I wonder if I could heat a tiny building with this one, and bring some LED lights to another building with this item connected to a tiny but steady water source next to it.
You could, but it's unlikely to work very well, won't generate much power, definitely won't be worth the cost.
The wind turbine suffers from the usual problems of small wind turbines, which are "They don't produce much power until they're about to blow down, at which point they shut down from protection." I
think the Chinglish talks about the controller being able to brake the turbine to prevent it coming apart from overspeed, but I'm not sure how that works. The older stuff needs diversion loads that can soak the full power from it, I'm not sure if the tiny Chinese junk will self brake effectively or not. I've no interest in them, because:
What's an honest wind profile of your place look like? 15mph is a decent breeze, and they make 50W. By the time they're making rated power, 30+mph winds, you've got some serious wind going on. And at some point above that, it needs to shut down for protection or it'll come apart.
The "20 year service life" for something like that is heavily based on "We won't be around to complain to when it does fail." I would be stunned to see one of those last 20 years without failure.
The little hydro generator also won't last very long, and doesn't produce much power. Plus regulations about waterways. I'd expect it to last a week or two in free water, maybe more, but probably not much more. Micro-hydro is a thing, and there are plenty of little off grid places with small hydro plants. They don't look like that, they look like a proper turbine with (again...) diversion load controllers to soak the output so they don't overspeed if the batteries are full.
I've been thinking about this forever, but I am slow on the uptake, have few occasions to sit down for longer periods and learn on my own, and forget easily. Basically a 40 yo with the attention span of a 5 yo, sometimes at least.
Then energy projects aren't the projects for you. There are a lot of things you have to understand, keep in flight, and take into account. The good news is that none of the stuff you've linked is likely to fail catastrophically in a way that would damage other stuff, it just won't last very long and won't do what you want.
1. connect lights and heat to a DC current power generator
Depending on the nature of the output from the turbines, just hook them up, or you may need current regulation - the windmill lacking anything resembling a datasheet means I've no idea what it will do in various conditions, but "It will be unreliable at est unless you want to use a 600W turbine to run 5W of lights" would be my guess.
Heat, forget it. It won't produce enough to be useful, and getting stuff dumped into a sane set of load resistors... you'd have to understand the output profile of the turbine or charge controllers, which you've got no data on there. And more trouble than it's worth. And you don't really want to be leaving 600W of thermal load unattended.
2. protect a wind turbine with maximum speeds of 50 m/s from breaking at higher winds (will I need to physically take it down?)
50m/s is 112mph. Is that actually an issue? And do you trust that it will actually stand 50m/s without coming to pieces? Again, it depends on how you're regulating it. There are various ways of doing it, and I don't know what their controllers support, and I sure wouldn't trust a Chinese charge controller to properly handle it. You can short the windings and gain a good bit of braking, you can offset the pivot point so it automatically cocks away from the wind under high speeds (the Otherpower designs do this), or you can hope it doesn't happen. Without specs and details, hard to say what would or wouldn't work. Sorry.
3. can a system like that work with no power saving/feeding unit (battery or grid) - direct production, direct use? Can it produce too much energy/more than used and break?
It depends on how you design it. You can make that sort of thing work if you use radically less than the system can produce, but it's quite challenging. Do you really want the lights flickering on a low wind day? As for too much energy, again, it depends. But I wouldn't leave a turbine of any sort fully unloaded, that
is a good way to have them come apart.
Rotary machinery for off-grid power generation is an awful lot more complex than solar panels, where you don't have to do anything special. If you wonder why off grid systems don't seem to be using wind or hydro as much, it's because in almost all cases, with the cost of solar so low, you'll have a far easier time of it with solar than you will with the others. Some people still build their own wind turbines, but consider that a "useful hobby" as opposed to anything sane at this point. Back when solar was $10/W, yeah, small scale wind made sense. At $0.50/W, it doesn't.
4. possibly convert it to 220-250V AC/DC to connect ordinary appliances (I am in Norway, my household runs on 254V IT nett)?
No. Now you're dealing with battery storage, inverters, grid tie interconnect agreements, whatever electrical codes are over there, etc. That makes no sense for 50W of power.
There's so much that I just don't know, I am sure there are a lot of possible problems I am not even aware of. If anyone can recommend a good channel/website for learning the very basics, I am all ears.
I'm sure you'll find plenty on YouTube. I won't recommend any because I can't stand video for learning. Be aware that for most of what you hear on YouTube, 90% is fine, 10% is badly wrong, and unless you're already an expert in the field, you can't tell the difference.
So a direct setup with, say, a 12/24V heater and a light bulb or two, just using the amount of power that is supplied directly, cabled to the windmill, would not work?
It might. It might not. What happens when the voltage drops because the turbine isn't producing enough power? Those things are a fixed resistance coil and fan, and as voltage drops, you'll get less heat... but at some point, the fan will stop turning. And the heater coils will still be producing heat - not much, but still more than enough to cause problems if they're not cooled. You could add a battery into the system to hold 12V, and toggle it on/off, but you're adding cost and complexity to do that. Electric heat from renewables is hard. I do it in my office, but I've got 5kW of panel hung on my environmental disaster of an off-grid office. :p It's a third of the house system, for one shed, and right now, in the rain, I have about 150W coming in, 400W going out. It's an interesting system to play with, and it's nice having standalone power, but I don't pretend it's cheap, or particularly environmentally friendly, beyond "My emissions for incremental kWh as long as I've got good sun are zero, all the emissions are from production of the stuff, and I could stand to replace the batteries in a couple years."
I mean, this is about cost, but also about simplicity and ecology.
It is an expensive, complex, and environmentally questionable way to accomplish what you're trying to do.
Deep cycle batteries are expensive here, and I just delivered what I had of 12V car batteries to the recycling center...
Car batteries don't work for stuff like this. They're not deep cycle. They're SLI, designed to be discharged 1-2% starting the car, and then charged back up. Deep cycle them, they have a lifespan measured on your fingers. I typically consider a car battery good for about one deep discharge and recharge, the second deep discharge is time to replace it, it won't start a car anymore. It matters a bit less for LED lighting, but they don't have a good lifespan when reasonably cycled, because they're not designed for it.
...getting a used EV battery would be nice for the house later (our Leaf is a candidate for that which is already parked outside). It's cost prohibitive for a project like this though, and these batteries are 400V, which would open a whole new can of worms if I even understand the consequences of that somewhat.
400V and potentially thousands of amps short circuit current, yes. Don't screw with them if you don't know what you're doing.
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Sorry, not trying to be a jerk, but standalone energy systems are somewhat complex, and have interesting failure modes you have to reason about. You can get cheap kits that claim to do stuff, which they mostly wont, or you can design it properly, but that's neither simple nor (usually) cheap.