AC-Coupled (OffGrid) Advice Requested

[TymerTopCat]

I am in the process of building an Off-Grid Solar System, Utilities are too far away, and will never be connected:
*2 Sunny Island 6048 (120/240)
*1 7kW SunnyBoy Inverter
*24 310 Watt Solar Panels
* Minimal Battery Bank (Enough for 1 night)
* Auto Start Generator

Please, those will experience please correct any of my statements. I like AC-Coupling because it allows the use of daily excess power to run various high loads: 240 volt Planer/Jointer/Air Compressor/Water Pump/Dryer. As long as the sun is shining I should easily be able to use all of the higher loads mentioned *one* at a time. This is nice because none of those high loads would be forced through the battery (no recharging batteries) because the power came from the AC Excess Power. Am I correct here? Does anyone see any problems that I might be missing?

My questions are about when:
1. The batteries are fully charged.
2. Full sunshine (say 5000 watts of power are available but currently limited because of #1).
3. Now turn on a high load: Say I kick on a 240 volt planer (5Hp)?
What happens? Can the Sunny Island respond fast enough to deliver power to my Planer via the solar Panels?

Finally my Questions:
Q1: How well does the (FSPC) Frequency-Shift Power Control work? How fast can the Sunny Island increase or decrease Inverter output when a cloud blocks sunshine and then clears up again? Is it seconds? Minutes? See (17.5 below).
Q2: I have two different older Sunny Boy Inverters. SB7000TLUS-12 (Circa 2007) and a SB7000TLUS-22 (Newer Model). Will the Sunny Island work properly (FSPC) with one or both of these older inverters?
Q3: Is there another way to do this (AC Coupling only)? The Sunny Islands are a bit on the expensive side (new). I am aware of the used DC Solar inventory (mostly gone by now).

(From 17.5 Sunny Island Manual)
If Sunny Boy inverters are connected to the AC side of the off-grid system, the Sunny Island must be
able to limit their output power. This situation can occur when, e.g. the Sunny Island battery is fully
charged and the (solar) power available from the PV array exceeds the power required by the
connected loads.
To prevent the excess energy from overcharging the battery, the Sunny Island 4548-US / 6048-US
recognizes this situation and changes the frequency at the AC output. This frequency adjustment is
analyzed by the Sunny Boy. As soon as the power frequency increases

Tks.

 

[toms]

1 - DC or AC coupled the excess power will run your loads. The advantage of AC coupled is higher PV voltages = simpler PV wiring.

2 - Either of the generations of the SunnyBoy will work with the Sunny Island. If they are used you will need to buy a grid guard code.

The FSPC works seamlessly with SMA equipment.

 

[westvandude]

You can only add 6700w of inverters behind each 6048. If you have two basically that's two 6kw inverters ac-coupled. The 56A transfer relay inside the sunny island limits this.
I don't know the answer but interfacing older inverters may be easier as they probably have rs485 communication vs the new speedware which doesn't work with 6048. I have new series 41 6kw and 7kw and I'm told to place the 6kw's in offgrid mode behind 6048's in that case the 6048 varies grid frequency to modulate ac-coupled sunny boy power output.

The newer -41 series have output power limits you can set so if your older 7kw's have a max output power adjustment you could just set that to 6.7kw or slightly less so you don't overload that 6048 relay. Or go with less panels. Limiting output power would give you more kwh daily vs less panels.

 

[GVSolar]

My sense is that member @Hedges knows a great deal about Sunny Island/Boy features and issues...

 

[Hedges]

Here I am! (but I only stumbled on the thread, didn't seem to get alerted.)

That 6700W of PV per 6048 is only if your system is going to backfeed the grid. If stand-alone or with a generator, no backfeed occurs so the only limitation is 56A coming from generator.
You can have about 12 kW of PV per Sunny Island, according to SMA documentation. I haven't pushed it far enough to verify that myself.

The TLUS-12 series inverters do work with Sunny Island when in "Island" a.k.a. Op.BckOpMod "OnAllPhs"
(It didn't support "grid-backup" properly and updated compatibility list reflects that.)

https://files.sma.de/downloads/SB-OffGrid-TI-US-en-22.pdf

This says that TLUS-22 works for grid-backup, but NOT for offgrid?? (as of 2016). That doesn't make sense, see if you can find out why, and since you have it might as well as try.

Installer password is free, just assure them of your competence.
"PUK" personal unlocking key for lost password supposedly costs a fee, but I was given a pair for two inverters at no cost.

Frequency shift takes a few seconds. Sunny Island instantly delivers power to start loads. With 11 kW for 3 seconds, a pair would deliver 22 kW, should be enough to start a motor up to 4kW running.

SMA says to have at least 100 Ah (of 48V) battery per 1 kW of PV, but I have about 1/3 or 1/4 as much battery. The issue is load dump, if a heavy load being carried by PV is suddenly switched off, Sunny Island needs to suck down that power for a couple seconds until it as swung frequency far enough to curtail.

After Sunny Island quick configuration, go in and adjust voltage settings for battery charge phases (assuming lead-acid) to match battery technical manual.
Adjust maximum charge current to match technical manual. Default is a current calculated based on 0.55C, which is excessive. If you had 100Ah per 1kW, it would be reasonable. I set mine to a current for about 0.2C.

You could have much more, almost 4x Sunny Boy.
I suggest getting more PV panels, orienting some toward morning sun, some toward afternoon. That way, power production is leveled throughout the day less cycling of battery.

AC coupling with Sunny Island lets you have excessive PV and undersized battery, while charging at a fixed optimum rate. You could have 100 Ah (if sufficient for power tool starting current) and 12kW of PV, about 2C, but regulate charging at 0.2C

Simple DC coupled systems would charge battery at excessive rate. Some, like Victron, use a shunt to measure battery current so can charge at correct rate. In that case, the current goes from PV to 48Vdc to 120/240Vac without charging/discharging battery.

To use the system well, try to enable/disable loads according to when surplus power is available. Well pump, water heating, A/C can be controlled to better match production.

I'm seeing Sunny Islands on eBay around $2000 to $2500.
The DC Solar trailers if not overpriced could be a good start, if 100 kWh of forklift battery appeals to you, and if if the trailer is useful.