Hi, We have situations where i would like to manually set ESS Fronius throttling (situations when Wholesale grid price goes negative etc). Only option I can find is by setting ESS to External Control, but this means everything is External control, which is not the intent.
I am hoping there is a register that i cannot find, that when non zero, commands Cerbo to set Fronius to that maximum value, but without affecting any other component of ESS algorithum.
Thoughts?
System - 3ph Multiplus II 5kVA with 2x Fronius Symo and 60kWhr non CAN jkbms, using VM-3P75CT grid meter). Cerbo linked to Home Assistant via ModbusTCP
If you’re running DESS (in Green mode with the Hack), the system will automagically throttle down the Fronius inverters when grid price is negative.
If you’re not running DESS or you want manual control, you’ll need to get creative in Node Red or HomeAssistant.
In this case you’ll need to somehow figure out when injection prices are negative and associate actions with it.
The options you have in Node Red:
- PV Inverter Control: set the output power limit of the Fronius inverter
You’ll need to calculate the PV Inverter’s maximum output to end up with zero feed in.
Trick to know: you need to inject that value every ~30 seconds or so, or after a while it’ll default to max power again. - Settings Control
Here you can set the Maximum System Grid Feed In power, or just straight (dis)allow grid Feed In of excess DC or AC coupled PV - this would seem like the easiest option.
Thanks @BartChampagne, I will look further into DESS, as the ESS just overwrites the value at the moment (not in external control)
Initially I didn’t consider DESS because my HA is doing all the dynamic price control, and I didn’t want conflicts
If you’re already doing price control in HA then I’d just set the “Disable AC Feed In” flag when prices get negative.
That should throttle the Fronius output power to just below feed in but at the moment I don’t have a grid connected Fronius system to confirm.
I’ll have a play with DESS, but it’s Negative Buy price that i was referring to, rather than sell.
So this means, i can be paid to use grid power, rather than generate my own. In this case, i want to limit to 5% or similar the solar generation capacity in both Fronius inverters, just like ESS mode does when throttling.
Negative buy prices are tricky, at least here in Belgium - because we have extra grid costs on top of the wholesale grid price.
So even when wholesale price is negative, actual end user price can still be positive.
Grid sell prices will be negative way before buy prices get negative.
Just to avoid surprises, make sure you count all costs before you start limiting PV in favor of the grid 