Using solar micro inverters with batteries instead of panels

[silverlexg]

I have been using m230 micros with 36v esccoter batteries and it works well. I tried to control the micros by automating on and off ? They take to long to start up and they are not efficent. My best move was to buy from ebay the envoys gateway? Now I leave all the micros on and the controller matches the generation to house demand. i use the zero export profile. Now no wasted generation? I have the batteries charged from mains on free power hours.

Mark - Can you detail how you are charging the batteries? Do you have other enphase microinverters for your solar production? Are you able to dyynamically control charge rate? otherwise i'd be worried about limiting PV production when you have an excess of power but the envoy limiting production. Would you be able to have 2 envoys? one for PV production and one for your battery inverters. I'm looking to do the same setup (powering micro inverters via battery during the night to cover the base house load to timeshift without expensive re-wiring. I'm looking to use the common 48v rackmount lithium batteries.

 

[kundip]

Mark - Can you detail how you are charging the batteries? Do you have other enphase microinverters for your solar production? Are you able to dyynamically control charge rate? otherwise i'd be worried about limiting PV production when you have an excess of power but the envoy limiting production. Would you be able to have 2 envoys? one for PV production and one for your battery inverters. I'm looking to do the same setup (powering micro inverters via battery during the night to cover the base house load to timeshift without expensive re-wiring. I'm looking to use the common 48v rackmount lithium batteries.

Mine is similar. I have 1 Envoy micro inverter per battery. You can have as many micro inverters as you like.
I have one 24V Battery with 5KW AC capacity running every night for 14 hours @ 300W AC (240 V)
Also one 24V Battery with 1.6KW AC Capacity running every night for 14 hours @ 200W AC (240 V)
Because my system is Micro Inverters everything is 240V AC.
So I charge my batteries during day with good quality 240V chargers.
I don't like the chargers that do everything (AGM, Lead Acid, LiFePo Etc - all in one) (I use Dedicated only)

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20Amp is a bit slower but the whole system runs quite cool.
I charge about 8 hours per day.

 

[silverlexg]

Mine is similar. I have 1 Envoy micro inverter per battery. You can have as many micro inverters as you like.
I have one 24V Battery with 5KW AC capacity running every night for 14 hours @ 300W AC (240 V)
Also one 24V Battery with 1.6KW AC Capacity running every night for 14 hours @ 200W AC (240 V)
Because my system is Micro Inverters everything is 240V AC.
So I charge my batteries during day with good quality 240V chargers.
I don't like the chargers that do AGM, Lead Acid, LiFePo Etc. (I use Dedicated only)

AC-DC 24V 20A Lithium LiFePO4 Battery Charger - Amptron

AC-DC 24V 20A Lithium LiFePO4 Battery Charger AMPTRON® Lithium Iron Phosphate (LiFePO4) battery chargers are state-of-the-art battery chargers with a charging profile specifically designed to charge and maintain Lithium Iron Phosphate (LiFePO4) batteries, and can safely achieve a 100% State of...

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20Amp is a bit slower but the whole system runs quite cool.
I charge about 8 hours per day.

Kundip - thank you for responding! Are you using an envoy to limit output from the battery or have you basically just assumed 1 microinverter with constant output for the whole evening? How are you controlling the charger? I know you can limit over/under charge on the battery via BMS but do you have some logic somehow setup to turn the charger on if over producing solar? How do you disconnect it in the evening once your PV power is gone? Appreciate the info - This really seems like a simple way to timeshift solar production into the evening hours.

 

[kundip]

I am grid connected. Any excess power from panels or batteries (minimal) goes to grid.
Trying to balance on your own excess power is too expensive & complicated. IMO
I use 240 Volt dedicated battery changers instead of solar chargers as I think they are better suited to charging LiFePo4 or any other batteries. IMO
A lot of the solar inverters that charge batteries do not do that good a job. IMO
My system is designed to use any battery that I buy cheap on local sites AGM, Lithium whatever & match charger to it.
For example high end Amptom Lithium batteries cost AUD $1,859 each NEW
I got two for AUD $800 each. (1 & 1/2 Years Old) to use. My payback time is under three years.
There may be some inefficiencies using a 240V charger but I just add more panels, with micro-inverters, to adjust the loss.
I buy the envoy micro-inverters for AUD $30 second hand. Other parts cost AUD $200 all up.
Each system costs about USD $700 all up.
I have three of these systems working flawlessly for over a year.
I now produce 900 Watt @ 240 V AC for 14 hours per night.
200 watts per inverter may not seem like a lot but it makes a big difference to your energy independence.
My picture in last post shows energy dependence is only 17% from grid.
This year 2023 so far my energy dependence is only 8% from grid.
I work small but get big results. IMO
Nothing is complicated & all is easily managed & maintained.
Please note my original design shows a buck converter - this is not required.

Added 14/04/23: PLEASE NOTE - I no longer use buck converters nor advocate in this situation. See my later posts.

 

[zalamandern232]

I am grid connected. Any excess power from panels or batteries (minimal) goes to grid.

My picture in last post shows energy independence as 83% meaning only 17% from grid.
I work small but get big results. IMO
Nothing is complicated & all is easily managed.

diy06.JPG, this look like what im trying to do but i working with 48vdc battery bank, does your setup still work? I cant see any fuses to protect the batteries or the inverter, how do you current protect the circuit? how high is your current when you start the setup?

 

[kundip]

diy06.JPG, this look like what im trying to do but i working with 48vdc battery bank, does your setup still work? I cant see any fuses to protect the batteries or the inverter, how do you current protect the circuit? how high is your current when you start the setup?

Yes I have 15 amp fuses at the battery

 

[zalamandern232]

Yes I have 15 amp fuses at the battery

ok, you use the one on the dc/dc converter. Somehow my fuse seems allways to blow tried lower the current limiter to what i guess, is half. will try to use a powerresistor

 

[kundip]

ok, you use the one on the dc/dc converter. Somehow my fuse seems allways to blow tried lower the current limiter to what i guess, is half. will try to use a powerresistor

Lowering the current is very hard.
I have found I can do without the buck converter since my last post.
The Enphase microinver itself only pulls 10 amp 24v DC and puts out 240v @ 200 watts per hour.
It should do same at 48v. I picked 24v originally because there are many more devices available at that voltage. (& Cheaper).
48v is catching up but dearer. IMO
I have put a 24v 30amp relay & power the inverter through that. I don't run the main current through the Victron Battery Saver any more as I had too many problems with the Victron even though it is rated at 65amp. It kept on complaing about "inrush current" or just cut the voltage from 24v to about 8v.
I use the Victron to turn on and control the relay.
The Victron cuts off battery @ 24v.

 

[fafrd]

I wouldn't do it! (but I think there is a solution...)
In the best case, the MPPT algorithm of the microinverter would never lock, and output would fluctuate.
In the worst case it would simply fry your microinverter and/or ruin your batteries.

There are some grid-tie inverters that are actually designed for this (like the SUN 2000W) , but I don't know of any microinverters that have this feature.

What the MPPT algorithm is looking for is a maximum power point. With batteries, the maximum power point is theoretically infinite.

But, maybe you can use one if these DC-DC boost converters in betweenyour batteries and the microinverter, which has a current limiting function.
For example, lets say you set your DC-DC converter to a maximum of 15 amps and 36v. If the microinverter will try to pull more than 15amps, the DC-DC will lower the voltage accordingly. The MPPT should then understand that it went too far with the current and slowly bring it down.

All this is in theory, I haven't tried it, but I did play with some of these DC-DC boost converters. They are pretty nice and cheap, but a bit if a pain to setup (using pots to set voltage and maximum current).

I would suggest you get one and experiment slowly. I would set the maximum voltage a bit less than your microinverter's maximum voltage, and the amps at almost the maximum the microinverters can handle.
But make sure that this is inline with your batteries abilities and your wiring guage.
If you set it properly, it should protect your batteries a bit, but still I would add proper fusing just in case.

There are different versions of these cheap DC-DC boost converters, but I would get the 1800w one, just because it has a temperature controlled fan, and its beefier.
These guys generate heat at high loads, so make sure to keep them indoors and properly ventilated.

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Good luck... and stay safe.

Did you ever get a working DC-DC boost converter and how did it work out for you feeding battery power to your Microinverter after sunset?

I just purchased one of these and am interested in anyone’s experience using these budget programmable current-limited DC-DC boost converters to limit output from a Microinverter when powering from a battery…

 

[kundip]

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.

Using solar micro inverters with batteries instead of panels

I have been using m230 micros with 36v esccoter batteries and it works well. I tried to control the micros by automating on and off ? They take to long to start up and they are not efficent. My best move was to buy from ebay the envoys gateway? Now I leave all the micros on and the controller...

diysolarforum.com

I am grid connected. Any excess power from panels or batteries (minimal) goes to grid.
Trying to balance on your own excess power is too expensive & complicated. IMO
I use 240 Volt dedicated changers instead of solar chargers to charge batteries when the sun is out as I think they are better suited to charging LiFePo4 batteries. IMO
A lot of the solar inverters that charge batteries do not do that good a job. IMO
My system is designed to use any battery that I buy cheap on local sites AGM, Lithium whatever & match a good charger to it.
For example two high end Amptom Lithium batteries I have cost AUD $1,859 each NEW
I got two for AUD $800 each. (1 & 1/2 Years Old). My payback time is under three years.
There may be some inefficiencies but I just add more panels, because I use micro-inverters, to adjust the loss.
I buy the envoy micro-inverters for AUD $30 second hand. Other parts cost AUD $200 all up.
Each system costs about USD $700 all up.
The first one has been working flawlessly for over a year.
The second 6 months.
My third one will be in production in a couple of weeks.
200 watts @ 240 volts may not seem like a lot but it makes a big difference to your energy independence.
My picture in last post shows energy independence as 83% meaning only 17% from grid.
I work small but get big results. IMO
Nothing is complicated & all is easily managed.

 

[Hedges]

Overall, this is an interesting topic for discussion, and I would be curious to hear from others who have experimented with <link "connecting solar panel"> micro inverters to battery banks.

Please do not link to web pages promoting your business.
That is against forum rules.
You should edit your posting to delete the link.

 

[fafrd]

It's an interesting idea to connect a solar panel micro inverter to a battery bank instead of a panel. In theory, it should work as volts are volts, and the micro inverter should be able to handle the MPPT tracking voltage of the battery bank.

However, it's important to ensure that the battery bank is properly sized to handle the load

Uhhh, don’t get that. This is grid-tied, so any energy you output shaves load and no need to size the battery bank to anything other than the amount of load you want to shave while the sun is not shining…

and that the micro inverter is compatible with the batteries being used.

Well if you want to attempt direct connection of battery to Microinverter (which I do not advise), then yes, you need to assure that the MPPT range of the Microinverter brackets your battery voltage.

But if you use a DC-DC booster as proposed by the OP in between the battery and the Microinverter, all you need to do is assure your Microinverters max MPPT voltage exceeds to batteries maximum fully-charged voltage…

Additionally, it's worth noting that using a battery bank to store solar energy and shift its use to expensive evening periods can be a smart strategy for reducing energy costs. However, it's important to consider the cost and lifespan of the batteries being used, as well as any potential safety hazards associated with battery storage.

A good reason to go with LiFePO4 rather than Lead Acid (or it’s variants).

Overall, this is an interesting topic for discussion, and I would be curious to hear from others who have experimented with connecting solar panel micro inverters to battery banks.

I just ordered one of the same budget DC-DC boosters as purchased by the OP to try exactly that. Will report back on what I find…

 

[Hedges]

Well if you want to attempt direct connection of battery to Microinverter (which I do not advise), then yes, you need to assure that the MPPT range of the Microinverter brackets your battery voltage.

And you have a way to stop discharge at low Vbat, not over-discharging.
If the battery has BMS which can disconnect, we recommend that be protection when other controls malfunction, not first line of defense.

 

[fafrd]

And you have a way to stop discharge at low Vbat, not over-discharging.
If the battery has BMS which can disconnect, we recommend that be protection when other controls malfunction, not first line of defense.

Absolutely. These budget programmable DC-DC converters supposedly also include programmable low-voltage protection, but that’ll be one of the first things I characterize (assuming I decide they are capable enough to warrant the investmevt).

Of course, as a fall-back, a battery voltage monitor can always open an AC relay connecting to the Microinverter output…

 

[fafrd]

Please do not link to web pages promoting your business.
That is against forum rules.
You should edit your posting to delete the link.

Good catch.

I didn’t bother to follow the link but the New Member with 3 posts should have been a tip-off…

 

[kundip]

Kundip - thank you for responding! Are you using an envoy to limit output from the battery or have you basically just assumed 1 microinverter with constant output for the whole evening? How are you controlling the charger? I know you can limit over/under charge on the battery via BMS but do you have some logic somehow setup to turn the charger on if over producing solar? How do you disconnect it in the evening once your PV power is gone? Appreciate the info - This really seems like a simple way to timeshift solar production into the evening hours.

Please lay out your questions so they are easier to read.
I use a 24 volt system to keep each in a small package size.
You can just plug the Enphase Inverter straight in to the 24 volts - the inverter starts producing after about 5 minutes.
Please look & read at pics I have supplied - I just use a Kaza timer set to run 14 hours to control charger. Any smart switch will do.
In my case I leave the charger coming on 365 days a year. We get so few rainy / cloudy days it is not worth worrying about.
You can put a light sensitive switch on your roof and add that to circuit easily.
If you have a proper charger for each battery type that will look after itself. My design keeps that part separate.
Not sure re your question "over producing solar" I have two Kaza switches connected to 1200 Watt 240 Volt heaters.
We cannot send more than 5 KW per hour to the grid. During summer one of those heaters comes on for 4 hours over the peak 10AM - 2PM
This keeps me well below 5 KW.
If one of my chargers are broken (never happened) I can put two heaters on.
Not sure re your disconnect question - the PV and batteries are married up so each just keeps working & doing their thing.
If you shone a strong light on a panel at night it would produce 240 V AC without affecting anything.
If you accidentally leave a battery on during the day it will produce 240 V AC during the day but your battery might not get fully charged as some of the charge would be going to the grid.

 

[fafrd]

I use a 24 volt system to keep each in a small package size.
You can just plug the Enphase Inverter straight in to the 24 volts - the inverter starts producing after about 5 minutes.
Please look & read at pics I have supplied - I just use a Kaza timer set to run 14 hours to control charger. Any smart switch will do.
In my case I leave the charger coming on 365 days a year. We get so few rainy / cloudy days it is not worth worrying about.
You can put a light sensitive switch on your roof and add that to circuit easily.
If you have a proper charger for each battery type that will look after itself. My design keeps that part separate.
Not sure re your question "over producing solar" I have two Kaza switches connected to 1200 Watt 240 Volt heaters.
We cannot send more than 5 KW per hour to the grid. During summer one of those heaters comes on for 4 hours over the peak 10AM - 2PM
This keeps me well below 5 KW.
If one of my chargers are broken (never happened) I can put two heaters on.
Not sure re your disconnect question - the PV and batteries are married up so each just keeps working & doing their thing.
If you shone a strong light on a panel at night it would produce 240 V AC without affecting anything.
If you accidentally leave a battery on during the day it will produce 240 V AC during the day but your battery might not get fully charged as some of the charge would be going to the grid.

View attachment 142901

No issues with direct connection to battery, huh? I suppose the Microinverters are just maxed-out and producing power at their mscimum rating? Or are they limited by maximum input current x battery voltsge?

 

[kundip]

No issues with direct connection to battery, huh? I suppose the Microinverters are just maxed-out and producing power at their mscimum rating? Or are they limited by maximum input current x battery voltsge?

Not sure - none of them get hot. They have all been running for over a year.
By ramping up the voltage to 30 volt using the buck converter one is producing 300 W @ 240 V AC and still not getting hot.
That one is still running.
I pefer my new method.

 

[fafrd]

Not sure - none of them get hot. They have all been running for over a year.
By ramping up the voltage to 30 volt using the buck converter one is producing 300 W @ 240 V AC and still not getting hot.
That one is still running.
I pefer my new method.

Oh, so you are also using a buck converter between battery and Microinverter now. Do you mean buck converter or boost converter?

Why do you prefer that method?

Can you share a link to the DC-DC converter you are using?

Does the DC-DC converter have a limited current output and is it below the maximum current rating of the Microinverters?

What is the maximum current rating of your Microinverter and does the power output you are getting match pretty closely to:

Imax x battery voltage when connected directly

Imax x boosted voltage of 30V when connected through DC-DC converter

When you say ‘that one is still running’ do you mean that the Microinverter which was directly connected to your battery is no longer running and has failed?

Thanks for sharing your experience as a pioneer!

 

[kundip]

It's an interesting idea to connect a solar panel micro inverter to a battery bank instead of a panel. In theory, it should work as volts are volts, and the micro inverter should be able to handle the MPPT tracking voltage of the battery bank. However, it's important to ensure that the battery bank is properly sized to handle the load and that the micro inverter is compatible with the batteries being used.

Additionally, it's worth noting that using a battery bank to store solar energy and shift its use to expensive evening periods can be a smart strategy for reducing energy costs. However, it's important to consider the cost and lifespan of the batteries being used, as well as any potential safety hazards associated with battery storage.

Overall, this is an interesting topic for discussion, and I would be curious to hear from others who have experimented with connecting solar panel micro inverters to battery banks.

Well it's worked for two years so far.

Re properly sized to handle load.
Keeping the voltage at the low end seems to work fine. The imicro-nverter can take from 20v to 46v. I stick with 24v. This gives me 200w @ 240vac.
I do have one set up from my original experimentation that has a boost converter taking the voltage from 24vdc to about 32vdc.
This setup produces 300w @ 240vac.
I plan to change this back to just 24vdc input as the boost converter is not needed and just adds to the complexity.I am not a big fan of the current boost converter design although I have had no problems with it.

Re cost:
My designs & methods have an under 5 year payback, from the battery alone, easily. Most advertising calculations by companies use money (savings) from the solar panels to pay back a large portion of the battery cost but it is hidden from the consumer.

Re lifespan:
I use commercial grade chargers that mange the batteries and watch the temperature very well. All of my systems have a battery protector in between the battery & inverter. The batteries never go below 23.5v
(MotorMate) or 24v (Victron Battery Protector).
They should last 10 years easily and possibly 20 years.

Re Battery storage:
I have only used high end batteries that are locally made here. Amptrons by an ex Schneider Electrical Engineer - Frick. Or EVPower Batteries made by Professor Rod Dilkes. They are considerably more expensive expensive than the rubbish i.see being sold in a lot of stores.They are set up under the well ventilated corner of the house in a kind of enclosed cellar only accessible from outside. We have up to 46 degree Celsius days here and it never goes above 30 degrees Celsius in the "cellar". Where we live: the codest it gets is -2 for an hour or so early morning. This has happened maybe 6 times in the last 10 years. The room itself never goes below 10 degrees. Each setup is three feet apart. All have heat sensing BMS's and I have a dedicated smoke alarm it that area along with two 5 KG dry powder fire extinguishers. I regularly check for hot spots.