Using solar micro inverters with batteries instead of panels

[chopwood]

The subject says it all. I was wondering whether anyone has tried connecting a solar panel micro inverter to a battery bank instead of a panel. I'm talking here about the grid connect micro inverters that go straight into 240V and have their own anti islanding protection. Obviously you would need to setup a battery bank that's in the MPPT tracking voltage of the micro inverter (say 36V).

My gut feeling is that is should work, volts are volts. But I was wondering if anyone here had tried.

My thinking is that by switching out a couple of panels in the evening and connecting batteries to the inverters instead, I can shift my solar power into the expensive evening periods. I'm on a wholesale plan, so I usually only need an hour or so of coverage to save several dollars in electricity.

Also I have a pile of old deep cycle batteries to experiment with. So I may as well put them to use.

 

[Dzl]

The subject says it all. I was wondering whether anyone has tried connecting a solar panel micro inverter to a battery bank instead of a panel. I'm talking here about the grid connect micro inverters that go straight into 240V and have their own anti islanding protection. Obviously you would need to setup a battery bank that's in the MPPT tracking voltage of the micro inverter (say 36V).

My gut feeling is that is should work, volts are volts. But I was wondering if anyone here had tried.

My thinking is that by switching out a couple of panels in the evening and connecting batteries to the inverters instead, I can shift my solar power into the expensive evening periods. I'm on a wholesale plan, so I usually only need an hour or so of coverage to save several dollars in electricity.

Also I have a pile of old deep cycle batteries to experiment with. So I may as well put them to use.

I'm curious to here the answer on a theoretical level

On a practical level, I bet there are more straightforward/on-the-beaten-path ways to accomplish your goal.

 

[Ampster]

The micro inverter is designed to be grid tied. It needs to be connected to the grid in order to operate. It won't work.

 

[Dzl]

The micro inverter is designed to be grid tied. It needs to be connected to the grid in order to operate. It won't work.

I think they are referring to using the battery on the input side of the microinverter. But I can't say I fully understand.

 

[Supervstech]

Most batteries would vaporize the circuitry in a micro inverter...

Solar panels are output limited... batteries are not.

 

[Supervstech]

I suppose you could tie the batteries to a regulated output and send that to the micro inverter, but it’s a lot of expense... and how would you charge the batteries?

 

[Dzl]

If the goal is to timeshift when you feed power back to the grid or when you pull from the grid, aren't there products designed for this. Isn't that one of the purposes of a powerwall?

 

[Ampster]

If the goal is to timeshift when you feed power back to the grid or when you pull from the grid, aren't there products designed for this. Isn't that one of the purposes of a powerwall?

Yes, a Powerwall or hybrid inverter contains the necessary hardware and software to time shift with batteries.

 

[Dzl]

OP can you confirm, is this what you are trying to accomplish?

 

[Ampster]

If the OP is trying to make 60Hz 120v electricity from a DC battery an inverter designed to do that is what he should use. A microinverter will not do that.

 

[chopwood]

Yes confirming that I'm trying to timeshift. And yes a powerwall or other similiar product would do exactly what I want. I just don't want to spend $15,000 especially when I have a number of the micro inverters already on the roof and hooked into the grid.

So in summary, yes, connect the battery to the input side of the microinverter. leave the output side connect to 240V as it currently is.

Interesting point about batteries not being current limited. I would have expected that the inverter would handle a panel that produced more current than the inverter was rated at. Interesting idea about current limiting the battery.

 

[Ampster]

I would have expected that the inverter would handle a panel that produced more current than the inverter was rated at. Interesting idea about current limiting the battery.

That is probably only one of the reasons it will not work. The microinverter has no mechanism for adjusting the output to match the load like normal inverters do. It expects a grid which presents as an infinite load. It actually has a boot up sequence that tests for various characteristics of the grid including the presence of a 60 Hz waveform. If it does not see that it will not start since it has no oscillator itself.

 

[chopwood]

That is probably only one of the reasons it will not work. The microinverter has no mechanism for adjusting the output to match the load like normal inverters do. It expects a grid which presents as an infinite load. It actually has a boot up sequence that tests for various characteristics of the grid including the presence of a 60 Hz waveform. If it does not see that it will not start since it has no oscillator itself.

Sorry, I wasn't clear. My intention is to have this functioning when the grid is available. This is an on grid scenario. So the microinverter will function. I just want it to function in the evening by switching the panel out and a 36V battery in.

Why? because the wholesale nature of the electricity plan I'm no means I'm not paid much for solar export during the day (6 cents/KwHr). So I'm better of pushing that energy into batteries or hot water. However what I've seen lately is that, come early evening the price spikes for an hour or so before settling down. Last night it was $2.46 KW/hr for about 1/2 an hour. It's a good time to be either on batteries, or exporting the energy stored earlier.

The microinverters I already have will do that. They just need to be powered.

 

[Dzl]

I think that there are almost certainly less complicated ways to accomplish the same goal. But I'm curious to see where this discussion leads.

 

[Ampster]

Okay my apologies. I thought this was another spoof the grid to make a micro inverter work off grid. I don't know why you can't spoof the sun and make it work. Some kind of DPDT relays, current limiting device to feed the micro inverters and whatever else
it might take to make the micro inverters to produce energy. That is the extent of my knowledge about how to do it. Keep us informed.

 

[pollenface]

To answer your question.

Yes, you can power micro inverters with batteries instead of solar panels.

 

[newbostonconst]

I have a IQ7X powered off my 60 volt battery bank to take out my base load that doesn't go through my hybrid inverter. It flashes orange (orange means AC good but not connected to Envoy). It makes a constant 312 watts.

Edit....this works on the bench but once connected to whole system and am guessing ground is introduced it faults the IQ7X

 

[newbostonconst]

If you cost out batteries verse water for solar for added storage, batteries are now cheaper if you already have an inverter/charger. The cost of an extra water tank is like $1000 and if I remember a 50 gallon tank only holds 6kwh of energy. Adding to a battery bank is cheaper. My numbers maybe off slightly because I am going off memory but I know it is the more cost effective way to go.

 

[kundip]

Has anyone got this to work yet please?
I have a 24 Volt Battery (3.2 KW). I have ordered a Buck Converter from Amazon:
Dasiter 600W High Power DC to DC Boost Converter DC 12-60V to 12-80V Boost Module Board Step-up Transformer.
I have an Enphase M215-60-230-S22 inverter.
Recommended maximum input power W 310 MPPT voltage range V 27-39 Operating range V 16-48
Looking at Doctorbass on Youtube Watch?v=GxSafeeUWB4&t=525s
The battery input voltage has to be above the maximum MPPT voltage (39 Volts).
...But below the maximum operating range (48 Volts). So I am thinking say 42 volts.
This switches off the MPPT which Doctorbass says causes problems for this use.
My grid connect is set up & working OK.
Just waiting on Buck Converter. Any assistance would be appreciated.
Added 14/04/23: PLEASE NOTE - I no longer use buck converters nor advocate in this situation. See my later posts.

 

[Ampster]

I assume you have a grid connection in order to enable the micro inverter to work. It needs 240 volt AC from the grid in order work. I don't understand what the buck converter is for?
I assume your goal is to harvest solar and produce AC or DC to power either a 24 volt DC device from the battery battery or some 120 or 240 volt AC device. That use case will determine which components you will need.
If you read this thread from the beginning, you will see several variations on this concept and no working examples.