microinverter + inverter offgrid, partial on batteries

[racmaster]

would this work?

microinverter.jpg

[SunEagle]

I don't know if the circuit for panel 2 will work. Most micros are looking for a current source like a pv panel and not a voltage source like a battery.

I am also thinking you will be adding in fusing or overcurrent protection where needed.

[Mike90250]

But why ?
Wire the panels in series, use a MPPT controller, a 24v battery bank ( two 6v, 200ah golf cart batteries) and a respectable 1kw inverter, which would have enough surge capability to start a fridge.

What's your plan - what do you need to do ? micro inverters have NO surge capacity, and would be unable to assist starting any motor loads.

And if your load diminish, or the sun brightens, the extra power from the micros will either fry the 100 inverter, or shut everything down. Microinverters want to see a stable grid, they have no self throttle, and will push power till they overvoltage and trip offline for 5 minnutes,

[SunEagle]

But why ?
Wire the panels in series, use a MPPT controller, a 24v battery bank ( two 6v, 200ah golf cart batteries) and a respectable 1kw inverter, which would have enough surge capability to start a fridge.

What's your plan - what do you need to do ? micro inverters have NO surge capacity, and would be unable to assist starting any motor loads.

And if your load diminish, or the sun brightens, the extra power from the micros will either fry the 100 inverter, or shut everything down. Microinverters want to see a stable grid, they have no self throttle, and will push power till they overvoltage and trip offline for 5 minnutes,

I just noticed the OP states this system is for Off grid. I don't think micro inverters will work Off grid.

[sdold]

It looks like he wants to use the inverter on battery #1 to fool the microinverters into thinking there is a grid. My guess is that if the microinverters ever did see a stable enough waveform to start, they would destroy the inverter.

[SunEagle]

It looks like he wants to use the inverter on battery #1 to fool the microinverters into thinking there is a grid. My guess is that if the microinverters ever did see a stable enough waveform to start, they would destroy the inverter.

Big mistake for the OP.

[racmaster]

i have 2 different 12v batteries (lifepo90 and lto 100ah), therefor cannot join together for 24v... also all my appliances is 12v, so switching to 24 would make everything obsolete and need to be replaced by new 24 v appliances or expensive 24/12/24 voltage changing... the worst plan.

the goal is to split the power needed for load to both batteries 50/50 or so. if i use one 2000w inverter, it would take up to 180A current from one battery, which is just too much, but splitting it to 50/50 would be much more acceptable, supported by datasheets of both batteries with reserve...

another goal is to power AC230V fridge. having the classical inverter with 2 fans on 24/7 would make so much noise, i just cannot accept. system is placed on cottage in mountains having heavenly silent conditions, im not gonna spoil such a treasure with some inverter with active cooling. microinverters are mostly passive - silent...

and the final goal is versatility. i could let the fridge running on 300W peaks, 50w continuous and if needed i could join more by ac coupling to reach higher power by just counting several microinverters power together on 230V output...

[SunEagle]

First lets get the terminology correct as well as what I think are some issues

The regulators should be called battery charge controllers and are either PWM or MPPT.

Next. Micro inverters usually require a "grid" connection to work. That is how they are built.

Next. Combining "inverters" may cause them to fight each other unless they are the same make and model.

Next. If your loads are big, like the fridge, you may be required to use an inverter that has cooling fans. You can keep them quite by installing sound proofing like some people do with generators.

Next. As you mentioned you have two different batteries. IMO you will need to either get the same type to build a single battery system or use each battery independently to run an inverter and specific loads.

Finally any off grid system requires some type of additional charging system because the sun is not always there. You should get some type of generator (they make quiet ones) and use that to keep the batteries fully charge as well as maybe running your big load.

Just a few things to think about.

[Mike90250]

To start the compressor motor in a fridge, requires a inverter with about 2,000 watts of surge capacity. That generally requires a 1kw inverter to have enough "kick" to start the compressor. A cluster of small inverters will not reliably be able to do this and your fridge compressor will stall and burn out.

There are some very new and expensive fridges and air conditioners that have a "variable speed inverter compressor", that requires very little surge capacity.

[racmaster]

sorry sun eagle, but your sollution is to throw existing equipment for 2000usd to scratch and buy new equipment for 4000usd to run a fridge for 200 usd...

i respect your electrical skills, but your invention skills doesnt seem to be on same level. peace.

what about this:

there are some MI able to run in offgrid gridfree configuration like:

https://www.youtube.com/watch?v=TgIK6n5P06Q

what about combining - ac coupling them? lets reinvent the same goal from the other side

microinverter2.jpg

microinverter 300w on scheme would not be able to run fridge, that makes 50 W AC power requirement on compressor? is there a way to count it exactly? not just to tel IMO?

[bob-n]

racmaster,

You're right. The EQ8 from Enphase enables this sort of off-grid system. We haven't seen them for sale yet, but there is a lot of marketing going on.

Our experiences are with the Enphase IQ7 and APsystems QS1, which will not work that way.

[sdold]

You have a panel feeding both a charge controller (not a regulator) and an inverter, which is not normally possible. Sun Eagle's advice is correct for the vast majority of equipment that is found on the market, and shouldn't be discounted simply because one inverter may be available (or not) that is capable of operating on its own without AC-coupling to a battery/inverter.

[Mike90250]

.....

there are some MI able to run in offgrid gridfree configuration like:

https://www.youtube.com/watch?v=TgIK6n5P06Q

what about combining - ac coupling them? lets reinvent the same goal from the other side.....

If you are sure that's going to work for you, awesome. Make me a believer that your fridge is gong to start with your own video, till then, I wish you luck.

[SunEagle]

sorry sun eagle, but your sollution is to throw existing equipment for 2000usd to scratch and buy new equipment for 4000usd to run a fridge for 200 usd...

i respect your electrical skills, but your invention skills doesnt seem to be on same level. peace.

what about this:

there are some MI able to run in offgrid gridfree configuration like:

https://www.youtube.com/watch?v=TgIK6n5P06Q

what about combining - ac coupling them? lets reinvent the same goal from the other side

microinverter2.jpg

microinverter 300w on scheme would not be able to run fridge, that makes 50 W AC power requirement on compressor? is there a way to count it exactly? not just to tel IMO?

Unless you have the EQ8 micro they will not work off grid. If you think that you have a solution to your setup then go for it. Just be careful and safely wire in over-current protection.

[Mike90250]

....... Just be careful and safely wire in over-current protection.

Ha ! The $90 MOSFET's always burn out before the $2 fuse kicks in.