A relatively nascent technology—wave-powered desalination—is gaining ground in the United States. One company, Resolute Marine Energy, has been testing this technology since 2012, and the results seem promising.
Advocates of the technology believe it can be most effective off the coasts of developing and island nations that face more-significant water challenges than developed countries.
Resolute Marine Energy’s technology, Wave2O™, is straightforward. Its central mechanism is a metal flap that oscillates with changing wave movements. The flap converts that energy into pressurized seawater, which is sent to the shore for filtration via reverse osmosis. Reverse osmosis is a water purification process that removes ions, unwanted molecules and larger particles from a water sample by passing the water through a partially permeable membrane. Once the water has been treated, the excess brine and other impurities are sent to the brine diffuser, which distributes the brine over a larger area so as not to adversely affect marine life. Because Resolute’s technology relies on wave power rather than fossil fuels, it does not produce greenhouse gas emissions associated with climate change.
SAROS (Swell Actuated Reverse Osmosis System), a group started as a senior design project at the University of North Carolina at Charlotte, deploys similar technology that captures wave energy. The SAROS system utilizes small buoys which rock back and forth with the passing swells. The wave energy captured by this motion activates pumps, which suck saltwater into the buoy. The saltwater then gets pushed through the buoy to an onshore facility where the reverse osmosis process begins. The SAROS technology is on a much smaller scale than Resolute Marine’s, producing on average 3,500 gallons of freshwater per day, as opposed to Resolute Marine’s estimate of 1.057 million gallons of freshwater per plant per day.
Resolute Energy claims that Wave2O™ can produce a cubic meter of freshwater for $1.25. To put this in context, it costs residential customers about $1.78 per cubic meter of water produced by the Carlsbad seawater reverse-osmosis facility near San Diego, California. The Carlsbad facility is a traditional desalination plant, a technology powered by tremendous amounts of electricity. In terms of acquisition costs, SAROS estimates that a smaller unit capable of approximately 3,500 gallons of freshwater per day would cost approximately $23,000 and have a 10-year lifespan.
To understand if Wave2O™ could be scalable to meet the water demands of a metropolitan area, it helps to look at how much water the average person consumes. According to the Environmental Protection Agency (EPA), the average American uses about 100 gallons of water per day. A city like Los Angeles could be a candidate for Wave2O™ as its coastline and stronger waves could provide the ideal environment for the technology. Los Angeles has about 3.9 million residents, so they might consume about 390 million gallons of water per day. Resolute Marine claims five of its plants could produce roughly 20,000 cubic meters of water per day. That equals 5,283,441 gallons of freshwater, which is less than 2 percent of the total amount of water consumed by Angelenos. If it were able to scale up to 10 or 20 or more plants, then the technology could potentially take a larger dent out of the total water usage in a city like Los Angeles. But as of now, it does not appear that Wave2O™ could be scaled to meet the water needs of a large city in the developed world.
The initial testing of this technology in the U.S. has been encouraging, however. The SAROS team reported that its device was easy to deploy and anchor, with the results exceeding expectations. The initial testing buoy produced freshwater despite being placed in a relatively low wave energy environment off of the North Carolina coast. In addition to the physical tests conducted in North Carolina, the National Renewable Energy Laboratory simulated the technology’s efficacy and economic feasibility using the power generated by waves at a reference point off the coast of Humboldt, California. This modeling experiment found that the technology could be “a viable near-term solution to provide the nation with drinking water.”
A few potential challenges are associated with this technology, for example, the wave height needed to generate enough power. According to Resolute Marine Energy, the minimum amount of power needed to start the desalination process is 10 kilowatts of wave energy per linear meter of wavefront. In some pockets around the earth, waves will not meet this minimum energy threshold, but it appears that most areas can produce enough.
It may be necessary to lower expectations for this technology in the short-term. As this technology requires low capital investment, can power itself, and can be deployed to most parts of the world, the temptation exists to treat this as a panacea. If the technology becomes more widely adopted and continues to perform to a certain standard, people and governments may see this as the answer to their water crises, as opposed to one of several technologies in a broader repertoire of solutions. While it seems promising, there is nothing to indicate that the technology has the capacity to currently address anything approaching all or most of the world’s freshwater needs.
Resolute estimates that five 4,000 m3/day Wave2O™ plants could meet the UN-mandated minimum daily water requirements for approximately 240,000 people. While this would no doubt be a tremendous step in the right direction, this number must be kept in perspective. Approximately 1.1 billion people worldwide lack access to clean drinking water. As this technology scales upward, it is critical that global expectations viewed it correctly: as one promising tool in the fight for increased water access.
Wave-powered desalination could also run into legal hurdles if it becomes more realistic on a large scale. Depending on the jurisdiction, local environmental and not-in-my-backyard groups may oppose adding buoys that could affect pristine coastal vistas and boating corridors in places like California or Massachusetts. There may, however, be fewer hurdles in the developing world where the technology is needed most. Coastal areas in Africa, Asia, South America and island areas facing water challenges may be more eager to deploy this technology and more likely streamline its implementation.
Wave energy technology has potential, but it is very early in the implementation phase. The technology can produce freshwater using only wave energy, reducing the need for expensive, energy-intensive traditional desalination. Wave energy technology does not produce any carbon byproducts, which represents a key development in the fight against climate change. And while there is hope that wave-powered desalination can help improve water rights worldwide, it should be treated as one of several technologies that could help achieve this end.