Practical limitation of a 24V system?. 4 x Victron (12000Kw) and 12.8Kw Solar

[mrdavvv]

Hello!

So im playing with the idea of building a "big" Victron system, but only the 24/3000 model its available and legal for grid tie around here. So probably sticking with a 24V system, like this:




Ive seen that this levels of power are not advice able for 24V systems, mainly for 2 limitations. The conductor sections required are too big, and the batteries need to handle all that amperage without failing. But with a modular system as this, i think both of them can be mitigated.

1.- Consider a big busbar, like this 600A one:



2.- Each inverter its connected to the 24V Bus by independent cables (AWG2 or 1)
3.- Each battery its connected also with separate cables. (Also AWG 1/0, 170A@90c insulation)
4.- Would be limited at 8Kw at the output (By AC breakers and calculated loads), the system its overpaneled and overinvertered just because we can only get this model of inverter, and the solar PV positioning its not ideal, so need more power to offset efficiency losses.
5.- System wont be limited at the input, so we can take advantage of 100% PV backfeed power (Grid tie).
6.- Independent fuses and DC switch's for each battery and inverter, so not need to use too big components.
7.- Considering 8000W max load, we have a maximum of 330A for the battery bank, 160A for each battery. This will be a worse case scenario, since the PV should supply most of the power. The AWG 1/0, appropiate fuses, switch and BMS should handle this.
8.- Will be back feeding to the grid, in this case we can use 100% of solar and inverter power. That would be 400A at the busbar.
9.- Batteries will only be used during nights (Small load) and in case of blackouts. During the day the inverters would be using only PV and Utility power (Pass trough).
10.- Would limit battery charge current to appropiate levels.
11.- Cant limit discharge battery current (Only by the BMS). But less than .5c would be "normal" (Less than 4Kw at the output), and as i mention only during blackouts .
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So what do you think about this arrangement?, i'm probably missing something important so i would really appreciate any pointers to see if this 10Kw are doable or recommended with 24V dc, or maybe should i just go for 48V (More difficult to source, and would not be able to grid tie, wich would means a lot of $$$ lost.

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Bonus questions:

- If we have batteries at 100% SOC, a load lets say of 8Kw, and PV its supplying the same 8Kw.... the battery wont be charged / discharged right?. The victron inverters take the 24Vdc directly from Busbar / MPPT chargers, without the battery getting involved at all?
- In a grid tied system. Supose we have some loads before the Victron inverter (Not supplied at all by solar). But still in the same building circuit. If we are backfeeding to the grid, the secundary loads of the diagram would take this energy before the grid?.... the energy send to the grid its only the surplus left after all the building loads?. This would be perfect to put big loads, as A/C or motors at the "input" of the inverter (In parallel), instead of the output (Would requiere an even bigger system!)

 

[schmism]

I think there is a ton of money wasted in trying to size this system around 24v.
If your requirement is high end expensive gear there are plenty of other options that offer 48v grid tie systems that are not victron.

 

[mrdavvv]

I think there is a ton of money wasted in trying to size this system around 24v.
If your requirement is high end expensive gear there are plenty of other options that offer 48v grid tie systems that are not victron.

Hell Schmism.

Understood, i know this its not ideal, but its really such a big waste?, id imagine you are talking about the big DC cables, busbars and such right?. But still need to buy them for a 48V system, only a little bit slimmer and around 50-30% cheaper?... not mentioned in the post but already have a 24V system with MPP solars, so most of the DC components are already here (Including the big DC bus bars and cables).

Can you please share some examples of grid ties systems with hybrid inverters?, looking for a solution that can work as a general UPS and compatible with generic batteries (24 / 48V lifepo4 DIY banks). Copying from my other post: Higher quality all in one's

Requirements:

• Automatic transfer switch to feed the installation with Solar / Utility or Bateries, depending of the programed conditions.
• Configurable priority of energy supply, putting first solar, then batteries, then Utility or any order you want.
• Able to charge batteries from Solar or Utility.
• Compatible with LIFEPO4 voltages, preferably with better configuration of charging voltages and times of charging. (24 and 48V its ok)
• Compatible with DIY powerpacks.
• Good monitoring, preferable with a web server and wifi.
• Split phase (220v) or 120V single phase (America installation)
• Be able to feed the grid.
• With UL1741
• Higher capacity in the MPPT and AC capacity, MPPs solars are very limited in this aspect, with only 150V and 2000W, im looking to work with higher voltage.
• Around 6 to 8KW capacity.

 

[jwu_cc]

Are the solar panels grouped by orientation already ? If so, I see there could be benefit for having a SCC for each group. Otherwise, going with 48V could save you one or two SCCs, which could be close to $2K in cost, as 250/100 should be able to support up to 5.8KWp.

 

[mrdavvv]

Are the solar panels grouped by orientation already ? If so, I see there could be benefit for having a SCC for each group. Otherwise, going with 48V could save you one or two SCCs, which could be close to $2K in cost, as 250/100 should be able to support up to 5.8KWp.

Not grouped or even installed yet .... still on the planning stage. Each 250/100 its $950USD, so thats $1900USD savings for going to 48V and only using two chargers... not even losing in capacity as 2 x 24V chargers = 5.8Kw, the same if we use only one at 48V.

Havent tough on this and its something to consider, thanks for input.

 

[schmism]

Can you please share some examples of grid ties systems with hybrid inverters?, looking for a solution that can work as a general UPS and compatible with generic batteries (24 / 48V lifepo4 DIY banks). Copying from my other post: Higher quality all in one's

You can add sol ark to the list.
looking at this chart it gives you all the major competitors also.

The victron equipment shown runs about $2100 for a pair of inverter-SCC. x4 = 8400. That solark 12k is 6800 and you have 3x less wireing at a smaller gauge.

 

[HRTKD]

- If we have batteries at 100% SOC, a load lets say of 8Kw, and PV its supplying the same 8Kw.... the battery wont be charged / discharged right?. The victron inverters take the 24Vdc directly from Busbar / MPPT chargers, without the battery getting involved at all?

I'm not a grid-tie guy. I didn't even know the Quattro could do grid-tie. To answer your question above, yes, the battery would not get involved. The initial 8Kw load will probably come from the battery. It takes the solar charge controllers a bit to catch up. If the battery was truly charged and was in a float phase, the solar charge controllers wouldn't be putting out the maximum watts. When that 8Kw load hits, the batteries will be faster to provide the power than will the solar charge controllers.

If I was doing a non-vehicle based system, I sure wouldn't be using 12v, probably not 24v. 48v is what I would start with.

 

[Hedges]

12kW on 24V ... I have 24kW on 48V
12,000/24 = 500A. Only 250A will flow in the busbar. As drawn, you could cut it in half, and each system would be 6000W, 24V, 250A. No current is trying to cross the middle. (Only if you put both batteries on one end of busbar would 500A go through it)

I got a busbar with holes through it, put one cable on top, one on bottom, bolt through it.

Consider putting on busbar: (top,bottom)
(SCC,INV) (Battery) (SCC,INV) (SCC,INV) (Battery) (SCC,INV)

Now, no point in busbar carries more than 125A. Each battery delivers 250A.

Of course, 48V would cut current in half.

I use SMA, so two SI6048 and two Sunny Boy would make a 12kW system for you. Maybe those are accepted in your market.

As for panels, rather than a charge controller dedicated to a panel orientation, I would put two orientations on one charge controller or Sunny Boy. About 50% over-paneled, but same peak watts and spread out over more hours.

 

[mrdavvv]

The victron equipment shown runs about $2100 for a pair of inverter-SCC. x4 = 8400. That solark 12k is 6800 and you have 3x less wireing at a smaller gauge.

Schism seriusly thanks a lot for the sugestion, i wasn't aware of that those inverters, and they seem to be a perfect fit for my project, they even have UL1741!.

You just changed all my plans but that's for good!

I'm not a grid-tie guy. I didn't even know the Quattro could do grid-tie. To answer your question above, yes, the battery would not get involved. The initial 8Kw load will probably come from the battery. It takes the solar charge controllers a bit to catch up. If the battery was truly charged and was in a float phase, the solar charge controllers wouldn't be putting out the maximum watts. When that 8Kw load hits, the batteries will be faster to provide the power than will the solar charge controllers.

As far as i know all multiplus and quattros can grid tie, however the 24 / 3000 has the UL1741, so only that one can pass permits. Thanks a lot for the confirmation of internal DC workings of the inverter.

12kW on 24V ... I have 24kW on 48V
12,000/24 = 500A. Only 250A will flow in the busbar. As drawn, you could cut it in half, and each system would be 6000W, 24V, 250A. No current is trying to cross the middle. (Only if you put both batteries on one end of busbar would 500A go through it)

I got a busbar with holes through it, put one cable on top, one on bottom, bolt through it.

Consider putting on busbar: (top,bottom)
(SCC,INV) (Battery) (SCC,INV) (SCC,INV) (Battery) (SCC,INV)

Now, no point in busbar carries more than 125A. Each battery delivers 250A.

Glad too see you in this thread Hedges.

I never stopped to think about the internal current flow in the busbars, but everything has a lot of sense!. I already have the monstrous busbars but this brings more peace of mind... knowing i wont be playing with too much current on my DC connections. I might even go for a 48V system, i really liked the Sol-Ark suggestion of Schism, wich will make things a little bit easier.

I use SMA, so two SI6048 and two Sunny Boy would make a 12kW system for you. Maybe those are accepted in your market.

As for panels, rather than a charge controller dedicated to a panel orientation, I would put two orientations on one charge controller or Sunny Boy. About 50% over-paneled, but same peak watts and spread out over more hours.

I will check more about SMA's, but havent found a good distributor around, as they are not that popular on this side. After all the reading ive made, i realize they are very simillar to the Victrons, in the way that they can AC / DC couple at the same time, with all the advantages that each method has. You also need an external charge controller in both brands. However, for my case i think Victron was a better choice at that time:

• Local distributor that knows a lot about them and can help with support / warranties.
• The main inverter can grid tie (Multiplus / Quattro), so with net-metering you can have a lot of savings (With SMA you will need to purchase a separate sunny boy / island to achieve this (i think....)
• Victron has their own charge controllers, that can comunicate with their control panel (GX device). This its pretty good as you can even control the charging current for your batteries, and leave all the remaining energy for loads / utility backfeed. Not having to closely match the PV size... and being able to only use DC coupling with a very big system
• SMA seems to be more expensive (And also would need double equipment).

That being said... SMA probably its the best quality inverters in the market, and theill probably last a life time.

--
In the end, im very exited with the Sol-Ark / Deyes as they seem to be a perfect solution for my needs, a very powerful hybrid all in one that seems to have decent quality and good configuration!.

As for panels, rather than a charge controller dedicated to a panel orientation, I would put two orientations on one charge controller or Sunny Boy. About 50% over-paneled, but same peak watts and spread out over more hours.

Diagram 1 ----------------- Diagram 2
Both this configurations wont achieve similar performance?... i need to read again the documentation about east - west orientations.
(Cannot do south orientation since the roof has around 30° degree angle, so it would requiere a lot of structure, that the roof cannot support.)

 

[Hedges]

Two strings of different orientations into one MPPT charge controller loses about 2% because Vmp slightly different between the strings.
It lets you put 50% extra panels beyond charge controller capability, without clipping (if 90 degree angle, area presented to sun is 0.7x as much)
Off-angle panels will produce fewer Wh/day than they would with optimum orientation.
Spreading power over the day reduces battery cycling, leaves more charge as night comes.

Sunny Island + Sunny Boy gets you grid-tie net metering and battery backup.
An additional charge controller is needed if you want DC coupling (not necessarily any benefit)

With just Sunny Island + charge controller, can still do net metering. But only by letting charge controller control its own voltage, exceeding what Sunny Island wants on the battery. Not particularly elegant.
DC charge controller current to battery is not regulated; DC coupled PV must not exceed maximum battery charge rate allowed.
Sunny Island doesn't have the control over current from separate charge controller current like Victron provides. It only does with AC coupling.

 

[the_colorist]

@mrdavvv Here are a few thoughts about SMA from an installer point of view. Bear in mind I just did a quick skim just now of the thread.

SI's can AC/DC couple (per Hedges notes) but generally AC-Coupling (even with Victron) I have found to be a superior solution. Currently, I'm installing Victron+SMA systems. At times I may install a small SCC to help with black-start but the reality is with an auto-genstart and load shedding contactors, this should never happen.

With AC-Coupling, I like the idea that the inverters get to rest. With a DC-Coupled system, the battery inverter is always under load. 24/7. Never gets a break. Particular stressful in grid-tie situations.

In an AC-Coupled system and DC/AC hybrid, there is a time of the day where the battery inverter gets to rest and is simply a voltage/frequency reference. The PV inverters rest all night.

SMA's answer to the GX devices/monitoring is the Data Manager M + COM Gateway.

SMA SI does work with DIY lithium batteries if you are using a compatible BMS. I have a list if you are interested. Currently using REC BMS but in talks with others (Orion), will deploy ZEVA in the future.

Per Hedges comment, you wouldn't need double the equipment. The Sunny Boys can replace the SCC's. The last batch of SB4KUS (4000W) I got were $550 ea. So 4 would be 12KW of power for $2200.

If a person wants new models (might be required in your location), the SB 7.7 (7700W) can be had for $1300 before shipping. A 5.0 is around $1K. With 600V strings, much less wiring to be done. DC Disconnect and MC4's built into the unit.

I would have to check on this to confirm but I have a suspicion you should be able to use SB's AC-Coupled to Victron inverters in a net metering scenario. Again this is just food for thought, I would need to follow this up.

If you don't mind my asking, where are you located? My real point in writing was to mention that there is a good chance I can get you some serious discounts on hardware. I get dealer and installer discounts on most things including SMA/Victron/etc. Feel free to PM me if you are interested.

There has been some interesting discussions in the past about using 120V Quattros grid-tied. Some utilities allow it as I recall (could be wrong, been awhile) but it's a case-by-case basis. It might be worth following it up.

I'm surprised Schnieder XW/SW hasn't been mentioned thus far.

 

[mrdavvv]

Hello @the_colorist

I appreciate all your comments, alternative solutions are very important at this stage.

I think i haven't put enough tough and attention to the AC coupled world, as im more familiar with the DC coupled systems that i already have.

In wich situations do you recomend Victron, and where SMA?... they seem to be very similar in specs and architecture.

One thing that i really like about Victrons and the Sol-Ark (Aside from such an easy setup / installation) is that you basically have a big UPS for your home, with transfer times low enough that sensible equipment dont notice faults (Like servers). Our situation its on grid, using solar, and then utility as sources. Battery its only relegated for night time (Low consumption) and blackouts). Transfer times are fast enough with AC coupled??.

SMA SI does work with DIY lithium batteries if you are using a compatible BMS. I have a list if you are interested. Currently using REC BMS but in talks with others (Orion), will deploy ZEVA in the future.

I guess it can also work with battery packs with generic BMS's?, using the AGM / Lead setup with some voltage tweaks?

I would have to check on this to confirm but I have a suspicion you should be able to use SB's AC-Coupled to Victron inverters in a net metering scenario. Again this is just food for thought, I would need to follow this up.

Thats a good question, can you backfeed to the grid from inverters conected after the SI?. With a grid tie system... will the string inverter backfeed all surplus energy to the grid?, independently of the size of the load?... I guess during the day the SI its only acting as a passtrough?.

Can you put string inverters (SB) before and after the SI like Victron systems?... in this scenario we might only put an smaller SB and SI to our critical loads (Probably 3 - 5K), leaving other SB's in the input, working only as regular string inverters.

If you don't mind my asking, where are you located? My real point in writing was to mention that there is a good chance I can get you some serious discounts on hardware. I get dealer and installer discounts on most things including SMA/Victron/etc. Feel free to PM me if you are interested.

Ill send you a PM.

There has been some interesting discussions in the past about using 120V Quattros grid-tied. Some utilities allow it as I recall (could be wrong, been awhile) but it's a case-by-case basis. It might be worth following it up.

Someone told us that in this particular case, its doable, since the string inverter (Fronius or SMA) are certified by UL1741, and the quattros have appropiate anti-islanding. Probably not a problem with an small installation like this, but with bigger ones its probably not adviseable since our utility company really check them close, and might deny permits with Non UL machines.

For no trouble the recomendation was the multiplus 24/3000, wich has UL.

I'm surprised Schnieder XW/SW hasn't been mentioned thus far.

Ha, seems like they are not that popular in the residential market?, i never saw them on the whild, its all microinverters and fronius around here.

load shedding contactors, this should never happen.

Do you use contactors to switch off loads?, or just rele's?. Don they have like 50W consumption all the time? (Contactors)

Two strings of different orientations into one MPPT charge controller loses about 2% because Vmp slightly different between the strings.
It lets you put 50% extra panels beyond charge controller capability, without clipping (if 90 degree angle, area presented to sun is 0.7x as much)
Off-angle panels will produce fewer Wh/day than they would with optimum orientation.
Spreading power over the day reduces battery cycling, leaves more charge as night comes.

Sunny Island + Sunny Boy gets you grid-tie net metering and battery backup.
An additional charge controller is needed if you want DC coupling (not necessarily any benefit)

With just Sunny Island + charge controller, can still do net metering. But only by letting charge controller control its own voltage, exceeding what Sunny Island wants on the battery. Not particularly elegant.
DC charge controller current to battery is not regulated; DC coupled PV must not exceed maximum battery charge rate allowed.
Sunny Island doesn't have the control over current from separate charge controller current like Victron provides. It only does with AC coupling.

As i mention a couple of paragraphs before, i havent put enough tough in AC couple systems, they might be a better solution in some cases. In particular, i will only use battery as backup or night loads... leaving utility and solar as main sources during the day. So AC coupling makes more sense, and as you mention, probably eliminating all DC coupling.

I might even reconsider putting such a big "off grid" system, just put an small SB & SI for critical loads, and additional SB at the regular loads.

One of the aspects that put me off a little bit about AC coupled, is that you have additional complexity with 2 separate units that need to comunicate with each other. For example, with victron i think they comunicate trough TCP / IP... so what happens if your network fails?.... and if any of the battery or string inverter fails, you endup without offgrid energy. You can see the same about the hybrids, but everything its inside a black box so you dont worry about comunication protocols between boards.

 

[Hedges]

Yes, grid-tied inverters on the output of Sunny Island just feed through its relay to the grid. Current limit is 56A, so SMA says maximum 6.7 kW of PV per (US spec 120V) Sunny Island if on grid. Europe/rest of world 220V model supports twice that (same relay, higher voltage)

I have four SI configured 2s2p so up to 112A 240V can pass through (in either direction) and that's how much AC coupled inverter can be on its output.

You can of course have additional AC coupled inverters on the grid side, no interaction with the SI grid backup system.

I use a 100A load-shed contactor. I don't have a generator and battery is so small it may not carry my house through the night, depending on loads. So SI will shed the house at 70% DoD but keep producing AC down to 80% DoD, so when the sun comes up the Sunny Boy AC coupled inverters can provide power to recharge battery. At 50% DoD the house reconnects.

My contactor isn't 50W. It runs on 48V battery, draws high current (5A!) to slam shut then switches to something low, a few watts. An AC relay could be used instead. SI has two SPDT relays programmable for various purposes. It provides 48V with 0.5A PTC fuse, or AC can go through the relays.

 

[mrdavvv]

Thanks for all the confirmation.

Haven't tough about using contactors /relays to lose some loads depending of certain SOC.. that would be very useful to disconnect the server room A/C in case of low battery.

Still researching!