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Thank you for the great forum, Safe Driving over the weekend. Sincerely Jason

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Greetings solar Yodas

Need some help please with the best design as the options below costs similar.  

Requirement is ROI & essentials up during load-shedding (lights, TV and internet - peaks at 0.75kw).  Installed is 4kw panels but existing inverter needs replacement.

Option 1) SMA/Fronius grid tried inverter, Victron 3kva MultiPlus 2 GX as UPS, Pylon 3KWh. Only essentials connected to the UPS, rest of the house from grid

  • Pro - maximises solar feed
  • Pro - essentials on battery > 3hrs
  • Pro - cleaner, less complex ... or is this subjective?     
  • Con - 2 web interfaces for data?
  • Con - less battery for daily discharge (non-load shedding).  Not sure if this is actually financially viable tbh

Option 2) Victron MPPT,  5kva MultiPlus 2 GX and 2 x Pylon 2KWh. Essentials on ACout1, rest of house on ACout2 (with exceptions like oven)

  • Pro - same web interface
  • Con - 50A transfer switch Multiplus limit means exceptions like oven must run directly off grid
  • Con - needs 2 batteries to match Multiplus output. I understand this affects warranty if only 1

Looks like Opt 1 is better and slightly cheaper ... but reading forums it's rarely deployed.  What am I missing :) ? 

Thanks in advance folk 

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With Option 1, if grid is down you can't charge your batteries.

In my case the oven is used mostly in the evening anyways, so it being on grid is not the biggest issue. Most of the time we're using the gas hob though.

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I'd go for option 1 if your costing is the same: as the efficiency is likely higher. Fronius feeds straight onto AC with a 99% efficiency (or something like that) and the excess power us used to charge the battery.

With option 2, the MPPT power goes to the battery, and from the Victron monitoring, there is a solid 10% loss going through the Multiplus from low voltage DC (48V) to AC (230V). Obviously, the same loss applies when using power that cames from the Fronius. If option 2 is setup correctly, it is super stable, and the MPPT state (bulk, absorption, float) is controlled by the GX.

The Fronius/Multiplus is to me the ultimate combo (but CoCT has just removed it from the list of approved inverters😑,  but then you can register the Multiplus II). Fronius can be setup to be controlled by the GX, and can also run on the Multiplus output (as long as you keep the sizing 1:1 - ie 3kVA Multi with a 3kW Fronius)

The communication works on MODBUS Tcp: so you need to setup the Fronius to do this, as well as the GX. The must obviously be connected to the same network (via one router or a network switch ideally so you don't lose communication).

All the best.

 

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50 minutes ago, gooseberry said:

With Option 1, if grid is down you can't charge your batteries.

In my case the oven is used mostly in the evening anyways, so it being on grid is not the biggest issue. Most of the time we're using the gas hob though.

Ah ...  so panels are still up when the grid is down for Opt 2. Another pro then for #2

 

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14 minutes ago, John Wise said:

I'd go for option 1 if your costing is the same: as the efficiency is likely higher. Fronius feeds straight onto AC with a 99% efficiency (or something like that) and the excess power us used to charge the battery.

With option 2, the MPPT power goes to the battery, and from the Victron monitoring, there is a solid 10% loss going through the Multiplus from low voltage DC (48V) to AC (230V). Obviously, the same loss applies when using power that cames from the Fronius. If option 2 is setup correctly, it is super stable, and the MPPT state (bulk, absorption, float) is controlled by the GX.

The Fronius/Multiplus is to me the ultimate combo (but CoCT has just removed it from the list of approved inverters😑,  but then you can register the Multiplus II). Fronius can be setup to be controlled by the GX, and can also run on the Multiplus output (as long as you keep the sizing 1:1 - ie 3kVA Multi with a 3kW Fronius)

The communication works on MODBUS Tcp: so you need to setup the Fronius to do this, as well as the GX. The must obviously be connected to the same network (via one router or a network switch ideally so you don't lose communication).

All the best.

 

Thanks for the advice John Wise.

Can you please explain this - Fronius can be setup to be controlled by the GX, and can also run on the Multiplus output (as long as you keep the sizing 1:1 - ie 3kVA Multi with a 3kW Fronius).    In our setup, we'll won't have a 1:1 as the Fronius will charge 4kw, and the MP a 3kva?

They'll be on the same LAN btw.

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Posted (edited)
59 minutes ago, Shubs said:

Can you please explain this - Fronius can be setup to be controlled by the GX, and can also run on the Multiplus output (as long as you keep the sizing 1:1 - ie 3kVA Multi with a 3kW Fronius).    In our setup, we'll won't have a 1:1 as the Fronius will charge 4kw, and the MP a 3kva?

From memory:

1. Victron states that exceeding the 1:1 rule will damage their inverter, no exceptions.

2. Victron also states that there should be a minimum of 5kWh of lead acid batteries/1kW of Fronius or 5kWh of Lithium batteries/1.5kW of Fronius.

Caveat: I am crystal clear on 1. and just pretty sure about 2.

This has to do with system being sized to absorb the surge of excess power during load and grid switching, (as the power control is not instantaneous).

The bi-directional inverter has to have a big-enough charger and the batteries have to be able to take it as well, (even if they're already fully charged).

Plenty of literature  for this rationale on the Victron website.

 

Edited by phil.g00

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Posted (edited)

Also I would not recommend you do a install without a MPPT.

If your system had a shutdown event (lets say you hit minimum SOC) and the AC falls away there is no way to start the PV Inverter again (Because it needs the AC from the Multi to couple to) so you would sit in a deadlock position where the sun could be shining but since your batteries are too low to start the AC Inverter, you also can't by proxy start the PV Inverter.

Edited by PJJ

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Posted (edited)

Just to be clear, the limitations I stated above only apply when the Fronius downstream of the Victron AC out, not when it's grid side.

 

Edited by phil.g00

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35 minutes ago, phil.g00 said:

Just to be clear, the limitations I stated above only apply when the Fronius downstream of the Victron AC out, not when it's grid side.

Correct.

The way it works is pretty ingenious. It simply scales the frequency up according to the battery voltage. Of course the PV-inverter needs some time to react to the frequency change, and the Victron unit is a low frequency design which means the PV-inverter pushes into the battery directly via the transformer, the battery has to be able to absorb the extra energy while the PV-inverter reduces power. So you need to put a bit of weight in there.

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9 hours ago, plonkster said:

Correct.

The way it works is pretty ingenious. It simply scales the frequency up according to the battery voltage. Of course the PV-inverter needs some time to react to the frequency change, and the Victron unit is a low frequency design which means the PV-inverter pushes into the battery directly via the transformer, the battery has to be able to absorb the extra energy while the PV-inverter reduces power. So you need to put a bit of weight in there.

Thanks guys for explaining, but do these challenges apply to Option #1?  Won't the Fronius be upstream from the Victron, or grid-side like the pic below?

 

image.thumb.png.1aed0fdc3b1126bf373c85ed6f8aa7dd.png

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Posted (edited)
16 minutes ago, Shubs said:

Thanks guys for explaining, but do these challenges apply to Option #1?  Won't the Fronius be upstream from the Victron, or grid-side like the pic below?

When the PV-inverter is on the grid side, then there is no 1:1 limit, ie you can make that PV-inverter as large as your connection allows, it is not limited to the size of the Multi/Quattro. But the downside is that when the grid goes down, your PV goes down too.

If you move the PV-inverter to the other side, then it stays up when the grid goes down (it ties with the AC output of the Multi), but then the 1:1 rule applies and the PV needs to be reduced to 3kw, or you need a 5kva Multi.

In both cases the grid meter will see any outflow caused by the PV-inverter and will attempt to import all of it, so as long as the batteries can be charged and/or you have loads anywhere, your PV will be used for that and won't flow into the grid. When the batteries are full or you have more PV than loads, only then will power start flowing into the grid... unless you turn on the limiter option (which btw is getting completely reworked in Venus 2.60... it's much nicer now!).

The "ingenuous bit" I speak of above comes into play when 1) there is a grid outage and 2) the PV-inverter is on the output. Then it uses frequency to throttle the PV-inverter, and the regulation loop is literally based on the battery voltage.

Edited by plonkster

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9 minutes ago, plonkster said:

Venus 2.60

Bit off-topic, how often are these releases done? I updated over the weekend to 2.51 I think, so waiting for the Pylontech Update for the 52.5 change ;) which you mentioned was also somewhere in the 60s?

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7 minutes ago, PaBz0r said:

how often are these releases done?

There isn't a set timetable. It is released when it is ready. Roughly once every 6 months. You can however select to follow the candidate releases. Then you will get 2.60 pre-releases and you can test it.

2.51 is a maintenance release. It contains a handful of fixes. 2.52 will probably follow soon now, which again is only a few small fixes, the bigger one being support for a new BYD battery.

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7 minutes ago, plonkster said:

When the PV-inverter is on the grid side, then there is no 1:1 limit, ie you can make that PV-inverter as large as your connection allows, it is not limited to the size of the Multi/Quattro. But the downside is that when the grid goes down, your PV goes down too.

If you move the PV-inverter to the other side, then it stays up when the grid goes down (it ties with the AC output of the Multi), but then the 1:1 rule applies and the PV needs to be reduced to 3kw, or you need a 5kva Multi.

In both cases the grid meter will see any outflow caused by the PV-inverter and will attempt to import all of it, so as long as the batteries can be charged and/or you have loads anywhere, your PV will be used for that and won't flow into the grid. When the batteries are full or you have more PV than loads, only then will power start flowing into the grid... unless you turn on the limiter option (which btw is getting completely reworked in Venus 2.60... it's much nicer now!).

The "ingenuous bit" I speak of above comes into play when 1) there is a grid outage and 2) the PV-inverter is on the output. Then it uses frequency to throttle the PV-inverter, and the regulation loop is literally based on the battery voltage.

Thank you, that makes perfect sense! We have no issue that PV is down when grid is down as the Pylon covers the essentials.

So it looks like Option #1 is the best design (for us) :)  

Why is it so rarely deployed if it offers higher solar consumption and is slightly cheaper?  Is it because Grid down = PV down?

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18 minutes ago, Shubs said:

Why is it so rarely deployed if it offers higher solar consumption and is slightly cheaper?  Is it because Grid down = PV down?

I would not say it is rare. In Europe it's fairly common to put the PV on the input side. In South Africa it's common to put at least part of the PV on the output side or on the DC side with an MPPT because of the relatively frequent and long outages.

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56 minutes ago, plonkster said:

I would not say it is rare. In Europe it's fairly common to put the PV on the input side. In South Africa it's common to put at least part of the PV on the output side or on the DC side with an MPPT because of the relatively frequent and long outages.

Yup, can see why. Cool beans

Another question :) does SMA integrate as well as the Fronius with the MP GX, allowing a single Victron web interface for both data?

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Posted (edited)
1 hour ago, Shubs said:

does SMA integrate as well as the Fronius with the MP GX, allowing a single Victron web interface for both data?

Everything works except for grid limiting. Earlier versions of the SMA firmware did not properly implement two of the things required to make it work. They have since fixed it, but unfortunately it is not as simple as just changing one line of code... you'd need to actually check for support because there are many many units out there running old firmware, simply never updated once they work... and you cannot break something overnight. So for that reason... don't expect support too soon 🙂

If you don't need to grid limit, then it works just as well as Fronius.

Edited by plonkster

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@plonkster does the Solis 4G work with the Multiplus II in this way too? And can you connect the output of the grid-tied inverter then again to the AC in of the Multi in order to charge the batteries? If so it seems a much better option than going with a MPPT charger.

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20 hours ago, plonkster said:

Everything works except for grid limiting. Earlier versions of the SMA firmware did not properly implement two of the things required to make it work. They have since fixed it, but unfortunately it is not as simple as just changing one line of code... you'd need to actually check for support because there are many many units out there running old firmware, simply never updated once they work... and you cannot break something overnight. So for that reason... don't expect support too soon 🙂

If you don't need to grid limit, then it works just as well as Fronius.

Thanks so much for the guidance everyone .... really appreciated 🙏

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