though there are a vast array of different designs, it’s possible that we have yet to invent the best WEC.6 Back in 2014 some experts estimated wave power to be about 30 years behind wind and solar.6 However, since then the number of papers published on wave energy has nearly doubled.7 Even though research is growing rapidly, what’s the big hold up?
Wave power faces more engineering challenges than other renewable energy generators. WECs, by design, have to be strong enough to get tossed around by the wind and water all day, every day, for decades.6 Again, surf’s up, dude, surf’s always up. There is no escape from the surf!! And that’s on a normal day. These systems have to be designed to withstand rough seas, and various storms and hurricanes as well. A poorly designed system will be slammed to pieces by waves.
The ocean itself is not particularly welcoming to our technology. Salt water is corrosive and can destroy metal and electronics. While waterproof casings and sacrificial anodes can help protect some structures, salt spray is still one of the major torture tests on ruggedized electronics and metals alike. There’s also bio-fouling, where organisms like barnacles and algae that will happily adhere to anything we toss into the sea and cause all sorts of problems.8
But despite these challenges, the clean energy potentially offered up by the seas is too good to pass up. And with the field as young as it is, there’s just a plethora of weird and wonderful devices all vying to efficiently overcome these challenges and become the industry standard. One promising up-and-comer is CalWave’s xWave series of wave energy converter devices.9 Are you tired of me saying “wave” yet?
What is xWave, and how does it work?
Designed and patented in 2012 by CalWave, this device converts the relative motion of overpassing waves into power. The xWave’s rugged design allows it to capture wave energy coming from any direction, and even reposition itself in the water column to maximize its capture potential.10 In 2016 CalWave won the $500,000 second place prize in the DOE’s Wave Energy Contest.11. Then it was off to Scripps Institute of Oceanography for a 6 month trial run, where the xWave held up against the biggest storm to hit the area in a decade. This actually brings up a good point. Large storms can bring waves that are too strong to convert into energy. Big waves may also damage WECs.12 But the xWave can autonomously detect oncoming storms and use its ability to reposition to safely duck beneath the waves.10
Pacific Northwest National Laboratory studied the xWave’s environmental impact, and gave the device some great all around grades. The threat of entanglement and collision were present but minimal. Any sounds or Electromagnetic Fields (EMF) emitted by the xWave were sufficiently dampened by its hull. And to top it off, the xWave only uses Green Marine approved lubes and oils, so any unfortunate chemical spills would be harmless.13 I never thought I would say “lubes and oils” in a video.
How does it compare to our other recent breakthrough, the Nankun? I couldn’t find any environmental impact studies for this device, but seeing as it only just began trial operations in June,4 I wouldn’t be surprised if such a study was forthcoming. It is important to note that the lubes, oils, and biofouling is another reason why wave energy hasn’t been utilized much in the past. It’s good to see companies like CalWave being proactive on that and also providing the results.
But all the environmental friendliness doesn’t mean much if the xWave isn’t good enough at generating energy to deploy in the first place! The smaller x1 devices can generate 100 kilowatts, which is enough for a larger apartment building, while their largest device, the xWave x100, can generate up to 500 MW. CalWave claims they’re scalable too, of course, just put more of them in the water. As we’ll see in a moment, this is a pretty important feature. Plus, the company claims their xWaves are built to last 20 years or more.9
According to CalWave, the xWave achieves a minimum capacity factor of 40% all on its own. But this can be boosted to over 80% if it is co-located and combined with offshore wind.10 Wind and waves actually form a dynamic duo. Remember how waves tend to be strongest in the winter months? Well wind tends to surge in the summer. When comparing the cost and lifetime power production for generators, we tend to use levelized cost of energy (LCOE), a calculation that tries to holistically measure how much power a given project will produce over its lifetime against how much it will cost over the same period of time. Both wave power and offshore wind tend to have high relative LCOEs for similar reasons, but co-locating these green energy devices can really help bring down this number. They can share electrical export infrastructure, two devices in one space saves on real estate costs, and it makes maintenance easier and cheaper to perform etc.14 15 16 So even though colocation isn’t a unique strategy to xWave, it’s nice to know that their device is being engineered both to work with wind and ala carte.
We’ve talked a lot about how the environment affects WECs, but how do WECs affect the environment? It’s frustratingly difficult to say exactly what the environmental impact of WECs are because the field is so young and there are so many variables. Literally tons of different designs, each doing different things with waves in different parts of unique marine ecosystems scattered around the globe. It’s a lot to calculate and it’s going to vary wildly from design to design.17 For example, many free-floating WECs utilize electrical cables to send the power they’ve collected back to shore. Marine life, like sharks, can sometimes be attracted to systems like this. For instance, some oceanic fiber optic cables have caused sharks to occasionally give ‘em a not-so-gentle test bite.18 19 The exact reason why is still kind of an unknown, so it’s something we have to understand better and address. For something like the loud air pump on an oscillating water column WECs, it might scare away resting seals and sea turtles. How do you account for all this? Further complicating things, these devices are supposed to last 20-plus years. Its difficult to study such a long-lived device in a field so young, especially in an environment as hostile as the ocean.20
Given the potential environmental concerns associated with WECs, it is comforting to know that xWave’s diligent studies show that marine life will be largely unaffected. 17 These studies even accounted for scale up. While scale up seems simple – just build more – the engineering and financial challenges have been a limiting factor in the past. 18 This is what makes xWave’s scalability and Nankun’s sheer size so exciting.
Of course, cost is always king and WECs have high initial costs. Installation and maintenance are often difficult and expensive because most WECs operate in or under choppy waters. We can see this play out with other renewables. Remember our similarly high-LCOE-havin’ offshore wind installations? There’s a reason why they tend to be significantly more expensive than their onshore relatives14 This is partly because finding a suitable underwater real estate and anchoring the WEC safely can cost 2 to 3 times more than the WEC device itself.21 And both installation and maintenance usually require waiting around for oceanic conditions to be safe or ‘just right’ which further drives up costs. These engineering and financial challenges surely don’t make it easy to test WECs at scale or in controlled environments.10 At the end of the day, the ocean is a difficult and expensive place to operate. It can feel like the ocean just doesn’t want us there.
But again, these challenges are worth addressing, due to wave energy’s crazy potential. University of California at Berkeley’s Reza Alam put it like this: Every square meter of a solar panel receives 0.2 to 0.3 kilowatts of solar energy, and every square meter of a wind tower absorbs 2 to 3 kilowatts. Every meter of the California coast receives 30 kilowatts of wave energy.22 Certainly puts the potential of wave energy into perspective. And there’s good reason to be optimistic. A 2019 study from NREL suggested that if all goes well the LCOE of wave energy converters could be as low as $0.30 per kWh by 2033, which would be $300 per MWh.23 LCOE of course varies a lot from site to site, but for comparison, a study from the Energy Information Administration (EIA) put the average LCOE for solar farms in 2021 at over $33 per MWh, and onshore wind at about $38 per MWh.24 It’s not expected for wave energy to get down to those prices until 2050. The conservative estimate is around $130 per MWh (plus or minus $60), and optimistically $70 per MWh (plus or minus $30). Considering solar is currently one of the cheapest ways to generate electricity, it looks like it won’t lose that crown anytime soon. But in the optimistic scenario wave energy can get into the ballpark.
Wave energy is still a new field, and its unique and expensive engineering challenges mean that it’s not nearly as ‘solved’ as wind or solar. But the sheer variety of ways we can turn waves into electricity has made wave energy an exciting field. And the potential, near-limitless clean energy provided by our seas is too good to pass up. As the Nankun and xWave show us, once the industry finds its sea legs, wave power may well be one of the most potent renewable energy tools in our utility belt … as long as the costs can come down.
- EIA – Hydropower explained: Wave Power ↩︎
- Sintef – Wave vs. Wind and Solar ↩︎
- Hydropower.org – A brief history of hydropower ↩︎
- Nation makes leaps with floating wave energy ↩︎
- Wikipedia – Wave Power ↩︎
- Yale – Why Wave Power Has Lagged Far Behind as Energy Source ↩︎
- Ocean Wave Energy Converters Optimization: A Comprehensive Review on Research Directions ↩︎
- Biofouling on mooring lines and power cables used in wave energy converter systems—Analysis of fatigue life and energy performance ↩︎
- Calwave – xWave Series ↩︎
- Ocean Wave Technology Makes a Splash in the Renewables Space ↩︎
- DOE Wave Energy Prize ↩︎
- DOE – CalWave Launches California’s First Long-Term Wave Energy Project ↩︎
- CalWave xWave Demonstration ↩︎
- Wave Energy Nails Spot Among 68 New Projects Getting $175 Million Love Tap From ARPA-E ↩︎
- Makai Ocean Engineering ↩︎
- Sinn Power ↩︎
- Wave-Energy Devices Might Affect the Natural Environment: Scientists plan research to better understand effects ↩︎
- The Global Internet Is Being Attacked by Sharks, Google Confirms ↩︎
- Effects of EMFs from Undersea Power Cables on Elasmobranchs and Other Marine Species. ↩︎
- Environmental Impact Assessments for wave energy developments – Learning from existing activities and informing future research priorities ↩︎
- Overtopping Wave Energy Converters: general aspects and stage of development ↩︎
- NBC – Why wave power may be the next big thing in green energy ↩︎
- NREL – Expert Elicitation for Wave Energy LCOE Futures ↩︎
- EIA – Levelized Costs of New Generation Resources in the Annual Energy Outlook 2022 ↩︎