@plonkster This one’s for you, as you are probably the only person in the big wide world who can answer it with a degree of insight.
Both the (ex)ABB and Fronius have a control mechanism above and beyond frequency-shifting to curtail their power output.
My question is in an off-grid scenario is two-fold:
Is this mechanism more responsive ( faster) than frequency shifting?
Of the two brands, in your opinion which has the faster response time to the non-frequency shifting controls?
If it makes a difference I am deciding between a 3kW Fronius Primo versus the (ex)ABB equivalent.
I don’t know which is faster. But I know the Fronius is very fast.
Depends on PV-inverter. With Fronius, after two minutes of no comms, it goes back to full power. If I read sunspec correctly, this is what it is supposed to do:
Each of the immediate control functions, except connect/disconnect, has an
associated enable (Ena) register. Each time a control value is changed, the
associated enable register must be written with the ENABLED value (1). If a
reversion timer is set for a given control, the associated enable register
must be cleared by the device when the timer expires.
Some of the internal solutions by manufacturers, eg a Fronius with its own smart meter or an SMA with a home manager, will stop making power if it loses contact with its own meter.
Edit: The two minutes isn’t Fronius specific. The protocol allows you to set the timeout. Every time you write to the PV-inverter, you tell it 1) this is the power limit, 2) it is valid for 120 seconds, 3) the limiter is ON. According to that blurb I quoted above, you must set the limiter ON every time you write a limit. That means you write 3 16-bit values every time, the limit, the timeout, and the enable flag. Well technically you write 5 values… there is also a ramp rate and a time window… but these are optional. A PV-inverter doesn’t have to support them. It need only support the limit and enable fields… if it supports model 123 at all.
My interpretation of what you are saying here is that there is no advantage in an off-grid situation versus any PV Inverter with frequency-shifting. That frequency-shifting is probably the mechanism that will be the most responsive anyway.
However, there may be another distinction, not curtailing power, but demanding curtailed power back again.
With frequency-shifting, the Victron will go up to 53Hz and switch the PV inverter off. The Victron then is locked at 53Hz until certain conditions are met. One is that the battery voltage drops. This can mean there is a fairly significant drop in SOC before the PV inverter joins the party again.
So, my question is if the frequency-shifting has locked the PV inverter out, is the ethernet control mechanism capable of bypassing these conditions and resetting the 53Hz thus bringing the PV inverter back earlier?
In an off-grid situation, we don’t use the soft-limiter. We use frequency scaling. In fact, when the grid fails the limit on the PV-inverter is immediately removed so that it does not interfere with frequency scaling.
No. Fronius PV-inverter always prioritises frequency over soft-limit. You can configure other options to take priority… eg (old picture from another post):
This one takes modbus as highest priority, Dynamic power reduction (which is not the same as frequency scaling, it’s using its own meter) as second highest, and IO control (it has GPIOs that you can configure to correspond to different power levels) third. But frequency scaling is not something you can de-prioritise.
@plonkster , Thanks for your answers, it would seem in my envisaged off-grid system there would no advantage to the expensive Fronius. The second hand SMA TL-21’s I’ve been accumulating will fit the bill. (The new Fronius models are rarely offered second hand and command a premium when they are).