MPP LV6548 and SMA Sunny Boy Grid Tie?

Sanwizard

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I recently purchased an MPP LV6548 for my present home to get started with solar. I also purchased 16 x 330W Q-cell panels, and 32 x Lishen 272Ah batteries. I also started building a ground mount for the panels. All was looking great, but then my Daughter had a baby, and now the wife wants to move to South Carolina. Plans change i guess. In any event, I just bought a house down there (currently live on Long Island), and it happens to already be grid tied with 25 LG 250w panels connected to 2 x SMA sunny boy 6K inverters.
My quandry is I want to keep the MPP Inverter, panels, and battery, but am wondering how to integrate the DC system with the AC based Sunny Boys.
I want to use the MPP as battery backup in case the grid goes down.
Does anyone have any experience or advice on how to get the best of both systems? I am thinking I could always use an AC connection from the grid tie system as the AC input to the LV6548, and ground mount my 16 Qcells as a secondary system with transfer switch to a sub panel for critical loads, but that leaves the 25 LG panels as useless when out outage occurs.

My other thought was to just buy another MPP LV6548 and simply replace the SMA's with the MPP's, and get off grid tie altogether, but that also seems wasteful.

Any Ideas or experience to share with battery backup for grid tied systems would be very welcome. Thanks in advance!
 

Leon

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How long is a likely grid outage? Will 5.2kW of solar tide you over until normal service is restored?
 

Lt.Dan

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Make sure you can grid tie with the LV6548 in your area. Remember it is UL compliant, but not UL listed.
 

Sanwizard

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Thanks LtDan. I do not want to grid tie the MPP LV6548. Thats already done by the SMA Sunny boy inverters. I am just wondering what the best way to use my still in the box brand new LV6548 with the house I just bought that is already grid tied with SMA. I dont want to not be able to use Solar during a power outage. Thats just a silly part of grid tied inverters that needs to change IMO.

I am thinking it may be best to just scrap the SMA inverters, and convert everything to off grid using my 26KW of Lifepo4, and add another LV6548 to make it 240V to the main panel, but I hate the idea od wasting all that good tech that ia already setup and running.
 

Mendo Home Power

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Thanks LtDan. I do not want to grid tie the MPP LV6548. Thats already done by the SMA Sunny boy inverters. I am just wondering what the best way to use my still in the box brand new LV6548 with the house I just bought that is already grid tied with SMA. I dont want to not be able to use Solar during a power outage. Thats just a silly part of grid tied inverters that needs to change IMO.

I am thinking it may be best to just scrap the SMA inverters, and convert everything to off grid using my 26KW of Lifepo4, and add another LV6548 to make it 240V to the main panel, but I hate the idea od wasting all that good tech that ia already setup and running.
Seems like the simplest way would be to leave the SMA's alone and create a new critical load panel for the items you can power with your LV6548. You can remain grid tied and power your loads independent of the grid until power is needed by the grid. I have set up a number of these and they work well.
 

Sanwizard

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Seems like the simplest way would be to leave the SMA's alone and create a new critical load panel for the items you can power with your LV6548. You can remain grid tied and power your loads independent of the grid until power is needed by the grid. I have set up a number of these and they work well.
Yeah, I have the 16 Qcells I can use to charge the batteries via the MPP inverters. Two seperate systems would provide redundancy.
 

Mendo Home Power

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Yeah, I have the 16 Qcells I can use to charge the batteries via the MPP inverters. Two seperate systems would provide redundancy.
Maybe not quite redundancy, but certainly the best of both worlds. I recommend this type of setup regularly for people who are stuck with solar leases and can't mess with the existing grid tied setup
 

Sanwizard

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Thanks for the tip! So how would the wiring work with something like that? Just a 50 amp from the Main TO the LV6548 foe backup power, and then move all the wires to a seperate Critical Loads Panel? (CLP), or, a transfer switch to a dual connected sub panel?
 

Mendo Home Power

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The grid
Thanks for the tip! So how would the wiring work with something like that? Just a 50 amp from the Main TO the LV6548 foe backup power, and then move all the wires to a separate Critical Loads Panel? (CLP), or, a transfer switch to a dual connected sub panel?
The grid tie inverter stays as it is. It automatically syncs to grid power. Other than that your explanation is correct. A 50 amp breaker from your main panel to a new sub panel that has an interlock lever that keeps you from operating both grid and inverter at the same time. The most substantial ones I have used are the Square D Interlock that fits their outdoor panels. They come in both 100 amp and 200 amp. Downside to Square D is that you are limited to their breakers if you use their box. The Home Line series is the ones I use mostly.
 

Sanwizard

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The grid

The grid tie inverter stays as it is. It automatically syncs to grid power. Other than that your explanation is correct. A 50 amp breaker from your main panel to a new sub panel that has an interlock lever that keeps you from operating both grid and inverter at the same time. The most substantial ones I have used are the Square D Interlock that fits their outdoor panels. They come in both 100 amp and 200 amp. Downside to Square D is that you are limited to their breakers if you use their box. The Home Line series is the ones I use mostly.
Thank you very much Mendo! That is actually VERY useful information. I love this forum!
 

Capt Bill

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I dont want to not be able to use Solar during a power outage. Thats just a silly part of grid tied inverters that needs to change IMO.
I have always thought the way many early and current grid tie system go to total off mode when the grid goes down is absolutely ridiculous when all those panels are available for power when the sun is shinning. I do understand the need of anti-island ability; to not be sending electricity back to the grid wires when the grid is down; but I do not agree with the (IMO:) the overkill way that is accomplished without full concern for user's home power needs and options. Re your wondering about your options: I would think keeping your grid tie would be good for this situation: When your home load is less that your solar panel output. There may be times when you have available Solar power, your battery is fully charged, and home ac load is low enough to see solar watts just idling in low watt mode. That is when I would appreciate having a legal grid tie to be turning the utility meter backwards. ... My two cents :+) Also Wondring: Maybe, if you have two separate systems there might be a solenoid way to switch some of the idling island solar panels to the grid tie inverter ?? ... Food for Thoughts on Options :+)
 

SalckwareRobert

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There may be times when you have available Solar power, your battery is fully charged, and home ac load is low enough to see solar watts just idling in low watt mode. That is when I would appreciate having a legal grid tie to be turning the utility meter backwards. ... My two cents :+) Also Wondring: Maybe, if you have two separate systems there might be a solenoid way to switch some of the idling island solar panels to the grid tie inverter ?? ... Food for Thoughts on Options :+)
a 3rd transfer switch to steal the load from grid tied, so all it's power has nowhere to go except to the power company when the off grid can handle it?
Electrons are fungible, who cares which ones get sent out. With 5 breaker panels you could divide the load into chunks and take it in 20% increments if you can't handle the entire thing. Just think of the new boat the building inspector will be getting approving the setup LOL
When I rewired my house I put everything on multiple sub panels knowing i'll be going off grid eventually, but can do it in stages, not forced to drop it all at once. I'm not interested in selling to power company at a loss so they can then gouge my neighbors with my power. I'm still peeved they wouldn't let me have the free 200' watch towers, only another government agency could have them. Could have put a water tank, and a 25 foot blade wind turbine on it.

years ago I watched a video where someone used an inverter plugged into a wall outlet to put an ac sine wave on house busbar so grid tie would see it and run. Of course if it makes to much power and wants to send it out, your inverter may be in for a real shock.
 

iamrich

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Without actually seeing your system or knowing how hard making changes would be I think I would run the whole house off the LV6548 and use the existing system to back feed the grid and feed the AC in on the LV6548. This way the entire house is isolated from the grid and the grid is isolated from your house. If the power goes out, the sunny boys automatically disconnect from the grid, and stop feeding your LV6548, but the LV6548 keeps happily chugging along with the ground mount solar array and batteries feeding it.

Best case, your Sunny Boys just feed the grid most of the day, but will also be available to top off the batteries or provide extra power if needed. At night your Sunny Boys will pull from the grid (if needed) and feed the LV6548. I would set the LV6548 to deplete the batteries first before asking for AC help. In theory you end up just feeding surplus power into the grid and never get a bill (or much of a bill).

Are you running anything in the house that needs the extra oompf that the sunny boy inverters will provide? (big motors or power suckers).
 

Hedges

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I just bought a house down there (currently live on Long Island), and it happens to already be grid tied with 25 LG 250w panels connected to 2 x SMA sunny boy 6K inverters.

What model Sunny Boys?
Do the PV panels have Rapid Shutdown boxes on them?

Newer Sunny Boy have "Secure Power" feature which can provide up to 2000W 120VAC directly from PV, manually enabled during a power outage.
That feature at one point was unavailable if RSD was used, but I think they found a way to make it work again.

Not as nice as AC coupling the SB to a battery inverter, but a practically free backup feature during power failures. Just needs an outlet and switch wired to it.

If LV6548 supports AC coupled PV and uses frequency shift for control, that's the cleanest approach.


Rewiring PV panels to a different inverter or charge controller is another option. Difficult to find a transfer switch rated for 600VDC. My idea for this is to use pluggable high voltage connectors (MC3, they don't require a tool. Or MC4 with clips cut off.), kept inside the enclosure of a disconnect switch. The switch could be either AC or DC, just has to cause the inverter to go offline so no current draw. Then the connectors can be unplugged and plugged into something else.
 

Sanwizard

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What model Sunny Boys?
Do the PV panels have Rapid Shutdown boxes on them?

Newer Sunny Boy have "Secure Power" feature which can provide up to 2000W 120VAC directly from PV, manually enabled during a power outage.
That feature at one point was unavailable if RSD was used, but I think they found a way to make it work again.

Not as nice as AC coupling the SB to a battery inverter, but a practically free backup feature during power failures. Just needs an outlet and switch wired to it.

If LV6548 supports AC coupled PV and uses frequency shift for control, that's the cleanest approach.


Rewiring PV panels to a different inverter or charge controller is another option. Difficult to find a transfer switch rated for 600VDC. My idea for this is to use pluggable high voltage connectors (MC3, they don't require a tool. Or MC4 with clips cut off.), kept inside the enclosure of a disconnect switch. The switch could be either AC or DC, just has to cause the inverter to go offline so no current draw. Then the connectors can be unplugged and plugged into something else.
The Sunny Boys are 2008 Vintage SB3000 US and SB6000 US. Not sure what the life on these are, but 13 years is a pretty long run for an inverter. I am sure newer models are much improved.

I am thinking just having standard Grid supplied to the house to provide the AC input to three LV6548 Inverters, would enable 24KW of panels, and almost 20KW of AC. Together with 26KW of Lifepo4, I am thinking the grid would kick in only after a period of bad weather where the panels cannot recharge the batteries.
During the day, since the MPP inverters can use solar, then battery, then grid automatically, most power would be via the panels, then battery at night, then grid if needed to keep the batteries charged.

That means no freaking fees or paperwork with Dominion energy!
The 6.5KW LV6548's are about $1300 each, so together very close price to one Sol-Arc or Sunny Island 6048.

DMI inc. And DanF seem to be doing well with these MPP inverters. So that is my hope also. Getting close to completing my NY based solar system too! This will be my test bed to see what works and what does not, before I implement down south.
 

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iamrich

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In my opinion, the second you decide to not feed the grid, everything becomes easier/simpler. You may still have rules and regulations to follow, but you are not at the mercy of the power company to approve anything.

I have been thinking that if you have a big enough battery (even without solar) that an average house can run on a single 120v 20amp circuit from the grid. That is 57.6kwh a day in power as long as you have a battery and inverter big enough to smooth the delivery out.
 

mrzed001

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I am building a system like you:
575369_grid_tie_ups.jpg



So a grid-tie produces power to sell and an UPS system (MPP Solar inverter) to power the house.
 

Hedges

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I am building a system like you:
575369_grid_tie_ups.jpg



So a grid-tie produces power to sell and an UPS system (MPP Solar inverter) to power the house.

Your diagram shows GT PV on grid side of UPS, so its PV is unavailable during power failures.
Ideally that PV could be made available (either AC or DC coupled)


Is the MPP grid-interactive so its PV can feed the grid as well? Or does it only supply house, lose any excess production not used immediately or charged to batteries?
Does it use 100% of PV plus draw additional power from grid to support larger loads?
 

mrzed001

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Your diagram shows GT PV on grid side of UPS, so its PV is unavailable during power failures.
Ideally that PV could be made available (either AC or DC coupled)

Yes, no power from Grid-tie in a blackout. It can be a problem only in a 2-3+ day blackout (never happened here).
If needed I can connect some solar panels to OffG inverter from the GT array. (GT produces more and I sell it to utility)

Also OffG battery can store power generated by GT (so that never ever leaves the house ... no need to sell and buy back).

Is the MPP grid-interactive so its PV can feed the grid as well? Or does it only supply house, lose any excess production not used immediately or charged to batteries?
Does it use 100% of PV plus draw additional power from grid to support larger loads?

MPP inverter is only off-grid, 5048MK 5kW model. It is like an Online (double conversion) UPS.
So no noise or high/low V / Hz is reaching the equipments it's powers.
Today not even a small solar panel is connected to OffG inverter. Not needed.


First I was thinking about a simple hybrid system like this (and the MPP - Voltronic hybrid inverter is allowed and certified here in EU):

575369_hibrid.jpg


But I wanted the Online UPS function.
With this hybrid the lights flicker when it changes, like from line to UPS (10-20ms transfer time).
With the Online UPS inverter not (0ms transfer time).
And I think it answers why I did not want any AC or DC coupled system :D (also they cost a lot) They have some sec of transfer times (need a PLC and ... ).
Here is nowadays many 1 sec blackout like 1 sec no power then 1 sec power then 1 sec no power (4-10 times yes-no-yes-no...). That's killing equipments. A DC or AC coupled system does not protect against that.

Larger loads:
The 5048MK 5kW inverter can do bypass if too big power is needed. I bought one and planning to put a 2nd 5kW next to them. They can be set parallel so 10kW on a single phase (peak 20kW for 5 sec).
 
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