Enphase with Battery Backup or Generator

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  • Updated 1 month ago
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This thread has been updated to allow members to discuss when the grid goes down during a power outage.

Jacob Michals, Community Manager

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Posted 3 years ago

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KW

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Madmerv, did you ever perform your experiment?

Merv Stauffer

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Not yet. I decided to try a small scale system so as not to destroy my big generator or my operational Enphase system. It is very difficult finding a small true sine wave generator that will output 240VAC,with tight enough specs to start a microinverter. In the mean time, I am playing with a single 230watt panel, battery, a 24VDC attic fan, LED lights, and a water pump. Too many ideas, not enough time..........

Andre Chaput

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Kohler and Generac claim to have very accurate true sine waves.
Has anyone tried using them?

Solar Fix

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I attempted the experiment discussed; however the attempt was unsuccessful as the output would not stabilize. It is possible that "Enphase" is somewhat of a misnomer in that the inverters may not generate a stable voltage or frequency at all - they could rely on the huge "inertia" of the grid power system to force them into voltage and frequency compliance - and of course, if the on-board sensors detect an out of tolerance condition, they shut down. If this is the case, a micro-grid for reference may have to be bigger than the array to force the enphase inverters into compliance. Given recent experiences in MD, OH, VA where millions are without power, those who suffered through Hurricane Katrina, etc. Enphase could at least provide full technical specifications and methods that would allow other parties to engineer an off-grid operational mode even if they don't want to take an active part in creating such a solution.

Solar Fix

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Recently purchased a MAGNUM inverter set (3) for my 8.35 kW array along with 790 aH of battery backup. This setup creates a micro grid with inverters capable of charging the batteries while operating in inverter / off-grid mode. The system also employs a voltage sense relay that cuts off the solar array if necessary to prevent over-charging the batteries. The caveat of this setup is that an external generator is required to boot-strap the batteries and start the array should the batteries ever become fully discharged.

Nick Pine

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You don't need that relay. Magnum inverters can shift their output frequency up to temporarily disable Enphase outputs.

Solar Fix

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Wholesale Solar recommended the relay as a safety backup in case a software glitch prevented the Magnum's from doing the frequency shift... Shouldn't happen, but my backup has a backup.

I have an external generator solution now - not hooked up yet, but it is a wind generator with a battery charge controller. Should the batteries become discharged to the point the Magnum Inverters can't come on-line, the wind generator will charge the batteries. While the batteries are fully charged, the wind generator dump load is a combination of low voltage / DC water heaters and space heaters. Of course... there's the risk of having to wait a little while for some wind...

Pete Vanderwal

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Hmm where did you get low voltage DC water heaters?

Solar Fix

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Low voltage / DC Water heater elements are available from various sources. Missouri Wind and Solar (mwands.com) is one possible source.

Ted Panofsky, Champion

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Jacob - I don't know about your "update" but if you want to make a consolidated thread for this I think it would be great, but should include, or point to all of the previous threads on the subject. Thanks!

This is clearly a subject that concerns a lot of folks and is indeed interesting, even if Enphase does not support the configuration.

turls

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I just had my Enphase system installed and I went ahead and had a Generac transfer switch installed at the same time. I was also switching to 400a electrical service at the same time since this is part of a large remodel/home addition project.

I had no trouble getting the utility to approve the configuration as part of a grid-tie interconnection agreement even though they had not seen the setup in the area before.

The disadvantage to putting the transfer switch ahead of time is that you lock yourself into a brand and are leaving yourself open to changes in technology or price drops.

The manual disconnect switch the utility requires will disconnect both the generator and the PV array from the grid. If I read this before, I don't remember the answer, but I don't see how the Enphase inverters would know the difference between generator power and grid power, so I would expect them to still operate when/if I add a generator when I am on generator power. Does this sound right?

EDIT: I see there are some other good threads on this topic. I need to verify my setup considering the caveats. Of course, since I don't have the generator yet it isn't urgent to completely figure this out at the moment.

Jagged Ben, Champion

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"Does this sound right?"

No. But I think you have already figured that out.

"The manual disconnect switch the utility requires will disconnect both the generator and the PV array from the grid."

This doesn't sound right to me. To do this right, your Enphase system should tie in to your service 'upstream' of the generator transfer switch, and the transfer switch should cut the generator and loads from the grid, and not the solar. But maybe I'm misinterpreting your description.

turls

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I think this is how it is wired but I will verify.

Alain Schiller

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The liability seems great to me. The Electric company has to rely on us to manual disconnect when using the batteries. What if a mistake is done or a malicious person starts our grid connection when the utility are off and one of their worker is working on the grid. He could be electrocuted.... Just a thought!

Aaron Mandelkorn

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If you are connecting a PV system to a house with a generator you can not connect the PV to the load center. This will most likely lead to the PV system back feeding the GENERATOR when the grid goes down and the Generator comes on. To get around this it is recommended to Line Side Tap the PV system to the utility side of the transfer switch. This will allow the PV system to shut down when it senses the grid is down.

Bob Beller

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You should talk to Generac. The generator is at risk from excessive power backfeed.

Powerskip

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Can't we just use a small true sine wave inverter? 12V to 240V AC
Powered initially by a small battery, which is charged back, when the PV system is running.
All this over a manual or automatic transfer switch to protect the poor guys working on the grid.

Powerskip

Merv Stauffer

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That was my plane, until...... Have you tried to find a true sine wave inverter, 12vdc to 240vac, that meets the tolerences of a micro inverter? I have had no luck, that is economical to make it worth while. I keep looking.......

mrbigh

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I run my PV system like that and works correctly. One must have in consideration the total house load not to have an excess of power production from the PV system. In my case, I shut down one of the Inverters string in order to balance the in and out wattage flow.
The correct power inverter I bought was not more than $150.00; search eBay

Rick Reinhard, Champion

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I think without a larger battery bank, you are asking for trouble. What happens once you are running on this setup and cloud cover comes over for 5 or 10 minutes?

mrbigh

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As we know, it will be not power generation and absolutely darkness. I was lucky during my test of no more than one hour to prove the point of operation but never got into the situation of real need.
My point was proven and in the event of an emergency, everything is ready to go, including my " gas mask" and the zombies blaster.

Powerskip

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On the same token, is it possible to "wake up" the inverters with just 120 Volt?

Powerskip

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Merv Stauffer

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I don't think so. Specs say 60Hz, plus/minus 2Hz.

Powerskip

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I know, but that's the only one which fulfills all the other requirements.

Jacob Michals, Community Manager

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Hi Powerskip,

Please note, Enphase Energy microinverters are a grid tied system only and this is not a supported application.

Jacob Michals
Enphase Community Manager

Rob Hilbun

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I always thought a small UPS to turn on the Enphase Inverters and keeping the load high enough so it wouldn't back feed the USP but could you even put diodes in to stop reverse flow into UPS? and keep the Enphase inverter running?

Ted Panofsky, Champion

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No, this is not sufficient. Also, diodes don't work on AC.

Rob Hilbun

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I was afraid of that diode theory, but I still can't believe there is not some way to electrically/electronically make it happen.........and it hasn't been hacked and put out there? ........ yet

Nick Pine

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I'd say no. The M215 requires 59.2 to 60.6 Hz, and that AIMS inverter makes 60Hz +/- 2%.

Nick

Curtis Anderson

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Hey Nick, would if they opened the inverters to 57.1 Hz.

Nick Pine

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What does that mean?

Ted Panofsky, Champion

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So, once you "wake up" the inverters, where is the power going to go? Unless you have an infinite sink in the system (like the grid), the solar generator will try to push energy back into your sine wave generator which will either shut down, or burn up.

While I admit it is probably possible to design a system that will work, it will need to be a total system design, including careful regulation of where the generated power will be directed either to a battery system or load bank. Without system design, hacking around will result in failure, possibly spectacular failure.

Take pictures!

Powerskip

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Maybe diodes at the sine wave generator?
Not sure. I am not an expert.
I can't imagine, that nobody has tried a off-grid installation with the Enphase inverters.

On the other hand, if your statement is true, where does the power from the panels go, if you switch of the microinverters, say you disconnect from the grid?

Ted Panofsky, Champion

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The panels simply get hot, just like a sidewalk.

Powerskip

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@ Ted,
do you think they get hotter, when not connected to the grid?
Are you saying the energy, they produce, will be converted to heat?

Ted Panofsky, Champion

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When the inverter is on and delivering power to the grid, the panels will be a little cooler than when the inverter is off.

When the inverter is off, the panels are not producing any power so the sun's radiation is simply converted to heat, just like any passive object exposed to sunlight. The panel output wires will be at the specified "open circuit voltage" but there will be no current flowing, therefore no power produced.

Powerskip

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I was trying to read as much as i had the time in this forum today.
Is there anywhere an answer from from am Enphase rep stating how to connect the Microinverters in an off-grid situation.
Which is what we are talking about here, right?

Jagged Ben, Champion

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"Is there anywhere an answer from from am Enphase rep stating how to connect the Microinverters in an off-grid situation?"

No, because it is not a use of their equipment that they approve of.

Nick Pine

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OTOH, Magnum has a nice 2-page ap note on how to use their inverters with an Enphase system. I've been through this process on paper and would be happy to help, for a fee.

KW

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Based on part on the comments here and some on pure conjecture, it appears that to use our inverters off grid, one would have to have a stable, clean sine wave generator that is x times larger than the array output and a load that is at least as great as the array at all times. The generator needs to be large enough to prevent the inverter outputs from changing the volt/freq of the generator. This means that the generator will always supply at least part of the load. The generator/array output needs to be large enough so that any sudden load (ac startup) will not jolt the voltage/freq. out of the inverters spec. or they will shut down. The inverters could be wired to be able to add/remove them as required to prevent the inverter outputs from backfeeding the generator as the load changes.

Jagged Ben, Champion

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Kim, you are grasping some of the key points pretty well...

"...a load that is at least as great as the array at all times."

Yes, this would be required. But it's impossible to guarantee, so you'd need fail-safes to shut things down if your load(s) quit on you.

"The inverters could be wired to be able to add/remove them as required to prevent the inverter outputs from backfeeding the generator as the load changes."

Well, yes, maybe they could , but that part is very hard. For one thing, the Enphases have a 5 minute startup delay, so this wouldn't work well for most intermittent loads.

What it comes down to is that a) you need some batteries, and b) you might be able to use something like the SMA Sunny Island (you'd need two of them) to manage the system. It would be a rather expensive experiment, and it might not work, and Enphase wouldn't honor their warranty if they found out.

Powerskip

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Are you sure, that the inverters have this 5 Min. delay, or is it only the Envoy?

Powerskip

Ted Panofsky, Champion

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It is the inverters. They require a stable "grid" for five minutes before they start up. I believe this is a code requirement.

Powerskip

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Thanks Ted!

Powerskip

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Just checked something, Ted.
The 5 Min. you are referring to is probably the time from "sleep" to "wake up", right?
I just tested what happens, if I disconnect from the grid.
They came right up after connecting again. . . Checked with a clamp on Amp meter.
Hhhmm, in this case they did not waited for the "5 Min. stable grid"

Ted Panofsky, Champion

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That's a surprise to me, and a bit disturbing. The operations manual for my inverters (D380) says "Turn ON the main utility-grid AC circuit breaker. Your system will start producing power after a five-minute wait time.". Check out this document: Enphase White Paper Utility Reconnection Timer.

Powerskip

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I read it and am surprised too.
But you can check it yourself.
I was directly in front of the main panel, clamp amp meter around one of the wires coming from one of my arrays.
Since it was raining, it showed only about .6 Amps.
I switched the CB off and it went to zero.
Switched CB on and it came right back on to about .6 Amps.

Ted Panofsky, Champion

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How many inverters do you have? .6 Amps could be the quiescent current consumption of the inverters showing up on your meter. The inverters look mostly like a capacitor to the AC line which has a very small power factor, and unless your meter is power factor corrected, it will read a much larger power than is the actual. Can you read which direction the current is flowing? I'll bet there is no actual production.

Jagged Ben, Champion

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"I believe [the 5 minute wait time] is a code requirement."

It's actually part of UL 1741.

Jacob Michals, Community Manager

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Hi Powerskip,

Your comment

I read it and am surprised too.
But you can check it yourself.
I was directly in front of the main panel, clamp amp meter around one of the wires coming from one of my arrays.
Since it was raining, it showed only about .6 Amps.
I switched the CB off and it went to zero.
Switched CB on and it came right back on to about .6 Amps.
needs clarification.

The .6 Amps AC you're Amp meter reads is the grid pushing against the microinverters. This is how they "sense" a stable wave form. There is no AC consumption during this period. If you wait 5 minutes, the total amperage should increase once they start producing power, per the UL 1741 certification.

Hope this help,

Jacob Michals
Enphase Community Manager

Powerskip

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Jacob,
I understand the "pushing" you described, but I don't get the fact that there should be no power consumption.
My clamp-on amp meter shows o.6 amps and therefor there must be a consumption, right?
As far as I know, the inverters use about 46 mAh in sleep mode.

Can you please explain, how this all relates??

Ted Panofsky, Champion

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Your clamp-on meter over-reads because it is not power factor corrected. A low power factor means that the "current" observed is out of phase with the voltage and therefore is not actual power consumption.

There is a detailed description HERE

Powerskip

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Geeez Ted, what did you do? :>)

I tried to read through the "power factor" explanation in wikipedia during the breaks in "So you think you can dance" and missed almost the finale. :>)
My head is spinning. . .

So, how about systems like TED500 and similar, does the MTU correct for the power factor?

Ted Panofsky, Champion

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Yes it does, at least pretty well. The MTU has current transformers to sense the current, and it connects to the wires to sense the voltage. It has a processor inside that samples the current and voltage many times per second and computes the phase of the current to voltage and instantaneous power, and sends reports to the gateway with one second intervals integrated RMS power, voltage, KVA, and power factor.

Jacob Michals, Community Manager

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Hey Powerskip,

Here is a link to the Enphase White paper on Verifying Five-Minute Timer Protective Requirements for Utility-Interactive Inverters (http://enphase.com/wp-uploads/enphase...)

Check on page 4. It covers in detail what you are seeing.

Jacob Michals
Enphase Community Manager

Powerskip

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@ Jacob and Ted
Ahhh, that could be.
It was pitch black and raining all day long.
Geez, I m learning something every hour. Thanks guys.

Ted, thanks for publishing your website. Awesome!
The TED 5000 looks really tempting to me. If I only could find some smaller CTs which are compatible with their MTUs.
Since you have the system installed, do you know what tech specs of the CTs are?

Ted Panofsky, Champion

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TED doesn't publish the CT specs, but there has been some discussion about this on their support board. Yes the CTs are big, but with careful manipulation of the wiring in my panel I manage to fit them in. They need to be big to fit primary wiring especially when there are multiple wires to sense with one transformer, and they don't want to stock too many part numbers.

Dawn Janz

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I initially wanted to have a battery back up, a generator is a good idea, assuming that you have access to fuel for it. If there is a catastrophic event that kills the grid, likely fuel will become scarce. My installer offered an option for me to have batteries, but it was double the price of the grid tie alone, so I'm hanging tight until a better/cheaper option becomes available.

Claude Cassagnol

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Enphase really needs to come up with a solution. Two years ago when we had our PV system installed, we were told we could have a battery backup but at the time, the enphase product was new and installers may not have been aware of battery backup limitations with enphase. Had we known, we would not have used enphase inverters.

Solar Fix

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I'm glad to see the continued interest of Enphase customers regarding the "off-grid" hybrid application. We've all seen major storms and natural disasters cause weeks-long extended outages. I live in the country where power sometimes goes out for days at a time. We have a wood stove for heat. If my array could be made to produce power- even if only during peak daylight hours, it could power my 600 ft deep well, fill my cistern, and keep my home livable through protracted outages. Enphase has the opportunity to assist in providing a solution that could minimize human suffering in emergencies... but that requires getting past Gaia-Minded Green Dogma, ceasing to hide behind policy excuses, actually listening to customer requests, and doing some honest creative engineering. Since they've finally condescended to "allow" this discussion thread, perhaps there's hope. Keep those comments and requests coming.

Josh Stapp

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Just found this:
http://www.altenergymag.com/emagazine...

Interesting answer to the question of where to send the energy created by the microinverters once the batteries are fully charged. The inverter adjusts its AC output so its out of range for the microinverters causing them to turn off.

It looks like these Xantrex XW systems may be the answer everyone's been looking for. Not sure of the total cost but I imagine it's several thousand dollars. I don't know that it would be worth the cost to accommodate the occasional power outage though it's definitely pretty cool.

Stan Morris

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I contacted the electric utility on Maui and was told these units are on the approved list. Maui uses a California list. http://www.gosolarcalifornia.org/equi...
Known as "dithering" or tricking the inverters into shutting down. Good podcast at www.solarpowerworldonline.com/2013/08... on AC coupling, dithering, and diversionary loads.

Alain Schiller

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Pretty interesting article indeed! The problem is to find the electric engineer.
A real electrician, not somebody trained for a specific installation, but somebody who is a real professional and can use his(her) brain power to engineer new system all-together.

Nick Pine

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I'm an EE. Magnum has a helpful 2-page AC coupling ap note written by Alan Santos-Busch and the Prosolar's August issue has an 18-page story on AC coupling.

I'm helping a family with an Enphase system and a well, who may end up with 3 $2500 Magnum MS4488PAE 4400 W inverters in parallel and a 48 volt battery bank with 8-12 $33 Group 27 deep cycle 12V battery "seconds" and a $500 used 4 kW 48V battery charger with a 240 VAC single phase input for use with their generator in a cloudy power grid outage.

Nick

Alain Schiller

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The liability seems great to me. The Electric company has to rely on us to manual disconnect when using the batteries. What if a mistake is done or a malicious person starts our grid connection when the utility are off and one of their worker is working on the grid. He could be electrocuted.... Just a thought!

don lunghi

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Interesting thread, people. My thoughts were to use a three position main disconnect: grid-tied, off, off-grid. Off grid would connect the "grid simulator waveform" to the inverters as well as connect the outputs to a separate four square receptical where emergency equipment (loads) could be connected. These would then be completely separated from the normal load wiring and circuits.

I thought this might resolve the islanding issues that are rightfully of such concern. I had not carried the thought any further than that, and certainly have done no testing, but find the idea of demand switching inverters, dummy load, and live loads very interesting. The five minute drop, required by IEEE code, can likely be accomodated in the scheme.

I'd like to add that I appreciate Enphase reticence to involve themselves in any way with this type of application. It is every bit as understandable as the desire to allow capable energy generation installations to do so during emergencies. I'll keep reading your posts, and promise to post any testing results (you'll get the good and bad, it's only fair).

MICHAEL BONARD

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Alain,
The liability you were mentioning could be avoided if you use an interlock system on your circuit breaker panel. The "Generator Inter Lock Kit" is produced by Interlock Kit (http://www.interlockkit.com). I used their idea and fabricated an interlock plate from a piece of 3 mm thick plexiglass. Very low cost, easy to make, and will provide a fool-proof safety without modifying your circuit breaker panel (you may have to move a few circuit breakers at most). I use this interlock to connect my standby generator.

Regarding the off-grid operation of the Enphase inverters, I tried a cheap inverter as a grid simulator. I had to use an auto-transformer to generate the two 120 volt legs from the single 120 volt inverter output. The results were not good, the inverter delivers a modified sine wave which reads "funny" voltages when using RMS multimeters, and the stability of the voltage did not meet the inverters required operating range.

However, I found excellent information from Wholesale Solar http://www.wholesalesolar.com/inverte....
They have a solution for the off-grid operation of a solar array using the Enphase Microinverters. A bit costly ($2,200 approx. for the 4,400 W inverter, plus batteries and wiring) but at least they seem to have solved the issues.Here is the link: http://www.wholesalesolar.com/grid-ti.... I am tempted to go this way, after nearly a week without power in a house on well and septic (15 miles from downtown Washington DC!).
I will post the results once I have installed the inverter.

Michael Bonard

PS: I am an electrical engineer

Alain Schiller

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Aloha Michael
Have you ever did the installation with wholesale?
Mahalo for many feedback.
Alain

Stan Morris

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I thought the Xantrex XW systems had the interlock built in. Was I wrong about that?

Mike Smith

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Yes the XW has a interlock built in. Grid 1 input goes to the Grid. Grid 2 input goes to the generator and since Grid 1 and Grid 2 can't connect at the same time then you have your required interlock.

The problem is you want to put your Enphase production on the output of the XW so that the solar will produce when the Public Grid is absent. That means the generator becomes connected to the Enphase a condition you can't allow.

What you really need is a Dual transfer switch to switch off the solar and switch on the generator. Not a switch between the generator or Solar. There is an important differance. Midnight solar has a 30amp for $129

MICHAEL BONARD

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Stan,
The interlock function you mention is provided by the MNE250XW E-panel designed for the Xantrex xw series inverters. This is a separate unit that you have to procure and install.

The interlock I am talking about is located on my existing circuit breaker panel. This configuration avoids the cost and complexity of installing the E-panel to feed only a limited and fixed set of electrical loads. My solution is much cheaper, simpler and offers the capability to feed any load (or combination of loads) that is currently connected to the existing circuit breaker panel. The drawback is that I have to actively manage the total power drawn by these loads. Using common sense, this is not a problem.

Gary Wheat

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As long as I place an automatic transfer switch between the main meter and my main panel, can I do a back up generator installation as I normally would?

When the grid goes down, the ATS senses that and starts the generator. The PV system would still be creating AC power until the micro-inverter sent a ping at it's five minute intervals. Would the generator falsely make the inverters think that the grid was still operating?

If the grid went down and the Inverters weren't fooled, is it OK for the PV system to operate for the short time between the grid going down and the inverter "ping"?

Ted Panofsky, Champion

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The PV system will notice and respond to the grid interruption much faster than any transfer switch, so the PV will be off when the generator starts. It is unlikely that a conventional generator will be stable enough for the PV to start up. However it is much safer to position the generator transfer switch so the PV system is on the grid side of the switch.

Umair Shafqat

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I am installing a 11.8kW system where it is difficult to run the conductors from AC array to the grid side of the GENREC ATS. The 25kW generator supposedly outputs close to 240V and works in a very close range of 60Hz. What are the chances I will back feed into the generator, in case where generator turns on and I am on the load side of the generator. Will M215 back feed into the generator or more importantly turn on?
Any help will be greatly appreciated.

Mike Smith

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Sure there is a chance the generator output may pass for the grid for brief periods. The real problem is a generator generates power it is not a load and cannot absorb power. Generators also need spin up time when loaded so when you switch on a load, for a moment the motor slows, frequency reduces and voltage fluctuates.

If you really want to test your this just plug the grid into the generator when it is off and stand back as it smokes.

DON'T CONNECT A GENERATOR TO A SOLAR POWER POWER SYSTEM.