I hope you got a lot of money, besides the cost of the "island".
Some. I'm planning to build three residences and a workshop.
The structure for the Tidal wave generator, specially HOME MADE is highly problematic if you do not have the mechanical and submerged equipment installation experience; also the behavior of the area during storms and how deep those effects are.
The hope for the Savonius design is that the only submerged part is the rotor. Think of a conventional Savonius windmill but turned upside down and dipped in water. Just making the rest (very) splashproof is what I'm hoping will do. It's in an estuary which is very sheltered from wave action, so I'm hoping to avoid the worst of the surf. I don't want energy from waves, I want energy from tides.
Installation consists of lifting a few planks on the jetty and dropping the mill into the water, then securing the generator to the floor.
But you're right, I don't have experience of sticking things in the sea for months on end, which is why I'm asking. :-)
I am a Design Electronic Engineer and your comments about the DC/AC converter worries me because your writing which clearly indicates what your electronic design capabilities are.
My BSc is titled "Electronics and Computer Science". I mainly work in software these days, but that's because I followed the money. So I oversimplified. It wasn't what I was concentrating on, to be honest.
You are suggesting that:
>A simple 3kW linear stepdown (three more microwave transformers, some diodes, and three opto-triacs) can charge them when there is power.
is a simple job, I wish it were -- starting with the transformers that have a very high voltage secondary.
Starting by removing the high voltage secondary and replacing it with an 100v 15A secondary. Microwave transformers provide cheap (free!) laminated cores and mains isolating hardware which can be rewound for up to 1500VA. It's hard for a hobbyist to find any transformer of this power, even new, other than in microwave ovens. But nobody would use one without rewinding the secondary, unless they wanted to build something inspired by Tesla. :-)
Rewinding the secondary is a bit tedious but it's hardly rocket science. Three of them, one on each phase, should do the trick. Of course, since we're no longer oversimplifying, the rectification needs to be completely isolated if they're not going to generate unexpectedly high voltages.
The triacs provide current control to limit the voltage, using optoisolators. That way the transformer circuit can be kept efficient, since the transformer is only powered when it is used. 50Hz is a low frequency for a switched mode system, but it can be done - think of how a light dimmer works.
My existing homebrew switched-mode battery charger is based on rewound transformers and it charges my AGMs at up to 20A. I built it about 10 years ago, from a circuit I sketched out myself, and it's doing fine, thanks. Took me three days to get working, and it's worked without a hitch for years of continuous use. I've never opened the case since - I'm not exactly sure I can remember the exact layout. The 200VA shop-bought invertor I bolted to the front has died, (and I haven't got around to fixing it,) which is a neat example of homebrew versus shopbought.
Also, you are not realizing the time needed to design and build such "device", including the size of it and the input voltage levels and currents for 12 KW "16 microwave transformers converter".
I have in mind 60v to 100v input, and if they are delivering 12kW then they have to manage 750W each. So that'll want 12A or 13A each. I've already built switched linear invertors that deliver more than this, and consider that to be a weekend's work. The only thing I haven't built is the control systems to switch in and out 16 of the things, and keep them accorate, since I like to use mains operated clocks.
My mains wiring includes rewiring the distribution board on our house to use RCCBs, since I have an 18-month-old son, who like most 18-month-olds likes chewing wires and sticking fingers in sockets. At least with a homebrew invertor I'd be able to turn it off, instead of having to pull the company fuse from a live supply. :-)
And, as someone else has pointed out, NiFe batteries, should I use them, almost require a homebrew invertor. Somehow I expect the batteries to be less reliable than the invertor, so that's where I'd like to concentrate. Those batteries will see maybe 1400 cycles a year. From what I do know of batteries, that worries me.
I am not trying to discourage you, but power design has been my job for years and I know the time needed to just prototype smaller units, and I have made modular 500+ KW units.
Well, most of my electronic design experience is in telecoms, so power electronics is something I've mainly done as a hobby. The powers I normally send into a transmission line you'd probably dismiss as noise. :-)
But it has been my experience is that getting a prototype working is not hard - the hard bit is getting from the prototype that works to a production line that has a decent yield and a decent cost. My secret of successful homebrew design is simple circuits and massive overspecification, which of course doesn't work too well for production, since you end up paying $20 each for power transformers when $5 ones could probably be made to do.
The other nice thing about modular design is that it's modular - building sixteen is significantly easier than designing sixteen, because if you can get one working, you can probably get all sixteen working.
Anyway, this is a bit off topic. Let's assume I can build linear battery chargers, since I have one in the next room that has been running for 10 years; and that if my invertor experiences turn out duff, I can buy one. I'm not discouraged about that stuff.
The key questions are about the stuff I don't know: working with the sea; scaling the "brake disc" generator; weatherproofing the "brake disc" generator; synchronising the generators; and battery wear.