Can you trick a 10.8kw solar grid tie inverter to work in a grid down scenario with a seprate inverter and battery bank

[Zero X]

So this is what I have.
10.8kw system using enphase m215 micro inverters

Trying to figure out if my grid ever goes out my whole solar system goes off line and all that solar is useless.

So I bought a mpp lv6048 inverter and a eg4 5.12 kw battery bank.
I hooked up 9 solar panels separate from my house to feed the mpp inverter and charge the battery bank completely off grid. I basically hooked up a 30 Amp 4 plug extension cord to power an window unit and fridge, and so far works perfectly.

So here's my question

Is it possible to safely shut the main breaker off feeding power from the utility power grid. And back feed my sub panel with the mpp lv6048 and put 120 volts on each leg to send power and fool my main solar system to think 240 is now present and for the whole system to come online.

I seen some post comments saying I'd have to use up all the available power my solar system would use to keep from frying things in my house. I'm a little confused as to why it would burn my devices up considering the grid is constantly having 240v sent to my house and if I'm not using alot or if I do power is always present no matter what. So how or why would it be different if I shut off power from backfeeding the grid and I just have a constant power source waiting to be used?

Also I have a metering device and even tho I have a 10.8 kw sticker plate output at best with optimal sunlight I max generate only 8.9kw max.

And I don't plan to try and run my whole house just to run the essentials like fridge and lights and window units. I know the main central ac unit will be too much for just 1 battery bank.

If anyone with knowledge can direct me how to do this safely or if they had success in fooling it please let me know thanks

 

[sunshine_eggo]

You can only do that with an inverter capable of frequency shifting. It's called AC coupling. You'd need an expensive 10kW+ inverter.

AC Coupling

AC Coupled Solar Power System - use your existing system to feed power into a battery based inverter/charger to charge the battery bank.

www.altestore.com

Grid tie inverters operate based on the assumption that there is an infinite grid that can accept its maximum power output. They do not regulate themselves when an acceptable grid is present.

Any grid forming inverter must be able to shift the frequency out of the acceptable range to force the grid tie inverter to disconnect and stop sending power as that power needs somewhere to go. The Enphase would just keep pushing power into the MPP until something bad happens.

I see no evidence that the MPP has any ability to frequency shift, so using it for a grid forming inverter would not work.

 

[schmism]

Can you trick the micro inverters to make power, yes.
Can you power devices off it directly safely, I would not.

The only implementation of it I have seen uses a Soark (as eggo above mentioned) to regulate the micro inverters and take all their available power and charge a battery with it at a constant (ish) rate. Using a second inverter to power the house with its transient loads. (as the micros cant respond fast enough to changes in demand, which results in high voltage spikes and low voltage brownouts, thus the burn up stuff in the house)

 

[MurphyGuy]

So this is what I have.
10.8kw system using enphase m215 micro inverters

Trying to figure out if my grid ever goes out my whole solar system goes off line and all that solar is useless.

So I bought a mpp lv6048 inverter and a eg4 5.12 kw battery bank.
I hooked up 9 solar panels separate from my house to feed the mpp inverter and charge the battery bank completely off grid. I basically hooked up a 30 Amp 4 plug extension cord to power an window unit and fridge, and so far works perfectly.

So here's my question

Is it possible to safely shut the main breaker off feeding power from the utility power grid. And back feed my sub panel with the mpp lv6048 and put 120 volts on each leg to send power and fool my main solar system to think 240 is now present and for the whole system to come online.

I seen some post comments saying I'd have to use up all the available power my solar system would use to keep from frying things in my house. I'm a little confused as to why it would burn my devices up considering the grid is constantly having 240v sent to my house and if I'm not using alot or if I do power is always present no matter what. So how or why would it be different if I shut off power from backfeeding the grid and I just have a constant power source waiting to be used?

Also I have a metering device and even tho I have a 10.8 kw sticker plate output at best with optimal sunlight I max generate only 8.9kw max.

And I don't plan to try and run my whole house just to run the essentials like fridge and lights and window units. I know the main central ac unit will be too much for just 1 battery bank.

If anyone with knowledge can direct me how to do this safely or if they had success in fooling it please let me know thanks

The technique is called AC Coupling, and it is what my system does. When the grid goes down, as it does out here in the rural countryside for days at a time when storms roll thru, I simply isolate the grid, then fire up the off-grid system.

The off-grid system consists of a battery bank + battery inverter capable of AC coupling. The inverters draw power from the battery and make power for the home. When the (normally) grid-tied solar system sees this, it thinks the grid is back up and running so the grid tied solar inverter starts making power.

If the grid tied array (now isolated from the grid), makes more power than the house needs, the inverters use the excess to charge the batteries. If the array doesn't make enough power, the inverters draw from the batteries to make up the difference to keep the house going.

Here's the tricky part... If the array makes more power than the house needs AND the batteries are fully charged, then the battery inverter raises the grid frequency from 60hz to 61hz, and then to 62hz in very small increments. This causes the (normally grid tied array inverters to "throttle" their output to a lower level.

The battery inverter system must be capable of this function, but the grid tied inverters need not be. If the (normally) grid tied inverters are incapable of throttling, then they will simply shut down and trip out when the grid frequency hits 62hz and they won't re-engage until the frequency falls below their trip threshold.

The magic is in the battery inverter, not the inverters on the array.. But it makes things go smoother if the (normally) grid tied inverters are capable of throttling.

In your case, you'd have to look up the capabilities of your micro inverters, but you could always disconnect some of them if they're too big for whatever battery inverter you get.

 

[Zero X]

The technique is called AC Coupling, and it is what my system does. When the grid goes down, as it does out here in the rural countryside for days at a time when storms roll thru, I simply isolate the grid, then fire up the off-grid system.

The off-grid system consists of a battery bank + battery inverter capable of AC coupling. The inverters draw power from the battery and make power for the home. When the (normally) grid-tied solar system sees this, it thinks the grid is back up and running so the grid tied solar inverter starts making power.

If the grid tied array (now isolated from the grid), makes more power than the house needs, the inverters use the excess to charge the batteries. If the array doesn't make enough power, the inverters draw from the batteries to make up the difference to keep the house going.

Here's the tricky part... If the array makes more power than the house needs AND the batteries are fully charged, then the battery inverter raises the grid frequency from 60hz to 61hz, and then to 62hz in very small increments. This causes the (normally grid tied array inverters to "throttle" their output to a lower level.

The battery inverter system must be capable of this function, but the grid tied inverters need not be. If the (normally) grid tied inverters are incapable of throttling, then they will simply shut down and trip out when the grid frequency hits 62hz and they won't re-engage until the frequency falls below their trip threshold.

The magic is in the battery inverter, not the inverters on the array.. But it makes things go smoother if the (normally) grid tied inverters are capable of throttling.

In your case, you'd have to look up the capabilities of your micro inverters, but you could always disconnect some of them if they're too big for whatever battery inverter you get.

Thanks. Yea I seen someone talk about an inverter increasing the hearts to fool the solar inverters from going offline making it out of sync with the grid to keep it from power spiking and eventually drawing the battery bank for a while. Then eventually the inverter sync within an acceptable range then the solar system recharges the battery bank etc...

Was hoping for a simpler solution but guess I'd have to gamble and risk burning something up.

I'll probably just use my extra solar panels and keep my house disconnected and just power my critical loads with just my battery bank and small solar array and don't risk burning up my 40 panels on my roof.

 

[Zero X]

You can only do that with an inverter capable of frequency shifting. It's called AC coupling. You'd need an expensive 10kW+ inverter.

AC Coupling

AC Coupled Solar Power System - use your existing system to feed power into a battery based inverter/charger to charge the battery bank.

www.altestore.com

Grid tie inverters operate based on the assumption that there is an infinite grid that can accept its maximum power output. They do not regulate themselves when an acceptable grid is present.

Any grid forming inverter must be able to shift the frequency out of the acceptable range to force the grid tie inverter to disconnect and stop sending power as that power needs somewhere to go. The Enphase would just keep pushing power into the MPP until something bad happens.

I see no evidence that the MPP has any ability to frequency shift, so using it for a grid forming inverter would not work.

Yea just looked it up. Seems u are right I need an inverter capable of ac coupling. Man them inverters are expensive seems like for what I need is going to cost like 5k to buy an inverter and not even including the critical load panel and wiring lol. Guess I'll stick to my small floor mount array and extension cord to power my very minimal load.

Thanks for the advice greatly appreciated

 

[MurphyGuy]

Thanks. Yea I seen someone talk about an inverter increasing the hearts to fool the solar inverters from going offline making it out of sync with the grid to keep it from power spiking and eventually drawing the battery bank for a while. Then eventually the inverter sync within an acceptable range then the solar system recharges the battery bank etc...

Was hoping for a simpler solution but guess I'd have to gamble and risk burning something up.

I'll probably just use my extra solar panels and keep my house disconnected and just power my critical loads with just my battery bank and small solar array and don't risk burning up my 40 panels on my roof.

There is no practical way to do it without a battery inverter capable of bidirectional power flow.

That said, there are ways to sort of cheat.. its not pretty, its not really practical, but it could be done.

Lets say you had a battery system with a blind inverter.. IE: Normal battery inverter.. and that inverter had to power a house that was drawing 1000 watts continuously. You could hook up a single microinverter on something like a 400 watt panel to the circuit.. And so long as the house was always drawing more than 400 watts, it would work.

If your home drew 700 watts, the battery inverter would see it as 300 because the microinverter is taking care of the other 400 watt input.

I recommend you not do this unless you're desperate and a life depends on it.. one slip and something is going to get smoked in that circuit.

 

[Zero X]

There is no practical way to do it without a battery inverter capable of bidirectional power flow.

That said, there are ways to sort of cheat.. its not pretty, its not really practical, but it could be done.

Lets say you had a battery system with a blind inverter.. IE: Normal battery inverter.. and that inverter had to power a house that was drawing 1000 watts continuously. You could hook up a single microinverter on something like a 400 watt panel to the circuit.. And so long as the house was always drawing more than 400 watts, it would work.

If your home drew 700 watts, the battery inverter would see it as 300 because the microinverter is taking care of the other 400 watt input.

I recommend you not do this unless you're desperate and a life depends on it.. one slip and something is going to get smoked in that circuit.

Yea seems like proper way is to buy an hybrid inverter that allows ac coupling. But man them things are expensive. Just going to use my small solar array I lay down in the yard as an emergency and just use my extension cord to power my fridge a few led lights and my one window unit. I at least know I can get about 6 hrs of continuous ac thru the night till the next day of sunlight.

Not going to spend 5k plus to have my solar on my roof power up. I'll just use a 600 dollar generator if I really need more power lol ?

 

[MurphyGuy]

The newer Enphase IQ8 micro inverters are capable of operating in grid tied mode, or in off-grid mode without a battery... but they only produce power while the sun is shining.
You could probably swap out a couple of your older units..

 

[Zero X]

The newer Enphase IQ8 micro inverters are capable of operating in grid tied mode, or in off-grid mode without a battery... but they only produce power while the sun is shining.
You could probably swap out a couple of your older units..

Yea I looked into that but my envoy system is not compatible with the new iq8 and even with their legacy upgrade program it's gonna cost 6k not including plus labor for my solar company to install it

 

[David Kay]

As others have said you need way to soak up extra power if there is too much.

Hypothetically, an all in one hybrid inverter that can put work with grid tie and put the surplus power in battery, and some sort of extra load(s) that kicks in when battery reaches 90%+, 95%, etc, like heating, heat pump, air conditioning, freezers, etc... can be ac and/or on the solar panel or battery dc side... (dc side you suck it out of solar panels so not available for grid tie inverter... lighting, resistance loads/heat and dc motor and ac/dc type motor and dc to 3 phase power controller are possible)

Hypothetically off grid hybrid inverter with "dry contact" generator input for when batteries are low. Set the battery low point quite high. "Generator" is some sort of combo involving your grid tie solar panels, some sort of electric generator/motor to provide the 60 Hz waveform. On generator startup, it uses electric power to reach 60 Hz, and a flywheel to help average load, and your grid tie inverters. When the power goes out of sync the hybrid inverter won't use it which protects your equipment. Its a game of using flywheel as capacator and trying to stay near 60Hz by extra loads (like hot water heater) kicking in and out. In theory a "single phase to 3 phase" VFD that is trying for a specific 60 Hz speed could be rigged up to help manage the speed by acting as motor when below 60Hz and regen braking when above 60 Hz, on the dc side it can handle 200 to 400 volts (dc is normally input from single phase, but instead could be pure dc). You have a diode setup to keep the dc side below 400 volts and it will regen brake the excess ac solar power to the dc. This sort of setup would be less efficient, but able to handle surge loads much better than electronics in an inverter.