diy solar

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Sunny Boy AC Coupling Q&A/options

Good if you can get by cheap.

Maybe a UPS, or a 12V battery and solar charger, to keep communication gear running during an outage.

If you browse eBay and other sources, maybe you can pick up a Sunny Island new or used cheaper. Add a transformer and it can take the place of a 120/240V backup generator to power your panel. It can keep an AGM battery floating while grid is up. When grid goes down, turn off the breaker feeding Sunny Island (so it doesn't power itself), flip the interlocked generator breaker, and the house is up on Sunny Island with Sunny Boy supplying PV. I think Sunny Boy set to Rule-21 frequency-watts instead of UL-1741 (if not already) will make it play nice. Might cost $5k depending on the Sunny Island price which could be $3000. About $1200 for 100 Ah 48V AGM, cheap used transformer.
 
I have a system based on a pair of SI 6048 (set of DC solar parts), with both AC (enphase micros) & DC (midnite 250) coupled arrays, supplying the whole house primarily off-grid now (new off-grid panels, SI AC1). I have an older grid-tied array (enphase micros), still connected to the house original panels (now the grid panels, SI AC2). I made an automatic transfer switch with contactors to move the GT array between the grid, and to the AC1 house panel. The SIs are set to not export, only connect to grid AC2 if extra power is needed off-peak (winter). I'm on time of use rate, so the solar and SI battery can avoid taking any power from grid on-peak. A RPi is the control, it is based on IOTstack and various items of python or C code. Mostly straight from github, piece by piece, with relatively minor changes, and a bunch of fiddling with nodered / influx / grafana to do control and monitoring.

The older Enphase micros that I have work fine in AC coupling, they trip off when SI raises the AC1 freq. I set the grid profiles different on the two AC coupled arrays so the off-grid trips out first, (60.5Hz default), the GT one a little later (61.3Hz) so it keep generating if possible. The GT has a generation meter which gets me a credit per kwhr just for generating power, even if I self-consume it in the house (it's renewable energy on their system).

I would recommend the newer Enphase micros because I understand they have power vs. frequency feature, ramping gracefully, instead of tripping on off. Or SMA SunnyBoy or any other inverters that offer a power vs. frequency limiting control. But, my 2010 era micros and their warranty replacements based on newer enphase micros, programmed with just the simple trip threshold, they work fine.

AC coupled is the way to go overall. For large loads when the sun is out, power gets converted only one time from the panels straight to your AC loads (air conditioning, EV charging), or it can go out to grid as-is. Much simpler to be code compliant, no special concerns about AFCI, GFCI, rapid shutdown if it's on your house, the GT inverters will cover those requirements.

If you don't care about losing excess solar production it works fine just with a bang off gt solar inverter (enphase micros or any UL compliant GT inverter). If you care, then some other controls to turn on load-dump loads when there starts to be excess is possible with a little control. My RPi watches the SI AC1 freq (it's a CAN signal in leadacid mode at very fast rate), and battery current & voltage vs the target voltage (rs485 signals I get at 5 sec rate), and turns on extra loads in the house when appropriate, with wifi relays and smartplugs. The GT array transfer switch is controlled similarly.

transfer switch pictures https://photos.app.goo.gl/UcDfekbC1J3qAJ6J9
system pictures, last picture is a simplified layout diagram https://photos.app.goo.gl/q1euFhioH266nPvW9
great info in the diagram. Thanks for posting it
 
Inverter wants nominally 400V (It accepts a wide voltage range, but limited current, so down around 100V could not produce enough watts.)
Perhaps enough batteries in series for 400V would be more watt hours (and dollars) than desired for this product, due to large cells. Perhaps multiple "D" size lithium batteries in parallel allows a cheaper BMS with less electronics. Using a boost converter also serves to limit short-circuit current (SBS says 40A max).

Really a boost converter and buck converter. Probably a circuit that does both, boost from 48V (96V? 144V?) battery bank to 400V output, buck from 400V "output" down to battery.

Somebody on the forum posted inside photos of an LG RESU-H battery.

High voltage batteries are used for larger inverters, like 60 kW to 4 MW 3-phase ones SMA sells in the US and elsewhere.
They are used for SBS, Tesla Powerwall, other consumer products here (sometimes with boost converter.)

But 48V batteries are what many systems use. They are available in server rack form factor, and people DIY using various BMS that are available. "16s" for LiFePO4 is 48V, and BMS are available down to 4s "12V" and up to 128s (well over 400V). But you ought to have communication compatible with the inverter, so BMS has to match it.

Sunny Island, Schneider, other inverters use 48V batteries and do AC coupling with GT PV inverters. Usually works well, but some reports of difficulty when battery inverter is "high frequency" vs. transformer-type low frequency. And more difficulty with microinverters (e.g Enphase coupled to SolArk)
 
Inverter wants nominally 400V (It accepts a wide voltage range, but limited current, so down around 100V could not produce enough watts.)
Perhaps enough batteries in series for 400V would be more watt hours (and dollars) than desired for this product, due to large cells. Perhaps multiple "D" size lithium batteries in parallel allows a cheaper BMS with less electronics. Using a boost converter also serves to limit short-circuit current (SBS says 40A max).

Really a boost converter and buck converter. Probably a circuit that does both, boost from 48V (96V? 144V?) battery bank to 400V output, buck from 400V "output" down to battery.

Somebody on the forum posted inside photos of an LG RESU-H battery.

High voltage batteries are used for larger inverters, like 60 kW to 4 MW 3-phase ones SMA sells in the US and elsewhere.
They are used for SBS, Tesla Powerwall, other consumer products here (sometimes with boost converter.)

But 48V batteries are what many systems use. They are available in server rack form factor, and people DIY using various BMS that are available. "16s" for LiFePO4 is 48V, and BMS are available down to 4s "12V" and up to 128s (well over 400V). But you ought to have communication compatible with the inverter, so BMS has to match it.

Sunny Island, Schneider, other inverters use 48V batteries and do AC coupling with GT PV inverters. Usually works well, but some reports of difficulty when battery inverter is "high frequency" vs. transformer-type low frequency. And more difficulty with microinverters (e.g Enphase coupled to SolArk)
I have opened it up and examined. They are heavy and stack up upon each other like Lego. There are contacts that appear like thick conical nickle plated copper and they also have a relatively smaller size electrical connections that fit together when dropped. It does make sense on what you say. This allows them to keep with run of the mill 48V energy units each with its own BMS and then have a control circuitry that slaves these BMS, and communicated with SMA Storage. There may be a boost converter below this circuit board because it has to have some heavy duty copper input (for 48V) and reasonable duty 400V connections. Its showing this data from my router when switched on.
 

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Screenshot looking at hardware you have?
Please create a thread maybe under Show and Tell, and post a link to it here!
I'd like to see what system you've got, and what it can do.

 
I'm especially interested in the frequency-watts response of SBS.
It supports Rule 21, ramping down output as frequency increases.

I would like to use it with Sunny Island. When grid is down, I want SBS to ramp down output as frequency increases. Then ramp up charging, reaching its maximum at a frequency lower than where Sunny Boy starts to ramp down PV power conversion.

My idea is to keep a modest AGM battery bank on Sunny Island, and have Sunny Boy Storage with lithium battery charge/discharge to AGM remains at float and surplus PV gets stored. I would want to make an economical high voltage (or boost/buck) battery. Possibly using REC; don't know if it talks to SBS as it can talk to SI.

I would keep lithium batteries away from the house. Either in an "ammo dump" at a safe distance, or possibly in the trunk of a vehicle.
 
Starting surge available is 9000VA, and 6000VA added load. (SB won't respond for a couple seconds). But SB could be powering a 5000W load when SBS starts a motor, then requests all 7700W from SB.

You need to figure out if SBS can start your motor loads. Multiply nameplate Voltage x Current x 5 to get estimate of starting surge.
If SBS is inadequate then 2x SI-6048US would be better. But about $5000 more than SBS + ABU (unless some liquidation sale new-in-box SI still available.)
Something to look at is the Micro Air Easy Start. My SI's had trouble starting the air conditioning with the 93A startup current. They did it, but under protest. The Easy Start reduced the startup amps from 93 A to 40A. Runs at about 20A. Now the SI's can handle most anything, even a 5 ton A/C.

The SBS system should backfeed grid and operate off-grid.
If you want to make it zero-export, probably some additional hardware or networking. I just read a data sheet that said SBS can control up to 3 SB via internet connection to Sunny Portal. But I would want it all local; I think Home Manager or something similar is supposed to support that. Not sure, seemed to be a European market document I was reading.

For me, if net metering is turned into a bad deal (zero net credit for export + $0.05/kW charge for all power I produce and make locally), then terminating net-metering and converting to zero export appears possible setting SI for "GridCharge" instead of "Grid". That would disconnect from grid by relay when SB production exceeds consumption. I would rather keep relay closed and adjust SB output without switching to island so frequency-shift can be done. US model SI doesn't have function storing/supplying with battery while on-grid, except it will supply to limit max current drawn from grid.
Wondering how the SB Storage works at night? I guess it is connected to the SMA energy meter so battery output equals loads w/o sending ay extra to the grid?

How can you operate SI's connected to the grid with zero export? You need some sort of current meter on the utility side of to determine 0 amps in or out? Not sure how it works. Or maybe since AC1 and AC2 are separated the SI handles the loads and ramps the frequency up or down to match the loads on AC1 while at the same time not sending anything out to the grid via that AC2?
 
That would be zero export measured at AC2 connection of SI, not zero export at the meter.
I can flip breakers to run 100% of loads through SI, making this possible.
I would rather have CT at the meter, export from SI to the house and have zero or limited export to grid.

Because it is not an on-line UPS, SI can't ramp frequency on AC1 while simultaneously receiving (or sending) power on AC2. Only by opening relays to disconnect (use grid as generator) could I achieve zero export. It may then decide to cycle my batteries, which I would prefer to float.

So, I contemplate feeding a spare SB with rectified grid AC. That would be grid AC coupled to island, and curtailed at a lower frequency than where PV is curtailed.

As for SBS, it probably relies on other gizmos to measure and communicate so it can perform functions like charging exclusively from PV (not grid), and inverting to peak shave or avoid all consumption during peak rates.
 
Right. Since AC1 and AC2 are separated with relays, the SI can open or close them as necessary. The SI can leave AC2 open and controll the Sunny Boys with frequency shifting on the AC1 side. If it see a big load, it can connect AC@ and get extra power from the utility. It gets a bit complicated in wiring. We have it wired for manual switchover if and when the utility power goes out. Wiring to reduce or eliminated export is a bit more complicated and requires different wiring set up for us.
 
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