The cure for anything is salt water—sweat, tears, or the sea
July 14, 2017 10:05 PM   Subscribe

Close to 200 trillion watts of kinetic energy lurk in the seas: more than enough to power the planet, if we could somehow extract it all.
posted by Chrysostom (30 comments total) 16 users marked this as a favorite
 
What a great read. As someone who knows nothing about it, the idea of capturing tidal energy always seemed so simple and I wondered why no one did it. Thanks for answering a years-old idle question I had.

They said Korea has a tidal power generator near Suwon, which is weird, because Suwon is completely landlocked. I am going to do some searching to learn about it, though.

Also, I saw some words in this article that I had never seen before. I am going to read about them and try to work them into my vocabulary. Ahem, I am looking for a very skookum bicycle. I intend to treat it harshly and I would like it to last.
posted by Literaryhero at 11:52 PM on July 14 [1 favorite]




Oh my! The Sihwa Lake Tidal Power Station is like ten minutes from my house! I have actually been on the tiny island where it is. They have a lookout tower and some other stuff there that I ignored because I assumed it was dumb, but now I am super curious. Oh boy oh boy oh boy! Thanks Chrysostom!
posted by Literaryhero at 12:26 AM on July 15 [2 favorites]


200 trillion watt-hours, perhaps. (2000 GWh)

or are they referring to sustained power delivery?
posted by oxidizer at 12:28 AM on July 15


Watts, as in power.
posted by pompomtom at 1:10 AM on July 15 [1 favorite]


During the latter part of the twenty-first century massive exploitation of tidal power began to have measurable effects on the rotation of the earth. This led to a period of unprecedented earthquakes and growing volcanic activity. Ocean currents were disrupted, making already unmanageable climate change faster and more chaotic. In addition instability began to affect the earth's magnetic field, leading to repeated switching and wandering of the magnetic poles, and intermittent leakage of cosmic radiation, leading to universal electrical outages, the effective termination of satellite communication and GPS systems, and steep increases in the incidence of various cancers.
posted by Segundus at 2:01 AM on July 15 [8 favorites]


I am Mithridates.
posted by Segundus at 2:07 AM on July 15 [1 favorite]


During the latter part of the twenty-first century massive exploitation of tidal power began to have measurable effects on the rotation of the earth.

The way you phrased your comment made me immediately think of this, and I couldn't unthink it.
posted by shapes that haunt the dusk at 2:32 AM on July 15 [3 favorites]


You know...
We've over fished the ocean. We've contaminated the snot out of it. We've driven ecosystems to the point of breaking by altering the shoreline significantly. Now, we want to revisit Hydro Electric power via tidal changes?

What could possibly go wrong.

Good for us != Good for the planet.
posted by Nanukthedog at 2:46 AM on July 15 [1 favorite]


Wave eneegy is my favorite. So much energy 'heh' has been spent on designing systems but not any real incentive; there's a lot of lip synch but that's not putting energy in the works. Even while wind tubines are being installed in the ocean.
posted by mightshould at 2:50 AM on July 15


There is incredible energy all around us, take out a penny, calculate the energy (e=mc2) but it's stable. The energy sources that are at that narrow range of just barely stable enough that all the energy is not released in under a second (fire, bombs, lithium) and very stable are few.

Ocean tides have huge dispersed energy over wide areas and also salt water that over time is incredibly corrosive (pour just a few drops of salt water into your computer :-) , anything with moving parts will need to be replaced frequently and if it's under the water it's a major diving project. Then the build needs to anticipate larger storms that take the gentle tide and turn it into a monster that will smash most any installation to twisted shreds.

It's an obvious powerful resource that has relatively few good natural locations to build and huge expensive equipment needed for minimal return -- until that big storm.
posted by sammyo at 6:06 AM on July 15 [3 favorites]


I would like to see some very strict and unforgiving cost analysis on wave/tidal energy harvesting that actually accounts for corrosion, upkeep, installation and repair costs in addition to the initial manufacturing.

My gut instinct tells me that you would never fully break even on energy costs due to how incredibly corrosive the ocean is. Every repair, replaced part and drop of anti-fouling paint would quickly add up and push the break-even point farther and farther away.
posted by loquacious at 6:21 AM on July 15 [3 favorites]


intermittent leakage of cosmic radiation

See, I know you meant to evoke a series of natural disasters spiraling out of control, but what I got from it was, "well, finally we can have superpowers."
posted by Halloween Jack at 6:26 AM on July 15 [4 favorites]


Why is no one investing in zero-point energy?
posted by blue_beetle at 7:15 AM on July 15 [2 favorites]


There's no point in it.
posted by Segundus at 7:48 AM on July 15 [9 favorites]


This reminds me of hearing about repeated efforts, recurring every year, where hippies try to make compost piles into natural water heaters.

Sure, there's a lot of latent heat inside an active compost pile. I've recorded temperatures up to 160 Fahrenheit. But that doesn't mean you can use that heat.

What happens is that someone puts a tank or a coil inside that compost pile, waits a few days, and it's hot! Yay! Then you use it. Then it's cold. Turns out that once you start using that heat, the compost pile can't produce it any more.

And people have to learn this for themselves every time.

so I'm skeptical that there would be no consequence for using tidal power, or wave power. Sure, there's energy there, and a lot of it. But once you try to use it, you might make it go away.
posted by yesster at 8:55 AM on July 15 [1 favorite]


They say they've done the modelling, and they can do it to an extent. A third of the power in the circumstance they detail is theoretically able to be extracted. That seems a lot to me, but that there is a safe skim also seems plausible.
posted by Peter B-S at 9:07 AM on July 15


Where the rivers meet the sea, there live the salmon, and the others that come and go.
posted by Oyéah at 9:45 AM on July 15 [1 favorite]


For those asking about the lifetime dollar cost of current or wave power, the term you're looking for is "levelized cost of energy": LCOE. That's essentially the NPV of the cost of generating electricity over the plant's lifetime. And since that's the number that investors use, it takes into account everything we know at the moment.

The DoE via NREL and EIA has done a lot of great work on studying LCOE in our various regions: overnight capital cost, fixed overhead (O&M), fuel costs, considering capacity factors, you name it. (DG ENER in the EU has some good work, too; I'm just giving US numbers because that's what I have on hand.) Their studies on current and wave generation aren't as comprehensive as on fossil, nuclear, PV, wind, etc., largely because we haven't converged on "best" solutions for the former yet, but it's worth reading some of their work.

TLDR: current wave energy plant designs are somewhere around $750/MWh LCOE, likely to come down a lot with improved technology but mostly with increased deployment scale. (DG ENER proposes possibly as low as $100/MWh at large scale by 2030.) PV solar without tax credits currently sits around $75/MWh and falling. Both are non-dispatchable and it's likely that PV and wave would receive similar tax / carbon cost benefits so those numbers can be compared without much hand-waving. For markets with poor solar LCOE things like wave might make a lot of sense for base capacity.
posted by introp at 2:17 PM on July 15 [2 favorites]


  But once you try to use it, you might make it go away.

I got that a lot when I was a wind developer: “You'll stop the wind!” “All that spinning machinery will make the earth turn more slowly!” I sometimes thought I was on the set of The Changes, or something.

Anyway:
  1. You can't take all the kinetic energy out of a moving fluid (air, water) in a turbine, because without kinetic energy the fluid stops moving in your turbine. So no more energetic fluid can enter the turbine if it's blocked. This was more elegantly shown by Betz to reach a theoretical energy efficiency limit of 4²/3³ (~ 59%)
  2. The sea is deep and wide, and the percentage of the tidal area you'll be taking energy out of is a very tiny fraction of the total. I would be amazed if you could detect any changes in current 10× rotor diameters downstream of a tidal turbine. You can do the same for a wind turbine: the atmosphere's about 10 km deep, and the tallest turbines are about 200 metres high.
Salter's work was, conspiracy theories aside, completely kiboshed by the nuclear-crazy UK government. Decimal places got moved the wrong way in the assessment report to make it look less favourable.

Wave power stations have to deal with huge variations in energy density, and many of the early ones got smashed apart in the first storm. The one I worked on, Osprey 1, didn't even make it on to its installation site. But I'm glad that Scotland's kept its wave technology: a former colleague from Toronto has just started working for the successor to Pelamis/Osprey in Edinburgh.
posted by scruss at 7:10 PM on July 15 [10 favorites]


As a follow up from my previous comment, I took the kids out to the tidal power generation plant this morning. I put some pictures here if you are interested at all.
posted by Literaryhero at 8:36 PM on July 15 [1 favorite]


many of the early ones got smashed apart in the first storm

Carnegie Clean Energy's CETO units are designed to avoid destructive storm turbulence by remaining fully submerged at all times.
posted by flabdablet at 8:54 PM on July 15 [1 favorite]


I wonder if some variant of a hydraulic ram would work here to convert a slow flow at a low head into a faster raised one that could power an elevated turbine. They're simple and structurally robust, and it would let you keep the turbine itself out of the water.
posted by Joe in Australia at 9:49 PM on July 15


Carnegie used that principle up to CETO 5; the only mechanicals associated with the buoys was a pump at the base end of the tether, and instead of an electrical umbilical cord connecting the buoy to the shore there was a high pressure salt water line.

That original design principle was one of the drivers behind Carnegie being able to use both desalination and electricity generation as selling points, since the energy consumed by a typical reverse-osmosis desal plant is only needed to pressurize the feed water.

Turns out that the efficiency loss from friction in the buoy-to-shore feed pipe overwhelms the cost advantages inherent in keeping the generators themselves onshore; for any given design output of water and generated electricity, overall system cost is lower if energy is moved from buoy to shore in electrical rather than kinetic form. The current CETO 6 design incorporates the generators into the buoys for that reason.
posted by flabdablet at 10:44 PM on July 15 [2 favorites]


That's a shame, especially if they couldn't make it work with nice clean pipes. I suppose they'd only degrade over time as barnacles and so forth grew over them. I was envisaging the current through The Rip turned to some productive use, but I couldn't imagine anything delicate surviving out there. Hence: hydraulic rams.
posted by Joe in Australia at 1:14 AM on July 16


Interestingly, the Danish designed Wave Star goes the other way and tries to keep as much as possible out of the water.

Literaryhero: your photo link isn't working, I would be interested to see your photos.

so I'm skeptical that there would be no consequence for using tidal power, or wave power. Sure, there's energy there, and a lot of it. But once you try to use it, you might make it go away.

The World Energy Council estimates that there is enough wave energy potential globally to meet all human energy needs for two years. Given that there is about 10MW installed globally it will be a long time before we have sucked it dry. But we never will because even if the tech gets working the realisable potential will be a lot less than the theoretical potential. And to get to the point of having zero wave energy then we have to stop the wind, which is what generates the waves, and the only way to do that is to turn off the sun.
posted by biffa at 8:02 AM on July 16


Those CETO units look interesting, but the fact that they were even considering hydraulic transmission shows they're still at the prototype stage. Wind power dumped hydraulic transmission in the early 1970s. Offshore electrics have their problems too: one of the big offshore wind farms was out of action for 18 months when its main transformer blew, and they discovered the lead time for getting an installation rig to site was over a year.

Most of the destroyed facilities were moving air-column types, though I think one of the Pelamis snakes came apart once.

Underwater turbines work nicely in the right kind of tide flow. They look like stubby wind turbines. I had friends who owned a very respectable wind O&M company who sold up and invested heavily in a couple of startups. They're both former Lloyd's marine engineers (and, oddly, car racing game developers) so knew what would work offshore.
posted by scruss at 8:02 AM on July 16


The main thing I like about CETO compared to the other wave energy recovery mechanicals I've seen so far is that the CETO buoys can move so freely that the only load the ocean can really put on them is tension on the tether cable. That, and the fact that they're well under the surface and therefore not susceptible to being smacked by megaton walls of angry water, makes them inherently damage-resistant compared to something like Pelamis, whose hinges would presumably be exposed to ridiculously high twisting and leverage forces under turbulent storm conditions.

Underwater turbines work nicely in the right kind of tide flow.

What's the standard method of dealing with the fact that tidal flows can hurl quite substantial boulders at anything fixed to the seabed?
posted by flabdablet at 8:55 AM on July 16


They say they've done the modelling, and they can do it to an extent. A third of the power in the circumstance they detail is theoretically able to be extracted. That seems a lot to me, but that there is a safe skim also seems plausible.

They have done a fair amount of modelling, but there is very little in the way of actual data arising from deployed wave energy devices, since so few have been deployed successfully under full operational conditions. The modelling I am aware of for wave energy reckoned you would be looking at around a maximum of 2% reduction in wave height at around 10 miles after the wave energy array, dependent on the wave conditions at the array.
posted by biffa at 10:07 AM on July 16


" if we could somehow extract it all"

This seems to always be where we start and thus we are in the Anthropocene.
posted by chance at 3:27 PM on July 18


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