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.
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.
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.
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.
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.