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.
Good evening. May i ask your feedback on my case? i’m installing at my home (already equipment in hands, wiring ongoing etc.) a 5kW MP-II mainly to maximize self-consumption. Already have a 6kW SMA ac-coupled installation in service since years, but unfortunately both Grid and PV delivery points are quite away from the house where the MP-II is installed.
My doubt so far is mainly about the energy metering.
I attach a picture with the 2 options i have, or at least the two i came up with after reading through VE docs and various community discussions.
Option1 :
the easier to implement and the cheaper, if it then works of course…
Option2 :
as per VE “manual” but costly and time consuming + LoRA required as Zigbee has too short range. ET112 wired connection to GX theoretically feasible but not easy due to distance, as well i have frequent nearby lightning strikes and prefer to avoid wired data links to home equipment
Note: Is won’t have on MP-II AC-OUT heavy loads, so fast response and accuracy of energy readings (ET112 vs CT) i think won’t be an issue.
Hi Alex. I am not an expert on these matters so treat what I say with caution.
I believe that in your first arrangement the CT would have to be the other side of the PV connection. In its current location the MP will think that power is coming in from the Grid when it is really coming from your PV system. Either that or you need to be able to deduct the PV reading from the MP’s CT reading. In my system I have to deduct the power sent to the immersion from what the MP sees. That is achieved by feeding the immersion power lead back through the MP CT.
How far away is the Cerbo from the point where the PV connects?
Hi Tony, thanks for prompt reply. Unfortunately i can’t put the CT upstream of the PV entry point because actually (my sketch is not showing clearly this) it is far away from house, means just besides the grid connection. Both (grid+PV) are located outdoor at approx. 60-70mt from the house where i have the Distribution board and where i’m planning to install the MP2 (and eventually the CT.
I need to investigate if the GX ESS , having available realtime SMA PV production data, is able to do all the calculations, i.e. automatically deduct PV from CT readings.
If the above is not going to happen, then i’m afraid the only way would be to put the ET112 outdoor at grid/pv place, and then bring the signal to the house somehow (by cable or LoRa wifi).
