Wire solar for both grid-tie and off-grid? To MAIN panel

[Mhoward84]

Hi, I am currently just brainstorming design for a way to use solar in a grid-tie and off-grid situation. I don't need immediate transfer of power, but the ability to go out and flip a few switches would be nice to enable my solar to continue running. I have been doing a lot of reading of forums and manuals and I am getting answers from "it can't be done" to "yes absolutely".

I know some hybrid inverters allow you to input utility AC power to the inverter, then power your load with that power if your solar + battery can't handle it. It appears like they may handle it different ways too, like with MPP's transfer switch - when power is insufficient it just transfers the whole load to utility, or with Outback Radian's Grid Zero mode - when power is insufficient, it blends utility power with the solar power to power your load.

I would LOVE to get a hybrid inverter and just power my entire home panel off hybrid inverters with utility input, but I need something that is more "reliable" than depending on inverters not failing. I may be out of the country for several months and have my property rented for a vacation rental property. I also have two air conditioners and can have massive current spikes, and if I pass through an inverter I may need to wayyyy overbuild my inverters just to do this? From what I understand, I can do an automatic transfer switch that will just connect directly to utility if my inverters fail but.... meh?

I also don't want to have an inverter subpanel that is protected, while the rest of the home is offline. I feel like I won't use the solar array to it's full potential then.

I am looking at hybrid inverters that can do both grid-tie and off-grid, like the Outback Radian. I drew up a very basic wiring diagram of what I imagine the system could look like in both grid-tie mode and off-grid mode.
Is this possible like the wiring diagrams?
Is there a better way to do this?
Would it be reliable enough going through the inverters?

EDIT: During power outages I don't need to run both my AC's. What the array generates is just fine during outages, but when utility is up I would like to be able to draw more than my inverter is rated for.

 

[NICOLAE]

If you use a tie grid inverter doesn't matter how big is your power consumption in yours places.
Inverter only tried to reduce consumption from grid. This model works only if grid is life.
If you want both try Victron

 

[Mhoward84]

If you use a tie grid inverter doesn't matter how big is your power consumption in yours places.
Inverter only tried to reduce consumption from grid. This model works only if grid is life.
If you want both try Victron

Thanks for the reply!
That was the appeal to me to grid tie, there is nothing "going through" the inverter this way and the inverter just reduces what I use, and in case of inverter failure, power will still work.

When you say "this model" do you mean the diagrams I posted? If so, then it sounds like this model would work?

Also, I have looked at Victron, but didn't find a nice model that did everything without using multiple pieces like a quadro or something else as a battery island.

If there is nice all in ones I am interested! I'll check out their models again.

 

[macheung]

I see what you are trying to do and was designing a similar setup. Use an interlocked backfeed breaker to send PV power produced by the inverter to your home panel when grid is out. I don’t see any reason why it should not work. Though you should check that the inverter will produce +\- 110V on both hot bus or only every other breaker will be powered. You can short the buses together via a jumper
On the backfeed breaker then all breaker will get 110V, the downside is that no fuel pole 220V equipment would work.

Can the inverter you selected provide AC through a back feed breaker operate without a battery? If it is dependent on the battery to draw power (with PV charging the battery), then you will need a big battery and it will get expensive. What inverter are you thinking of?

 

[Mhoward84]

I see what you are trying to do and was designing a similar setup. Use an interlocked backfeed breaker to send PV power produced by the inverter to your home panel when grid is out. I don’t see any reason why it should not work. Though you should check that the inverter will produce +\- 110V on both hot bus or only every other breaker will be powered. You can short the buses together via a jumper
On the backfeed breaker then all breaker will get 110V, the downside is that no fuel pole 220V equipment would work.

Can the inverter you selected provide AC through a back feed breaker operate without a battery? If it is dependent on the battery to draw power (with PV charging the battery), then you will need a big battery and it will get expensive. What inverter are you thinking of?

Hi macheung I think I messed up my diagram. I just re-read over the inverter documents and I don't even need that switch. I can natively connect the subpanel/off-grid output to the main panel directly (through ac shutoff switch). Then I would just need to make sure the generator interlock was connected to the subpanel/off-grid output.

The model I'm looking at is the Radian Outback GS8048A and it does do 240v output on two wire that would connect one wire to each pole on the breaker.

Yes it does need batteries for the off-grid mode, and I was looking at building a ~280ah 48v battery from the EVE/Lishen/etc lifepo4 cells with BMS, disconnect, breaker and any other safety mechanisms I can research before I build it. I expect the cost on the battery to be around $2500-3000. The off grid mode is called Mini-Grid in their documentation.

 

[macheung]

That’s right, the breakers are your manual transfer switch. Just make sure the interlock works and everything is done in the right order.

280Ah 48v is 13kwh of battery which is quite a bit, at say $500 per kWh, that would be like $6000 in batteries. Do you really need that much battery for the setup? When the grid is out, you are only running basic loads (no AC). Maybe you just need say 4kwh if battery to satisfy the inverter and rely on solar? Does the radiant uses the PV power directly for the inverter in off grid mode? Or does it only charge the battery and all power for the inverter must come from the battery?

 

[newbostonconst]

I have a large house we built that we had a main panel and a lighting sub panel.
I put in a GS4048 and converted the lighting panel to a critical loads panel and moved a few circuit I wanted powered on during an outage over to that panel.

The GS4048 now feeds the critical loads/lighting panel off a side breaker but there is still the old feed to if from the main panel(this is off during normal operations). When the power goes out we don't even notice it, the inverter switches over so fast. We usually only know because we hear the neighbors generators.

But if the power is off for a long time I can switch off the main grid feed and turn back on the old power feed to the lighting/critical loads panel to back feed the main panel from the critical loads panel and have the whole house running off the GS4048.

The only thing you have to watch is your main panel feeds the GS4048 normally. This feed is used to supply power to the GS4048 and it passes this power though the unit to power the critical loads panel and uses power to charge the batteries under normal circumstances. But when the grid is down and you want to back feed the main panel, this will also supply power to the GS4048's main input feed. So the GS4048 thinks the grid is up and passes the power through the unit to the critical loads panel which is back feeding the main panel which is feeding the GS4048. It is like a loop. The GS4048 keeps the power on but throws an error for low voltage and also my AC coupled micro inverters don't run when it is in this loop situation. You just need to remember to flip power off feeding the GS4048 when back feeding the main panel. I have 3 breakers to switch if I want to back feed the whole house. I made sure all the wires had the same phase through this loop, not sure what would happen if they weren't.

I have AC coupled Enphase Micro's (7kw) and APsytems Quad Micro's(3kw) that the GS4048 controls when the power is out. Works fine.

Note: The GS4048 can also run an 18 cell pack so you can get a little extra power (2kwh of battery) without having to add a whole other set of batteries....I have 18 280Ah cells in parallel with 2 BattleBorns(plus 2 100Ah cells) for around 20kwh of battery. As long a sun is out we can run off grid as long as we want. We normally use 26Kwh's a day in electricity.

 

[Mhoward84]

Macheung - those are good questions, I am asking them now. As for the battery, I was looking at cells either from a group buy here on the forums or from one of the links from Will Prowse - https://www.mobile-solarpower.com/raw-lifepo4-deals-page.html. The cost for 16x 270-300ah lifepo4 cells shipped is around $2k-2400 and then the safety hardware anywhere from 200-500. As for the sizing, I am not running either home AC, but I would still run a window AC at least overnight at ~900w draw + kickstart and the 14k would be plenty, plus fridge, etc.

newbostoncons - very interesting idea. I could then just use the protected load panel to feed it back to the main panel (with interlock) instead of a switch box. The only thing I don't like about that idea is the protected panel going down with an inverter failure, which seems ironic to me. In case of inverter failure, I guess I could just shut off the inverter to the protected panel and then turn the breaker from the main panel to the protected panel on. Having a separate panel as well seems like a bit of a pain, I'm not sure how much slack is in the lines already at the main panel, but I guess I can try to look.

 

[newbostonconst]

I think you got it... Good luck... There are so many options today...

I did install my GS4048 without the lower disconnect panel and used a cheap breaker box instead of you want to save more money.

 

[Anit767]

I think you got it... Good luck... There are so many options today...

I did install my GS4048 without the lower disconnect panel and used a cheap breaker box instead of you want to save more money.

Any hybrid inverters out there that are battery agnostic?

 

[12VoltInstalls]

Any hybrid inverters out there that are battery agnostic?

All inverters believe there is a battery. And I think all the latest ones not only believe in and acknowledge a battery, but they are capable of knowing information about the battery.

 

[MurphyGuy]

We use our grid tied solar system in an "off-grid" mode when storms knock out the power....

I flip two breakers, push a couple buttons, and we're up and running within a minute.

We use an off-grid AC Coupled system that consists of a 25kWh lithium battery and a couple of SMA Sunny Island inverters.

The Sunny Islands (SI) inverters are connected to our main breaker box through an interlocked generator breaker that can't be turned on unless the main breaker (from the grid) is turned off. (this is perfectly legal and up to code)

So it goes like this:
Storm knocks out power and lights go off. I go downstairs and turn on the off-grid system. While the system is "booting up" doing its self-checks, I walk over to the breaker panel, turn off the main breaker, flip up the metal interlock plate, and turn on the interlocked generator-input breaker. At this point, I am now isolated from the grid.

The off-grid system finishes booting and I push the start button.. (total elapsed time = 60-90 seconds) the lights come back on immediately and the entire house runs as normal.. a minute or two later, my solar system thinks the grid has been restored and it also starts making power.

If the solar makes more power than the house needs, the SI's use the extra juice to charge the batteries.. if solar doesn't make enough, then the SI's make up the deficit by drawing from the batteries and adding that juice to whatever the solar is making. If the solar makes too much and the bats are fully charged already, the SI's throttle the solar array to exactly match the house loads.

Our entire home runs as if nothing was wrong.. and does it silently.

If we run into a situation were the sun just isn't cooperating for days on end, our battery bank can start to run down.. at which point, we can connect a generator to the SI's and the SI's will combine generator power and solar power to keep the house going and charge the batteries back up. This usually means running the generator at 80% load for about 3 to 4 hours..

Our grid tied solar inverters are just standard SMA Sunny Boy SB6.0.. nothing special.

Here's a picture of the off-grid system.

 

[Larry Oswald]

We use our grid tied solar system in an "off-grid" mode when storms knock out the power....

I flip two breakers, push a couple buttons, and we're up and running within a minute.

We use an off-grid AC Coupled system that consists of a 25kWh lithium battery and a couple of SMA Sunny Island inverters.

The Sunny Islands (SI) inverters are connected to our main breaker box through an interlocked generator breaker that can't be turned on unless the main breaker (from the grid) is turned off. (this is perfectly legal and up to code)

So it goes like this:
Storm knocks out power and lights go off. I go downstairs and turn on the off-grid system. While the system is "booting up" doing its self-checks, I walk over to the breaker panel, turn off the main breaker, flip up the metal interlock plate, and turn on the interlocked generator-input breaker. At this point, I am now isolated from the grid.

The off-grid system finishes booting and I push the start button.. (total elapsed time = 60-90 seconds) the lights come back on immediately and the entire house runs as normal.. a minute or two later, my solar system thinks the grid has been restored and it also starts making power.

If the solar makes more power than the house needs, the SI's use the extra juice to charge the batteries.. if solar doesn't make enough, then the SI's make up the deficit by drawing from the batteries and adding that juice to whatever the solar is making. If the solar makes too much and the bats are fully charged already, the SI's throttle the solar array to exactly match the house loads.

Our entire home runs as if nothing was wrong.. and does it silently.

If we run into a situation were the sun just isn't cooperating for days on end, our battery bank can start to run down.. at which point, we can connect a generator to the SI's and the SI's will combine generator power and solar power to keep the house going and charge the batteries back up. This usually means running the generator at 80% load for about 3 to 4 hours..

Our grid tied solar inverters are just standard SMA Sunny Boy SB6.0.. nothing special.

Here's a picture of the off-grid system.

Great if you are at home, and awake but what about the linemen who get zapped a half hour after the outage? I want a transfer switch that automatically just shuts off when the grid goes down. No transfer. I can later do that manual stuff also. I also do not want my small batteries on automatic to get discharged while I am still sleeping. Neither the fridge nor the freezer nor the well will care.

 

[MurphyGuy]

Great if you are at home, and awake but what about the linemen who get zapped a half hour after the outage?

Why would a lineman get zapped? Our off grid input breaker is interlocked. That means it is not possible to activate the off grid system unless the main breaker is off and we are isolated from the grid. There is zero chance of a lineman getting zapped and it is code compliant.

I want a transfer switch that automatically just shuts off when the grid goes down. No transfer. I can later do that manual stuff also. I also do not want my small batteries on automatic to get discharged while I am still sleeping. Neither the fridge nor the freezer nor the well will care.

The Sunny Island's do have an internal transfer switch, I just don't use it because it would require me to have them connected at all times and I don't want that. I keep my system entirely isolated so a lightening strike doesn't turn my $6000 investment into a paper weight.

Keeping the off-grid backup system isolated has only one serious drawback, and that is that it doesn't engage automatically, it must be physically turned on, which means your clocks are going to start blinking and you're going to be without lights for a few minutes. It's not an issue for us.

 

[Larry Oswald]

Great if you are at home, and awake but what about the linemen who get zapped a half hour after the outage? I want a transfer switch that automatically just shuts off when the grid goes down. No transfer. I can later do that manual stuff also. I also do not want my small batteries on automatic to get discharged while I am still sleeping. Neither the fridge nor the freezer nor the well will care.

I misunderstood not reading your interlock description.

 

[timselectric]

Why would a lineman get zapped? Our off grid input breaker is interlocked. That means it is not possible to activate the off grid system unless the main breaker is off and we are isolated from the grid. There is zero chance of a lineman getting zapped and it is code compliant.


The Sunny Island's do have an internal transfer switch, I just don't use it because it would require me to have them connected at all times and I don't want that. I keep my system entirely isolated so a lightening strike doesn't turn my $6000 investment into a paper weight.

Keeping the off-grid backup system isolated has only one serious drawback, and that is that it doesn't engage automatically, it must be physically turned on, which means your clocks are going to start blinking and you're going to be without lights for a few minutes. It's not an issue for us.

My grid input is also isolated and only a manual option. I have a couple of UPS’s to keep some things going, while we switch over if needed. There's always someone here. And they know what to do. Plus, I'm only a phone call away.

 

[MurphyGuy]

My grid input is also isolated and only a manual option. I have a couple of UPS’s to keep some things going, while we switch over if needed. There's always someone here. And they know what to do. Plus, I'm only a phone call away.

Yup, me too. UPS's on anything important like the desktop computers and the modem (stupid modem takes like 5 minutes to boot)

I use a little APC UPS 750Pro unit I found at a garage sale for five bucks. Pulled out the ridiculously small battery and ran the cables to 100 amp-hour deep cycle battery that is also hooked to a NOCO 4 amp charger. That gives me about 2.5 hours of run time, of which I don't think I've ever used more than 10 minutes of.

 

[timselectric]

Yup, me too. UPS's on anything important like the desktop computers and the modem (stupid modem takes like 5 minutes to boot)

I use a little APC UPS 750Pro unit I found at a garage sale for five bucks. Pulled out the ridiculously small battery and ran the cables to 100 amp-hour deep cycle battery that is also hooked to a NOCO 4 amp charger. That gives me about 2.5 hours of run time, of which I don't think I've ever used more than 10 minutes of.

I have APC 1500 units. I put them on customer's equipment. And sometimes an "extra" one finds its way into my home, occasionally. lol
One has batteries at their end of life. I'm considering switching to LFP. But the more I think about it. I'm not sure it's a good use case for LFP. Since it will almost never get cycled. Plus the battery information on the APC screen would be useless.