Solar inverter as whole house UPS system

[rGlory]

Most MPPT controllers can only manage Current sources (PV)

How do they "manage" it? They change load to maximize power - then current and voltage changes and MPTT controller tries to find maximum. But what if voltage does not change when MPTT controller changes load? Simple - MPTT will maximize current and that would be a point where power is maximum. Period. I do not really understand why you have to make this MPTT logic sound like voodoo, it is not that complicated. (I mean implementation details could be quite complex but main point is quite clear)

I seriously doubt your PV input circuit is designed to handle both a Current (PV) and a Voltage ( Wind, rectified generator output) input.

It is designed to maximize power from source which maximum power depends on load. Voltage source just does not require such logic, so it would be overkill to use it. But I hardly doubt MPTT controller can harm generator or battery by trying to maximize power (assuming it has limit of what current it can draw from that source)

Be sure of your plan before you spend a lot of money on things that won't work as you would like them to.

This is what I do here, I plan in advance and try to realize what are my options. I do not quite understand why your responses are quite aggressive. I do not suggest anybody than me is doing it, I just want to clarify things I may not understand.

[solardreamer]

I wonder then how they managed to feed from AC - they have to change it to DC first. And what did they do to design DC-DC converter to work from AC? They rectified it and smoothed with capacitors. Maybe they added inductive to reduce noise inverter can push back to the grid, but this is not case here. What else?

Typical off-grid inverter/charger with generator support will simply pass through AC power from the generator to loads and also run the inverter in reverse to work as an charger (i.e. AC-DC converter) to charge the batteries. So, AC power from generators don't go through the PV MPPT tracker or DC-DC converters.

[rGlory]

Typical off-grid inverter/charger with generator support will simply pass through AC power from the generator to loads and also run the inverter in reverse to work as an charger (i.e. AC-DC converter) to charge the batteries. So, AC power from generators don't go through the PV MPPT tracker or DC-DC converters.

Yes but when this inverter charges buttery from AC it takes 5KW (100A at 50V) and it uses DC-DC converter. I do not see principal difference from converting 60Hz 240V to DC at 5KW inside inverter vs 8KW I would do for AC generator by myself, if capacitors work in the first case why they would not in the second? Of course I have to consider that capacitance and ripple current of capacitor has to be increased accordingly

[solardreamer]

Yes but when this inverter charges buttery from AC it takes 5KW (100A at 50V) and it uses DC-DC converter. I do not see principal difference from converting 60Hz 240V to DC at 5KW inside inverter vs 8KW I would do for AC generator by myself, if capacitors work in the first case why they would not in the second? Of course I have to consider that capacitance and ripple current of capacitor has to be increased accordingly

There is more to it than just capacitors. You can research AC-DC converter design to learn more. In any case, it seems you won't be convinced until you see it. So, perhaps you should just try it at your own risk.

[Mike90250]

Well, build it up and be sure to let us know how it works out,

Just because I cannot explain in laymans terms why a Current Source can easily be managed by a conventional MPPT converter, does not mean it will work at all with a stiff voltage source.
MPPT circuits "detune" the best power point of a PV array, both by letting voltage rise, or pulling the voltage down, in order to test & regulate it. it's trivial to load a 3kw PV array down to half it's voltage if that's all the power you need. But you take a battery or a generator, and say wow, that's too much voltage, better load it down to something I can manage, When the MPPT tries to regulate the 120VAC generator to 87V, smoke is going to flow from somewhere. This happens when the controller makes it's regular sweeps, looking for the prime MPPT point. Works fine with a current source ( PV ) not so good with a voltage source (battery, generator )

https://www.mepits.com/tutorial/459/...-tracking-mppt only talks about PV cells, not wind or batteries or generator.

[rGlory]

In any case, it seems you won't be convinced until you see it. So, perhaps you should just try it at your own risk.

I think this is a wrong conclusion. I try to understand how it works or does not work and when I see explanation that does not make sense to me (it certainly does not mean that explanation is nonsense, most probably I do not understand something) I try to show my point and asking were I have mistake. Unfortunately it is often considered as I am arguing.

[rGlory]

But you take a battery or a generator, and say wow, that's too much voltage, better load it down to something I can manage, When the MPPT tries to regulate the 120VAC generator to 87V, smoke is going to flow from somewhere. This happens when the controller makes it's regular sweeps, looking for the prime MPPT point. Works fine with a current source ( PV ) not so good with a voltage source (battery, generator )

I understand that, but we should consider that there is current limitation set to MPTT charger which it cannot overload, which mean it will try to regulate AC generator to 87V would hit current limit and get stuck there. Am I wrong?

On top of that all commercial generators have overload protection, so in the case MPTT will try to put voltage down to 87V I hardly doubt there would be smoke, generator would just stop providing power. It is not good outcome for sure, but it is not as dramatic as having smoke somewhere.

[solardreamer]

I think this is a wrong conclusion. I try to understand how it works or does not work and when I see explanation that does not make sense to me (it certainly does not mean that explanation is nonsense, most probably I do not understand something) I try to show my point and asking were I have mistake. Unfortunately it is often considered as I am arguing.

Your original question of whether it's fine to feed rectified AC from generator into PV input has been answered by multiple people. Now you want to understand why it won't work in detail which is a different question that requires some adequate background to understand. Unfortunately, based on the incorrect way you think how the inverter works, it seem you are missing the necessary background understanding that cannot be quickly addressed in a forum. I mentioned trying it yourself as an option because sometimes that's the fastest way to learn. Otherwise, as I also mentioned, you can research AC-DC converter design and engineering to learn more but that will likely take more time.

[rGlory]

Otherwise, as I also mentioned, you can research AC-DC converter design and engineering to learn more but that will likely take more time.

Sure let's do some research. We can take as source computer power supply, as it is quite easy to find schematics for it and it is AC-DC converter indeed. If you know where to find schematics for solar inverters I would be happy to look. So for example:

s_atx01d.png


As I see here AC to DC converter is rectifier bridge and 2 capacitors - 680x250V. Can you point me what I am missing? One inductivity?

There is more to it than just capacitors. You can research AC-DC converter design to learn more. In any case, it seems you won't be convinced until you see it.

[solardreamer]

Sure let's do some research. We can take as source computer power supply, as it is quite easy to find schematics for it and it is AC-DC converter indeed. If you know where to find schematics for solar inverters I would be happy to look. So for example:

s_atx01d.png


As I see here AC to DC converter is rectifier bridge and 2 capacitors - 680x250V. Can you point me what I am missing? One inductivity?

That is a basic design which is okay for a few hundred watts computer supply but is unlikely to work for your target power of 8kW. Even in this basic design, do you not see all the components besides the bulk caps before and after the rectifier? They are all necessary to produce practical DC power and quite expensive at high power levels. On top of the basic design you will likely need to add in-rush current limiter or soft start and active power factor correction to have a practical 8kW converter.

[rGlory]

That is a basic design which is okay for a few hundred watts computer supply but is unlikely to work for your target power of 8kW.

I do not see such a big difference btw 1KW and 8KW, assuming capacitors can handle the load.

Even in this basic design, do you not see all the components besides the bulk caps before and after the rectifier?

Components before the rectifier are there to limit the noise this power supply will provide to the grid. I think my generator would not care at all. For Components after the bridge, I think only induction is missing, that probably helps, butt it is not a big deal to add. Resistors and 2 capacitors are there because this supply has to switch btw 240V/110V and that is not the case for me. I do not see anything else.

On top of the basic design you will likely need to add in-rush current limiter or soft start and active power factor correction to have a practical 8kW converter.

Active power correction? Why ? I am not going to connect to it anything rather than inverter through AC-DC.

[MJSullivan56]

Good thing here in Massachusetts the building inspectors are very demanding that all permits follow the (rather strict) NEC 2020. Sadly, many Harry Homeowners out there still feel they’ve “done their own research” and have no intention of following the code. One hopes that one of these folks doesn’t happen to live next door…

[J.P.M.]

Sadly, many Harry Homeowners out there still feel they’ve “done their own research” and have no intention of following the code. One hopes that one of these folks doesn’t happen to live next door…

Or, you're not the one that buys their house someday.

[Mike90250]

If you are so bent on slamming something together here's a link to a fairly decent discussion about design of MPPT controller

https://www.thebackshed.com/forum/ViewTopic.php?FID=10&TID=14158

Another link to a book for sale, for a proven DIY 6kw inverter The OzInverter , tweaks needed to get 60hz 240v split phase

https://levivray.com/new-book--make-a-6kw-inverter.php

Another DIY solar site is https://www.thebackshed.com/forum/index.php BUT, I have little confidence in your background and ability to build this stuff. I'm
putting this out as an example that solar gear is so much more than a 600w PC power supply. These are ways to do it right, and there is some safety stuff discussed, but
most of this assumes you know the more advanced levels of electronics, and that you can spot an obvious error before powering it up

[rGlory]

Anyway we decided to switch from Growatt Inverter to Victron Energy Quattro 48V 230V which has separate AC input for generator and proper configuration not to overload it. Looking on feedbacks on this forum as well growatt seems to be not the best solution anyway. Thank you guys for the answers, problem is solved.