question

It looks like you want to build an ESS. You should check this webinar from Victron: https://youtu.be/tbpQzEZTElI

Yes if both the PV and the Immersuns are on the AC-In side and the CTs for the Immersuns measure the surplus power at a point before it reaches the MultiPlus, then the water heating will have priority.

Bear in mind also the 1:1 rule which is why you can't have 8kW of PV on the AC-Out of a 5kVA Multi. If however you can you partition it so there is 5kW or less then having some of it on the AC-Out has the advantage that it will keep going in a blackout. If the existing inverter setup doesn't make this easy then you might want to split one array and direct some of it directly into the battery through an MPPT.

The BMS will control the charging current via the Multi so the battery will not receive more than your 3.36kW, whatever and wherever the source is, this is not dependent on the topology.

Thanks Tom W, I have already watched that webinar and several others from Victron and got a lot out of them but not the answer to my question.

Thanks to Sharpener too. I will be building a grid parallel system due to the 1:1 rule as you say. I want the battery to have priority and send any excess to the water heating. It looks to me like the Multiplus will take what it needs to charge the battery then, when it's charged, I can activate a relay to turn on the water heating. I can't see any way to charge the battery at the full rate and send excess anywhere else. OK, I can use the excess by turning on the kettle or whatever but how can I have the water heating, only using excess power, while the battery is charging?

<I can't see any way to charge the battery at the full rate and send excess anywhere else. >

Easy, it is what I and many others do. In my setup the immersion heater is on the AC-Out but its current sensor is on the grid connection, so only takes what would otherwise be exported.

ESS is designed to meet loads, charge battery and then export, in that order. So you need to position their current sensors so that the Immersuns are not regarded as loads and only use what would otherwise be exported.

What I posted upthread will give first dibs on the PV that is on AC-In to the Immersuns, which is the reason to put enough of it on AC-Out to charge the batteries at the max rate. Or put the immersun CT(s) on the grid connection, then the battery has first claim on the whole PV production. No relays required in either case.

Much will depend on how the wiring between the two buildings, the solar inverters and the Immersuns is arranged (presumably there are several CUs involved) and the distances involved, a diagram would help. Also what permissions do you have from your DNO at present?

Sharpener, how does you battery know that there is excess solar power and it should start charging? With my grid parallel system, I will have to install an energy meter so that the Multiplus knows when to charge the battery. If I have a CT clamp on the grid connection for the Immersuns then it and the Multiplus will be competing for power won't they? The Multiplus 5000 can only output 4kW and I have 6kW of immersion heaters so they can't go on AC out. I think I would just have to give excess power away until the batteries are charged which perhaps isn't such a big deal.

My panels are ground mounted and my Fronius inverter is in a barn 70m from the house. I have permission to export 8kW to the grid but, of course, my intention is to export nothing. .

Sharpener, how does you battery know that there is excess solar power and it should start charging?

The Multi sums the currents available from the PV on AC-Out (3.68kW) and from the MPPT, deducts the load current on AC-Out and increases the charge rate until either there is export as measured by the internal CT on AC-In or it hits the CCL set by the BMS.

With my grid parallel system, I will have to install an energy meter so that the Multiplus knows when to charge the battery. If I have a CT clamp on the grid connection for the Immersuns then it and the Multiplus will be competing for power won't they?

No. In my scenario I have an immersion controller which requires ~100W of export to fully turn on the heater. As above, this cannot happen until the battery is being charged at the CCL so the Multi gets first dibs. I do not know but I imagine you can set something similar up in the Immersun, you certainly can with an Eddi or a Zappi. Failing which you can set the Multi to require a small (50W) level of import, this should be enough to give it priority by keeping the Immersuns shut off.

The Multiplus 5000 can only output 4kW and I have 6kW of immersion heaters so they can't go on AC out.

No, the limit on what you can have on AC-Out is the 50A total passthrough rating not the 4kW inverter rating. It is generation that cannot exceed the 4kW (actually the 1:1 advice says 5kW though I don't follow the reasoning).

What is important is where you put the Immersuns' CT(s), their actual circuit location does not matter. I have left my immersion wired through the original house CU on AC-Out 1, but you might want to wire them to AC-Out2 so they are disconnected in a power cut. Or have them on AC-In as you say.

I think I would just have to give excess power away until the batteries arecharged which perhaps isn't such a big deal.

You can avoid this very simply with an external grid CT connected to the Multi, they are cheaper and faster acting than e.g. the ET112 meter.

My panels are ground mounted and my Fronius inverter is in a barn 70m from the house. I have permission to export 8kW to the grid but, of course, my intention is to export nothing.

Provided their feed is teed in at point close enough to the Multi to put its CT on the grid side of the tee (can be >10 metres away) that will work.

Thanks for taking the time to explain Sharpener. I though the Victron stuff was fairly flexible but it seems like you can do just about anything. One of my Immersuns is broken and irreparable. I've repaired it before but it's too far gone this time so I'm putting the second one on another installation and I'm about to build a MK2 PVRouter that can supply 6kW. I don't think it has a threshold but I shall contact the designer and ask.

Thanks again, Stuart

I have finally installed my Victron Multiplus II GX and three 4.8kW Pylontech batteries and the water heating is not working as expected at all.

I built a MK2PVRouter which can handle 2 x 3kW heaters and it was doing so perfectly before I installed the battery system. Now, if I turn on the MK2PVRouter, it goes to full power and starts discharging the battery. I have an ET112 grid meter and the current sensor for the MK2PVRouter is the first thing after the meter. Does anyone know what the problem is?

Can you post a single-line diagram of your setup?

Here's what I have

I've just tested the system with the battery disconnected and it works as expected but whenever I connect the battery, the diverter goes to full power and starts discharging the battery.

Firstly is the CT for the diverter the wrong way round?

Did you try setting an offset of + 100 or 200W on the diverter or on the grid setpoint setting?

Is the PV configured correctly in Setup as being on AC-In?

Is the ET112 configured correctly as a Grid Meter (it looks like it is but I do not understand how 2 x 3kW heaters can show up as drawing 9552W).

You wrote <I have two solar PV systems on two buildings using excess power to heat hot water>, but your diagram shows only one, where is the other?

Also you don't have anything metering the output from the PV inverter before the tee below it, I think you at least need to add this. I would move and reconfigure the existing ET112 for this purpose, and measure the net grid current with an external CT (see above, cheaper and faster). AFAIR this link was posted by ANO here but I do not warrant it is suitable.

Lastly you might want to put the water heaters on AC-Out2 so if the grid fails they will be disconnected and cannot discharge the battery. Not sure why they aren't on the AC-In as you originally proposed upthread.

Hello Sharpener, thanks for your input.

It looks like the CT for the diverter could be backwards doesn't it, but it is the correct way as it works fine with the battery disconnected.

The diverter doesn't seem to have an offset threshold, it seems to work at a very low level, monitoring every cycle of the 50Hz. I haven't tried altering the offset on the Multiplus yet.

The PV is definitely on Input 1

The ET112 seems to be wired and working correctly. I think I had the car charging when the screen shot above was taken, hence the 9kW.

The second PV system is totally independent but it feeds a third immersion in the tank. It is working fine.

The PV inverter is a Fronius and is connected to the internet so the Multiplus can see it so I don't believe I need to monitor it. An external CT sounds better if it will work but I was just following the Victron instructions by fitting the ET112. I actually have one of the CTs in your link.

Your final point could well be the solution but wouldn't the battery still feed the heaters under normal circumstances, when we have grid power? The water heaters are in a boiler house and I thought it was connected directly to the meter but it is actually fed by the main consumer unit in the house. It would take a bit of work to get it on AC-in but it's not impossible.

The designer of the MK2PVRouter has supplied this link which might be helpful.

https://docs.openenergymonitor.org/pv-diversion/usingmultiplediverters/usingmultiplediverters.html

I have exactly the same problem and turned off my diverter. It was upgraded to include a time delay function so it could be set to start diverting after a delay and over a certain wattage to hopefully allow only the surplus power to be diverted. I have Aquions which prefer a lower/longer charge so the charging amps are reduced. Then as soon as the diverter is on and there is surplus the system increases power via the diverter to 100% not the net surplus and the balance comes from the batteries. My CT clamp is on the main incomer before the CU. I have not found a solution so the diverter remains off.

My diverter is an Apollo Gem.

Freddyuk, sorry to hear you have the same problem. I'll start another thread and maybe someone will know the answer.

Stuart

You wrote <The PV inverter is a Fronius and is connected to the internet so the Multiplus can see it so I don't believe I need to monitor it.>

OK, and it seems to register correctly on the dashboard so that isn't likely to be the problem.

<Your final point could well be the solution but wouldn't the battery still feed the heaters under normal circumstances, when we have grid power? The water heaters are in a boiler house and I thought it was connected directly to the meter but it is actually fed by the main consumer unit in the house. It would take a bit of work to get it on AC-in but it's not impossible. >

Yes, it wasn't intended as a solution for your underlying problem and if not practical then don't bother, I don't think it will help.

<The designer of the MK2PVRouter has supplied this link which might be helpful.

https://docs.openenergymonitor.org/pv-diversion/usingmultiplediverters/usingmultiplediverters.html>

There is I know similar advice on the myenergy web site but I think what you have done follows both so am now stumped for a solution, sorry I couldn't help.

I'll start another thread and maybe someone will know the answer.

Not sure this is best practice. Continuing this thread will enable others to follow the discussion and see what has been suggested/tried already.

EDIT: It just occurs to me that you need to have the Multi set to export any surplus PV in the first place, in addition to whatever the Grid Setpoint is configured as. Or there will be no export for the diverter to measure, which is what turns it on. But I am still not sure that will fix the battery drain problem.

Sharpener,

Thanks again for your response. I know starting a new thread is maybe not good but I felt the title is now incorrect and doesn't fit the problem.

Stuart