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Comment by TheManInThePub | Hacker News Reader

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.

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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.

> 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).

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/

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.

> massive volume with really little head

This is really key, there just isn't that much energy available in a small enough area for utility scale production. I would add the caveat that for small scale production, some schemes could actually work quite well, like some kite schemes. But no one is investing in small scale, all the development is for multi megawatt systems.

The linked article is a perfect example. Created to fit one specific location where it just might work and produce a pittance of energy twice every day. I'm curious if it will survive the first real test: a good storm. Never mind the power that it generates. But for sure a lot of money got blown on this.

Storms create issues at depth? Even 45m under the sea?

Yes. Single waves can be 10 meters or more, the resulting currents and direction changes can easily affect the ocean up to 100 meters down from the surface.

Really, marine engineering is an art, and anything that isn't solidly anchored is going to be the oceans plaything sooner or later.

The existence of fundamentally non-effective wind capturing technologies, such as rooftop windmills, vawts, and kites, does not preclude existance of effective designs aka multi-megawatt 3 bladed wind turbines.

By analogy, just because early attempts to build a concept does not work, can you prove future attempts won't work? As far as I know, the energy potential in the ocean is not disputed, just the initial attempts to build the machines have not been successful. Many attempts at flying machines were unsuccessful before the wright brothers.

Windmills have been making usable power for millennia. They are well understood.

Tidal energy has been tried time and again and nobody has managed to make anything that would work at scale.

Well the comment you replied to that you agree with "100%" also said wave energy + tidal energy.

Your method of analysis is assuming we exist in the best of all possible worlds. "Flying machines have been tried time and again" is valid right until wright brothers. "Electric cars have been tried time and again" right before Tesla enters the market.

It's one thing to say "roof top wind" and you can look at the loads an average roof can support, realize it will be a small swept area at a low elevation and conclude that roof top wind couldn't power the building its mounted on. There is no way to write off tidal with the same sort of first principles analysis, the power is there, its a matter of design whether or not it can be captured efficiently.

Electric cars were proven to be viable in the early 1900's. We've had electric vehicles in one form or another in all that time since then.

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.

> 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.

> 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.

"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

Except that they are not trying something new. They are trying something old. Again. And again.

> 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.

> 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.

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

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.

So instead of that what is done is 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.

> Release water so its easy to lift again

How? Don't you have to pump it out since it's below sea level?

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

(Sending the water through bi-directional turbines, to get power from the inflow and outflow)

Sihwa Lake's working basin is 30 square kilometers. Rance's is 22.5.

And while Rance could take advantage of an estuary with a dam just 750m wide, Sihwa uses a 12.7km long seawall.

Sihwa's seawall was actually built for flood mitigation before SK realised it could work for power generations, building a 10km seawall solely for power generation sounds insane.

Other people addressed the specifics but to add more generally, the key question is almost always not “can we do it”. It is almost always “can we do this more economically than other methods” and the answer is no. It takes more time, money, resources, etc. for a given amount of power than other clean energy technologies.

It is not very likely that there are tech improvements that would make things like this more viable. Salt water is super hard on equipment and that will always be true. Any improvements in durability would likely also apply to wind components. Gravity is only powerful at large scales, so just using tidal forces means you have to harness a lot of water, which means use land use and environmental disruption. Water batteries are economical only in places with extremely specific geography.

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.

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.

> 30 years ago wind power was to be found at the hobby level in hippy farms

factually lacking and basically an insulting word IMO

> 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.

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

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)

> 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?

Wind. Waves.

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.

Thanks!

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.

In addition to mechanical wear and corrosion, marine growth such as barnacles cause huge maintenance problems for any equipment in that environment.

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.

>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.

> 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...

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.

doesn't mean they will always fail to deliver.

I think that unless you drastically change the parameters of the implementation then yes it does mean it will always fail.

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.

> 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.

Wind routinely rises fall on the scale of entirety of UK, having multiple windfarms around the country doesn't seem to help that much.

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.

Why don't they scale? is there not enough ocean in the world or something?

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/ 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).

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

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?

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

Blimey, I remember seeing that covered on Tomorrow's World when it was being built. It seemed like an interesting idea at the time.

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.

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 ;)

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.

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.

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.

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.

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?

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.

> 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.

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.

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.

Thanks for clarifying! So are the true wave energy designs the variants that use vertical oscillations rather than propeller designs?

Wave energy would be any type of machine that uses the motion of individual waves or swells, rather than tides.

There is a wide range of ideas, most are at small scale, early stage, and no winner has emerged the same way that wind energy has seen the 3 bladed turbine win out.

Wave energy devices exist using almost any type of power take off mechanism - direct drive electric generators, linear generators, compressed air, and hydraulic actuators. Some may even use propellers in water but that's not as common since direction is always changing.

In theory, tides are more reliable and independent - it happens even if it's not windy or sunny, and it happens on a schedule that's more regular than the weather.

> the tide doesn't always flow when you want it to

So what? You can store tidal water and let the store always flow.

Flow to where?

Low tide only occurs twice a day.

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.

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

> Schemes such as this have been proposed

Lol well if you knew that then why did you ask me to explain it?

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