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Comment by bjourne | Hacker News Reader

How on earth can such a small device generate so much energy? Wouldn't 1.2 MW of power make it very brittle just like a real kite? Or else why not scale it up and make one 100 times larger that generates 120 MW of power? Since tidal currents are much more reliable (I think) than offshore wind it almost seem to good to be true. There has to be a catch.

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The speed of the tide between those islands is something like 5-6mph, and in some places much much higher (think tens of miles an hour).

Water is 800 times more dense, so moving water contains much much much more kinetic energy when its moving.

But that also means it has a lot more drag. That drag can be quadratic, meaning that you'd need to a monster fucking cable to stop it being dragged away by the tide.

The Grey Dogs channel between the Scottish islands of Lunga and Scarba has a peak flow of about 15km/h with large standing waves - quite incredible to watch this up close and watch the sea shooting past!

And of course some lunatics will go and find a way to have fun in them! Here's a sea kayaker at Penrhyn Mawr off Anglesey in Wales.

https://www.youtube.com/watch?v=l5o7qV1Gy04

Looks like fun! FPV [1] and drone footage [2]

1: https://www.youtube.com/watch?v=Qo28x0CYBaA 2: https://www.youtube.com/watch?v=ehN9c7WfLMI

Here is a video from a boat in the Grey Dogs:

https://www.youtube.com/watch?v=zLFG7x6rrKw

Definitely not somewhere I would want to fall in!

> There has to be a catch.

I'd wonder how long it'll last; it's a very harsh environment.

That said, there's a lot of energy available.

It may be that lots of small units like this will be more practical than one big one.

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