Planning to install a multiples II with a GX. The multiplus has a single CT clamp input that I’m planning to use as the grid meter.
My question is do I need another meter either a CT or ET based on to measure the PV? My PV solis inverter will be grid tied on the AC1 and is independent of the ESS. It will be metered separately by a shelly device. I’m assuming the multiples will be happy with the grid meter to know when to charge/discharge and that having a PV meter in the GX just provides a nice graphic.
Can you explain why it will function better? I’m happy to install one, not an issue at all but trying to understand what the benefit is.
I assume that an ess attempts to keep grid at the setpoint. Excess is absorbed by the battery. Deficit results in output by the battery. Is there some documentation about the benefits of the PV meter?
I use the external CT clamp of the Multiplus II as the grid meter for my ESS, and it seems to work OK. I cannot compare it to an external meter, but it is sufficient for my needs. I have my grid setpoint at 0W and I see the grid consumption figure jumping around in the range +/- 20W most of the time and sometimes +/- 40W. There is maybe 0.2kWh grid feed-in per day according to my utility meter. My PV inverter is AC-coupled and connected via Modbus.
Generation is determined by looking at current 180 degrees out of phase.
The accuracy of a CT is more than adequate for billing by power companies, IIRC 0.1%.
I use a second CT to measure my AC coupled SMA PV inverter. Without measuring the PV input the DESS system will have greater difficulty in establishing what your daily consumption is, as it is skewed by the AC coupled PV. I tried to go without a second CT but it was not very fruitful. The second CT (Victron equipment, not a standard CT) is reasonably cheap and easy to install.
I’m not really interested in measuring or metering, I have a whole other system that takes care of this already. I will not be reading values from the Cerbo GX regarding PV production, Grid consumption as I already have CT clamps measuring about 4 other things including these. I’m on octopus so its tracking the various tariffs that they provide I’ve got a modbus connection to my solis inverter so I know exactly how much solar I’m making from the source.
I’d be very interested to hear if the PV input to the Cerbo has any effect on the ability of the Cerbo to function as an ESS.
@teejay how did you connect this second CT, I’m struggling to find a simple CT energy meter. Victron’s one is £170 and 3 phase which is overkill.
Just make sure that you have the current flowing in the right direction and that the output wires are the correct way round. It doesn’t matter if you get them wrong as it is easy to rewire.
If you need any more info just let me know.
I configured the Assistant to show that the PV was coupled on AC Output side, even though it felt, to me, that AC input 1 was the correct solution (I tried that and the results weren’t as expected).
Ah got it. You’ve used the CT input of the inverter. I was going to use that for my Grid Sensor. Do you have a RS485 grid input sensor then as your grid meter.
As far as I understand there can only be one CT clamp input to the multiplus, and to have more you need to use the Cerbo GX which then requires the extra modules described in their metering document.
@sticilface I thought you could only have one CT too, then I spotted someone else’s post who had used two. However they didn’t explain how things were configured. That led to a lot of ferreting around and I discovered that you can have one CT on the Grid connection and one on the Aux Input (both on the Multiplus). You can choose other inputs but this is the one that worked for me. The latter requires the AC Current Sensor Assistant to be loaded. The Grid CT is just a standard CT but the second one must be the Victron device.
My system is proof that two CTs can be installed. I think if you click on my name you can see it operating. It is only a very simple system. 16kW Seplos battery with a Cerbo GX, a Multiplus ii and 4 kWp of solar connected to a SMA Sunny Boy inverter. I also have a PV Diverter that sends excess solar to my immersion heater. The latter device is one designed by Robin Emley.
I should add that when setting up my system I had strange values on my display that I struggled to resolve. Things like the AC loads would go to zero or the PV figure would be deducted from AC loads. Eventually I discovered that after doing any downloads or configuration activities I needed to shut off both my Cerbo GX and the Multiplus by their mains switches and restart them. My system still suffers from this issue today. I just downloaded the configuration file to upload an image of the Assistant settings, for this post, and then noticed that my display was wrong again. That triggered the memory. I shut the units down and restarted them and all is back to normal. That is just from doing a download and not doing any configuration at all.
