AC Coupling for off grid applications

[DENWA]

Hello this is my first post and I'm glad to found a place of like minded folks!

I recently heard an application from enphase on how to use their grid tie micro inverters on an off grid system.

So the idea is this: use a small battery ( or solar powered converter) and small inverter to make a "grid" power.

Connect the AC grid tie modules to the inverter for high demand daytime loads.

Enphase 215W AC micro inverters are extremely efficient ~$60 new on ebay and a lot less used

The reason I ask this is because I hate batteries. For a million reason just trust me, I'd love system that runs without them as long as the sun's out.

ALL of my demands are to run ~1/2 hp air pumps during the day for pond aeration.

My off grid place its remote(WV) and prone to theft as I live 5 hours away.

Thanks

Dennis

 

[svetz]

Tricking Enphase microinverters with a cheap inverter to simulate a microgrid being up is a Really bad idea.

The first problem most folks would have is a legal one; once you do that you'll start back feeding the grid. So first you have to find some way to ensure that the grid is disconnected before you do this - and no it can't be two switches as they're afraid you'll do it in the wrong order or forget (same as the generator rules). Update: Not an issue for you as you're off-grid.

The other problem is Enphase microinverters act as "charge" sources. Hold that for a second, to make sense I have to explain voltage sources.

A voltage source is what you're familiar with, a battery or wall socket. While you draw current the source tries to hold the voltage constant.

Charge sources work the other way. They try to push as much current as they can and vary the voltage; obviously this can have very nasty consequences. It's one of the reasons they shut down when they detect the grid isn't present.

If you google "AC coupling solutions" you'll find some white papers from vendors like Outback describing all the engineering it takes, usually this includes frequency shifting the microinverters, relays to cut them off, and BIG battery banks to absorb power surges for the time component. If the inverter's solution doesn't address all of those, it'll cause problems.

 

[svetz]

Now for the really Good News!

Enphase is releasing their IQ8 Ensemble solution soon (next few months?). With it you'll be able get power when the sun is shining and the grid is down. No batteries required and backwards compatible with some of their previous microinverters.

 

[monty]

He's not back feeding the grid as he's not attached to it.

 

[Vanhalo]

Enphase 215W AC micro inverters are extremely efficient ~$60 new on ebay and a lot less used

I just bought a case of 12 new for $460 shipped.
M215-60-2LL-S22-IG
If you consider the 30% tax credit they were $27 each ....or without $38

 

[svetz]

He's not back feeding the grid as he's not attached to it.

True, but it's informative for other's on the grid that might not know.

 

[monty]

True, but it's informative for other's on the grid that might not know.

Well I assumed you were trying to answer the OP's question...and I would like to know as well and I would assume anybody reading the OP's question would want to read answers that were relevant to such..

 

[svetz]

The post does answer the OP's question, it's a really bad idea. The rest of the first paragraph is the only thing that pertains to the grid; the remainder of the post explains why it's a bad idea technically and is irrelevant to being on or off grid. I edited the post to split the first sentence out of the first paragraph, hopefully that will make it clearer.

 

[Mike Fox]

OP was really asking how to run 1/2 HP pumps (plural?) on solar during daytime without batteries.

1/2HP ~375Watts AC load (at least) With inductive surge to start the motor you'll need more than just a 500W intverter.

375W AC with ~80% eff. = ~470W DC @ 12V = ~40Amps and 20Amps at 24V roughly

If you consider the nightime lets say 12 hours you'll need 12hour * 470W = 5-6kW battery minimum to get through the night!

In reality that's not a good idea as 100% discharge every night will destroy your battery, no matter the chemistry, in very short time.

What the OP really needs is a good 1kW inverter that runs directly on a solar Bank large enough to provide it power and inside the inverters input voltage range. Which I don't think exists.

Engineer in me thinks experiment:

Solar--> small voltage regulator 24V ( LDO + a diode?)--> feeds 40A MPPT battery terminal enough to start "charging"-->LARGE capacitor? -->24V 1kW inverter

Concerns:

24V LDO tricking the MPPT into powering inverter could be a good way to destroy MPPT.

Maybe a good Youtube Video?

 

[Archetype-IS]

OP was really asking how to run 1/2 HP pumps (plural?) on solar during daytime without batteries.

1/2HP ~375Watts AC load (at least) With inductive surge to start the motor you'll need more than just a 500W intverter.

375W AC with ~80% eff. = ~470W DC @ 12V = ~40Amps and 20Amps at 24V roughly

If you consider the nightime lets say 12 hours you'll need 12hour * 470W = 5-6kW battery minimum to get through the night!

In reality that's not a good idea as 100% discharge every night will destroy your battery, no matter the chemistry, in very short time.

What the OP really needs is a good 1kW inverter that runs directly on a solar Bank large enough to provide it power and inside the inverters input voltage range. Which I don't think exists.

Engineer in me thinks experiment:

Solar--> small voltage regulator 24V ( LDO + a diode?)--> feeds 40A MPPT battery terminal enough to start "charging"-->LARGE capacitor? -->24V 1kW inverter

Concerns:

24V LDO tricking the MPPT into powering inverter could be a good way to destroy MPPT.

Maybe a good Youtube Video?

For the micro-inverters to work OFF-Grid applications, like a micro-grid, you would need a battery-less expensive inverters like Sol-Ark, Sunnyboy with Secure Power Supply or Outback Skybox to have run in offgrid application.

Why not get the cheap MPP PIP inverters that could do batteryless and use their MPPT controllers with solar panels for the pump. It will work without the micro-inverter complications. They made a model just for the pumping needs. https://www.mppsolar.com/v3/sp-series-3-phase/




Do wish the vendor

 

[Mike Fox]

I just looked but didn't see any 120V. I'd be interested in one of those!

 

[Vanhalo]

Why not get the cheap MPP PIP inverters that could do batteryless and use their MPPT controllers with solar panels for the pump. It will work without the micro-inverter complications. They made a model just for the pumping needs. https://www.mppsolar.com/v3/sp-series-3-phase/

I am just going to run 2 independent arrays.

4.88kw grid tie (Microinverters)​

2.4 - 4.88kw off grid
​

 

[Archetype-IS]

I just looked but didn't see any 120V. I'd be interested in one of those!

Try this Made in the U.S.A newly announced product that will run purely off solar panels without battery or inverter. Sounds like what you want. Just $$$ expensive.

Technology • SunTechDrive

suntechdrive.com

Intro video in action by Engineer775 @ youtube.

Pico In action video at a job site:

His website where you could found all the products he used for customers: https://practicalpreppers.com/
https://practicalpreppers.com/product-category/water-storage-delivery-and-purification/ (for Water pumps..etc)


Extracted from SunTechDrive's website:
"
The PicoCell can run either single or three phase pumps, both 115 and 230Vac, and 50 or 60Hz, just by selecting the correct DIP switch combination that matches the AC pump’s parameters.

Firmware based...flexible.
...
....

The PicoCell represents a truly universal solar controller where the same unit can run any AC motor load: pump, compressor, fan, etc. To optimize system efficiency the unit generates a true sine wave with variable frequency to match the available power coming from the solar PV with pump power at all times.


"

 

[DENWA]

Those look very cool but way out of my range especially i'd need two of them!

I still think AC coupled system can work as long as its under load of a pump, sorry everyone here is so down on the idea.

I just haven't seen any solution that is reasonably priced and 120V.

Mike, I like your idea too but its a little more advanced.

 

[L-P-G]

I've done exactly what you mentioned but on a much larger scale. I don't feel like reposting the whole thing here but here's a link to my build

60kW Whole House Powerwall build

I currently have a 13kW (Peak) solar system that's grid tried using Enphase micro inverters, after doing a ton of research on energy storage for existing grid tied systems I ended up going with the same process Tesla uses with the PW. AC Coupling, it's not as efficient as DC coupling but I'm not...

secondlifestorage.com

A couple things to keep in mind. The battery inverter that will produce the source sine wave (grid) to turn on the inverters should support backfeeding (they usually have an H bridge transformer). The reason for this is because the micros will always (with two exception, see further down) try to push 100% of the power produce out to the grid (be it the actual grid or your micro-grid), if your loads happen to stop consuming the power being produced now you have surplus and the micros will still continue to produce, that power has to go somewhere. Normally that somewhere is back into your battery which is why your inverter needs to support backfeeding.

The 2 exception are curtailing. Which is when the battery based inverter increases the grid frequency which tells the micros to produce less. In the Enphase micros anything above 60.5 (I think) will lower output by a certain percentage per hz then at 62.5 they'll stop producing.
The other way to do this is if your BMS has an aux output that you can program to trigger when your battery is full this can open a contactor to disconnect the micros AC trunk.

 

[Archetype-IS]

Those look very cool but way out of my range especially i'd need two of them!

I still think AC coupled system can work as long as its under load of a pump, sorry everyone here is so down on the idea.

I just haven't seen any solution that is reasonably priced and 120V.

Mike, I like your idea too but its a little more advanced.

Again, the existing Enphase micro-inverter you listed (M215) can't do offgrid without the grid; not even the IQ6 or IQ7. Only the upcoming Enphase IQ8 could run without batteries or the grid or an inverter with frequency shifting. Plus, Enphase micro-inverters only works with 240v voltage.

You could get an ACME transformer or Victron Energy AutoTransformer or MidNite AutoTransformer(SMA rebranded) to step down the 240V MPP Solar/PIP Inverter to 120V. The ACME eBay 1KW or 2KW transformers are cheap. I am just not sure any of the products are protected from the elements for outdoor use. You would need to build a power shed to house them from the weathers. Either way, it would be costly. Good luck.

 

[Supervstech]

Hello this is my first post and I'm glad to found a place of like minded folks!

I recently heard an application from enphase on how to use their grid tie micro inverters on an off grid system.

So the idea is this: use a small battery ( or solar powered converter) and small inverter to make a "grid" power.

Connect the AC grid tie modules to the inverter for high demand daytime loads.

Enphase 215W AC micro inverters are extremely efficient ~$60 new on ebay and a lot less used

The reason I ask this is because I hate batteries. For a million reason just trust me, I'd love system that runs without them as long as the sun's out.

ALL of my demands are to run ~1/2 hp air pumps during the day for pond aeration.

My off grid place its remote(WV) and prone to theft as I live 5 hours away.

Thanks

Dennis

There is a guy on YouTube that built a supercapacitor bank and a 200 watt panel arrangement with a 2000 watt inverter. It worked for quick bursts of a circle saw cutting lumber in his video.
Not cheap, as SC cost a bunch, but if you only want power for an aeration pump during the day, it should work great.
A cheaper option would be a bank of LiFePO4 batteries like 2kwh in size, and a 2000 watt inverter tied to the panels, and have the bms set to shut off when the solar stops... battery would last forever, as it would never discharge, and it wouldn’t cost much.
There is a setup for sale in the marketplace batteries for sale page.

Valence 12V 138Ah Valence Lithium Phosphate Batteries (2)

SOLD

diysolarforum.com

Sounds like you might be close to him...
And in the panels for sale section, there is the rest you would need...

Panels, charge controller, and inverter

I have (5) 130w Stion Elevation STN-130 solar panels, Lumiax 30a MPPT 12v/24v charge controller, and a 1000w continuous/2000w peak (24v in/125v out) Pure Sine Wave inverter Im looking at selling. Inverter has never been used. Looking to get $500 for everything. Located in southwest Louisiana...

diysolarforum.com