Using solar micro inverters with batteries instead of panels

[kundip]

These are the cheapo DCDC boosters I’m going to be experimenting with:

View attachment 143196

They have two potentiometers hard-wired in for control, one to set current limit and one to set voltage limit,

Any idea whether a design using a wired-in (settable) resistor can suffer from the uncontrolled boost you experienced?

I suppose adding a monitor circuit to shut everything down if any boost voltage exceeds 150% or even 125% of target wouldn’t be the end of the world…

You are still talking about charging a phone, or is that somehow relative to the thread topic?

Sounds like more phone charging stuff. Appreciate any input you have on how to prevent against the possibility of a DC-DC boost converter exceeding the maximum input voltage rating of a Microinverter, but the subject of charging mobile phones or any other electronics for that matter is really not relevant to the subject of this thread…

These are the cheapo DCDC boosters I’m going to be experimenting with:

View attachment 143196

They have two potentiometers hard-wired in for control, one to set current limit and one to set voltage limit,

Any idea whether a design using a wired-in (settable) resistor can suffer from the uncontrolled boost you experienced?

I suppose adding a monitor circuit to shut everything down if any boost voltage exceeds 150% or even 125% of target wouldn’t be the end of the world…

You are still talking about charging a phone, or is that somehow relative to the thread topic?

Sounds like more phone charging stuff. Appreciate any input you have on how to prevent against the possibility of a DC-DC boost converter exceeding the maximum input voltage rating of a Microinverter, but the subject of charging mobile phones or any other electronics for that matter is really not relevant to the subject of this thread…

These are the cheapo DCDC boosters I’m going to be experimenting with:
_I have some notes here:
_https://diysolarforum.com/threads/u...-batteries-instead-of-panels.8353/post-753344

They have two potentiometers hard-wired in for control, one to set current limit and one to set voltage limit,
Any idea whether a design using a wired-in (settable) resistor can suffer from the uncontrolled boost you experienced?
_I swapped out the potentiomers for much better ones but it did not help in my case.

I suppose adding a monitor circuit to shut everything down if any boost voltage exceeds 150% or even 125% of target wouldn’t be the end of the world…
_This is not an area I have researched. The MicroInverter may have some sort of surge protection.
_You have a good range to play with 22V to 36V plus. You don't have to use the highest voltage 24V gives you some room for surges.
_With a direct battery connect you should not have to worry about having a monitor circuit or the buck or boost converter.

 

[kundip]

Sorry, one more quick question for you about battery voltage:

All of your results after 2 years of continuous use have been with a 24VDC battery, correct?

You experimented with DC-DC boost up to 32V and maybe even close to 48VDC but you have not yet tested anything running directly off of a 48VDC battery, correct?

You are planning to get an EV battery and to break the cells down to 24VDC cells/batteries, correct, or will you now plan to go straight to 48V cells/batteries?

Since you have been running the one Enphase M215 off of one of those cheap DCDC boosters for over two years now, I’d appreciate to know the boost voltage used over the majority of that time - 32VDC?

Sorry, one more quick question for you about battery voltage:
All of your results after 2 years of continuous use have been with a 24VDC battery, correct?
_Correct
You experimented with DC-DC boost up to 32V and maybe even close to 48VDC but you have not yet tested anything running directly off of a 48VDC battery, correct?
_Close to 40VDC. No I have NOT tested 48VDC battery. I would use an IQ7Plus for this. It can take up to 60VDC input.
_I think a fully charged LiFePo4 48VDC battery would be ~57.6VDC.
You are planning to get an EV battery and to break the cells down to 24VDC cells/batteries, correct, or will you now plan to go straight to 48V cells/batteries?
_Not sure until I play around. I have never touched one yet. Not sure how easy each type battery will be to pull apart. I would compare cost of chargers 24V vs 48V. Just for starters.
Since you have been running the one Enphase M215 off of one of those cheap DCDC boosters for over two years now, I’d appreciate to know the boost voltage used over the majority of that time - 32VDC?
_Yes 32VDC to ~34VDC - I was just away for 7 weeks & turned it down to 29.24VAC before I went as I was the only one who looked after the system. I am replacing the buck/boost converter setup soon.
_You can ramp up the amps via the on board potentiometer.
_I am not sure why the direct battery connect is self limiting & yet the buck or boot converter can seem to push more amps into the Micro-Inverter.

 

[Hedges]

_IMPORTANT ...My observations - Because of the MPPT the micro-inverter takes a fair while to start. So you have to have patience. Quite often mine restart at least once.
_So the micro inverter, from cold, will start to produce.
_So there is no slower start like you would get with the sun.
_The micro inverter decides this is a bit strange and cuts you off. (Because it has gone from cold to full production IMO)
_The second time around things have warmed up and the micro inverter is good to go. (Please let me know if you observe similar)

The attraction of using the DC-DC boosters, if they can be made to work, is dialing-in a preprogrammed output level rather than letting the Microinverters run full tilt…

Ideally you would get them to simulate PV, that is have output voltage ramp down as current increases. A circuit sensing current and controlling voltage setting pin, perhaps.

There are a couple current-limiting techniques, one ramping up gate voltage of a FET with charge-pump. Another a resistor (and capacitor?) circuit enabling a FET. These work for no-load soft-start to charge a capacitor, but would dissipate significant power used to limit current.

Thermistors are used to limit inrush, but work by decreasing in resistance when they get hot, and sit there burning watts. OK for single operation then bypassed.

I suppose adding a monitor circuit to shut everything down if any boost voltage exceeds 150% or even 125% of target wouldn’t be the end of the world…
_This is not an area I have researched. The MicroInverter may have some sort of surge protection.

Surge protection is usually something like MOV, a device that turns on with a diode-like curve above some voltage. They can take a smack of hundreds or thousands of amps, but only for milliseconds or microseconds due to the massive power dissipation. Things like 100A @ 100V = 10,000W, which for 1 second would be 10,000 Joules. But for a millisecond, 10 Joules.

Over-voltage and over-current protection is usually analog or digital control circuitry. Over-voltage is more difficult to protect against because no way to limit it. Some devices will crowbar (which is fine for PV but catastrophic with battery.)

_You can ramp up the amps via the on board potentiometer.

Doing that dynamically is what I mean. Likely needs current sense resistor and op-amp. You may be able to get a Hall-effect module. I bought some active ones on eBay for around $6, haven't tried yet.

 

[fafrd]

_Anything that reduces Greenhouse gasses I am for it!


_Sounds Good. Not sure what brand or type you have....So...Do one side first. That way you might get 2 chances is something goes wrong.
_Start with the lowest voltage you can first & work up from there.

Good advice, thanks.

I’ve got NEP 600X Dual Microinverters: https://northernep.com/downloads/technical-sheet/BDM-600X-Microinverter.pdf

_IMPORTANT ...My observations - Because of the MPPT the micro-inverter takes a fair while to start. So you have to have patience. Quite often mine restart at least once.
_So the micro inverter, from cold, will start to produce.
_So there is no slower start like you would get with the sun.
_The micro inverter decides this is a bit strange and cuts you off. (Because it has gone from cold to full production IMO)
_The second time around things have warmed up and the micro inverter is good to go. (Please let me know if you observe similar)

Will do. I plan to use multiple DC-DC converters set for different current levels and switched through relays to ramp up output with a 3-4 bit ‘staircase’, so I may avoid the startup issues you experience.

But I appreciate the heads-up.

_When adjusting the buck converter you will find the micro inverter "trips" at various times and restarts.
_I think it is better to adjust the buck converter using some sort of separate, constant load, at the right amperage, first, as the MPPT makes it really hard to adjust the potentiometers.

I’m pretty sure these little DC-DC converters are boost, not buck. But I’m guessing the advise still stands - adjust current output first before connecting to a Microinverter…

The attraction of using the DC-DC boosters, if they can be made to work, is dialing-in a preprogrammed output level rather than letting the Microinverters run full tilt…
_I have read articles where people are pumping out more than 350W @ 240AC and running voltages higher than the maximum voltage.
_The Enphase inverters seem to be able to take a beating.
_At 24V (28.8V when battery full) the inverters pump out 226W @240VAC each which is not much above the 215W Rated Output Power

The NEP 600X Microinverters put out 590W sustained (despite the fact that the datasheet says 580W).

I’m going to use two BDM600s to deliver up to 1180W of max output but with digital consoles through relays do reduce output to under 100W…

Hope to be a fast follower in the trail you have blazed .

 

[fafrd]

I'm apologize for coming back with all these additional questions, but I've been carefully reviewing the detailed pictures you attached and just want to assure I've got the details correct:
_No problem.

Initial Setup: Victron Battery Protector inline (and no other relay) - Battery Connect disconnected from over-current often when not necessary - do you know what the over-current limit of the Battery Connect was?
_No I don't.

Second Setup: Victron Battery Connect controlling inline Relay: - what was the amperage rating of the DC relay you used?
_20Amp

Latest Setup: MotorMate 24V Battery Protector inline (and no other relay): what is the over-current limit of the MotorMate and can you program the low-voltage limit where the MotorMate disconnects the system or is it fixed?
_MotormMate 24V version is rated at 30Amp. https://www.master-instruments.com.au/file/63492/1/Motormate-SBP-12030.pdf
_There are only 3 switched cut out settings 23V 22V 21V. I use 23V.

Other than the use of the MotorMate, are there and DC fuses or breakers in your Latest Setup other than whatever fuse you are using for each of your 24V batteries? Oh, wait, I see an inline blade fuse holder connected to the MotorMate - what size fuse are you using there and is that the only DC fuse outside of the batteries?
_At the MotorMate I use 20A fuse & 10A fuse at each inverter. I have updated picture.

Clear. Thanks.

 

[fafrd]

You are planning to get an EV battery and to break the cells down to 24VDC cells/batteries, correct, or will you now plan to go straight to 48V cells/batteries?

_Not sure until I play around. I have never touched one yet. Not sure how easy each type battery will be to pull apart. I would compare cost of chargers 24V vs 48V. Just for starters.

You’ve provided so much useful information and guidance, I thought I’d provide some back.

Unless it is your passion in life, messing around with used EV battery cells is a waste of time in this day and age.

I was going to make a battery out of used Leaf Cells and even bought a BNS for tat purpose.

Once I understood him much more dangerous lithium-ion (Lion) cells were than the new LiFePO4 cells were that just started becoming available, I switched to LiFePO4 and built a 2.6kWh 24V battery from 8 100Ah cells.

I followed that up by building an 8S 2P 14kWh LiFePO4 battery from 16 280Ah cells.

If I ever need another battery, I would not build my own from cells but purchase an off-the-shelf LiFePO4 battery.

To ‘play around’, you can now get a completed 2.6kWh 24V LiFePO4 battery like the first one I built for $580: https://www.amazon.com/LiFePO4-Port...9032078&hvtargid=pla-1139080633677&psc=1&th=1

Once you factor in the greatly higher cycle time versus lead-acid, as well as the 80% usable versus 50% usable of Lead-Acid, this is cheaper than Lead-Acid.

I’m not sure why you seem to be motivated to move from 24VDC to 48VDC. The only benefit is reduced I2R losses and thus slightly higher efficiency, but efficiency does not seem to be a high priority for you, 24VDC is safer than 48VDC, and you already have a completed rig at 24VDC, so I don’t understand the motivation to go to 48VDC (unless it’s for the pure joy and challenge of it).

New LiFePO4 cells rather than used Lion EV cells (that’s a strong recommendation).

Buy a finished battery rather than building your own (that’s a friendly suggestion).

Stick to 24VDC unless you have a compelling reason to move to 48VDC (that’s just common sense ).

 

[kundip]

Thanks very mIuch for this.

I had a sneaking suspicion about this.

I decided to use, after much research, to use 24V because it has been around a long time and there are a lot of devices that just work with it really solidly & robustly.

Initially I only purchased 2 new 24v LiFePo4 batteries to get my ideas on the road and to contribute to reducing green hose gasses. Both at home and to others that could not afford the Tesla type system but who wanted to do something.

Since my initial Purchase I only buy premium LiFePo4 batteries that are one or two years old. I watch many local sites and grab batteries when they come up and only pay half price. Patience is my go to weapon of choice on this.

On top of my working 34 panels with micro-inverters. I have about 40 brand new micro- inverters spare that cost me $30 each. (USD 20.) The rest of the gear required I buy new.

The idea I had re electric vehicle batteries was to put up my research on DIYSolarForum for assisting others.

I don't want to change my own setup to 48v.

After 3 years of part time research - My 24v system has worked out fantastic in so many ways it would take me a long time to describe.
It is just so durable & reliable. Easily maintained.. I could go on.

48v came to mind because there is a lot of talk on these sites about 48v and I thought I would do my bit to contribute.

I was expecting an electric vehicle battery later this year for a nominal cost. I have not done any research on them at all & I did not know they were only Lion cells.

So... I won't bother with getting that electric vehicle battery now I know from someone like yourself who has done it. Re-inventing wheels is no hobby of mine.

From your advice I will keep improving my 24V setup and work with others in a better & better way to replicate and learn from them also. (Like yourself) So thanks again.

 

[fafrd]

Thanks very mIuch for this.

I had a sneaking suspicion about this.

I decided to use, after much research, to use 24V because it has been around a long time and there are a lot of devices that just work with it really solidly & robustly.

Initially I only purchased 2 new 24v LiFePo4 batteries to get my ideas on the road and to contribute to reducing green hose gasses. Both at home and to others that could not afford the Tesla type system but who wanted to do something.

Since my initial Purchase I only buy premium LiFePo4 batteries that are one or two years old. I watch many local sites and grab batteries when they come up and only pay half price. Patience is my go to weapon of choice on this.

On top of my working 34 panels with micro-inverters. I have about 40 brand new micro- inverters spare that cost me $30 each. (USD 20.) The rest of the gear required I buy new.

The idea I had re electric vehicle batteries was to put up my research on DIYSolarForum for assisting others.

I don't want to change my own setup to 48v.

After 3 years of part time research - My 24v system has worked out fantastic in so many ways it would take me a long time to describe.
It is just so durable & reliable. Easily maintained.. I could go on.

48v came to mind because there is a lot of talk on these sites about 48v and I thought I would do my bit to contribute.

I was expecting an electric vehicle battery later this year for a nominal cost. I have not done any research on them at all & I did not know they were only Lion cells.

So... I won't bother with getting that electric vehicle battery now I know from someone like yourself who has done it. Re-inventing wheels is no hobby of mine.

From your advice I will keep improving my 24V setup and work with others in a better & better way to replicate and learn from them also. (Like yourself) So thanks again.

Unfortunately, the mainstream market for modest-powered hybrid inverters seems to be focused on 48VDC and there are very few 24VDC hybrids out there (Conext SW being one of the few UL-listed options, on top of several budget Chinese alternatives.

I’m powering my GTIL inverters off of a /4V LiFePO4 battery and it works well, but I bought 16 cells organized currently as 8S2P (8 parallel 2S cells connected in an 8S series string) because that leaves me the option to reconfigure for 1P16S / 48V if I ever conclude I have no choice.

Microinverters are 1S with Vmp of ~30-35VDC and so, for that reason alone, powering Microinverters off of a 24V LiFePO battery (25.5-28.8VDC) is a much better fit for how those Microinverters operate hooked up to solar panels.

24VDC is also safer than 48VDC, and at least in the US, wiring and safety standards are more relaxed for 24VDC batteries than 48VDC.

Of course, panel Vmp keeps creeping up and most modern inverters can operate up to 50VDC if not 55VDC or even 60VDC, do the landscape is changing.

That being said, the only argument I can see from powering Microinverters off of a 48V LiFePO4 battery rather than a 24V LiFePO4 battery is that you are trying to run off of the same battery being used to power a hybrid inverter or 24VDC LiFePO4 batteries become a niche product costing an unacceptable premium over the cost of 48V LiFePO batteries.

But my view is that the increased efficiency argument alone is certainly not enough of an advantage to switch to 48VDC from 24VDC…

To the extent that what you are doing is motivated by wanting to share the results of your long-term experiments to benefit followers in your footsteps. I would think the long-term reliability data at 24V is far more valuable than anything you could offer at 48V…

The biggest difference between what I am aiming at and what you have done is that I will be dynamically changing power/current level through the day as loads turn on and turn off.

So transients when Microinverters are being powered at near-max levels then being reduced close to zero then being cranked back up near peak levels again is my biggest concern.

I’m using GTIL inverters with CT sensors that do exactly that without issue currently but I am concerned about what the impact of those power-up / power-down transients may be on Microinverters…

The GTIL inverters are more expensive than Microinverters and also have much worse efficiency of ~80% versus the ~95% efficiency of Microinverters…

 

[kundip]

Unfortunately, the mainstream market for modest-powered hybrid inverters seems to be focused on 48VDC and there are very few 24VDC hybrids out there (Conext SW being one of the few UL-listed options, on top of several budget Chinese alternatives.

I’m powering my GTIL inverters off of a /4V LiFePO4 battery and it works well, but I bought 16 cells organized currently as 8S2P (8 parallel 2S cells connected in an 8S series string) because that leaves me the option to reconfigure for 1P16S / 48V if I ever conclude I have no choice.

Microinverters are 1S with Vmp of ~30-35VDC and so, for that reason alone, powering Microinverters off of a 24V LiFePO battery (25.5-28.8VDC) is a much better fit for how those Microinverters operate hooked up to solar panels.

24VDC is also safer than 48VDC, and at least in the US, wiring and safety standards are more relaxed for 24VDC batteries than 48VDC.
One of my many reasons for sticking with 24V.
Of course, panel Vmp keeps creeping up and most modern inverters can operate up to 50VDC if not 55VDC or even 60VDC, do the landscape is changing.
Yes
That being said, the only argument I can see from powering Microinverters off of a 48V LiFePO4 battery rather than a 24V LiFePO4 battery is that you are trying to run off of the same battery being used to power a hybrid inverter or 24VDC LiFePO4 batteries become a niche product costing an unacceptable premium over the cost of 48V LiFePO batteries.
Agreed
But my view is that the increased efficiency argument alone is certainly not enough of an advantage to switch to 48VDC from 24VDC…
I find most efficiency arguments very weak. If you have plenty of roof space just add another panel.
To the extent that what you are doing is motivated by wanting to share the results of your long-term experiments to benefit followers in your footsteps. I would think the long-term reliability data at 24V is far more valuable than anything you could offer at 48V…
With your tips I am on board with that now.
The biggest difference between what I am aiming at and what you have done is that I will be dynamically changing power/current level through the day as loads turn on and turn off.
Not tried this - Enphase might not like this.

I have seen some videos about MPPT turning off on nearly all Micro-Inverters. Then they might behave similar to a GTIL inverter. How this works using M215 as an example:

• Peak power tracking voltage: 27V – 39V
• Operating range: 16V – 48V

All Micro-Inverters have a MPPT voltage range. In this case 27v-39v. But the operating range is up to 48v
So..... from what I have seen if you go over 39v the MPPT turns off. You don't really need MPPT if you have constant power from a battery.

So transients when Microinverters are being powered at near-max levels then being reduced close to zero then being cranked back up near peak levels again is my biggest concern.

I’m using GTIL inverters with CT sensors that do exactly that without issue currently but I am concerned about what the impact of those power-up / power-down transients may be on Microinverters…

The GTIL inverters are more expensive than Microinverters and also have much worse efficiency of ~80% versus the ~95% efficiency of Microinverters…

How micro-inverters perform when you "switch of" MPPT I do not know.

 

[zanydroid]

I was expecting an electric vehicle battery later this year for a nominal cost. I have not done any research on them at all & I did not know they were only Lion cells.

There are quite a few EV models now with LFP batteries. Might be too early though for used ones to be available for DIY.

 

[kundip]

OK thanks. I will keep an eye out.

 

[jimbob232]

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.

Hi All, and especially Kundip, i have been reading this thread with interest as i'm trying to do something similar. I'm in the UK and have 2.2kw of solar panels on the roof, which due to the feed in tariff i am on, i cannot modify the system (i can add another alongside though). I get paid on generation not how much i send back to the grid, so it makes sense for me to use all i can.
I have built an arduino based power controller & logger (CT measurement of power to/from the grid) which controls some wifi sockets to turn on heaters / dehumidifiers etc, and also diverts some power via a power controller to my water immersion heater with closed loop control to hit zero export. This all works pretty well but as i also have a solar water heater i am often still exporting lots when the sun is out.

The data logger has also shown me how much base load i have - generally in the 100-250w range - and how much i could save if i could cover this from my solar production (probably about 6 months a year) with a fairly cheap storage system.

Following on from you guys, i have bought an Enphase M250 microinverter cheap second hand, which i want to power with 24v batteries to cover this base load - i can control a battery charger with one of the wifi sockets to recharge whenever there is sufficient solar available.

Initially i am looking to get this running just as a full power unit, but i am also keen on experimenting with modulating the inverter output to match my usage - i am wondering about using a DC PWM unit between the battery and inverter (along with smoothing capacitors) controlled by my arduino power controller. Has anyone tried similar?

Also, Kundip, would you please share the inverter AC pinout or wiring colours with me so i can give it a try?


The future project would then also be building a closed loop control charger to use only the excess solar - again probably PWM control between a power supply and the battery but this is probably a bit further in the future!

 

[kundip]

You need more panels IMO as many as you can get up.
These do not need to be connected to the grid or system you have - they can just charge the battery(s).
No one can stop you doing that.
I have not done it that way myself as I don't have the same problems.
The M250 MicroInverter will produce 250W AC per hour.
2 x 24V 200AH batteries should give you about 5KW each night - depending on sunlight.
Trying to regulate the DC is just too hard. I have tried & built all sorts of devices.
I have bought an Auto-switch - Current Sensing CT to test out on one AC phase.
My idea is to use this to activate, say, a 15 minute delay switch, in turn activating the Enphase inverter (via the DC side) for that period.
This will happen when I am drawing from the grid.
So...instead of regulating the DC from the 24V battery - I am turning the DC on & off.
There are complications here - (the MicroInverter takes time to start)
This will be months away.
Just concentrate on the battery & inverter. You will have enough headaches there.
The timer can turn on & off many times per night to suit you & the battery.
Once you have that running that will be you "base system" - to mitigate (possibly cover?) your main nightly power consumption.
Then you can play with another system with a small 24V battery (2nd hand bike battery?) to see if you can get your ideas to work.
Never touch your"base system" until you are really really sure.
I started all my ideas with an old $50 UPS that did not run for long but I proved my (ever so small) theories before I up-scaled slowly.
I need more detail & photos re your AC pin-out question.

 

[zanydroid]

Any reason to consider/not consider microinverters with export control like Hoymiles? ncsolarelectric has a project on here using the closed-loop export control feature on Hoymiles.

Another possibility is to use the %-base active power throttling, this is somewhat cheaper than the approach on ncsolarelectric's thread, which requires a RS485 power meter + DTU + Microinverter, with the power meter locked with DTU in a feedback loop to limit the output wattage. The Modbus just needs DTU + Microinverter.

(DTU is the control gateway that transmogrifies modbus to HoyMiles 2.4G and Sub-1G radio protocols)

https://www.shinetech-power.de/wp-content/uploads/2021/07/Technical-Note-Modbus-implementation-using-3Gen-DTU-Pro-V1.2.pdf

It can be done on a per-microinverter, per-port basis

If you cut the DC to Hoymiles microinverters they will restart since they get their power from the solar panels (this is standard right? across different vendors).

 

[kundip]

Thank you. Very interesting.
I have never heard of these.
Despite the fact that there are 6 pages of threads on this forum. (I just searched)
My profile says MicroInverter Enthusiast maybe I should add Enphase to that.
I will have to take time to study these.
Especially the "%-base active power throttling" you have noted.

I am not a fan of the idea of throttling or regulating the DC off a big battery.
Sizing everything nicely to a point where it is very useful with minimal parts is my preference.

 

[Hedges]

but i am also keen on experimenting with modulating the inverter output to match my usage - i am wondering about using a DC PWM unit between the battery and inverter (along with smoothing capacitors) controlled by my arduino power controller. Has anyone tried similar?

My thought would be emulate the I-V curve of PV panel, varying the power available to microinverter.
If you found a DC/DC supply with CV/CC output, you could have a PID or other control loop varying CV setting with the goal of keeping a CT (x V) on utility connection around zero amps & watts.

But likely not cheap to get several hundred watt DC/DC supply. Custom designs would be used for a product like this, and for one-off experimenting it would be time consuming and likely expensive.

PWM between two voltage sources (battery and capacitor) would have repeated capacitor charging inrush. So an inductor and diode is used in a boost converter. Voltage difference and PWM duty ratio determines current draw.

Easier would be to have a bank of microinverters, and enable more/fewer of them.

 

[zanydroid]

There is a buck step / PWM step already in a buck MPPT. I wonder what custom programming or circuit tweak one would do to make it better for powering from a battery

There is this open source ESP32 based design for an MPPT SCC. Probably add an input current limiter in software, maybe change the input filtering done by discrete components to reduce the slope of current change when PWM switches in?

1kW Arduino MPPT Solar Charge Controller (ESP32 + WiFi)

1kW Arduino MPPT Solar Charge Controller (ESP32 + WiFi): Build a 1kW WiFi MPPT Solar Charge Controller, equipped with phone app datalogging telemetry! (Android & IoS) It is compatible with 80V 30A solar panel setups and all battery chemistries up to 50V. The project is based on an Arduino ESP32...

www.instructables.com

 

[kundip]

Also, Kundip, would you please share the inverter AC pinout or wiring colours with me so i can give it a try?

Hello JimBob232,
I worked out what you were asking.
AC Pin-out diagram below.
The plug receptors are USD $30 each they are too expensive IMO.
You definately need the plug receptors if using MicroInverters outside.
So if you buy a buch of MicroInverters make sure you get the plugs with them.
In your case I suggest cutting off the plug so you can re-use.
Then just use a junction box & connectors to hard wire in your MicroInverter.
On mine this AC wire goes through Envoy first then to grid.

 

[kundip]

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.

Hello Meetyg,
You were right. ("I wouldn't do it")

I know this reply, to this part of your assistance, is a long time coming.

There are many types Buck Converters I have tested.
Only one is working.
I bought 3 of the particular type that worked and, of them, only 1 worked properly.
No buck converter has fried my batteries or the MicroInverter.
I have stopped using them & I don't recommend them.
Locking was not a problem & the output kind of fluctuated initially but settled down.

I just found the potentiometer current adjustment too flaky on all of them.
The buck converters were all an extra I just did not need.
Thy have their place but, just not in this situation IMO.

So...Thanks very much!

 

[jimbob232]

Hello JimBob232,
I worked out what you were asking.
AC Pin-out diagram below.
The plug receptors are USD $30 each they are too expensive IMO.
You definately need the plug receptors if using MicroInverters outside.
So if you buy a buch of MicroInverters make sure you get the plugs with them.
In your case I suggest cutting off the plug so you can re-use.
Then just use a junction box & connectors to hard wire in your MicroInverter.
On mine this AC wire goes through Envoy first then to grid.
View attachment 144645

Thanks for this, i have now got the inveter running off a power supply on the bench. It is a little different in the UK, i use L1 and N at 240v for the single phase supply here. As i'm just bench testing at the minute i've just used 4mm plugs on the DC side but it will all get proper connectors on the final system - which will almost certainly be indoors anyway.

In the attached photo the PSU is set to 23v and also current limited to ~2.6A - when the inverter goes active the voltage fluctuates a little bit and the PSU is moving between CV and CC mode - i guess this is the MPPT doing it's thing. It does show that it is possible to run the inverter below full power somehow - i just need to mimic the PSU!