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spicedreams asked

AC couple EasySolar II GX with Inverter RS SmartSolar?

We are off grid with an EasySolar II GX 48 3000 (probably "at capacity"- 12x 320 Wp panels, 8x 260 Ah@100h AGM batteries). We need to add more Solar, more storage, more AC output current.

There is some attraction to adding a Inverter RS Smart Solar 48/6000 with its own set of panels (12x 390 Wp), batteries and this taking over supplying the AC load.

Can we AC Couple the two Victron devices, connecting the AC output from the Smart Solar to the AC input of the EasySolar?

I know of the "Factor 1.0 Rule" but unsure how it applies here.

EasySolar All-in-OneAC PV Couplingac couplinginverter rs
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Alexandra avatar image Alexandra ♦ commented ·

@spicedreams

This is not a supported set up.

What you can do is split your DB up and have the 3kva run light essentials and use the RS in its own system to run the big stuff.

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spicedreams avatar image spicedreams commented ·

Thanks a lot @Alexandra . Is there a list somewhere I can go to, to avoid bothering people with simple "not supported" questions? I would like to understand the context of supported vs not supported configurations.

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Alexandra avatar image Alexandra ♦ spicedreams commented ·

Not really. It is electrical theory you would need to know. The problem is an electrical/ sine wave synchronisation issue.

You would need to program two of exactly the same inverters combine their output and add their output to loads. The models you have chosen are not the same at all. That fact is documented in the three phase parallel manual.

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spicedreams avatar image spicedreams Alexandra ♦ commented ·

Thanks for your advice @Alexandra .

Yet, I see a diagram in the Inverter RS Smart Solar datasheet showing an Inverter RS, AC coupled with a completely non-similar AC PV inverter. I am just substituting Victron EasySolar for a generic AC PV inverter in this diagram. I understand the two would need to synchronise their waveforms; that's the essence of AC coupling.

I am curious why you say "two of exactly the same" where mixing Victron and Fronius, for example, seems perfectly OK.

Also I wonder why you refer to the three phase parallel manual? I have not suggested three phase and I am completely clear why it would need at least three single-phase inverters not the two I am asking about.

Thanks

Graham

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Alexandra avatar image Alexandra ♦ spicedreams commented ·

@spicedreams

Mixing two DC based inverters is different to AC coupling so it is not really the same. The DC ones can determine their own wave form.

For the DC ones being set up the same way as an AC PV it is called a cascade set up. And it is not an officially supported set up. There are guys that do it though still. There are quite a few discussions on the forum about them. With tips like not sharing a battery bank.

So it also depends on what you meant by combine their output?

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Ronald Rink avatar image
Ronald Rink answered ·

Hi @spicedreams I know that your question has been around quite some time, but as I had a similar scenario and could not totally follow the other answers, here is what I concluded:


* The RS Inverter SmartSolar does not have an AC output _and_ AC input, but only a single AC connection, on which it generates its sine wave. This is in contrast to the "Multi"-family that have dedicated inputs and and outputs, where the input synchronises its sine wave from an external source if available and then either passes this through or generates its own sine wave.


-- > (from an AC perspective) so when connecting the RS Inverter SmartSolar to the input of the EasySolar, the latter will pick up the frequency and consider this input as any other input (such as grid or generator). I do not see a way to connect them the other way round (but this was also not something you were asking).


However, as far as I understand Victron this is _not supported_ though _technical possible_.


- you would cascade or "daisy-chain" both inverters and with PowerAssist (or PowerControl, I always mix these up) the EasySolar would be able to deliver its own 3000VA _plus_ the maximum 6000VA (depending on temperature and voltage, see also below) to the loads which would _all_ be connected to the output of the EasySolar.


- there will be not power feedback from the EasySolar to the RS Inverter SmartSolar. So the EasySolar does not behave as a grid-tied PV inverter and the "factor 1" rule would not apply. And there should be no frequency shifting on the RS Inverter SmartSolar either that would affect the EasySolar.


- I have never tested when both chargers (and the MPPT charger of the EasySolar which is technically a separate device) are connected via DC to the same battery bank. But you would have to consider that all devices charge the same time and that they do not communicate on what they are doing (such as accidentically overcharging the battery). You might want to use a relay to stop one device from charging at a SoC that is much lower than the other one. The maximum charge current and maximum discharge current has to be considered as well (is the combined maximum of both chargers higher than the battery can handle at any given load and temperature?). But again, I do not know if this can work at all.


- sudden changes in load might more easily lead to overloading.


- the AC input of the EasySolar needs to be "fixed" to a certain maximum input current (less than the maximum output of the RS Inverter SmartSolar. This can only be adjusted in 0.5A or 1.0A steps. So, in order not to overload the RS Inverter SmartSolar you would need to choose a value depending on the maximum temperature you are expecting. The data sheet shows minimum values from 3000W (~3750VA) @60°C, 4500W (~5625VA) @40°C and 4800W (~6000VA) @25°C. So "safe" values would range from 16A to 26A. But this in turn would lead to a probably nearly always higher utilisation of the RS Inverter Smart and its battery, but in turn never be able to provide its full power. Higher utilisation will also have a lower efficiency (meaning you burn more power) and drain your batteries on that inverter faster. On the other hand the EasySolar will only really invert with loads higher than the RS Inverter SmartSolar can supply. This will lead to batteries that are more seldomly used on that inverter. Plus, the EasySolar would try to constantly charge its own batteries from the RS Inverter SmartSolar batteries (as it seems to be "grid-connected). Some thoughts on that: With one of the "recent" firmware updates and the "Prioritise other energy sources" option you could try to change that behaviour (not to charge all the time, but I never used that feature). Or, depending on your EasySolar-connected battery you could try to toggle "allow-to-charge"/"allow-to-discharge" on your battery based on a certain SoC. "Inverter only"-mode will not help here, as then the AC input seems to be ignored completely. Or lastly (as I did), use the MultiPlus assistant. There is the "Virtual Switch" with the "dedicated ingore AC load" option. This lets you use AC input on the EasySolar based on load and SoC.


- when cascading the inverters the EasySolar and to each output an RCB is added, the likelihood of tripping it might increase.


- the RS Inverter SmartSolar has a VE.Can connection and can be connected to the GX, but I do not know how this works together with the EasySolar. As there is only one global DVCC option that would control both chargers it might be better not to integrate them into a single GX but maybe use an separate GX if you plan to connect your BMS to the GX as well.


That being said, I have a similar setup running and working without problems for a couple of months now, but I know this is _not supported_ but it is technically possible (in addition, I have a DC/DC charger so I can shift power between batteries either way when needed).


If anyone spots a mistake or disagrees I am happy to hear about it.

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Alex Pescaru avatar image Alex Pescaru commented ·
Nice and quite complete explanation !
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spicedreams avatar image spicedreams commented ·

Thank you very much for that clear and pretty complete answer, @Ronald Rink .

Could you possibly describe how your system is set up and working, to provide a template to follow?


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Ronald Rink avatar image Ronald Rink spicedreams commented ·

I have some plans of how I cascaded my inverters with two separate battery banks (see link below). The "front" battery drives a 1-phase MultiPlus-II 48/3000 and the "back" battery bank drives 3-phase MultiPlus-II 48/5000. One phase of the 3-phase system feeds into the input of the "front" MultiPlus-II. In addition, I there load from the "back" battery into the "front" battery via a DC-DC 480W, so this is topped up all the time (as I do not have solar connected to this "front" battery). My solar panels (not yet on the drawing) feed via 3 RS MPPT chargers into the "back" battery which can also be charged via a 20kVA generator. I am running two separate GX. The "front" is never backfeeding via AC into the "back". And I could use RS SmartSolar Inverters in the "back" if I did not have a generator.

Remotely starting the 3-phase "back" inverters via a relay in case of a higher power requirement to have the front sync to the sine wave takes around 15s.

It is not the same setup (but I said this already in my post). But the principle of the cascaded inverters is the same. See here for more details including a plan: Current state of our electric installation – Our Journey to Scotland (watenan.uk).

In case you have more questions, something is not clear or you spot a mistake feel free to contact.

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