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Comment by gehsty | Hacker News Reader

The turbines are very interesting, these demonstrator projects seek to answer questions like how do you even make one, how do you install it and how do you maintain it… a very interesting piece of hardware required to scale this up (in deep water anyway!) is a subsea substation to up the voltage from the array to export voltages…

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The article mentioned 100-160ft from the surface, so i'm not sure where the "deep" part mentioned in the headlines comes in. Perhaps their ultimate plan is for deep & this demo didn't try to address the deep part? That said, if 100ft below had enough forces to produce 100kw (ecological issues aside) that sounds pretty fantastic, even if just a demo.

I imagine the "deep" aspect is that it seems to be well below surface waves that seem to reek havoc on other projects. That depth is still pretty difficult to service as install without pretty sophisticated planning I would think.

They would be easier to service than off-shore wind turbines. You just need a light cable attached to a buoy, the service ship goes to the boy, pulls up a heavier cable with the light cable, then pull up the whole structure.

Come to think of it, the turbine pods may include a ballast tank that can be evacuated, to adjust the height in normal operation or to pull itself up to the surface for maintenance.

unless it's a rigid structure mounted to the ocean floor then it will almost definitely have ballasts

The article explicitly states they are free floating tethered to the ocean floor. And this is by far the easier way, I'd think.

I'm not so sure. For a wind turbine a lot of maintenance can be done without any additional vessel / cranes. If you need to do a major component change you do it with a similar vessel to the ones which installed the turbine. For a subsea tidal turbine you'd need some frame or similar to land the tidal turbine onto, you'd need to clean it before anyone could access it for the maintenance etc. Generally speaking if you have something subsea it should be designed to be maintenance free as recovery costs are so high (like subsea oil and gas production systems).

I actually thought the 100kw number sounded awfully low. A typical wind turbine generates around 2 or 3 MW of power at capacity.

That’s the rating at capacity though, which barely ever happens. The ocean current will never stop, so over the course of it’s life the ocean turbine might well beat out a wind turbine (ok, I consider that mildly unlikely, but it’s nice to have power generation that’s less susceptible to suddenly not producing anything).

Also note they say it produced 100kw, not what it was rated for.

I'm not good at nautics, but in my understanding currents slowly stop and later turn around. Most tide charts are more or less a sine wave, with different highs and lows.

So it's interesting how this 100kw was produced.

The article only says: "The business was able to generate roughly 100 kilowatts of steady electricity during demonstrations earlier this year."

So is this over a few days or just a few hours while peak flow? While currents change, their change is highly forseeable - unlike wind.

The pods with the turbines are floating in the water, tethered to the seafloor, so they will turn in any direction the current is going.

Currents are relatively unrelated to tides, and are fairly consistent over time (with some seasonal variation due to differences in hemispheric temperatures).

From [1], "the large scale prevailing winds drive major persistent ocean currents..." Keyword is persistent.

[1] https://en.m.wikipedia.org/wiki/Ocean_current

Everything is fairly consistent until you monitor it 24/7, and put a bunch of junk in the way to extract meaningful work.

That's when life starts taking on a surprising level of detail that no one ever stared long enough to notice before.

I imagine that's one goal of the project? I can't imagine that there hasn't been a shit ton of experiments with "deep" sea currents before this power experiment. I mean it's dead obvious and they wouldn't have ponied up the cash for this if ocean currents were all over the place.

The turbine capacity is reached quite regularly, particularly during windy days.

UK Crown Estate have a map of current renewable generation (https://www.thecrownestate.co.uk/en-gb/what-we-do/asset-map/) and right now the Hornsea 1 field is generating nearly 900MW (~90% capacity) on not a particularly windy day for the North Sea. The capacity factors you read are averaged over a year.

Those wind turbines have been refined for decades and are now a lot larger than they have been at the start.

As far as i know these questions were answered more than 20 years ago.

I'd be worried about corrosion over time... especially in deep sea regions how do you go about maintaining them?

I'd imagine if the energy output ends up being worth it they could manufacture the turbines from some sort of plastic or composite that doesn't corrode in sea water.

This is a solved problem, oil rigs, off shore oil platforms, etc.

Maintaining subsea turbines is not a solved problem - they exist but none have been around a long time, and no large utility scale projects use them so no one has experience with a fleet of subsea tidal turbines. Static subsea structures are proven by the industries you state, but not large turbines.

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