Micro inverters

[KauaiMolokai]

Greetings all,
I'm very new to solar and trying to learn as much as I can.

My primary interest will be building, for my own use, more than one "vastly over-powered", off grid system. I plan to mount the panels on a ground rack similar to those used in commercial solar generating farms.

Of course I have 4000 questions. The first one is:

How are the feeds from multiple micro inverters connected? Obviously its AC so a simple series or parallel - as one would do with DC - is not possible. Do micro inverters "talk to each other" to stay "in phase"? Is there a master and slaves system?

My plan would be to connect the outputs from multiple micro inverters together at the rack, and run the resulting 120 or 240 AC line to my house - to replace the grid AC line. This would seem more feasible than running wires able to carry 48V high amp DC (from PV panels without inverters) 300 ft to my building to connect with a large inverter(s).

Thanks. And thanks for all who so generously contribute so much information and knowledge.

 

[jasonhc73]

For now, just forget about Micro Inverters for off-grid use. They are not yet available for the public. They will be, and unfortunately are kind of a rip-off. Enphase IQ8 EQ8 is the only micro inverters there are that can do an AC directly from the panel, but not released to the world for some reason yet.

Nearly every purchased system you buy and have installed by a "licensed" installer is only going to do a grid-tied install. This is because the utility is going to get your energy and control your output if the grid goes down. UL1741 is that standard.

In the off-grid world of solar though, you get to just put panels up anywhere and basically any way you want. So long as you don't back-feed into the grid!

I presently have two solar systems in my house. The grid-tied and the off-grid setup. Had I of know what the F to do before getting the grid-tied setup, I would have never done or spent so much to have it done.

 

[GVSolar]

It is possible to be off-grid and use micro-inverters. I have 3kw of DC coupled panels - and 1.5kw of AC couple panels, using micro-inverters. And I am in the process of adding 1.5kw more. The micros are Enphase m215s, legacy micros available new at rock bottom prices on the internet. There are others as well. The key is to use an hybrid inverter - one designed to both DC and AC couple. Schneider Conext systems (like mine) do it seamlessly. Others do as well. THE KEY IS TO RESEARCH THE ENTIRE SYSTEM BEFORE YOU BUY ANYTHING. Lots of good resources on the net and other places. My system is entirely DIY (with a good electrician as a friend). A sample of some methods attached.

 

[GVSolar]

By the way, DC coupling is, on the whole, much simpler (because of the difficulting in regulating the AC charge on batteries). And your 300ft can easily be overcome by running higher voltage DC with MPPT or inverting to AC and then running 240v to the house. I am doing something similar (barn to house) - only the AC is generated by micros. Start with your load calculations and then work backwards from there. FYI: A hybrid inverter will also allow you to use the utility as an emergency battery and self-consume all the power you generate.

 

[DThames]

You have been told already that micro inverters are meant to be grid tied, but I want to still answer your question about connecting them. Consider them as AC power devices. The ones that I have are 5 amps at 240v. So putting 3 of them (15amps) on a 20amp 240v circuit would be to code. I have two 30 amp circuits with 4, 1200 watt micro inverters per circuit, grid tied.

 

[jasonhc73]

It is possible to be off-grid and use micro-inverters. I have 3kw of DC coupled panels - and 1.5kw of AC couple panels, using micro-inverters. And I am in the process of adding 1.5kw more. The micros are Enphase m215s, legacy micros available new at rock bottom prices on the internet. There are others as well. The key is to use an hybrid inverter - one designed to both DC and AC couple. Schneider Conext systems (like mine) do it seamlessly. Others do as well. THE KEY IS TO RESEARCH THE ENTIRE SYSTEM BEFORE YOU BUY ANYTHING. Lots of good resources on the net and other places. My system is entirely DIY (with a good electrician as a friend). A sample of some methods attached.

Does the m215 have to have all the gateway and enlighten ensemble stuff?

I just want this:

 

[JeepHammer]

For now, just forget about Micro Inverters for off-grid use. They are not yet available for the public. They will be, and unfortunately are kind of a rip-off. Enphase IQ8 EQ8 is the only micro inverters there are that can do an AC directly from the panel, but not released to the world for some reason yet.

Nearly every purchased system you buy and have installed by a "licensed" installer is only going to do a grid-tied install. This is because the utility is going to get your energy and control your output if the grid goes down. UL1741 is that standard.

In the off-grid world of solar though, you get to just put panels up anywhere and basically any way you want. So long as you don't back-feed into the grid!

I presently have two solar systems in my house. The grid-tied and the off-grid setup. Had I of know what the F to do before getting the grid-tied setup, I would have never done or spent so much to have it done.

I'm with Jason on this one...

Some, and I stress very few, inverters will sync with each other and contribute to the total line load.
Most of these are industrial and cost big bucks, and are usually used with constant Loads (like water pumping stations, factories, etc) or the energy is lost without HUGE batteries or grid intertie.
Not everywhere has a functioning power grid...

On a down to earth system that doesn't go a couple million to get started,

1. Increase Voltage.
Easier to step down the Voltage than to step up, convert Amps into Volts.

2. Smaller wiring runs with higher voltage, lower amps.
Copper costs real money, and when you spread out like I am, the copper gets REAL EXPENSIVE, real quick.

3. Sun Track.
10% to 20% increases in energy output with sun tracking which means 10% to 20% less panels, racks, wiring runs, etc when a lot of panels are involved.
Economy in scale.

4. Off Grid, winters need 5 times the panels they do in summer.
Lower sun angle means more atmosphere, less energy reaches panels,
Shorter days means less energy.

 

[svetz]

Microinverters are the cat's meow in terms of redundancy and expansion. If one dies, it doesn't take out everything. To expand, you just add another one. The only limitation is how much current the wire can handle, and then you add a new wire. So, it does make good sense to look into them.

...Do micro inverters "talk to each other" to stay "in phase"? Is there a master and slave system? ...

As has been mentioned above, this is the rub. Microinverters synchronize with the grid... so being off-grid it won't work without something to provide the signal.

This has already been solved via the "powerwall", it acts as the grid. But you need one specifically designed to work with microinverters (they use techniques like phase shifting to control the microinverter, but be aware not all powerwalls will work with microinverters and that can be dangerous). You can find out more by looking into the various AC Coupling solutions. Also, as Jasonhc73 pointed out, Enphase has a solution (aka Ensemble) they're just coming out with that would also work with this (currently only available to installers, but should be available to all before too long).

 

[KauaiMolokai]

Thank you ALL! I read every single word. Very, very helpful.

So to summarize:
Microinverters are available, and legacy ones are "cheap"
Panels need to be compatible with the microinverters.
Synching the microinverters' output "might" be possible, but is definitely not "plug and play"

My intentions:
Research availability of excess inventory panels - this might require me to buy a lot more than I need initially but appears to be very low cost vs new.
I do not need or want anything grid tied. I will simply disconnect my ingoing grid service at the box in the house, and substitute the incoming AC line from my panel array. This AC line will be powered either by multiple microinverters connected at the array, or if that is not feasible/practical/possible by the output of an inverter at the array which has the PV DC panel outputs as inputs.
The 300ft distance will be AC, eliminating the need for large DC expensive copper wire.

Since I want to fully replace 200 Amp 240 VAC grid service - 48kW - with PV panels I'll need a lot of panels. I'll get far more than I need, regardless of my current usage. I'll live by my pilot maxim that you can never have too much power. I have no concern about having "excess power" - I'll find a use for it. (I need to check if my grid service really is 200A/240VAC)

In theory this system should give me vast amounts of power on sunny days. And nothing at night or on cloudy days. But with this much power I should be able to charge up a large bank of batteries with simple chargers just plugged into wall outlets (as a start), and power an inverter to give me AC power for things like fridge, internet, lights, at night. There are only very few things I want powered when I'm not there - fridge/freezer - so initially I have no wish to have batteries capable of fully substituting for my grid connection. In fact initially I'll just disconnect the PV AC line and reconnect the grid AC line when I'm leaving, and before I have batteries. (Obviously, or maybe not, I'm using terms and speaking very loosely here - I'm not going to have AC lines just hanging disconnected or such. I'll install heavy switches and/or large fuses to be sure when some source is connected or disconnected it really is. And to charge big batteries adequately obviously will need more than just a car battery charger or 10)

Now I'll stand back and listen to why I'm insane!

Thanks again to all. Have a great, sunny, day!

 

[kernel]

Good thing is that mocroinverters parallel connect to a trunk line and they all synnc to each other based on the beat freq of the grid signal, so even mixing inverters will not be a issue.

Enphase m215 do not require any monitors or other equipment. Led indicator will tell.

And if you want to ac couple to charge a lithium battery it is much simpler for the software and hardware as the battery does not need to finish and modulating the array against ac load of the charger and house loads becomes less of an issue..... no absorb taper to hit that sweet full spot. The lithium does not care about it.

 

[KauaiMolokai]

Good thing is that mocroinverters parallel connect to a trunk line and they all synnc to each other based on the beat freq of the grid signal, so even mixing inverters will not be a issue.

Enphase m215 do not require any monitors or other equipment. Led indicator will tell.<<



Thanks!

Ah, this sounds great; but if I have no grid signal - because I'm off grid (disconnected grid line) - can I still get the microinverters to sync?

 

[KauaiMolokai]

Sorry Kernel, my reply got confused with your quoted reply. I'll get this figured out ;-)

Thanks!

Ah, this sounds great; but if I have no grid signal - because I'm off grid (disconnected grid line) - can I still get the microinverters to sync?

 

[svetz]

...Since I want to fully replace 200 Amp 240 VAC grid service - 48kW - with PV panels I'll need a lot of panels....

You might have a 200 amp service panel, but that's a max. Your actual number of panels can be calculated based on the actual amount of power you need including round-trip battery losses. All of those calculations are in the FAQs.

... if I have no grid signal - because I'm off grid (disconnected grid line) - can I still get the microinverters to sync? ...

You just need something that both provides the signal and controls the micro-inverters (e.g., phase shifting). Enphase is just releasing an IQ8 battery / system (called Ensemble) that will do that. Outback (and I believe others) also have solutions. See AC Coupling solutions.

 

[KauaiMolokai]

Thank you svetz. Much appreciate it. This forum is like a university!

 

[GVSolar]

Does the m215 have to have all the gateway and enlighten ensemble stuff?

I just want this:

Hi Jason,
Those IQ8's are sweet. But they are pricey.
The M215's are legacy... inexpensive, and you can run them without the Envoy, ensemble & gateway... as long you are providing an AC pilot voltage - and have somewhere to put the amps. That's what the hybrid inverter does - routes the ac to loads or converts it to DC to charge the battery. When the battery reaches a set voltage the Conext SW 4024 inverter ramps the AC frequency above 62.5 hertz and that shuts off the micros - it's an essential safety cutoff - or you boil the batteries. Using the micros in AC couple allows me to add AC load capacity without buying a new inverter.

 

[KauaiMolokai]

Hi GV,
Am I understanding correctly that you are using grid power as the AC pilot voltage? Or do you have another source for this pilot voltage?

 

[offgriddle]

For now, just forget about Micro Inverters for off-grid use. They are not yet available for the public. They will be, and unfortunately are kind of a rip-off. Enphase IQ8 EQ8 is the only micro inverters there are that can do an AC directly from the panel, but not released to the world for some reason yet.

Nearly every purchased system you buy and have installed by a "licensed" installer is only going to do a grid-tied install. This is because the utility is going to get your energy and control your output if the grid goes down. UL1741 is that standard.

In the off-grid world of solar though, you get to just put panels up anywhere and basically any way you want. So long as you don't back-feed into the grid!

I presently have two solar systems in my house. The grid-tied and the off-grid setup. Had I of know what the F to do before getting the grid-tied setup, I would have never done or spent so much to have it done.

Thanks for the microinvertor status, I was wondering why no one ever speaks of them.

 

[GVSolar]

Yes K-Molokai. I am using micros and I am off-grid only - haven't had a utility bill for 30+ years. The Schneider SW4024 (and my DC battery bank) is providing the pilot signal - the smart hybrid inverter does the AC to DC charging and the frequency shifting for shutdown. I also have Conext DC charge controllers charging the batteries and accessories. Everything talks to each other. Carefully wired it is a very robust system.

 

[KauaiMolokai]

Awesome!!! Wow!! Thank you GV!! You can bet I'll be asking you a lot more questions ;-) I owe you big time for this education already. Now I'm fired up.

 

[kernel]

Sorry Kernel, my reply got confused with your quoted reply. I'll get this figured out ;-)

Thanks!

Ah, this sounds great; but if I have no grid signal - because I'm off grid (disconnected grid line) - can I still get the microinverters to sync?

Yes, i didnt include it as it was already said by another.

If you provide a clean sine wave from an inverter capable of ac coupling, then yes that will be your grid signal.

The ac coupled mode will generally use frequency shift to knock the grid tie inverters off line for 5 minutes as a standard protocol.