14 ms·

I've worked in the UK offshore power industry. Wave and tidal energy schemes have failed to deliver useful and reliable energy after over 50 years of investiga

I've worked in the UK offshore power industry. Wave and tidal energy schemes have failed to deliver useful and reliable energy after over 50 years of investigation and research funding. Putting moving parts in salt water off the UK coast is always a tough prospect. By contrast, UK offshore wind power is delivering energy cheaper than ever and has emerged as a clear winner. Given the above, I'm honestly puzzled why offshore tidal energy projects are continuing to attract major funding. Incidentally, the argument that the tide is more reliable as it always flows twice a day is a rather moot point, as like wind, the tide doesn't always flow when you want it to.

nicoburns 5y ago
> By contrast, UK offshore wind power is delivering energy cheaper than ever and has emerged as a clear winner. > Given the above, I'm honestly puzzled why offshore tidal energy projects are continuing to attract major funding. Having a diversity of energy sources seems sensible...
- TheManInThePub 5y ago
  That is why we have a diversity of wind farms! Wind turbines scale much more easily than wave/tidal, both the size of the turbines themselves (much larger than a wave/tidal system could ever be) and where they can be located around the UK coast. A diversity of renewable energy sources is sensible (nuclear, wind, biofuel etc), but wave and tidal are difficult to scale and have failed to deliver.
  - Quarrelsome 5y ago
    doesn't mean they will always fail to deliver.
    - Guthur 5y ago
      I think that unless you drastically change the parameters of the implementation then yes it does mean it will always fail.
      - Quarrelsome 5y ago
        you're assuming the rate of improvement is constant? I feel like progress is a process that staggers. There may well be a future where tidal provides better or more cost effective yields.
        542354234235 5y ago
        > There may well be a future where tidal provides better or more cost effective yields. Based on what? With solar, we understood it was chemical science that would improve it. With wind, it was blade design, materials weight and durability, and generator technology. For tidal, what would improve that wouldn’t also improve wind? Improvements in durability, turbine, or generator tech would almost certainly also improve wind. Salt water will always be harder on equipment than air. Tidal forces are strong on large scales but on footprints similar to wind turbines, we aren’t talking about orders of magnitude more potential energy.
  - ClumsyPilot 5y ago
    Wind routinely rises fall on the scale of entirety of UK, having multiple windfarms around the country doesn't seem to help that much.
    - TheManInThePub 5y ago
      As my comment clearly said; add other renewables into the mix, but not wave/tidal. These technologies are a dead end and do not scale.
      - toecutter 5y ago
        Why don't they scale? is there not enough ocean in the world or something?
VBprogrammer 5y ago
> Incidentally, the argument that the tide is more reliable as it always flows twice a day is a rather moot point, as like wind, the tide doesn't always flow when you want it to. Producing energy on a completely predicable schedule, while being less useful than at will, is much easier to deal with than producing energy on a modestly predictable but highly variable basis. But on the general point about funding for tidal energy I agree with you. To make it work we'd need to make bold and highly disruptive changes to the environment, for example the tidal barrier across the Bristol Channel.
- TheManInThePub 5y ago
  > Producing energy on a completely predicable schedule, while being less useful than at will, is much easier to deal with than producing energy on a modestly predictable but highly variable basis I agree in theory, but in practice tidal doesn't scale like wind does (both in terns of the size of turbines and where they can be located around the coast). The predictable but small amount of energy it can produce is of limited use.
londons_explore 5y ago
> the tide doesn't always flow when you want it to. It is possible (although complex and expensive) to construct a tidal scheme that can generate power consistently 24x7. Conceptually, you can imagine two pools - one of which is filled on each high tide, and the other of which is emptied every low tide. There is always a water height difference between these two, so you can generate energy anytime with a generator between them. It turns out such a scheme is less profitable than just generating lots of energy when the tide is flowing fast.
- chriswarbo 5y ago
  Similar schemes have been proposed before. In the UK the Swansea tidal lagoon is particularly notorious, due to environmental concerns and the project's dodgy financials https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay
MichaelApproved 5y ago
> Putting moving parts in salt water off the UK coast is always a tough prospect. I’m guessing salt corrodes metals and barnacles grow on them which make the moving parts seize up. What are some of the less obvious issues that they face?
- dboreham 5y ago
  Wind. Waves.
- pony_sheared 5y ago
  I work in the sector (offshore renewables and O&G), here are a couple of interesting ones: 1. Short installation window: they can only install this machine when the tides are changing (i.e. not much flow), so they only have a couple of hours to collect the moorings and it hook it up to the grid 2. Fatigue: loads of areas, not just the turbine blades... variable loading on the mooring lines, vortex induced vibration of the power offtake cable, wave induced motion on the offtake cable On the two you mentioned: Marine growth (barnacles etc.) is generally manageable with anti fouling paints, or PTFE (teflon) coatings, wipers and bearings around the things that you don't want to seize up. The animals will have a hard time getting a footing in this high flow environment anyway, it'll be pretty well self cleaning. Saltwater / corrosion is also manageable with coating systems, cathodic protection and large corrosion allowances. While these two do cause issues, they're kinda "solved", you can generally apply the same straightforward techniques and they don't take up as much engineering effort as solving the installation, system design and fatigue.
  - MichaelApproved 5y ago
    Thanks!
viraptor 5y ago
> I'm honestly puzzled why offshore tidal energy projects are continuing to attract major funding. Is this a globally significant wasted funding? If not, it sounds like a reasonable idea to try something new from time to time. Worst case, some project trial fails and we learn a new failure mode / limitation. Best case, we get a new reliable power source.
- TheManInThePub 5y ago
  > If not, it sounds like a reasonable idea to try something new from time to time. Oh certainly! But funding is always finite. Unless some radical new wave/tidal technique comes to light (and it hasn't, yet!), then the project funding would surely be better directed to other renewable energy sources. The cynic in me says wave/tidal projects based on existing technologies (shown to perform or scale poorly) are simply to grab funding for green energy projects. The Swansea Tidal Lagoon fiasco is a classic example.
  - ClumsyPilot 5y ago
    "But funding is always finite" I am no longer confident in this seeming obvious statement, our ability to pump money into unproductive assets appears to be infinite, looking at the surging realestate prices, shares and crypto
- jacquesm 5y ago
  Except that they are not trying something new. They are trying something old. Again. And again.
chrisseaton 5y ago
> the tide doesn't always flow when you want it to So what? You can store tidal water and let the store always flow.
- TheManInThePub 5y ago
  Flow to where? Low tide only occurs twice a day.
  - chrisseaton 5y ago
    Other pools, which you then empty on low-tide. That way you can start draining your main pool as soon as high-tide is reached - you don't need to wait for low-tide. With a set of pools you can keep draining 24 hours a day.
    - TheManInThePub 5y ago
      Schemes such as this have been proposed, see the Swansea Tidal Lagoon [0]. The bottom line is that they are crazy expensive for the power they deliver and just don't compete against other renewables. [0]https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay
      - chrisseaton 5y ago
        > Schemes such as this have been proposed Lol well if you knew that then why did you ask me to explain it?
Mauricebranagh 5y ago
When I started work 79/80 I worked at BHRA (hydrodynamics research) and we had a load of RnD projects for things like the Salter duck etc and those still haven't gone anywhere
algo_trader 5y ago
Do u have any info on floating-solar-in-salt-water? (I have seen some in lakes/reservoirs. Surprisingly, less than 20% cost premium) > why offshore tidal energy projects are continuing to attract major funding Yeah. Agreed. Solar/wind/batteries/EVs will dominate. Everything else will get "scraps" from a $trillion/year energy industry ;)
- ashaikh 5y ago
  The largest floating solar under development that I know of is in Seychelles. It’s about 5MW. Haven’t heard much on the development timeline post Covid.
- roland35 5y ago
  With solar, available land isn't really a constraint so I don't think there is a huge need to put solar panels in the water versus just putting them on empty land or roofs.
  - oh_sigh 5y ago
    It could be used with pumped storage to reduce evaporative losses. Pumped storage doesn't really care what the temperature of the reservoir is, so instead of heating it up with the sun, you keep more water in the reservoir through less evaporation, and extract the solar energy that would otherwise do nothing.
- Qwertious 5y ago
  Floating solar makes sense in some dams that want to reduce evaporation, as they need something floating there anyway and it's almost always freshwater. I don't think land is more than 10% of the cost of solar in most places anyway - rooftop solar can cost $5000, and I'd expect rural areas to cost less than $500 for a paddock with the area of a house.
throwaway0a5e 5y ago
Wave energy is one of those things that only works at the "ghetto contraption I built with crap I had lying around" scale. Combine something that pumps, two check valves, some hose and creative plumbing (alternatively, replace creative plumbing with a lever and hydraulic cylinder) and you've got a really low pressure pump. From there it's just physics. Doing this kind of thing at scale just doesn't work. Between expensive engineers, permitting, code, surveys, OSHA, etc. etc. etc. there's no scale at which you can do this where you more than break even generating eletricity. Electricity travels great so you're competing with all sorts of other sources. It just doesn't work. But if all you want is to pump enough water into a tank so you can hose bird crap off your dock and you want to avoid digging a 300ft trench for a water line at the same time it works great. If you need real power somewhere remote go solar/wind. If you need better uptime than that then add lead acid to the mix. But once you start breaking into mid-range power needs (think gravel pit mine running crushers or something) it's hard to beat diesel.
chippy 5y ago
Like how just 30 years ago wind power was to be found at the hobby level in hippy farms but now has gradually matured, improved efficiency and is more stable, what's to stop tidal power gradually maturing and becoming more stable and efficient over a similar time frame? To me, this seems more like a pioneer project and one where we will learn lessons from.
- idiotsecant 5y ago
  Saltwater is the enemy of moving parts. We've been sailing ships for millennia and we haven't figured out a way to reliably solve that problem. Saltwater boats are constantly fighting a battle against corrosion and take huge amounts of maintenance and they are basically just painted hulls with a few little moving bits sticking out. This isn't a problem with a magic answer or a problem that will benefit substantially from incremental improvements to materials and designs.
- mistrial9 5y ago
  > 30 years ago wind power was to be found at the hobby level in hippy farms factually lacking and basically an insulting word IMO
jacquesm 5y ago
100% in agreement with this comment. All the tidal energy projects that I've seen to date except the very first ones were simply subsidy grabs or even outright scams. Highly annoying to see ideas that were - solidly - discredited decades ago come back in a slightly different guise for a re-run. Based on past performance I predict that this setup will right up until the first major breakage, after which it will be uneconomical to even salvage it. The temptation of the tides is easy to understand: the power is immense, it is essentially the power inherent in the gravitational attraction of the moon orbiting the earth conveniently transferred onto a moving fluid. So on paper it is trivial. But that's where it stops being simple. The forces being immense is also a force that tries to destroy your gear. Corrosive salt water is the nastiest working fluid you could pick outside of acids. The wind & the waves combined can really stretch the limits of engineering (I've seen a minor bit of water hammer effortlessly flip an 8 cubig meter concrete cube right across a dam, like a 2x2 lego brick only slightly larger and heavier). The 'head' compared to most hydro installations is limited (though in some locations it can be of usable height), the flows are hard to trap without interfering with the rest of the environment and so on. As a 'mere matter of engineering' it is probably one of the hardest jobs you could tackle including going to space, the ocean is an extremely dynamic environment and near the ocean shore that is even more true. And finally, to be economical such an installation has to work for a very long time after initial deployment because it is very hard to work on once deployed.
- porker 5y ago
  > Highly annoying to see ideas that were - solidly - discredited decades ago come back in a slightly different guise for a re-run. Any pointers to the ideas that have been discredited? This is a technology I dearly want to work, and I had bought into the narrative that it doesn't "because we haven't invested enough" (compared to offshore oil and gas production).
  - jacquesm 5y ago
    Gah where to start... anything capturing flow (it won't work, you are going to have to deal with massive volume with really little head), vertically oscillating elements anchored to the seabottom driving pistons, impellers driven by waves trying to enter constricted passages, horizontal device driven by waves running up the tidal grounds, under water turbines of all sorts, shapes and sizes, scissor arrangements (with or without floats attached to the far end). You can broadly group all tidal devices into several simple groupings and for each of those there were a number of initial prototypes and all of those did not make it past the POC or initial deployment. Anything the future is likely to come up with will be variations on those themes. That won't stop people from trying and it won't stop future subsidy grabs because this all falls under the 'wouldn't it be nice if it worked' heading. Yes, it would be very nice. But no, it doesn't work and if you're not going to come up with something radically new you are better off reading the literature on what exactly made it not work the first time. Those who don't know history... Here is a very nice example: https://teamwork.nl/category/teamwork-technology/ https://teamwork.nl/category/teamwork-technology/ I'm sure they pocketed a ton of subsidy by now. In the same vane (pun intended): rooftop windmills, vertical axis turbines, kites, sound to energy conversion and on and on.
grey-area 5y ago
Wave has obvious problems with mechanical wave action and corrosion quickly destroying any machine you leave in the waves, access and maintenance. It's unsurprising this is very difficult to scale and it does seem a dead end. Tidal energy does seem like in principle it should work without many moving parts at all save the turbines, which don't have to be metal. Is it the turbines themselves which are very difficult to maintain in salt water? This one is a floating design, which isn't ideal for maintenance, but I imagine at a large enough scale a dam between two bits of land with turbines in it would work - something we already do with hydro power and fresh water, and a concrete dam with access tunnels would solve a lot of problems with access and maintenance.
- nradov 5y ago
  In addition to mechanical wear and corrosion, marine growth such as barnacles cause huge maintenance problems for any equipment in that environment.
  - markbnj 5y ago
    That's for sure. I don't know anything about this specific application but having worked in the shipping business and in commercial fishing I can attest to the problems with marine growth and corrosion, not to mention electrolytic issues for any contacting dissimilar metals that are immersed. Presumably all this is accounted for but I have to think the maintenance requirements for a long-term floating installation like this are no less than they would be for a commercial vessel, i.e. about 10% of the "hull value" per annum at a minimum.
- 542354234235 5y ago
  >Is it the turbines themselves which are very difficult to maintain in salt water? The real key is they are far more difficult to maintain than wind turbines. Also, dams are ecological nightmares and disrupting huge swaths of coastline is not ideal. Dams also made use of very specific geological conditions where a maximum amount of water power could be achieved with the least amount of money, time, materials, etc. Coastlines don’t have steep cannon walls to build up hundreds of meters of water to push through turbines at high pressure. Coastal tides are moving water meters high, not hundreds of meters. It isn’t that it can’t be done, it is just that it can’t be done more economically than other technologies.
kumarvvr 5y ago
I have seen designs where moving tidal water compresses and pushes air inside a concrete structure to move air turbines. Any idea about those projects?
- TheManInThePub 5y ago
  An air driven Wells turbine? As with other wave/tidal schemes, they are not viable at scale. Consider the flagship 'LIMPET' project: https://en.wikipedia.org/wiki/Islay_LIMPET https://en.wikipedia.org/wiki/Islay_LIMPET
  - noneeeed 5y ago
    Blimey, I remember seeing that covered on Tomorrow's World when it was being built. It seemed like an interesting idea at the time.
mustafa_pasi 5y ago
That is what I was going to say. Is there any particular reason why they are trying to harvest wave energy? Is it more abundant or more reliable?
- bumby 5y ago
  I don't work in the industry, but I've often wondered if the allure of wave energy comes from the fact that the theoretical energy available is proportional to the density of the fluid. So a turbine driven by water would have a much higher theoretical power capacity than one in the air for the same fluid speed.
  - TheManInThePub 5y ago
    > the allure of wave energy comes from the fact that the theoretical energy available is proportional to the density of the fluid. But the power generated by a turbine is proportional to the cube of the air/fluid velocity..... and the wind normally moves much faster than tidal flow.
    - bumby 5y ago
      Right, that's why I wanted to make sure to add the caveat about fluid velocity. But the density of water is almost 1000x that of air so there's a large benefit to water at lower fluid speeds. A rough back-of-the-envelope calculation shows the crossover is when airspeed is about 9.2x the speed of the water flow under perfect theoretical conditions. It's also worth noting that when dealing with centrifugal devices, the realized power never actually follows the power law. It's usually degraded quite a bit due to linear losses. A common power used in air systems is 2.1 rather than the cube; using that value, the airspeed must be almost 24x the water velocity. I've never personally seen anything greater than 2.7 (the higher numbers, IMO, tend to be used as a sales pitch rather than an engineering decision), but again, I don't work in these particular systems.
  - toecutter 5y ago
    Quick note, confusingly throughout this thread people have used the phrase "wave energy" as essentially a synonym for "tidal energy", they are separate technologies sometimes talked about under the combined category of ocean energy or marine hydrokinetics. Increased power density is indeed one allure of wave energy vs wind. In the same way that wind is concentrated solar energy, studying the mechanisms and origins of waves show they are essentially a form of concentrated wind energy. So if the difficult design challenges are solved, there is potential for greater energy per unit of structural material which some believe could be associated with competitive cost of energy. Other allures of wave energy include that it is fairly consistent, with some seasonal variations, and its decoupled from solar or wind which decreases the chance that all renewables resources aren't producing at the same time. Of course this is talking about wave energy where oscillations occur with a period of approximately 4-18 seconds rather than tidal with several periods per day, and for these periods of time flow is essentially unidirectional. Tidal energy, like the link in this thread, often uses underwater turbine but wave energy devices rarely use this design.
klmadfejno 5y ago
I'm not an engineer so this is probably a stupid idea, but, rather than moving turbines with the tide, couldn't you: * Hollow out an area of the beach that's underwater at high tide * Install a big tank that lifts up some number of meters. * Lift the tank at low tide * Let water fill the tank at high tide * Drop your tank of heavy water like a gravity battery to generate power, at whatever rate you choose * Release water so its easy to lift again
- andechs 5y ago
  How big is this tank? Water is heavy, and we're talking about an insanely massive tank to generate any reasonable amount of energy... that can also move and be used as a gravity battery. Anything you build the tank from would also be vulnerable to the corrosion of the sea water. Hydroelectric dams essentially build a tank, but they only build one wall of the tank. Hydroelectric turbines are about 90% efficient, so you're essentially looking to extract the same amount of energy from the weight of the sea water... with the complicating factor of needing to peak smooth due to tides.
- Avshalom 5y ago
  So instead of that what is done is https://en.wikipedia.org/wiki/Tidal_barrage https://en.wikipedia.org/wiki/Tidal_barrage You open gates; let high tide naturally fill a reservoir; close the gates; let the water back out through a turbine. They have been built but the largest are only producing ~250 MW (ETA: thats 250 PEAK, actual generation is more like 50MW) which is nothing compared to what it takes to get that, like if you're already building a seawall it only might be worth installing turbines.
- riquito 5y ago
  > Release water so its easy to lift again How? Don't you have to pump it out since it's below sea level?
- chriswarbo 5y ago
  Gravity is incredibly weak; you'd need a huge tank. This proposal has a footprint over 11 square kilometres: https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay (Sending the water through bi-directional turbines, to get power from the inflow and outflow)
gns24 5y ago
Tidal energy doesn't compete with wind, it competes with energy storage. Having virtually no wind production over the whole UK for a week happens regularly; in fact this last week is a good example - production has averaged well under 2GW according to https://www.gridwatch.templar.co.uk/ https://www.gridwatch.templar.co.uk/ On a windy week production can average over 10GW, but as yet grid scale storage is about as immature a technology as tidal generation (with the exception of pumped hydro, and there is a limited number of suitable sites for that).
ggm 5y ago
If tidal or wave had been viable i think by now the offshore oil industry would have been exploiting it at their installations. For contrast, some of the fastest deployments of autonomous vehicles, solar energy and novel digital communications come at Australian remote mine sites. I badly wanted to read takedowns of your summary, but I'm forced to say absent well constructed arguments of viability i think you're carrying the room. Obviously the backers, grant or seed capital aided believe in what they're doing and we're a long way down the road from Salter's ducks. But on balance I think this is a niche product. Some places like the bay of fundy, if you took local ecology out of the picture, look like 80% of the construction cost of a tidal race is done for you by nature. It doesn't mean they would work, it only means the initial capital investment might be better. I think the same is true of the Scots waterways used for these tests, but the volume of power remains below wind and you would be right to say it questions why the investment given the balance of returns. The same is true of Carbon Capture and Storage: huge but elusive upside for the coal power sector, exploiting something known to work, from gas and oil well injection. It's had billions pumped in (hah) worldwide and doesn't seem to work in practice. Fugitive gas is a problem and the chemistry is complex and consumes energy ferociously to do the conversions. Had the same funds been spent on battery tech, improvements in transmission and other change to power, we'd be significantly better off (in australia) (Not an engineer, not in the power sector)
eloff 5y ago
I understand what you're saying, and I agree. But if we only tried things that were known to be the most efficient we'd never make progress. Negative results are also progress. I'm glad there is research into all angles of the energy space, we have an incredible need for green energy if we're going to move forward without destroying our planet.

nicoburns 5y ago

> By contrast, UK offshore wind power is delivering energy cheaper than ever and has emerged as a clear winner. > Given the above, I'm honestly puzzled why offshore tidal energy projects are continuing to attract major funding. Having a diversity of energy sources seems sensible...

TheManInThePub 5y ago
That is why we have a diversity of wind farms! Wind turbines scale much more easily than wave/tidal, both the size of the turbines themselves (much larger than a wave/tidal system could ever be) and where they can be located around the UK coast. A diversity of renewable energy sources is sensible (nuclear, wind, biofuel etc), but wave and tidal are difficult to scale and have failed to deliver.
- Quarrelsome 5y ago
  doesn't mean they will always fail to deliver.
  - Guthur 5y ago
    I think that unless you drastically change the parameters of the implementation then yes it does mean it will always fail.
    - Quarrelsome 5y ago
      you're assuming the rate of improvement is constant? I feel like progress is a process that staggers. There may well be a future where tidal provides better or more cost effective yields.
      - 542354234235 5y ago
        > There may well be a future where tidal provides better or more cost effective yields. Based on what? With solar, we understood it was chemical science that would improve it. With wind, it was blade design, materials weight and durability, and generator technology. For tidal, what would improve that wouldn’t also improve wind? Improvements in durability, turbine, or generator tech would almost certainly also improve wind. Salt water will always be harder on equipment than air. Tidal forces are strong on large scales but on footprints similar to wind turbines, we aren’t talking about orders of magnitude more potential energy.
- ClumsyPilot 5y ago
  Wind routinely rises fall on the scale of entirety of UK, having multiple windfarms around the country doesn't seem to help that much.
  - TheManInThePub 5y ago
    As my comment clearly said; add other renewables into the mix, but not wave/tidal. These technologies are a dead end and do not scale.
    - toecutter 5y ago
      Why don't they scale? is there not enough ocean in the world or something?

VBprogrammer 5y ago

> Incidentally, the argument that the tide is more reliable as it always flows twice a day is a rather moot point, as like wind, the tide doesn't always flow when you want it to. Producing energy on a completely predicable schedule, while being less useful than at will, is much easier to deal with than producing energy on a modestly predictable but highly variable basis. But on the general point about funding for tidal energy I agree with you. To make it work we'd need to make bold and highly disruptive changes to the environment, for example the tidal barrier across the Bristol Channel.

TheManInThePub 5y ago
> Producing energy on a completely predicable schedule, while being less useful than at will, is much easier to deal with than producing energy on a modestly predictable but highly variable basis I agree in theory, but in practice tidal doesn't scale like wind does (both in terns of the size of turbines and where they can be located around the coast). The predictable but small amount of energy it can produce is of limited use.

londons_explore 5y ago

> the tide doesn't always flow when you want it to. It is possible (although complex and expensive) to construct a tidal scheme that can generate power consistently 24x7. Conceptually, you can imagine two pools - one of which is filled on each high tide, and the other of which is emptied every low tide. There is always a water height difference between these two, so you can generate energy anytime with a generator between them. It turns out such a scheme is less profitable than just generating lots of energy when the tide is flowing fast.

chriswarbo 5y ago
Similar schemes have been proposed before. In the UK the Swansea tidal lagoon is particularly notorious, due to environmental concerns and the project's dodgy financials https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay

MichaelApproved 5y ago

> Putting moving parts in salt water off the UK coast is always a tough prospect. I’m guessing salt corrodes metals and barnacles grow on them which make the moving parts seize up. What are some of the less obvious issues that they face?

dboreham 5y ago
Wind. Waves.
pony_sheared 5y ago
I work in the sector (offshore renewables and O&G), here are a couple of interesting ones: 1. Short installation window: they can only install this machine when the tides are changing (i.e. not much flow), so they only have a couple of hours to collect the moorings and it hook it up to the grid 2. Fatigue: loads of areas, not just the turbine blades... variable loading on the mooring lines, vortex induced vibration of the power offtake cable, wave induced motion on the offtake cable On the two you mentioned: Marine growth (barnacles etc.) is generally manageable with anti fouling paints, or PTFE (teflon) coatings, wipers and bearings around the things that you don't want to seize up. The animals will have a hard time getting a footing in this high flow environment anyway, it'll be pretty well self cleaning. Saltwater / corrosion is also manageable with coating systems, cathodic protection and large corrosion allowances. While these two do cause issues, they're kinda "solved", you can generally apply the same straightforward techniques and they don't take up as much engineering effort as solving the installation, system design and fatigue.
- MichaelApproved 5y ago
  Thanks!

viraptor 5y ago

> I'm honestly puzzled why offshore tidal energy projects are continuing to attract major funding. Is this a globally significant wasted funding? If not, it sounds like a reasonable idea to try something new from time to time. Worst case, some project trial fails and we learn a new failure mode / limitation. Best case, we get a new reliable power source.

TheManInThePub 5y ago
> If not, it sounds like a reasonable idea to try something new from time to time. Oh certainly! But funding is always finite. Unless some radical new wave/tidal technique comes to light (and it hasn't, yet!), then the project funding would surely be better directed to other renewable energy sources. The cynic in me says wave/tidal projects based on existing technologies (shown to perform or scale poorly) are simply to grab funding for green energy projects. The Swansea Tidal Lagoon fiasco is a classic example.
- ClumsyPilot 5y ago
  "But funding is always finite" I am no longer confident in this seeming obvious statement, our ability to pump money into unproductive assets appears to be infinite, looking at the surging realestate prices, shares and crypto
jacquesm 5y ago
Except that they are not trying something new. They are trying something old. Again. And again.

chrisseaton 5y ago

> the tide doesn't always flow when you want it to So what? You can store tidal water and let the store always flow.

TheManInThePub 5y ago
Flow to where? Low tide only occurs twice a day.
- chrisseaton 5y ago
  Other pools, which you then empty on low-tide. That way you can start draining your main pool as soon as high-tide is reached - you don't need to wait for low-tide. With a set of pools you can keep draining 24 hours a day.
  - TheManInThePub 5y ago
    Schemes such as this have been proposed, see the Swansea Tidal Lagoon [0]. The bottom line is that they are crazy expensive for the power they deliver and just don't compete against other renewables. [0]https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay
    - chrisseaton 5y ago
      > Schemes such as this have been proposed Lol well if you knew that then why did you ask me to explain it?

Mauricebranagh 5y ago

When I started work 79/80 I worked at BHRA (hydrodynamics research) and we had a load of RnD projects for things like the Salter duck etc and those still haven't gone anywhere

algo_trader 5y ago

Do u have any info on floating-solar-in-salt-water? (I have seen some in lakes/reservoirs. Surprisingly, less than 20% cost premium) > why offshore tidal energy projects are continuing to attract major funding Yeah. Agreed. Solar/wind/batteries/EVs will dominate. Everything else will get "scraps" from a $trillion/year energy industry ;)

ashaikh 5y ago
The largest floating solar under development that I know of is in Seychelles. It’s about 5MW. Haven’t heard much on the development timeline post Covid.
roland35 5y ago
With solar, available land isn't really a constraint so I don't think there is a huge need to put solar panels in the water versus just putting them on empty land or roofs.
- oh_sigh 5y ago
  It could be used with pumped storage to reduce evaporative losses. Pumped storage doesn't really care what the temperature of the reservoir is, so instead of heating it up with the sun, you keep more water in the reservoir through less evaporation, and extract the solar energy that would otherwise do nothing.
Qwertious 5y ago
Floating solar makes sense in some dams that want to reduce evaporation, as they need something floating there anyway and it's almost always freshwater. I don't think land is more than 10% of the cost of solar in most places anyway - rooftop solar can cost $5000, and I'd expect rural areas to cost less than $500 for a paddock with the area of a house.

throwaway0a5e 5y ago

Wave energy is one of those things that only works at the "ghetto contraption I built with crap I had lying around" scale. Combine something that pumps, two check valves, some hose and creative plumbing (alternatively, replace creative plumbing with a lever and hydraulic cylinder) and you've got a really low pressure pump. From there it's just physics. Doing this kind of thing at scale just doesn't work. Between expensive engineers, permitting, code, surveys, OSHA, etc. etc. etc. there's no scale at which you can do this where you more than break even generating eletricity. Electricity travels great so you're competing with all sorts of other sources. It just doesn't work. But if all you want is to pump enough water into a tank so you can hose bird crap off your dock and you want to avoid digging a 300ft trench for a water line at the same time it works great. If you need real power somewhere remote go solar/wind. If you need better uptime than that then add lead acid to the mix. But once you start breaking into mid-range power needs (think gravel pit mine running crushers or something) it's hard to beat diesel.

chippy 5y ago

Like how just 30 years ago wind power was to be found at the hobby level in hippy farms but now has gradually matured, improved efficiency and is more stable, what's to stop tidal power gradually maturing and becoming more stable and efficient over a similar time frame? To me, this seems more like a pioneer project and one where we will learn lessons from.

idiotsecant 5y ago
Saltwater is the enemy of moving parts. We've been sailing ships for millennia and we haven't figured out a way to reliably solve that problem. Saltwater boats are constantly fighting a battle against corrosion and take huge amounts of maintenance and they are basically just painted hulls with a few little moving bits sticking out. This isn't a problem with a magic answer or a problem that will benefit substantially from incremental improvements to materials and designs.
mistrial9 5y ago
> 30 years ago wind power was to be found at the hobby level in hippy farms factually lacking and basically an insulting word IMO

jacquesm 5y ago

100% in agreement with this comment. All the tidal energy projects that I've seen to date except the very first ones were simply subsidy grabs or even outright scams. Highly annoying to see ideas that were - solidly - discredited decades ago come back in a slightly different guise for a re-run. Based on past performance I predict that this setup will right up until the first major breakage, after which it will be uneconomical to even salvage it. The temptation of the tides is easy to understand: the power is immense, it is essentially the power inherent in the gravitational attraction of the moon orbiting the earth conveniently transferred onto a moving fluid. So on paper it is trivial. But that's where it stops being simple. The forces being immense is also a force that tries to destroy your gear. Corrosive salt water is the nastiest working fluid you could pick outside of acids. The wind & the waves combined can really stretch the limits of engineering (I've seen a minor bit of water hammer effortlessly flip an 8 cubig meter concrete cube right across a dam, like a 2x2 lego brick only slightly larger and heavier). The 'head' compared to most hydro installations is limited (though in some locations it can be of usable height), the flows are hard to trap without interfering with the rest of the environment and so on. As a 'mere matter of engineering' it is probably one of the hardest jobs you could tackle including going to space, the ocean is an extremely dynamic environment and near the ocean shore that is even more true. And finally, to be economical such an installation has to work for a very long time after initial deployment because it is very hard to work on once deployed.

porker 5y ago
> Highly annoying to see ideas that were - solidly - discredited decades ago come back in a slightly different guise for a re-run. Any pointers to the ideas that have been discredited? This is a technology I dearly want to work, and I had bought into the narrative that it doesn't "because we haven't invested enough" (compared to offshore oil and gas production).
- jacquesm 5y ago
  Gah where to start... anything capturing flow (it won't work, you are going to have to deal with massive volume with really little head), vertically oscillating elements anchored to the seabottom driving pistons, impellers driven by waves trying to enter constricted passages, horizontal device driven by waves running up the tidal grounds, under water turbines of all sorts, shapes and sizes, scissor arrangements (with or without floats attached to the far end). You can broadly group all tidal devices into several simple groupings and for each of those there were a number of initial prototypes and all of those did not make it past the POC or initial deployment. Anything the future is likely to come up with will be variations on those themes. That won't stop people from trying and it won't stop future subsidy grabs because this all falls under the 'wouldn't it be nice if it worked' heading. Yes, it would be very nice. But no, it doesn't work and if you're not going to come up with something radically new you are better off reading the literature on what exactly made it not work the first time. Those who don't know history... Here is a very nice example: https://teamwork.nl/category/teamwork-technology/ https://teamwork.nl/category/teamwork-technology/ I'm sure they pocketed a ton of subsidy by now. In the same vane (pun intended): rooftop windmills, vertical axis turbines, kites, sound to energy conversion and on and on.

grey-area 5y ago

Wave has obvious problems with mechanical wave action and corrosion quickly destroying any machine you leave in the waves, access and maintenance. It's unsurprising this is very difficult to scale and it does seem a dead end. Tidal energy does seem like in principle it should work without many moving parts at all save the turbines, which don't have to be metal. Is it the turbines themselves which are very difficult to maintain in salt water? This one is a floating design, which isn't ideal for maintenance, but I imagine at a large enough scale a dam between two bits of land with turbines in it would work - something we already do with hydro power and fresh water, and a concrete dam with access tunnels would solve a lot of problems with access and maintenance.

nradov 5y ago
In addition to mechanical wear and corrosion, marine growth such as barnacles cause huge maintenance problems for any equipment in that environment.
- markbnj 5y ago
  That's for sure. I don't know anything about this specific application but having worked in the shipping business and in commercial fishing I can attest to the problems with marine growth and corrosion, not to mention electrolytic issues for any contacting dissimilar metals that are immersed. Presumably all this is accounted for but I have to think the maintenance requirements for a long-term floating installation like this are no less than they would be for a commercial vessel, i.e. about 10% of the "hull value" per annum at a minimum.
542354234235 5y ago
>Is it the turbines themselves which are very difficult to maintain in salt water? The real key is they are far more difficult to maintain than wind turbines. Also, dams are ecological nightmares and disrupting huge swaths of coastline is not ideal. Dams also made use of very specific geological conditions where a maximum amount of water power could be achieved with the least amount of money, time, materials, etc. Coastlines don’t have steep cannon walls to build up hundreds of meters of water to push through turbines at high pressure. Coastal tides are moving water meters high, not hundreds of meters. It isn’t that it can’t be done, it is just that it can’t be done more economically than other technologies.

kumarvvr 5y ago

I have seen designs where moving tidal water compresses and pushes air inside a concrete structure to move air turbines. Any idea about those projects?

TheManInThePub 5y ago
An air driven Wells turbine? As with other wave/tidal schemes, they are not viable at scale. Consider the flagship 'LIMPET' project: https://en.wikipedia.org/wiki/Islay_LIMPET https://en.wikipedia.org/wiki/Islay_LIMPET
- noneeeed 5y ago
  Blimey, I remember seeing that covered on Tomorrow's World when it was being built. It seemed like an interesting idea at the time.

mustafa_pasi 5y ago

That is what I was going to say. Is there any particular reason why they are trying to harvest wave energy? Is it more abundant or more reliable?

bumby 5y ago
I don't work in the industry, but I've often wondered if the allure of wave energy comes from the fact that the theoretical energy available is proportional to the density of the fluid. So a turbine driven by water would have a much higher theoretical power capacity than one in the air for the same fluid speed.
- TheManInThePub 5y ago
  > the allure of wave energy comes from the fact that the theoretical energy available is proportional to the density of the fluid. But the power generated by a turbine is proportional to the cube of the air/fluid velocity..... and the wind normally moves much faster than tidal flow.
  - bumby 5y ago
    Right, that's why I wanted to make sure to add the caveat about fluid velocity. But the density of water is almost 1000x that of air so there's a large benefit to water at lower fluid speeds. A rough back-of-the-envelope calculation shows the crossover is when airspeed is about 9.2x the speed of the water flow under perfect theoretical conditions. It's also worth noting that when dealing with centrifugal devices, the realized power never actually follows the power law. It's usually degraded quite a bit due to linear losses. A common power used in air systems is 2.1 rather than the cube; using that value, the airspeed must be almost 24x the water velocity. I've never personally seen anything greater than 2.7 (the higher numbers, IMO, tend to be used as a sales pitch rather than an engineering decision), but again, I don't work in these particular systems.
- toecutter 5y ago
  Quick note, confusingly throughout this thread people have used the phrase "wave energy" as essentially a synonym for "tidal energy", they are separate technologies sometimes talked about under the combined category of ocean energy or marine hydrokinetics. Increased power density is indeed one allure of wave energy vs wind. In the same way that wind is concentrated solar energy, studying the mechanisms and origins of waves show they are essentially a form of concentrated wind energy. So if the difficult design challenges are solved, there is potential for greater energy per unit of structural material which some believe could be associated with competitive cost of energy. Other allures of wave energy include that it is fairly consistent, with some seasonal variations, and its decoupled from solar or wind which decreases the chance that all renewables resources aren't producing at the same time. Of course this is talking about wave energy where oscillations occur with a period of approximately 4-18 seconds rather than tidal with several periods per day, and for these periods of time flow is essentially unidirectional. Tidal energy, like the link in this thread, often uses underwater turbine but wave energy devices rarely use this design.

klmadfejno 5y ago

I'm not an engineer so this is probably a stupid idea, but, rather than moving turbines with the tide, couldn't you: * Hollow out an area of the beach that's underwater at high tide * Install a big tank that lifts up some number of meters. * Lift the tank at low tide * Let water fill the tank at high tide * Drop your tank of heavy water like a gravity battery to generate power, at whatever rate you choose * Release water so its easy to lift again

andechs 5y ago
How big is this tank? Water is heavy, and we're talking about an insanely massive tank to generate any reasonable amount of energy... that can also move and be used as a gravity battery. Anything you build the tank from would also be vulnerable to the corrosion of the sea water. Hydroelectric dams essentially build a tank, but they only build one wall of the tank. Hydroelectric turbines are about 90% efficient, so you're essentially looking to extract the same amount of energy from the weight of the sea water... with the complicating factor of needing to peak smooth due to tides.
Avshalom 5y ago
So instead of that what is done is https://en.wikipedia.org/wiki/Tidal_barrage https://en.wikipedia.org/wiki/Tidal_barrage You open gates; let high tide naturally fill a reservoir; close the gates; let the water back out through a turbine. They have been built but the largest are only producing ~250 MW (ETA: thats 250 PEAK, actual generation is more like 50MW) which is nothing compared to what it takes to get that, like if you're already building a seawall it only might be worth installing turbines.
riquito 5y ago
> Release water so its easy to lift again How? Don't you have to pump it out since it's below sea level?
chriswarbo 5y ago
Gravity is incredibly weak; you'd need a huge tank. This proposal has a footprint over 11 square kilometres: https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay (Sending the water through bi-directional turbines, to get power from the inflow and outflow)

gns24 5y ago

Tidal energy doesn't compete with wind, it competes with energy storage. Having virtually no wind production over the whole UK for a week happens regularly; in fact this last week is a good example - production has averaged well under 2GW according to https://www.gridwatch.templar.co.uk/ https://www.gridwatch.templar.co.uk/ On a windy week production can average over 10GW, but as yet grid scale storage is about as immature a technology as tidal generation (with the exception of pumped hydro, and there is a limited number of suitable sites for that).

ggm 5y ago

If tidal or wave had been viable i think by now the offshore oil industry would have been exploiting it at their installations. For contrast, some of the fastest deployments of autonomous vehicles, solar energy and novel digital communications come at Australian remote mine sites. I badly wanted to read takedowns of your summary, but I'm forced to say absent well constructed arguments of viability i think you're carrying the room. Obviously the backers, grant or seed capital aided believe in what they're doing and we're a long way down the road from Salter's ducks. But on balance I think this is a niche product. Some places like the bay of fundy, if you took local ecology out of the picture, look like 80% of the construction cost of a tidal race is done for you by nature. It doesn't mean they would work, it only means the initial capital investment might be better. I think the same is true of the Scots waterways used for these tests, but the volume of power remains below wind and you would be right to say it questions why the investment given the balance of returns. The same is true of Carbon Capture and Storage: huge but elusive upside for the coal power sector, exploiting something known to work, from gas and oil well injection. It's had billions pumped in (hah) worldwide and doesn't seem to work in practice. Fugitive gas is a problem and the chemistry is complex and consumes energy ferociously to do the conversions. Had the same funds been spent on battery tech, improvements in transmission and other change to power, we'd be significantly better off (in australia) (Not an engineer, not in the power sector)

eloff 5y ago

I understand what you're saying, and I agree. But if we only tried things that were known to be the most efficient we'd never make progress. Negative results are also progress. I'm glad there is research into all angles of the energy space, we have an incredible need for green energy if we're going to move forward without destroying our planet.