Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

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ecat   10 W

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Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by ecat » Dec 02 2018 2:16am

I bought a dozen of these M215 grid tie inverters with the idea of being able to switch between feeding a charge controller and battery bank, and sending power back into the grid. The panels are all connected in parallel. One M215 works fine, it is self limiting, but hooking two up to the same DC source in parallel kills them both. (I now have four dead M215🙄.
Any idea why? And could I isolate the inputs with diodes or?

Thanks!
Last edited by ecat on Dec 02 2018 1:59pm, edited 1 time in total.
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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by eee291 » Dec 02 2018 7:29am

I think there are some inverters with CAN-Bus that can talk to each other to synchronize outputs.

If the sine waves aren't synchronized then one inverter will feed voltage into another one and it will go boom.
I'm not qualified to explain this really.
There are plenty of discussions about this though, you just need to look.

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by ecat » Dec 02 2018 11:23am

Thanks for the reply. These are grid tie inverters, so they automatically sinc with the grid. I am talking about the DC input side.
2007 Catrike Expedition, dual Grin Through axle hubs, Dual PhaseRunners, 72V V 20 AH samsung 25R CA3
Edgerunner W Nuvinci hub, Patterson overdrive, Stokemonkey mid-drive. Expedition 19.8 AH Sony V3
Bike hauling trailer with two NC M3007RC hub motors on 20" wheels, two Grin 25A cont, CA3, Prius Plug-in 52V 17 AH
I am an official Grin Tech and Expedition Battery dealer on Salt Spring Island, BC Canada.
***Now the official Canadian wholesale distributor for Juiced Bikes***
http://juicedriders.ca/

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by eee291 » Dec 02 2018 12:02pm

I'm pretty sure the DC side is irrelevant.
I could hook up a 1000 different kinds of inverters to one battery without a problem.
It becomes a problem when the inverters get connected in parallel on the outputs.

Or did they blow up without even having the outputs connected?
Maybe you connected them L-N, N-L instead of L-L, N-N? just a guess.

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by ecat » Dec 02 2018 1:58pm

You are forgetting that these are grid tie micro inverters. They are meant to be hooked up to split phase 240V in parallel. Maximum 16 to a circuit I think. They only work when fed AC power, and shut down when AC from the grid is interrupted.
Each one mounts under its own dedicated panel as designed. I am try to use them in an unconventional way, mounting them back in the equipment room, and to more than one panel in parallel. It all works fine until I try to parallel another inverter to the same group of panels.
2007 Catrike Expedition, dual Grin Through axle hubs, Dual PhaseRunners, 72V V 20 AH samsung 25R CA3
Edgerunner W Nuvinci hub, Patterson overdrive, Stokemonkey mid-drive. Expedition 19.8 AH Sony V3
Bike hauling trailer with two NC M3007RC hub motors on 20" wheels, two Grin 25A cont, CA3, Prius Plug-in 52V 17 AH
I am an official Grin Tech and Expedition Battery dealer on Salt Spring Island, BC Canada.
***Now the official Canadian wholesale distributor for Juiced Bikes***
http://juicedriders.ca/

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by eee291 » Dec 02 2018 2:12pm

I guess it should be possible but the documentation is lacking quite a bit, to be honest.
You're probably better off contacting them: https://www.bluepacificsolar.com/home-s ... -6000.html

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by solarKings » Dec 03 2018 12:51pm

Actually, the M215 can have 17 micros in a single 240V string with a 20A double-pole circuit breaker.

The micros are for parallel use. They won't work in serial fashion. Maybe the upcoming IQ7A might where the DC source could be multiple solar panels or batteries. It might be 2 different sub-products, but it is on Enphase's radar. Reason for them to do this with the IQ7A is that at 450-Watt peak, it would pair great with some of their partner's panels — SunPower NGT, Solaria 72-cell, etc. But, it would also work with (2) "dumb" cheap mono 250W panels, too.

The IQ8 is going to have a built-in charge controller, so this is probably the product you are looking for. 2019 will be its debut.

Go Enphase!

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by billvon » Dec 03 2018 1:06pm

ecat wrote:
Dec 02 2018 2:16am
I bought a dozen of these M215 grid tie inverters with the idea of being able to switch between feeding a charge controller and battery bank, and sending power back into the grid. The panels are all connected in parallel. One M215 works fine, it is self limiting, but hooking two up to the same DC source in parallel kills them both. (I now have four dead M215🙄.Any idea why? And could I isolate the inputs with diodes or?
1) You can of course parallel the outputs of the inverters. That's how they work.

2) You can't parallel lots of panels and feed them into one M215. Might work but the inverter isn't spec'd for it.

3) You can't use one panel and parallel the inputs into two inverters because both inverters will want to adjust the V/I curve to find the optimum power point, and they will drive each other nuts trying to do that.

4) You can't do what you want anyway because an M215 cannot drive a charge controller or battery bank.

Your options are:

a) use a regular array of M215's and a plain old AC charger. The M215's generate AC, the AC charger converts it back to DC.

b) switch the panel output between the M215 and a charge controller. Do this only when AC power is off, and use switches/relays that are rated for DC and the max voltage/current of the panel. This, of course, eliminates the benefit of having a microinverter.

c) get a completely separate array to run the battery bank. Panels are cheap nowadays.
--bill von

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Re: Question for the Wizzards...why can’t Enphase micro inverters be connected in parallel?

Post by ecat » Dec 05 2018 2:06am

A little back story...

This system has evolved to where it is now, with cobbled together parts on a budget. I picked up a dozen M215 for like 50.00 each on ebay, with the thought that they would be better that the cheap chinese grid tie inverters. They are a total steal at 50.00 each, and work great with one panel. They even work great in a battery discharge application, drawing about 215 watts for as long as the battery holds out with not much heat generated. Only problem is you have to have access to 240V split phase to hook them up to.
The system is mostly battery based, using a pair of 5.3 kw Tesla modules in parallel to charge my Nissan Leaf through an inverter. Thing is in the summer, 9 X 250 W panels produces more power than I can use for charging the leaf, so therefore the grid tie to use the excess power. The house has a grid tied system, so turning the meter back a bit more is not an issue with the utility.

Bill, thanks for your carefully considered response:

1. Yes got that.

2. Actually it works just fine. I have had 1000 watts of panels in parallel hooked up to one inverter. It just clips the power at 215 watts. It even works connected directly to the 22V the tesla module. Barely even gets warm.

3. OK, I didn't think of the MPPT of each inverter trying to adjust the operating voltage and fighting each other. I can see that being less than optimal, but why does it just kill both inverters instantly, and permanently? I'm trying to figure out why, and if anything can be done to isolate them from each other, short of a pair of isolated DC-DC converters.

4. I am just trying to feed excess power back into the grid once the batteries are charged.

a) The way the system is set up for battery charging is 9 panels, 3S, 3P, so this would require a total re do, and would not work when the grid is down, and I use it for backup power.

b) This could work, but I would have to switch between parallel/series wiring the panels to get the voltages right, as well as switching between the charge controller and grid tie, so really complex switching.
Right now I am switching one M215 using the charge controller's "waste not" setting, it switches the AC on to the M215 when the batteries are floating. The DC side is permanently connected to the batteries, this works fine, but will not be enough in the summer.

c) No room left on the shed roof for more panels.

The simple thing would be to purchase a hybrid inverter, but that would require big $$$
The other way would be to purchase a single larger grid tie inverter, but the good ones need a minimum of 150V so would require series parallel switching again, as the charge controller maxes out at 150V.
2007 Catrike Expedition, dual Grin Through axle hubs, Dual PhaseRunners, 72V V 20 AH samsung 25R CA3
Edgerunner W Nuvinci hub, Patterson overdrive, Stokemonkey mid-drive. Expedition 19.8 AH Sony V3
Bike hauling trailer with two NC M3007RC hub motors on 20" wheels, two Grin 25A cont, CA3, Prius Plug-in 52V 17 AH
I am an official Grin Tech and Expedition Battery dealer on Salt Spring Island, BC Canada.
***Now the official Canadian wholesale distributor for Juiced Bikes***
http://juicedriders.ca/

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