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Chilicon CP-720 grid tie inverters - keeping the power on when the grid goes down

SparkyJJO

(un)Certified Arc Generator
Joined
Jan 31, 2022
Messages
1,634
Location
Ohio
Hi everyone,

I've been lurking for a few weeks trying to read up on stuff. Now I'm looking for some expert advice on what I'm thinking of accomplishing.

First off, I'm located in Central Ohio. 11x Chilicon CP-720 microinverters connected to a 8.3kw array on the roof of the house facing south/southwest with no tree cover. Two lines come down from the roof, each to a 30A 2P breaker in a small subpanel, that then feeds the main panel through a 45A 2P breaker.

Given some geo-political nonsense that has been brewing for some time, and concern about long-term stability of the grid, I've considered adding battery backup to the solar. I did not realize that our solar would shut down when the grid went down, at first (after thinking about it, I totally understand why it would). So I've been considering ways to not only add battery backup, but something to keep the grid-tie solar turned on safely to run from during the day and charge batteries to be used at night in case of extended grid downtime.

First, I understand that the inverter setup I select has to:
1) support AC coupling to an existing grid-tie system
2) support frequency shifting to manage the Chilicon microinverters
3) support the max power output of the microinverters so as to not blow stuff up

So a couple inverters that I believe can do this, with some possible caveats:

1) Outback Radian GS8048A
The Outback only can support up to 6kW of grid-tie solar. To work with my setup, I would either need to have two of them, or use a GS4048A in parallel with the GS8048A to get me enough capacity. Alternatively, I think I could run one string of the Chilicon inverters (1 30A breaker) with the GS8048A running the critical loads panel, and put the other 30A breaker in the main box. During a grid outage, I'd be running approx half of the solar panels at ~4kW. Not ideal but I think it would work?

2) Victron Quattro 5000VA/48V
It appears from Victron's documentation that the Quattro also supports frequency shifting. I would need two of them to generate split phase, and this would cost roughly $1000 more than a single Outback Radian GS8048A. However, two Quattros would allow for use of all the solar panels I have.

For batteries, I was planning on 16x EVE230 Lifepo4 batteries using a JBD 16s 250A BMS. I could maybe do a second set at a later date to double my battery capacity, but I'm already looking at more money spent than I was originally thinking for this project. Maybe a different BMS would be better (I've seen some chatter about Seplos, for example), but this is my current plan.

Any opinions on which route is more recommended? Or, am I totally missing something and I'm on the wrong track entirely? Or, other ideas/input?
 
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Edited the post for some clarification.
Does anyone have some input? Maybe I am missing something obvious that was already discussed somewhere else, but I did spend a lot of time reading stuff trying to figure it out.
Maybe a different section would have been a better spot to post my question?
 
Outback along with Magnum and Schneider are the long time providers of hybrid inverters for AC coupled systems so they are all safe choices. Newer more integrated offerings like Sol-Ark appear to be easier for DIY installs. You may also want to check out what Generac has to offer since they acquired Chilicon.
 
I looked at Generac briefly (PWRcell I think they called it), but it seems they do the install (it is a high voltage battery pack) and they put it on the outside of the house which is total nuts due to temperature issues charging the batteries. There were a lot of complaints about the thing not charging due to being too cold outside.

I also did not like that I had to request a quote and all sorts of stuff just to get pricing from them. I found it listed elsewhere to get an idea and I found a place listing it at $15k for a 13kWh unit. Ouch!
 
Hey Sparky, you and I seem to be on running parallel paths. I'm in the Arkansas Ozarks and have an Enphase grid-tied system and am working in the same direction. The Enphase micro inverters need to see power with <5% total harmonic distortion before they allow operation, so I started there looking for an inverter/gen that meets the criteria and large enough to carry my house loads. I found the DuroMax 9000 and its thd is <3% so I think I'm good to go on that front. Then I need somewhere to store the excess power my 5kw grid system produces during daylight hours and so I'm also looking for just the right AIO to match up.
I'll be following your progress! :)
 
Any more input? I like the Outback (documentation seems clearer) but I like the Victron's price point to be able to use all the solar panels if I am correct in my assessment.

I should look at the Schneider more but I seem to recall some possible problem there when I looked at it earlier. Magnum is something I did not look at previously so I'll do that.
 
Seems Outback upgraded the Radian's specs? According to this on page 6
https://www.outbackpower.com/downloads/documents/appnotes/ac_coupling_radian.pdf

The Radian now supports 7.6kW of grid tie inverter power. Closer, but still 0.6kW away from my 8.3kW array.

The Skybox was brought up as an option.

I like the price point better. Less output available, but may be OK (I need to do a power survey here soon to find out). The documentation for AC coupling only says that if the array is more than 5kW it needs to support frequency-watt control, which the CP-720 inverters do. However, it says "5- 7.6kW) so I suspect my system is still going to be too big. Plus, I saw something on Outback's support forum from a couple years ago that said the Skybox wouldn't allow more than 5kW of export to the grid (If I'm pumping 8kW from the array, and only using 1kW at the time, I'd like to be able to pump the excess 7kW to the grid and get "paid" for it). I don't see that in Outback's AC coupling documentation anywhere though...
 
Did you happen to find what the 12kw Sol-Ark would support concerning a grid-tied system?
 
I did not think of Sol-Ark. I think it is 9.6kW. Hmm.... this sounds appealing.

I do see that it is a HF vs a LF inverter, and as such doesn't handle surge loads as well. Only bigger surge load I'd have is AC, if I was to hook it up. The other thing is it apparently doesn't like imbalance very well, so I might have to be careful with how I put the breakers in the box. I have no idea what kind of balance we have in this house right now.

It is also rather expensive, though not as bad as two GS8048A units are (but two of those would be insane overkill).

One thing I should remember- I have an 8.3 kW array but 11 of those CP-720s will max out at 7.9kW. 300 watts away from the GS8048A.... dang it. I know that is the absolute max that could be sustained, reality is likely a little less, but I suspect it would be too risky to say "close enough." Unless I could guarantee a minimum 300W load during the daylight. Hah, I know, put a solar eye on a circuit only activated when the grid goes down, that as long as the sun is up, the 300W heater is running! What could possibly go wrong...(uh oh my name is coming into play again)
 
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I have no idea what kind of balance we have in this house right now.
You could simply put a clamp-on amprobe or equivalent on the neutral ground conductor. That will show your total imbalance. Then you can start moving 120volt loads from the high current leg over to the other to bring it into some semblance of a balanced load. If your neutral ground ever gets to 0 amps your system is either perfectly balanced or de-energized. ;)
 
I'm was going to contact Outback to see what their recommendation would be with the 300W excess, then I saw they have a new Mojave inverter specifically for this type of usage that supports up to 8kW of grid tie inverters. At first glance it at least looks promising.
https://outbackpower.com/products/item/mojave-inverter

They have a full ESS for this but it is something like $15k for their full system including the 14kWh battery (usable 11kWh). Ouch. It does have a 10 year warranty which is nice but ouch... I'm hoping the inverter by itself is closer to the price of a Radian. Somewhere between the Radian and Skybox would be great but I'm not holding my breath.
 
I got an email from Outback - they are expecting the inverter only Mojave to be available sometime in the May-June timeframe, but they have no MSRP for it yet.
 
FYI, and I know this is not likely a solution you'll chase but might help others:

The Growatt SPF 6000T DVM supported a separate grid tie inverter for me for awhile for testing. The grid tie inverter did not have any zero export options, so I decided to see what the Growatt would do when power was pushed into its AC output.

It charged the batteries.

?

In fact, I had to be careful, because while it would shut off its own internal MPPT once the batteries were fully charged, it continues to charge the batteries with any extra power from the grid tied unit - even beyond the battery settings.

This is not mentioned in the manual, and I can only assume it's unsupported. The only response I got from SignatureSolar when I asked about it was that it's not supported, that battery damage could occur, but as long as the inverter was larger than the grid tie it should work with those caveats. This was when I asked if I could buy one of their surplus solar city Delta H6 inverters and grid tie it to the growatt - and I mention this because they said yes at the time - probably to encourage me to buy the grid tie inverter - but when I asked again later about grid tie support they indicated it would be considered mis-wired and any resulting damage would not be covered by the warranty.

So while it looks like you're building a system that follows all the specifications of each part, and thus this wouldn't be a fit for you, it may be useful to others who want the same thing for cheap and are willing to accept the risks for doing so.

It was neat watching the batteries charge from the grid-tie source, though. The off grid low frequency growatts really do act like a power company. I don't know about any other units from growatt, and since I've upgraded to the 12k version I haven't needed to connect the grid-tie inverter. The biggest drawback to the growatt off-grid units is their solar input is a fraction of their inverter output. So the 6kva unit could only handle 3.5kw - 4kw of solar input, and the 12kva unit can only handle 7kw of solar. The correct solution is adding another MPPT, but adding a grid-tie inverter increases total inverter capacity during the day. This is useful if you don't want to have a huge battery bank, and if your highest usage is during the day. The fact that it essentially performs the function of an MPPT to charge the batteries with excess power means a separate MPPT isn't needed.

As others have pointed out, balancing is annoying. They have a split phase transformer, however they measure the current on each leg and if either leg goes over 1/2 the total inverter output then it shuts down (with a 30 second delay if the imbalance isn't large). I've added a separate transformer which took care of a lot of that imbalance, but balancing the loads in the breaker box would be better.
 
I've been reading on HF vs LF inverters for this application. Seems the LF handle it better (and seem to generally have a better life expectancy anyway).

I've written off Sol-Ark for now, mainly because it is a high frequency inverter with load balancing concerns that is still really expensive. If it was cheaper it would maybe be worth dealing with the inherent shortfalls of HF, but for what they want for the thing I'm just not going to mess with it.

I asked Outback whether the upcoming Mojave inverter was HF or LF. They responded it was LF, which is great (and makes sense given it is 133 pounds. But on the note of their response, I've been impressed that both times I emailed them I had a response within a few hours. That gives them a leg up. I just hope the price is reasonable once that's established.
 
Hi everyone,

I've been lurking for a few weeks trying to read up on stuff. Now I'm looking for some expert advice on what I'm thinking of accomplishing.

First off, I'm located in Central Ohio. 11x Chilicon CP-720 microinverters connected to a 8.3kw array on the roof of the house facing south/southwest with no tree cover. Two lines come down from the roof, each to a 30A 2P breaker in a small subpanel, that then feeds the main panel through a 45A 2P breaker.

Given some geo-political nonsense that has been brewing for some time, and concern about long-term stability of the grid, I've considered adding battery backup to the solar. I did not realize that our solar would shut down when the grid went down, at first (after thinking about it, I totally understand why it would). So I've been considering ways to not only add battery backup, but something to keep the grid-tie solar turned on safely to run from during the day and charge batteries to be used at night in case of extended grid downtime.

First, I understand that the inverter setup I select has to:
1) support AC coupling to an existing grid-tie system
2) support frequency shifting to manage the Chilicon microinverters
3) support the max power output of the microinverters so as to not blow stuff up

So a couple inverters that I believe can do this, with some possible caveats:

1) Outback Radian GS8048A
The Outback only can support up to 6kW of grid-tie solar. To work with my setup, I would either need to have two of them, or use a GS4048A in parallel with the GS8048A to get me enough capacity. Alternatively, I think I could run one string of the Chilicon inverters (1 30A breaker) with the GS8048A running the critical loads panel, and put the other 30A breaker in the main box. During a grid outage, I'd be running approx half of the solar panels at ~4kW. Not ideal but I think it would work?

2) Victron Quattro 5000VA/48V
It appears from Victron's documentation that the Quattro also supports frequency shifting. I would need two of them to generate split phase, and this would cost roughly $1000 more than a single Outback Radian GS8048A. However, two Quattros would allow for use of all the solar panels I have.

For batteries, I was planning on 16x EVE230 Lifepo4 batteries using a JBD 16s 250A BMS. I could maybe do a second set at a later date to double my battery capacity, but I'm already looking at more money spent than I was originally thinking for this project. Maybe a different BMS would be better (I've seen some chatter about Seplos, for example), but this is my current plan.

Any opinions on which route is more recommended? Or, am I totally missing something and I'm on the wrong track entirely? Or, other ideas/input?
I'm desperately looking for information on my used cp720 inverters. I'm losing communication with the gate way, one of the inverters shows as s repeater, but I can't find any documentation on "repeater" setting or changing. Or even what it's for. Can you help?
 
I have no idea. Mine has been just fine aside woth issues remaining connected to wifi, but I'm pulling a cat5e cable to it at some point.
 
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