Sunny Island Sunny Boy AC Coupling Grid Tie System

[Hedges]

What do you mean by "rotating machinery"?

A generator, which spins at somewhat higher RPM under no load.

SMA in describing use of generators feeding Sunny Island indicate that with such behavior, as generator gets loaded down Sunny Boy would start producing full power, and unloaded Sunny Boy respond to increased frequency by ceasing to deliver power.

While battery needs a charge, Sunny Island would suck down whatever Sunny Boy produces and more if needed from generator. If it detects Sunny Boy backfeeding into generator (because producing more power than needed), it would disconnect from generator (or grid, if told not to backfeed.)

Maybe you could get away with just a rotating generator. Need to avoid backfeed.

It would be enough to use a relay to disconnect the solar panels from the heating rods, right? The problem is, I can't find a suitable DC relay for the 5 kW I need per heating element, e.g. 200-250 volts at 20 amps.

Yes, just need to connect/disconnect. Probably existing thermostat and overtemperature switch could handle pilot duty.

Somewhere on the forum there is a posting for an electronic controller which drives water heater with PWM. This can accomplish MPPT without needing inductors.


If you have 12 kW of PV and 3 Sunny Boys, that could be handled off-grid by one Sunny Island and an auto-transformer. I would set up the PV array 6 kW SE and 6 kW SW orientation, maybe 4 strings, with one SE and one SW string feeding of two each Sunny Boys. Wouldn't need the 3rd one.

That would give a full system, and use a SoC based control relay to switch AC to your water heater as a dump load.

 

[timselectric]

The problem is, I can't find a suitable DC relay for the 5 kW I need per heating element, e.g. 200-250 volts at 20 amps.

CEV40C 750VDC photovoltaic power supply high voltage contactor DC12V/24V relay | eBay

At our warehouse.

www.ebay.com

 

[OSchubert]

Somewhere on the forum there is a posting for an electronic controller which drives water heater with PWM. This can accomplish MPPT without needing inductors.

Thanks, I'll do some research on it.

If you have 12 kW of PV and 3 Sunny Boys, that could be handled off-grid by one Sunny Island and an auto-transformer. I would set up the PV array 6 kW SE and 6 kW SW orientation, maybe 4 strings, with one SE and one SW string feeding of two each Sunny Boys. Wouldn't need the 3rd one.

twice approx. 4500 CAD for Sunny Island is too expensive for me in relation to the entire system, moreover, I would pay for functions that I do not want to use.

Thank you for all the information, I will do a little research to see if I can not somehow outsmart the Sunny Boys and if that does not work I will probably have to resort to the direct DC variant.

 

[OSchubert]

CEV40C 750VDC photovoltaic power supply high voltage contactor DC12V/24V relay | eBay

At our warehouse.

www.ebay.com

Great, thanks for the link, my plan B seems to be realizable with this relay ;-)

 

[shortman]

So I want to connect 4xSI 6kw to power my whole house (only about half what I use today but we can make adjustments). I would like to use my 4x Old SBs to bring in the solar but these SB units don't support Freq Shift Scaling. SMA is telling me in emails that if I connect the SIs to the RS485 module on each old SB it will still work and the SBs will adjust output rather than disconnecting when the solar input is higher than the SIs are able to put somewhere else (like charging the battery bank). Does anyone know if there is truth behind the RS485 connection allowing output adjustment similar to the newer Frequency Shift Scaling?

 

[Hedges]

What model is your Sunny Boy?

The following list tells what is supported for grid-backup and for off-grid. A couple that say not supported for certain configurations can actually be made to work.

If you are using the system entirely off-grid you may be able to just change configuration (requires a communication product.)
If on grid, used for backup, then you're supposed to either configure for "Rule-21" frequency watts (newer models) or for "backup" and connect RS-485. The RS-485 lets Sunny Island tell Sunny Boy when grid has been disconnected and should allow wider voltage/frequency, including ramping down power output from (default) 100% at 61 Hz to 0% at 62 Hz. Some models are pre-configured, will respond as soon as RS-485 is connected.

Frequency Shift Scaling isn't new, SMA has been doing that for a couple decades. What is new is Rule 21 for the grid to do frequency shift.

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

 

[goldserve]

Knowing my US-TL22 sunnyboys are behind my hybrid inverter on the critical loads side, I was comfortable in setting the SB to island mode and it does support frequency scaling in this mode. I tried it and it worked. I can make further refinement to the slope of the adjustment if needed.

 

[Hedges]

4x Sunny Boy is nice, but expensive.
2x SI is very capable, and might meet your needs. If you have more than 13.4kW of SB and are doing grid backup, the excess could be manually transferred by interlocked breakers between [direct to grid] and [on SI only when SI is not on grid]

 

[Hedges]

Knowing my US-TL22 sunnyboys are behind my hybrid inverter on the critical loads side, I was comfortable in setting the SB to island mode and it does support frequency scaling in this mode. I tried it and it worked. I can make further refinement to the slope of the adjustment if needed.

And yet, SMA's list says TL-US-22 is OK for battery backup but not for off-grid "1) not supported since 2016"

So it does have an off-grid mode that works, with no RS-485 needed?
I've only speculated on why they say off-grid is not supported.
Is it a matter of what year's firmware?

I do have my concerns about SB "off-grid" behind SI for grid-backup. SMA Germany (manuals) said to use "backup" setting of Sunny Boys. SMA America (video) said to use "offgrid" setting of recent model SB. There are reports of relays sticking, which I figured was the reason for always using either RS-485 communications to switch, or else Rule-21 setting.

 

[goldserve]

I'm not sure what battery mode vs off-grid vs Island 60hz mode differences are. I'm assuming off-grid is able to completely operate without a valid 60hz grid frequency where as battery and (island?) requires the 50/60hz?

 

[Hedges]

Off-grid, island, backup when grid is down ... Sunny Island generates 120Vrms 60 Hz.
On-grid, if AC input from grid is close enough to 120Vrms and 60 Hz, it can connect and pass through. It can also blend in power from battery.
Either on or off grid, Sunny Island can charge battery from AC.

The Sunny Boys can be put in one of several modes (varies by model.)
All can be on grid, UL-1741. They perform active anti-islanding.
Some can do UL-1741-SA (Rule 21), which has wider limits, longer times slightly outside limits, ability to ramp down power with increasing frequency.

Off-grid or "Island" Sunny Boy allows much wider voltage and frequency limits. It does not perform anti-island testing.
When the Sunny Boy is in this mode, it still requires valid 60 Hz +/- frequency and 120Vrms +/- voltage, just wider limits. Won't put out any power without it.

"Backup" is a setting where, when signaled by RS-485, Sunny Boy switches from on-grid UL-1741 limits and performing anti-islanding, to the wider off-grid settings.

A few newer models of Sunny Boy (and Sunny Boy Storage) have "Secure Power" feature. When grid is down you can flip a switch and they will put out 120V 60 Hz up to 2000W. That they will do without needing to see 60 Hz 120Vrms; they create that themselves.