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SMA Sunny Island grid charging settings questions

daklein

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May 8, 2020
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Hello, for background, I have a system made from a DC Solar trailer, and some extras:
A pair of SMA SI6048US Sunny Islands, with 1080Ah lead in a box & vented, 1kw PV on a Midnite Classic 250 straight to battery, and about 3.5kw AC coupled with Enphase m210s behind the SI's AC1 port. A lot of pictures if you're interested: System pictures
The whole house is also behind the AC1 port, having moved 95% of the house circuits into 2 new loads panels. Those panels can be switched manually with a pair of interlocked breakers between the 'island' and the big bad grid.
The original main panel is still on the grid, along with the house AC, attic fan, a 4.7kw Enphase grid tied system still net-metered for a few more months, and a feed to the SIs AC2 port. The net-metered system makes enough off-peak (before 11am and weekends), that there is banked power available off-peak. I'm saving up the on-peak bank energy which I'll use another way later.

I'm trying to baby the lead acid battery, keeping it above 80%. I plan to add soon a Leaf battery with additional charger / inverter setup, and let that handle the average daily loads, and let the SMA & lead handle the surges.

I switched to a time of use rate, and generally the off-grid system keeps up with the house summer usage. Cloudy days it meets the day load, but doesn't get back up enough to run all night. If the SOC gets low, during the off-peak time period, it will connect on AC2 and charge & run house loads. On peak SOC reconnect thresholds are set a little lower, so generally it won't do it during on-peak.

I have the SIs set up about how I want, but have two additional desires, currently I go punch in different settings to make it do what I want occasionally. Then I forget to undo it later.

Desire #1. I havent' found a manual workaround for this: The electric dryer is not used often and generally only off-peak, but it's higher power, so I use the power based grid reconnect settings, 233.07 (set around 3-4kw), 233.08 (set around .5 to 1.5kw) so it will avoid discharging for a whole laundry load, just to recharge again afterwards. It seems to take maybe 5 minutes to recognize the extra load and connect. Is there a way to make it respond sooner, without setting the .07 value so low that other loads in the house can make it connect. And when the dryer element cycles off, to not disconnect right away.

Desire #2. After cloudy days, I'd like to connect to grid for low SOC, but have a low battery charging limit, so it doesn't just charge up and discharge again the rest of the night. I set it to 10a 222.01 battery max charge current, the lowest available setting. That makes it so it takes a few hours at least to go from my min 81% to 84% SOC, meanwhile also running all the house loads from the grid. First thing in the morning, I need to open that limit back up to the normal value I have of 95a, otherwise, the SI will raise the frequency and shut off all the AC coupled solar. The DC coupled still goes into the battery though. I tried using the inverter limit 210.02, but this limits the AC coupled charging power also. I think I also tried using the Grid current limit also, 232.03, but then this makes the SIs pull from the battery if loads are high even if connected to grid (see desire #1).

I think I may need to come up with some system controller that will change settings in the SIs over CAN. I also will be wanting to control some loads in a greedy solar manner, EV charger, heatpump water heater. Anyone do that sort of thing yet? YASDI, and figuring out the CAN messages I think. And figuring out the RS485 or CAN communication with the SIs.

Thanks in advance for any ideas or inputs!
 
#1 - it takes 5 minutes monitoring grid, when grid returns after a failure, before connecting. Maybe they use the same delay for this function, rather than continuously monitoring to connect on a moment's notice.

Wonder what it does with a generator - if you told it had a generator available rather than grid, would it "start" the generator (grid) and connect sooner?

How about just wiring dryer straight to grid, not through SI?

Looks like "AutoLodExt" connects/disconnects a load based on having grid/generator available (and something else), but you want the reverse, control of grid connection.

#2 - my suggestion to take dryer off SI would mean 10A AC charge might be OK.
You could program one of the relays to a particular limit and have that connect/disconnect AC by a relay.
For instance, I use the default 70% DoD for load-shed, and that reconnects at 50% DoD. You can set a higher value for another limit, not sure if you can tighten the spread.

Looks like 10% spread:

1. Select the parameter "242.01 Lod1SocTm1Str" and set it to the lower SOC threshold.
2. Select the parameter "242.02 Lod1SocTm1Stp" and set it to the upper SOC threshold. The
upper SOC threshold must be at least 10 percentage points above the lower SOC threshold.
 
Thanks Hedges,

#1 Yeah, having the dryer on the grid panel is an option too. I moved it to the island side for the following reason: In the future, when we lose netmetering, the grid-tied 4.7kw system will want to be used in the house on weekend or off peak, and the dryer is one good consumer. Off-peak value is minimal. So for that I'll want both on the island side. During on-peak, any excess from the grid-tied, that I can't use in the house, it's ok to send out for, the on-peak value is not as good as net-metered, but something at least. What I might do is have a 30A transfer switch on a 7 day timer, moving the grid-tie output from the grid panel, onto the island house panel during off-peak.

Somewhere here today I read 3 min is the time the SI uses for over / under power grid start/stop. I haven't timed it exactly. Just seems like a long time, standing there watching over 100a discharging.

#2 The main issue with 10A AC charge limit is that it also limits AC coupled charging. When charging, I get up to 20A from the midnite which the SI can't stop, but the SIs then raise frequency and kill all output from the AC coupled microinverters. Really what I'd want is a charging limit from the grid when the relay is closed, without limiting any AC coupled charging through AC1 when the relay is open.

Load shedding relay function: yeah, maybe something could be done with that. Definitely I could use that to enable extra energy consumption when solar is available (thus the SOC has gotten back up), like running the heatpump water heater and EV charger. Once those loads are enabled, I still need to make those loads variable so they just match the available solar, not take the battery back down as clouds go past.
 
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