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Comment by davedx | Hacker News Reader

I did some reading about this yesterday:

* this is a record for the time a turbine has been under the sea without any maintenance, which proves its commercial viability

* because it generates powers during high/low tide, and because the lunar cycle is different to the solar cycle, it could help fill in the parts where solar falls off in a predictable way

BUT:

* Tidal energy is valuable but geographically constrained

* Only a few countries have suitable locations for it (UK, Canada, France, South Korea)

* The Global Technical Potential (in TWh/year) is 1/10th of offshore wind

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>* The Global Technical Potential (in TWh/year) is 1/10th of offshore wind

I assume the value is still massive? The UK is still aiming to 4x its Off Shore wind by 2030. That would be 60% of UK electricity. If the new Nuclear Power plant actually deliver double its current 15%, that would be total 90%. The rest could just be solar and underwater turbine.

I am just wondering if underwater turbine causes any issues with marine life. If not we could absolutely deploy them on massive scale and avoid the eye sore of Wind Turbine.

South Korea was going to build a large one but canceled it due to the marine life threat. One way they try to fix it is by having a safety mechanism that turns the blades off when marine life passes through but this increases operating costs on something that is already high maintenance.

> Canada

The Annapolis Royal Tidal Station shut down 5 years ago, because it had a strong tendency to chop up all and any fish that went through the intake.

The Annapolis looks like a fundamentally different design: direct turbine driving instead of low-speed / high-torque windmill design.

https://www.youtube.com/watch?v=pxCPXLv--U4&t=71s

Yes, the Annapolis station was conceptually very much like a hydroelectric dam generator. When the tide was coming in sluice gates were opened to allow a reservoir to fill, then when the tide was going out the water was sent through a high-speed turbine.

It's unlikely that Nova Scotia will see tidal power again in the near future. There's been some attempts at in-stream generation, but the projects have been opposed by the local fisheries, and the federal regulators don't seem interested in helping define the requirements.

Plus a newer one off Vancouver island BC shut down after a couple years because its operating costs made it economically infeasible. Had to get fixed and upgraded a few times. Which I why the maintenance thing in the headline is probably relevant.

"Tidal energy is valuable but geographically constrained" Is this really a negative? Can it not be simply viewed as a boon for places where geographically reasonable? I live in Arizona, I'll not be upset when left out of tidal energy - I've got solar and a sunshine surplus.

the hard part with geographically constrained sources is that they have a harder time getting economies of scale. solar works everywhere and is really easy to install, so the market cap is massive, leading to corresponding increases in production efficiency.

And importantly, China isn't on the list of places this works, and China is the only place in the world for generalist manufacturing at scale.

> because it generates powers during high/low tide,

At high and low tide the water isn’t moving much. Surely it generates most at mid tide, with the flow reversing direction causing a lull?

This makes the useful portion of the cycle far far larger.

> * Tidal energy is valuable but geographically constrained

Yes, of course. I do not get the point, this is not a solution to every electricity generation problem

> * Only a few countries have suitable locations for it (UK, Canada, France, South Korea)

There are more than that. I have a seven knot tidle current 5km from my house, not mentioned in your list. I know of others. The costal conditions are quite common for this. The same technology will be useful in rivers too

It will be a far higher proportion in the countries where there are suitable locations.

it is predictable and reliable, so has significant advantages over wind.

Quite possibly, with a suitable distribution of sites around the UK coast, the total power generation might be nearly constant over time.

A guaranteed minimum power generation would presumably be very useful.

> Tidal energy is valuable but geographically constrained

Don't tides happen everywhere there is a coast (which is a lot of places)? Or is this only effective in certain tidal conditions?

Tides happen everywhere, but not to the same extent and not always at useful times. If your peak production times don't line up with peak demand times, then you need expensive energy storage. (This would change with the phase of the moon, so sometimes you'll get lucky and sometimes you won't.)

One thing that's relatively unique about the UK is that different parts of their coastline experience tides at different phases -- meaning with carefully chosen placement of different tidal energy plants, you can always have some of them operating near peak production. Click around https://www.tidetimes.org.uk and you can find places with high tide times happening at just about any time of day.

If you look at a map like http://www.bidstonobservatory.org.uk/wp-content/uploads/2016..., the best places to use tidal energy would be red areas with lots of white lines hitting the coast -- these would give you the highest-amplitude tides with the most opportunity for phasing. The UK has both.

The issue is clarified with a map like this: https://i.redd.it/rontertecjqd1.jpeg

Most regions have very small tidal ranges. That doesn't mean they have small tidal currents (think of fjords or straights for example), but it does make it more likely.

And in those fjords and straights, I reckon yhese solutions will compete with boat traffic.

Fascinating. I wouldn't have expected the English Channel to have the strongest tides. I would have expected it to be the Atlantic coast of Ireland or France.

Earth without land masses would have around 0.5m to 1.5m of tides, depending if it is springs or neaps. All the higher amplitude tides are caused by resonance in the sea. The North Sea and the Channel and Irish straight are quite resonant.

Naively, you'd expect the tidal current to be proportional to (tidal range/water depth). Which causes that map to be a lot less informative.

> * The Global Technical Potential (in TWh/year) is 1/10th of offshore wind

To put this in perspective, less than 1% of the world's land area would be needed for wind turbines to power the current energy needs of the globe (according to NREL). So this is not a limiting factor.

1% of the world's land surface is massive! That's about 1.5 million square kilometers. That's more than 4 times the land area of Germany or apparently about as much as the entirety of the built up area on Earth.

But that's non-exclusive use of 1% of the surface. Land under wind turbines can and is actively used for farming et al. The actual area that's prevented from other use is much less than 1%.

For reference the Sahara desert is 9.2 million square kilometers (obviously covering the entire desert in turbines is impractical, but we might be able to come up with 1% “useless” land if needed)

So we would need to cover 4% (1% * 10 GTP * 30% land / 70% water) of the ocean to power the world? Seems like a lot

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