How to achieve off grid operations with existing SMA Inverters and new battery system

[corey66]

I have a dual SMA 7.7 + 3.8 with about 9.5Kwh operation NEM2 operation today. Using Tigo optimizers and Panasonic 330-335 WATTs Panels. 4 MPPTs. I have a full 200amp service/meter and 200amp load panel before my 100amp house feed. My desire is to buy a battery system, something like the Anker Solix X1 that would drive the load panel (minus ac and pool pump) and feed the house. I use around 1.6kwh normally.

I would like to keep both inverters, as the system works great. Plug in my battery feed that charges on solar peaks and dispense the energy after sunset for NEM3 operation. I would desire when the grid is cut I would manually switch over and let the X1 take control of the load panel but I also want to run one of my SMA inverters (3.8) with only 1-2 MPPT strings operational. (I would airgap the off-grid) I can do this by using specific CCAs on Tigo and Home automation scripts. I don't want to use SMA SPS as that feature is 15a with only one phase.

The SMA inverter must have carrier L2 240v in order to feed power back to off grid. The battery system would move to charge mode most likely, thus loosing the 240v carrier then SMA inverter goes offline. I was thinking maybe to have two battery systems one charge mode and one powering the grid as an option. This would be a closed system operation which get pricey. At that point of buying two battery systems I'm now into the hybird inverters and HV battery system and I would go the path of the new SMA SBSE.

The over-voltage and load issue I think would also arise if I produce too much energy, I would have to have a special device to unload the excess energy off the closed system as a varience operation with a great earth-ground. Not sure if the SMA would in parrallel supply power in a closed off grid battery system. Has anyone ever tackled something like this. Or am I just headed for disaster and nimheadedness.

 

[Hedges]

Several hybrids advertise AC coupling to GT PV, but tend to have issues and want a relay port used so that can be dropped. Works best with DC coupled PV greater than AC coupled.

2x Sunny Island is the best way to AC couple with your inverters. Works great for off-grid and grid-backup.
What it doesn't offer is features to live within NEM 3.0 (Solar Billing Plan). For that you want peak/valley shaving, and forced export during super-peak.

How long do you have on NEM 2.0? Buy Sunny Island (for $3900 delivered, get two in a DC Solar box) and compatible battery. AGM is fine for backup. To use LiFePO4 consider either compatible BMS or run open-loop with VRLA settings.

I'm contemplating SBSE for a relative. However, she has NEM 2.0 reservation, and compatible batteries cost 2x what server rack or PowerPro do.
Midnight The One + the coming Midnight battery is another option. But I may give her SB + SI, as I use.

 

[corey66]

Thanks, PTO was on June 2020. My true goals are to extend my power generation into storage for later sunset operation and temporary off grid when power is down. Surviving (1-5 days off-grid is also a awesome goal, but the operational threshold is harder to achieve as time increases). NEM2 > NEM3 change is only worth the investment if the battery system is sustainable (10yrs out) and can do the features and ROI.

I'll check out Sunny Island as if it can be automated then there may be a solution behind it.

 

[Hedges]

Stick with NEM2 for the remaining 16 years.
A 100% efficient "battery" of unlimited capacity that stores power for 12 months.
(Fixed fee for infrastructure is increasing, however.)

Some people are having success with PowerPro closed-loop on SI.
Other batteries are getting cheaper, may put price pressure on it.
DIY works with some BMS, REC is the premium one. I'm a bit nervous about parallel cells now, and 16s REC costs almost as much as 16s cells.
These days lithium costs less up-front than AGM or premium FLA.

I bought SunXtender AGM 4 years ago, and picked up used FullRiver AGM last year for cheap.

 

[zanydroid]

N.B. I see your location as Sacramento. We don't have many SMUD customers on this forum compared to PG&E/SCE/SDGE, so you will need to confirm POCO policy by somehow networking with other SMUD solar experts / enthusiasts.

I have a dual SMA 7.7 + 3.8 with about 9.5Kwh operation NEM2 operation today. Using Tigo optimizers and Panasonic 330-335 WATTs Panels. 4 MPPTs. I have a full 200amp service/meter and 200amp load panel before my 100amp house feed. My desire is to buy a battery system, something like the Anker Solix X1 that would drive the load panel (minus ac and pool pump) and feed the house. I use around 1.6kwh normally.

Your numbers/units are kind of confusing and expressed in a logically dissonant way.

9.5kWh is very low for this time of year in northern California. I did 45kWh today. Do you mean 9.5 kW peak?
1.6kWh is a very low daily load. 1.6kW is a somewhat normal average load with AC on.

Not a fan of Anker. There's no track record of permitting / interconnection agreement success on this forum. You will want to double check a few forums. Given how much of an embarrassment their cloud-based security cameras have been this year, I'd rather not rely on them for anything outside their core competency of USB power bricks and power banks.

What level of DIY are you going to do?

I would like to keep both inverters, as the system works great. Plug in my battery feed that charges on solar peaks and dispense the energy after sunset for NEM3 operation.

"NEM3 operation" doesn't make sense. You can go from NEM2 to NEM2+Storage as long as you don't add solar panels / expand kW-AC inverter capacity. Do you mean Time Of Use "arbitrage"?

NEM2 + zero export expansion is another thing that is allowed, that often has an advantage over battery wrt ROI if the problem being solved is significant underproduction compared to demand.

Picking between the different alternatives is all quite complicated because it is dependent on system size, curve of supply/demand mismatch across the year, etc. I haven't yet tried the ROI modeling software a few people recommended to me.

With the model I built for myself (underproduction but no space to expand with more solar, so cannot use zero export expansion), MidNite ONE and 18kpv have ROI of 7 years. I would be switching to PG&E superpeak plan and doing forced export during superpeak ($0.60/kWh), and all consumption via import at offpeak ($0.25/kWh) or self consumption.

Sadly, I'm disappointed that my spreadsheet model looks really promising and is conning me into spending more time on this. Rather than fast failing so I can move on to non-Solar hobbies. LOL. Also, the spreadsheet model assumes a lot more annual EV mileage than I drive today. I don't have a second spreadsheet checking different scenarios by which those EV miles come (IE, road trip miles are ineligible b/c they aren't charged at home). So if the demand model is busted, then the ROI model will be super busted too, and I'm looking at 12 year break-even instead of 7 year.

I would desire when the grid is cut I would manually switch over and let the X1 take control of the load panel but I also want to run one of my SMA inverters (3.8) with only 1-2 MPPT strings operational. (I would airgap the off-grid) I can do this by using specific CCAs on Tigo and Home automation scripts. I don't want to use SMA SPS as that feature is 15a with only one phase.

Why do you want to turn the strings on and off? Even if you can't capture the output in batteries because of control loop bugs or difficulties, you might as well blast it out to the grid and get a credit.

The SMA inverter must have carrier L2 240v in order to feed power back to off grid. The battery system would move to charge mode most likely, thus loosing the 240v carrier then SMA inverter goes offline. I was thinking maybe to have two battery systems one charge mode and one powering the grid as an option. This would be a closed system operation which get pricey. At that point of buying two battery systems I'm now into the hybird inverters and HV battery system and I would go the path of the new SMA SBSE.

The over-voltage and load issue I think would also arise if I produce too much energy, I would have to have a special device to unload the excess energy off the closed system as a varience operation with a great earth-ground. Not sure if the SMA would in parrallel supply power in a closed off grid battery system. Has anyone ever tackled something like this. Or am I just headed for disaster and nimheadedness.

It sounds like you have some really interesting home grown automations in mind. However, based on the tier of equipment you're willing to buy, there's probably much easier ways to achieve this.

I would recommend looking at 18kpv / SolArk 15K / MidNite One's price points and scheduling featureset. 18kpv is $4900 for 12kW inverter and $3000-3500 per 14 kWh of batteries. I don't remember how many MPPTs since my existing is microinverters. It is probably most efficient to move as much as possible onto the MPPT of the AIO because of the more efficient conversion path into the battery, and the simpler control loop.

EDIT: MidNite ONE's price point for batteries is coming out something in July or August. The MidNite and CurrentConnected owners have been teasing that it'll be good

 

[zanydroid]

So generally speaking, I don't think storage to do TOU arbitrage has good ROI in California. The$/kWh spread between day/night is not good enough for that. Now, places like Texas with free nights, sure (but then you are exposed to the risk of the plan going away, so you realistically want like a 5 year break even if you believe that the macro fundamentals allowing free nights to be viable are only guaranteed for 3 years).

Forced export is better because it expands the size of the pie. BUT you need to have the ability to consume the extra credits (whether from increasing your demand, or from being on a POCO that will give you meaningful cash credits out. There's a minority of Community Choice Aggregators that do this)

NEM3 has a better ROI than TOU arbitrage because you get a much lower effective rate by virtue of self-consuming solar.

 

[Hedges]

NEM3 you'll want to use battery rather than export, since the spread is about $0.05 to $0.40 or $0.60 per kWh.

And you'll want to do forced export to grid between 7:00 and 9:00 PM in September, because credit will be $3.50 +/- per kWh. That'll pay for a lot of imports other months.

But that's for people on NEM 3.0, stick with NEM 2.0

 

[zanydroid]

NEM2 storage and zero export expansion also calculates import and export in very wide buckets of time. NEM3 is order of minutes. So you are forced to have a battery to self consume to get value even for export/import within the same day

 

[zanydroid]

(Expressing the project goal as TOU shifting and off grid operations under NEM2 makes me worry a lot about reasonable ROI. I hope that is fine to allow project to go, or I misunderstood)

 

[kommando]

I run two Sunny Islands in closed loop with DIY batteries using the JK PB BMS, all my inverters are set to respond to the SI frequency shift and so curtail production when the batteries are full and the house load is satisfied. However I also monitor the frequency and use Node-red to switch on and off Wemo wifi switches and Shelly switches to add and drop loads so the curtailment frequency is never reached. I use this to heat up a 210L hot water tank, clothes drying racks, dehumidifiers etc