Force a charge based on energy meter reading from the grid?

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partrg asked May 17, '24

Force a charge based on energy meter reading from the grid?

Hey Folks

I have a grid-tied, 3 phase PV system that exports excess power to the grid for a pittance.

I also have a separate Victron ESS system (comprising an MPII, Cerbo, MPPT 250/100 with separate 6 kW of PV). I’m hoping to make this system a little smarter by using the excess solar from the grid-tied system to charge the battery on my Victron system.

My ESS is currently set to ignore AC input until battery drops to 10% or if loads are high and I need to keep this feature on, but then I want to also force a charge when there is power being exported to the grid from the other grid-tied system (& at a rate equal to whatever the export is).

I’m thinking I need to use the VM-3P75CT to monitor export on Phase L1 (the one connected to my ESS), but I’m not sure how to program the system to force the charge at the rate equal to the exported power? Has anyone got any experience with this or any ideas? Not sure if it’s possible on ve.config or whether it’s a Node Red job??

Hope it all makes sense. Schematic below to help with my explanation.

Cheers

ESS Energy Meter Node-RED

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Modifications Space

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Answer 1 · 2024-05-17T15:43:56Z

matt1309 answered · May 17 at 03:43 PM

Hi @partrg

If you ignore the fact you Grid tied PV Is 3 phase, you could much have this setup (snipped below)

So you're right if you just let victron system monitor L1 (or whatever phase victron ess is on) of the grid tied PV then you'd have the below diagram.

If your metering with grid/energy provider is done as the total of all phases then you could just use the three phase meter you already have on 3 phase grid tied PV and set ESS mutiphase regulation to "Total all phases":

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/multiphase-regulation---further-information.html

This setup will then send all "Excess power" from grid tied PV (up to max victron inverter can charge of course) into battery of victron ESS and only export once battery is full. You wouldnt need to program for that. That's just how ESS (with ac coupled PV on AC in works, as per diagram below taken from here:

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/ess-introduction---features.html

This doesnt factor in you need for ACIN to be disabled until 10%. You can likely achieve that with node red. However is there a reason why the normal ESS mode isn't what you're looking for as that would be as described above.

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Answer 2 · 2024-05-18T02:51:31Z

partrg answered · May 18 at 02:51 AM

Thank you very much @matt1309. Seems like I've been overthinking this and that it is actually very easy! Great to hear.

Just to clarify, I don't currently have any 3 phase metering on the grid-tied system. So I do need to buy a VM-3P75CT to make this work right?? (I don't think I can use an EM24 as I need to measure the export in front of the meter and therefore need the CTs)

So I just change this grid metering setting to "External meter", change the Multiphase regulation from "Individual Phase" to "Total of all phases" (yes my utility meters on net of all phases) and it shoud work?

The reason I'm using the AC ignore is because under the standard ESS settings, it was always pulling a steady ~200W from the grid, regardless of what I had the Grid Set Point set to (I tried 50W, zero and even negative). I couldn't work how to fix this, so the ignore AC input was a work-around to minimise grid use. Once I implement the above will try and putting it back to the standard setup and see what happens.

Thanks again!!

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matt1309 commented · May 18 at 10:23 AM

So if you have three phase grid tied pv you'll need a 3 phase meter on that.

You'll also need a three phase meter on grid.

I believe the system would then try to balance phase 1 so that sum of phases = grid setpoint.

Assuming ess setting set to to total all phases on multiphase regulation it.

That 200w issue is it maybe because you've got a load somewhere between multiplus and meter?

That might be cause. Changing to use external meter might solve this as well

It should bounce around 0, maybe 50w here -100w there but constant 200 sounds odd.

However I think the system you're describing is pretty much the stock examples given in the section

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/multiphase-regulation---further-information.html#UUID-09600a81-ae3d-8b42-9c9b-a35274184f00

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