Avoid open neutrals!

[Hedges]

You may have difficulty replacing the battery in the middle of the apocalypse, so would be good to save its cycle life for then.
Consider chart on last page of this manual:

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

At 50% DoD, 1000 cycles. In three years it will be worn out if you let it cycle to that point every night.
Compare to 10 year float life.

I use these batteries (8x L16 size 6V 405 Ah) in a grid-backup system. Batteries are kept at float so long as grid is up. Grid down, GT PV responds to frequency shift, supplying power needed for loads and to keep battery at float or recharge if needed. Batteries only cycle if PV insufficient for loads, and at night.

I don't anticipate needing 650 cycles to 70% DoD out of them before they reach old age. If usage pattern did change I would try to cut off more loads at night, limit to 15% DoD for 3650 cycles. 4x inverter idle consumption of 100W over 12 hours would be 6% DoD, might be able to cut that to 3% with 3 out of 4 sleeping and an auto-transformer to create missing phase.

 

[Sanwizard]

Was switching neutral necessary? Advisable? Do you bond neutral to ground locally?

It gets switched in mobile applications, along with neutral/ground bond being made locally, when shore power is disconnected. Or, could be shore power failed but still connected, can't tell the difference, so want to separate from neutral's (presumably ground bonded) shore power when bonding locally.

For my fixed application, I have neutral and ground always coming from main panel, only switch L1 & L2.

Hedges, how are the Sunny Islands working out for you? I am reading the manual for the 6.0H and 8.0H, and have some concerns. The 6.0 is actually only 4.6KW continuous, and the 8.0 is 6KW. It looks like unlike MPP inverters, and more like Victron, they need a seperate MPPT charger, comms, etc. Is it worth the additional costs and complexity for the 30 min of surge current?

 

[Hedges]

Key difference with SI it is only has to power some of the loads, some of the time.

The Sunny Islands are working fine.

I've managed to trip them up a couple of times. One time doing my mad scientist stuff in the lab, I created a bonded fault and tripped several breakers (but not any feeding SI). One of the SI though there was a fault possibly involving its grid relay and shut off. Restarted with a button push.

Something tripped a thermal-magnetic breaker feeding two SI, and one SI had a fault requiring power cycle. The tripping may have been an aged breaker and high PV backfeed. I see Midnight uses 60A magnetic-hydraulic on input and output of SI. Considering them, and $45 for 2-pole. Other brands go to 63A, possibly 70A, but price and lead time aren't very good.

I would like a fail-safe automatic transfer switch, so house and refrigerators are restored to grid power if SI goes down. This could be a relay (if large enough spacing to be reliable transfer switch), or a knife switch, spring loaded but held in one direction by a solenoid. The failures that have occurred, absent my messing around, were due to high continuous loads through breakers. Wouldn't want that to happen while away for a long time.

The European 8.0H may have new software features good for peak shaving and shifting time of use. In the US, Sunny Boy Storage is marketed for that.

MPPT charger? Only if you want DC coupled, which SMA doesn't seem to support much (maybe more so in Europe.)

With Sunny Boys AC coupled, during the day SI delivers starting surge of 11 kW each for 3 seconds, and ramps up output of PV inverters to take the load. Presumably for loads like A/C, you will have enough PV to supply 100% plus charge batteries, so SI doesn't carry load most of the time. An application with night time loads from battery, of course it does carry them.

With the newer model Sunny Boys having Rule 21 or other frequency-watts, the only comms needed either off-grid or grid-backup is an RJ45 cable between SI (no daughter boards required.) I'm using older models, with RS-485 telling them when to switch from UL-1741 to frequency watts and wider limits.

One other piece of "comms" is a twisted pair to load-shed relay. This lets SI disconnect all loads while keeping SB connected, in case battery gets low.

The European 8.0H I think supports an external 200A grid connect relay, thought I saw that at one point. I think it also has the smaller 56A internal relay.
SI fits 220V market better. Single 6kW SI works with two SB totaling up to 12kW, whether off-grid or backfeeding grid (220V x 56A)
And then you can parallel up to four of those for single-phase (probably some issues with balancing bypass current as I have, unless a 200A relay is part of it.) You can also use three for 230/400Y.

I would still have done Sunny Island if I didn't get bargains, but wouldn't have quite so many of them. Maybe just two for 120/240V split phase, Some Sunny Boys always on them, some manually switched from direct on grid to on SI (due to lower pass-through wattage at 120V.)

 

[Sanwizard]

Key difference with SI it is only has to power some of the loads, some of the time.

The Sunny Islands are working fine.

I've managed to trip them up a couple of times. One time doing my mad scientist stuff in the lab, I created a bonded fault and tripped several breakers (but not any feeding SI). One of the SI though there was a fault possibly involving its grid relay and shut off. Restarted with a button push.

Something tripped a thermal-magnetic breaker feeding two SI, and one SI had a fault requiring power cycle. The tripping may have been an aged breaker and high PV backfeed. I see Midnight uses 60A magnetic-hydraulic on input and output of SI. Considering them, and $45 for 2-pole. Other brands go to 63A, possibly 70A, but price and lead time aren't very good.

I would like a fail-safe automatic transfer switch, so house and refrigerators are restored to grid power if SI goes down. This could be a relay (if large enough spacing to be reliable transfer switch), or a knife switch, spring loaded but held in one direction by a solenoid. The failures that have occurred, absent my messing around, were due to high continuous loads through breakers. Wouldn't want that to happen while away for a long time.

The European 8.0H may have new software features good for peak shaving and shifting time of use. In the US, Sunny Boy Storage is marketed for that.

MPPT charger? Only if you want DC coupled, which SMA doesn't seem to support much (maybe more so in Europe.)

With Sunny Boys AC coupled, during the day SI delivers starting surge of 11 kW each for 3 seconds, and ramps up output of PV inverters to take the load. Presumably for loads like A/C, you will have enough PV to supply 100% plus charge batteries, so SI doesn't carry load most of the time. An application with night time loads from battery, of course it does carry them.

With the newer model Sunny Boys having Rule 21 or other frequency-watts, the only comms needed either off-grid or grid-backup is an RJ45 cable between SI (no daughter boards required.) I'm using older models, with RS-485 telling them when to switch from UL-1741 to frequency watts and wider limits.

One other piece of "comms" is a twisted pair to load-shed relay. This lets SI disconnect all loads while keeping SB connected, in case battery gets low.

The European 8.0H I think supports an external 200A grid connect relay, thought I saw that at one point. I think it also has the smaller 56A internal relay.
SI fits 220V market better. Single 6kW SI works with two SB totaling up to 12kW, whether off-grid or backfeeding grid (220V x 56A)
And then you can parallel up to four of those for single-phase (probably some issues with balancing bypass current as I have, unless a 200A relay is part of it.) You can also use three for 230/400Y.

I would still have done Sunny Island if I didn't get bargains, but wouldn't have quite so many of them. Maybe just two for 120/240V split phase, Some Sunny Boys always on them, some manually switched from direct on grid to on SI (due to lower pass-through wattage at 120V.)

Thanks for the update buddy. Much appreciated, and much to think about and digest.

 

[svsagres]

Weird - an open neutral should have just resulted in an open circuit, which should have just made it not function. Not sure how you'd have 240V.

It all depends on what's connected to the same neutral from the other leg. If it's a relatively heavy load (say a heating element, you're going to wind up with close to 240v between neutral and phase.