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Combining Solar, wind into 48v off grid system.

I have been searching through the articles to see how best to combine solar and wind with lithium batteries.
I am providing power for a remote radio/ comm tower. The setup I have 2400 watts of solar, going into a smart solar 150/100 mppt. this charges 324 ah 48v lithium battery bank. This feeds into 3kva multiplus. I have a constant load of +- 300 watts going out the ac side. I have a BMV700 and everything is interconnected using Venus GX to make monitoring and remote configuring easier.
This all works well on 90% of the days when there is good sun, the only time I have issues is on prolonged overcast days. What i am looking at is a way of maximising the battery life by decreasing the DOD as much as possible.
The idea I have had is to install a 600 watt wind turbine and controller. I don't like the controllers as they do not seem to work well with lithium, and have rudimentary controls or setting points and from what I have read you cannot really put them through an mppt as it tracks to slow for the fluctuations of a wind turbine system.
I thought the best way to get around this is to take the controller that comes with the wind turbine and push this up to 64v and then string a number of supercapcitors with their balance boards together to make up 64vdc. then run this into an mppt on the input side. I can then monitor flow of power, and the GX / multiplus can control the system to maximise the power usage. has anyone tried this or had any luck with something similar.

Hydro and Wind Power
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3 Answers
ceriw avatar image
ceriw answered ·

Supercaps on the PV input of the 150/100 MPPT can damage it. The maximum PV short circuit current of that model is 70A. Charged supercaps will be able to deliver many times this current.

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mmmmmm hadnt thought about that. would the super caps deliver this if you not shorting or would the mppt only allow a certain current through. Could you limit this on the mppt?

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maxxpwr answered ·

Both suggestions are improvements on mine, the streetlight function is a solid idea, eliminating another point of failure by omitting a timer, if the turbine has a brake then that can be manipulated as well, it's a twofer as it's a method of control that's effective and reduces bearing maintenance, however from my research most turbines under 800w don't have a brake system and rely purely on thrust kick out for over speed and a waste energy block built into the controller to dump unused current.

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the wind turbine I am looking at has a controller which you can set to max 64v output. What this would do is allow the Super caps to charge up to 64v. at which point they will be 5v higher than the battery voltage allowing the mppt to charge. as both the solar and the wind mppts would be connected to the same GX and bmv they can enter float or absorbtion and the mppt can take what it needs from the super caps to power the load through the mutliplus as happens with the solar currently.
I had a second thought of when the batteries reach a float stage the relay activated triggering a dump load, but the controller for the wind turbine should do this anyway. This may not be needed with the above setup.

I want to test this but parts not so easy to find where I am will take a few months to get everything in maybe longer.

If your contemplating floating the maximum controller voltage with the capacitors then I'd have to say the controller will be mighty confused in the morning if there is wind, pv voltage is coming up and the batteries will take bulk charging amps, as the caps shed voltage fast when the current drawn from them is high, so the controller will likely see 64v for a few seconds then significantly less, followed by trailing whatever voltage the controller can put out depending on the wind. The end result may be the controller going to absorption or even float straight up before re bulking, I'm not certain if it will be detrimental or not but it's a risk, and considering the alternatives are worth a reasonable attempt, from a purely pragmatic point of view, I'd say try the simplest solution first as it may be the best, and a dc contactor should be easily available.

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maxxpwr answered ·

Sounds like fun, I too have considered this and I think the most reliable way to do this is to have the output of the turbine controller wired into a suitably sized DC contactor with timer attached, set the timer to close the contactor at the latest time sunset occurs, the solar chargers will be off and this way you'll benefit from power in for 12 additional hours depending on location, this should help minimize dod nicely and be reliable and cheap.

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You could use the street light option on your mppt connected to the solar to activate a relay on the brake switch for the wind turbine as an option for what you suggesting.

Or maybe you can control that contactor with the voltage from PV panels. If the voltage drops below minimum for MPPT it will turn on input from wind turbine.

This way during overcast days an plenty of wind your batteries will be charged.

You would need to use separate MPPT for the wind input.