Because I don’t want feed in solar power to the grid, I need to know which solar power I have available to switch on next devices.
I found out, that there is IMT Si-RS485TC sensor, but hard to find near seller. Is there any other way how to find out, how big power isn’t used in my solar panels ?
You could possibly do this by looking at the controlling parameters for the charger, though this also depends on the battery / BMS system being used.
e.g. if the solar charger is a 70A model, and is in CC/CV mode as opposed to MPPT mode, then it is being limited, and excess solar is available. This can be done using VE-direct hex commands, so possibly can also be implemented through the CERBO using node red.
when the charging is being limited by voltage regulation this makes life a little more difficult as the charge voltage limits only change slightly, and the MPPT may add a small amount for the exact purpose of exporting solar power.
It may be easier to use a small solar panel (2 - 5W) with a high power resistor on an analogue input to the Cerbo as an irradiation sensor.
I’m interested about small solar panel solution. How to connect resistor? Parallel? For which power must be this resistor?
As the analogue inputs are normally configured as resistive tank senders, I’ll have to do a bit of research to finalise this.
However, the general idea is that the resistor is connected in parallel to the panel, and is sufficiently low in resistance such that the output voltage never reaches the Vmp of the panel, this way, it’s always operating in the linear part of the power curve.
The power rating of the small panel, hence the need to keep this small - typically < 5W.
Ok, so The Tank input can be set to 300 ohm. This gives a 100% indication with 1.6V input.
I have for example, a 1.5W module, with an Isc of 284 mA. The sensing current from the cerbo is 11.3mA , or ~4% of the Isc. We can ignore this, and trim it out with the zero ohms setting.
for 1.6V @ 284mA, we need a resistor of 5.6Ohms in parallel with the module. Using I^2*R to determine the power for the resistor = 0.455W, so a 1W resistor should be used. This will give ample temperature rating. The resistor should be mounted as close as possible to the module, and then losses in the connecting wires will not offset the measurement. If this needs linearisation, then the tank shape coefficients can be entered.
It’s very good idea. I ordered for tests one solar panel 6V 4,5W.
But I will connect him into arduino analog input near to the panel, because cerbo is far away and I don’t want place new wire. Arduino will share measured value via wifi with my home automatization SW (OpenHab) and this SW will do the rest (modbus communication with victron).
I now have a basic version of this working on the cerbo, but it’s limited to being a ‘tank’ of the same capacity as the power of the adjacent solar system.
Which module did you used ? And resistor value ?
I Have a small 1.5W module, that used to be used for recharging a small portable light.
Resistor value was 5 ohms, though this is determined by the Isc of the module, and the max Vin of the ADC.
yesterday was cloudy, we’ll see what it looks like today.
this morning, showing good correlation between irradiance and MPPT charge current.
looks good. I also received panel for testing. I will share my results when I’m done.
