What causes a seismic sea wave?

What is the difference the Wave energy platforms "Sea Raser" and "CETO Wave Power"?

• The "Sea Raser" and "CETO Wave Power" on the face of it seem very similar in the way they work, almost to the point that they could clash over copyright, what am I missing?

• Answer:

  The Searaser uses the bobbing of a surface buoy as the driving force for a piston-pump. The CETO uses the bobbing of a submerged buoy. Different enough to get around patents but same basic idea. From my understanding of waves & buoyancy, Searaser should generate a lot more power per buoy. Wave energy drops off rapidly with depth below surface. (I'm just starting to get into wave motion mechanics professionally so take that with a grain of salt). But the CETO being submerged is a significant reliability advantage -- the wave splash zone is a very challenging engineering environment. Being entirely submerged is a big advantage in corrosion potential and storm loads. Frankly, I'm skeptical of the power production of either. I would have to do some more research to figure out the theoretical pump horsepower this type of system would produce. Bigger buoys and higher waves should linearly increase the potential power output, but I'm not sure how that plays into the manufacturing costs. I'm also not sure how practical it is to expect these to produce enough pressure to directly act as reverse-osmosis pumps. Including line friction losses you're looking at needing about 1000 psi of pump pressure from the wave energy system. That's not a completely unrealistic number, but it's a hell of a lot higher than your garden hose. You're probably looking at high upfront cost for stronger pistons and pipelines. Just for a really rough power estimate for Searaser, let's look at some made-up numbers. (This is sanity-check math, nothing rigorous.) Let's assume a 6' diameter spherical buoy as a starting point. This is 113 cubic feet or 845 gallons. To maximize power for a two-stroke pump (as Searaser uses) we need a buoy that has approximately equal buoyed negative weight and unbuoyed positive weight. This will give it the same up-force during a wave crest as down-force during a wave trough. (The down-force is required to cycle the pump piston to its retracted position.) The average density of buoy to produce equal up and down force below/above seawater is 4.3 lbs/gal, because seawater is 8.6 lbs/gal. So our 6' spherical buoy should weigh about 3633 lbs in air and -3633 lbs submerged. If we want to produce 1000 psi of pressure, this system must have a piston cross-section of 3.6 square inches. If we then assume a reasonable wave height of 6 ft with a 10 second period (varies by region and season), we get 259 cubic inches of fluid every 5 seconds on both directions of stroke. 52 cubic inches per second (13.5 gpm) at 1000 psi comes out to 7.9 horsepower or 5.9 kilowatts. It's not very much, but the construction cost could be cheap per unit. Unfortunately scaling up to larger sizes will be difficult because larger buoyed mass means more lethargic response to wave motion, and thus lost power. I really think the two key challenges will be high-pressure pipeline connection cost to connect hundreds of these things together, and issues with bio-fouling the seawater intake/pumping system. Barnacles forming on piston surfaces will instantly destroy the pressure seals so great care is needed in the design of the pump system. I don't really see either design being economical compared to normal wind turbines, but I wouldn't rule out the possibility.