Which Victron devices do I need for an off grid 12kW system?

cajocars · Dec 26, 2023

I'm planning on building an off grid 12kW system with 30kWh battery.
The panels I'm looking at have an open circuit voltage of ~50V and I was going to create two strings of 12 panels each, but I can't see many MPTTs accepting 600V, so maybe I need to limit myself to 9 panels per string, 10kWp total power.

I've looked at all in one systems and I think it would be quite straight forward, but when I look at the Victron ecosystem, I'm not quite sure what I need.

I was guessing I need an off grid inverter like the "Multiplus II 5000VA" and a solar charge controller like the "SmartSolar MPPT RS 450|100"; is this fine or is there anything else or anything better that I should consider?

sunshine_eggo · Dec 26, 2023

450 is a NEVER exceed, so you need to allow for cold temp effects. You're likely limited to 7 or 8 in series.

The 100 IS 100A output meaning you'll only capture about 5800W of the arrays output. If you want the full 10kW, you'll need the 200

time2roll · Dec 26, 2023

Morningstar 600 volt $1100

sunshine_eggo · Dec 26, 2023

time2roll said:
Morningstar 600 volt $1100

Great unit but would need 3 to capture 9600W peak

cajocars · Dec 26, 2023

sunshine_eggo said:
450 is a NEVER exceed, so you need to allow for cold temp effects. You're likely limited to 7 or 8 in series.

The 100 IS 100A output meaning you'll only capture about 5800W of the arrays output. If you want the full 10kW, you'll need the 200

Yes, maybe I need to look at different panels with lower Voc that allow me to have 12kW; for example the Canadian Solar 595W are 41.1V so I could get 2x10 of them and still get 12kW (I need to look at the low temperature effects)

My question was more about the Victron devices I need.
Maybe 2x Multiplus II 5000/48 would allow me to have 8kW and be futureproofed if I need to install a heat pump and three phase supply by just buying a third inverter?
And yes, I see why I would need the SmartSolar MPPT RS 450|200

Adam De Lay · Dec 26, 2023

cajocars said:
My question was more about the Victron devices I need.
Maybe 2x Multiplus II 5000/48 would allow me to have 8kW and be futureproofed if I need to install a heat pump and three phase supply by just buying a third inverter?

I’ve got a pair of the Multiplus 2 5kVa inverters. They work great and can run a lot!

marionw · Dec 26, 2023

with 12 panels at 50 VOC each you can create 2 series strings with 6 panels in each string (6 * 50 = 300) then wire two strings in parallel. The string will have 300 VOC but you will need to ensure the parallel/series string does not exceed the max amps of the MPPT.

Volts added up in series while the amps will be that of one panel. Amps adds up in parallel and the volts will that of one series string.

sunshine_eggo · Dec 26, 2023

cajocars said:
Yes, maybe I need to look at different panels with lower Voc that allow me to have 12kW; for example the Canadian Solar 595W are 41.1V so I could get 2x10 of them and still get 12kW (I need to look at the low temperature effects)

You need to consider volts and amps. The /200 has 4X independent MPPT, so you can effectively have 4 different arrays attached.

Each tracker can use up to 450Voc (must include temp allowance) and 18A of INPUT current. I'm assuming the 595W are around 33Vmp, so that would put their input at about 18A, so...

9S each on 4 MPPT would yield about 370Voc at 18A (Imp) input - well under limits (20A Isc)

9 * 595W = 5355W / tracker (each over-paneled by about 25%)
4 * 5355W = 21,420W total array size.

11,520W maximum usable of the above array, max 4000W on any MPPT.

cajocars said:
My question was more about the Victron devices I need.
Maybe 2x Multiplus II 5000/48 would allow me to have 8kW and be futureproofed if I need to install a heat pump and three phase supply by just buying a third inverter?

No. You will have 10kW. ALL INVERTERS are rated in VA (VA = Watts when power factor = 1.0). Victron just confuses everyone by expressing it as such. For example, the Magnum MS4024PAE inverter is a "4000W" inverter, but when you look at the detail specifications, they indicate 4000VA.

In short, if you have pure resistive loads, you have 5000W of power. If you have inductive loads (motors), you have up to 4000W of power.

Yes, if you want three phase, you would need a third identical inverter. All phases must have an equal number of inverters on them, and you must use the same model and size of inverter.

It's really hard to recommend what you need when we don't know what you need.

cajocars · Dec 26, 2023

sunshine_eggo said:
You need to consider volts and amps. The /200 has 4X independent MPPT, so you can effectively have 4 different arrays attached.

Each tracker can use up to 450Voc (must include temp allowance) and 18A of INPUT current. I'm assuming the 595W are around 33Vmp, so that would put their input at about 18A, so...

9S each on 4 MPPT would yield about 370Voc at 18A (Imp) input - well under limits (20A Isc)

9 * 595W = 5355W / tracker (each over-paneled by about 25%)
4 * 5355W = 21,420W total array size.

11,520W maximum usable of the above array, max 4000W on any MPPT.

No. You will have 10kW. ALL INVERTERS are rated in VA (VA = Watts when power factor = 1.0). Victron just confuses everyone by expressing it as such. For example, the Magnum MS4024PAE inverter is a "4000W" inverter, but when you look at the detail specifications, they indicate 4000VA.

In short, if you have pure resistive loads, you have 5000W of power. If you have inductive loads (motors), you have up to 4000W of power.

Yes, if you want three phase, you would need a third identical inverter. All phases must have an equal number of inverters on them, and you must use the same model and size of inverter.

It's really hard to recommend what you need when we don't know what you need.

I just need the same load capacity as the current meter: 6kW, but possibility of going up to 1.33 times that (8kW) for up to 3 hours; that’s what the family are used to.
I would be fine having a small inverter (4-5kW) if they could supplement demand by partially drawing from the grid, but it’s becoming clear that off grid inverters canNot do that unless they are made to work in grid tie mode with a current clamp (in which case they are not off grid anymore).

12 kWp or close is what I need to maximise return on investment
The distance to the arrays will be 100m, that’s why I want to get close to max input voltage for each MPPT, but also minimise the number of strings if possible.

sunshine_eggo · Dec 27, 2023

cajocars said:
I just need the same load capacity as the current meter: 6kW, but possibility of going up to 1.33 times that (8kW) for up to 3 hours; that’s what the family are used to.
I would be fine having a small inverter (4-5kW) if they could supplement demand by partially drawing from the grid, but it’s becoming clear that off grid inverters canNot do that unless they are made to work in grid tie mode with a current clamp (in which case they are not off grid anymore).

Victrons can be programmed to switch to bypass if a load exceeds X for Y seconds. Once on grid, they can then supplement grid power if grid power exceeds the allowable input. Example:

MP AC input current limit set to 4000W max (this is set in amps, but I'm using power because I don't know your power type).
MP set to switch to grid if power exceeds 4000W for 5 seconds.
Once on grid, the MP will supplement anything over 4000W with inverter power - effectively giving you 8000W.
MP set to switch back to inverter if power is lower than 2000W for 30 seconds.

@Adam De Lay has his system configured in a similar fashion and can elaborate/correct my example.

cajocars said:
12 kWp or close is what I need to maximise return on investment.

PV?

cajocars said:
The distance to the arrays will be 100m, that’s why I want to get close to max input voltage for each MPPT, but also minimise the number of strings if possible.

Maximize voltage and minimize # of strings are counter to each other. Fewer strings means higher current and more wiring losses thus countering the benefit of high voltage.

297Vmp, 18A, 100m and 8awg wire yields 2.5% voltage drop for each 9S string:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

cajocars · Dec 27, 2023

sunshine_eggo said:
PV?

Maximize voltage and minimize # of strings are counter to each other. Fewer strings means higher current and more wiring losses thus countering the benefit of high voltage.

297Vmp, 18A, 100m and 8awg wire yields 2.5% voltage drop for each 9S string:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

yes, 12kWp of PV

I mentioned minimising the number of strings to minimise the amount of cables to run underground, but it's not very expensive so it's a constraint I can relax.

sunshine_eggo said:
Victrons can be programmed to switch to bypass if a load exceeds X for Y seconds. Once on grid, they can then supplement grid power if grid power exceeds the allowable input. Example:

MP AC input current limit set to 4000W max (this is set in amps, but I'm using power because I don't know your power type).
MP set to switch to grid if power exceeds 4000W for 5 seconds.
Once on grid, the MP will supplement anything over 4000W with inverter power - effectively giving you 8000W.
MP set to switch back to inverter if power is lower than 2000W for 30 seconds.

It's a logic whose intent I don't understand; it would make more sense to start drawing from the grid only what's necessary, rather than drawing a fixed amount from the grid and supplementing with inverter power, but maybe there is a technologic limitation I'm not aware of.

Hedges · Dec 27, 2023

cajocars said:
I just need the same load capacity as the current meter: 6kW, but possibility of going up to 1.33 times that (8kW) for up to 3 hours; that’s what the family are used to.

Sounds like you are estimating power draw by capacity of your present grid connection. Although that would be a small grid connection for newer homes in the US.
With a logging meter or one that records peak you might get better figures.
There may be some resistive heating load you could leave off the inverter.

Peak watts isn't that hard to deliver, but kWh in a day can require a large battery.

cajocars said:
Yes, maybe I need to look at different panels with lower Voc that allow me to have 12kW; for example the Canadian Solar 595W are 41.1V so I could get 2x10 of them and still get 12kW (I need to look at the low temperature effects)

Voltage increase of 16% when cold is a conservative estimate. You can get a more precise number using temperature coefficient of Voc from PV panel data sheet, and historical record cold for your location.

Sounds like 10s2p of that panel should work for a 450V controller.
You can do more strings in parallel if you fuse each string.
You can orient the strings differently, for morning and afternoon sun, reducing peak current.

cajocars · Dec 27, 2023

Hedges said:
Sounds like you are estimating power draw by capacity of your present grid connection. Although that would be a small grid connection for newer homes in the US.
With a logging meter or one that records peak you might get better figures.
There may be some resistive heating load you could leave off the inverter.

Peak watts isn't that hard to deliver, but kWh in a day can require a large battery.

6kW is pretty standard in Italy (and 3kW is enough for most homes with gas central heating), 6kW is the nominal, but you can draw 33% more for up to 3 hours before the meter disconnects. I've got logs for the last 2 years, with average power draw taken every 10 minutes, the maximum draw has been 6.6kW (as a 10 minutes average, but I know it cannot be more than 8kW). I've modeled a year with different size of PV and battery storage. Annual consumption is 16000kWh and the optimal size of PV and battery based on the prices available to me are 12kW of PV and 30kWh of battery. By optimal I mean the one that gives me best ROI and minimum break even time.

Hedges · Dec 27, 2023

We used to have as little as 30A, 120/240V service, so similar. Then 100A, now 200A and sometimes more.
Lots of homes are all electric.

12kW PV might make 72kWh/day in the summer.
Do you get to export to the grid for net metering, or do you have to store everything you don't use in the battery?

SMA makes single phase and 3-phase hybrid inverters for the European market which take a 400V battery.
For instance, 32kWh BYD battery, which I've seen priced around $18,000
Server rack batteries (48V) cost about half as much, and DIY with 280 Ah cells can be half that.

Signature Solar has their PowerPro battery, 280 Ah, which is in a weatherproof enclosure. It looks like an attractive offering and price.

Victron is well regarded, and has better offerings for European market than US.

In the US, many people are using the somewhat expensive SolArk. Apparently Deye has similar products for much less that serve your market (not the same software or support as SolArk.)

It is good to know what premium tier-1 products are out there as well as economy versions, before selecting. Features vary, like shaving grid consumption or increasing export when rates are high.

cajocars · Dec 27, 2023

Hedges said:
We used to have as little as 30A, 120/240V service, so similar. Then 100A, now 200A and sometimes more.
Lots of homes are all electric.

12kW PV might make 72kWh/day in the summer.
Do you get to export to the grid for net metering, or do you have to store everything you don't use in the battery?

SMA makes single phase and 3-phase hybrid inverters for the European market which take a 400V battery.
For instance, 32kWh BYD battery, which I've seen priced around $18,000
Server rack batteries (48V) cost about half as much, and DIY with 280 Ah cells can be half that.

Signature Solar has their PowerPro battery, 280 Ah, which is in a weatherproof enclosure. It looks like an attractive offering and price.

Victron is well regarded, and has better offerings for European market than US.

In the US, many people are using the somewhat expensive SolArk. Apparently Deye has similar products for much less that serve your market (not the same software or support as SolArk.)

It is good to know what premium tier-1 products are out there as well as economy versions, before selecting. Features vary, like shaving grid consumption or increasing export when rates are high.

32kWh BYD battery for $18000 is a lot! I’ve built a 14kWh one for £2500 last year for my other house

You can get paid to export to the grid but it’s never clear how much is it and you need to have the on-grid system professionally installed, but it’s very difficult to have an installer pick up the phone, let alone getting a quote! That’s why I’m going full DIY on this, and I also know it will be cheaper, I just have to forego being paid for export

Brucey · Dec 27, 2023

Hedges said:
SMA makes single phase and 3-phase hybrid inverters for the European market which take a 400V battery.
For instance, 32kWh BYD battery, which I've seen priced around $18,000
Server rack batteries (48V) cost about half as much, and DIY with 280 Ah cells can be half that.

There must be big margins on that 18k BYD battery.

They are selling entire cars (Seagulls) starting at $12K in China with a 30kWh pack:

BYD Seagull EV Priced From $11,400, Gets 10,000 Orders On First Day

Source: https://insideevs.com/news/663595/byd-seagull-ev-priced-11400-usd-gets-10000-orders-first-day/ BYD has officially unveiled the Seagull subcompact EV and kicked off pre-sales at Auto Shanghai 2023. The B-segment hatchback is shaping up to be a big success, with the automaker already report...

www.mycarforum.com

Hedges · Dec 27, 2023

Yeah, everything we buy for high prices in department stores was made cheap in China.
Does it do V2H?

We have a special program to allow import of cars not approved to our standards, for limited mileage use.
It was called "The Bill Gates Bill", after he bought a Porsche 959 and couldn't get it through customs. So he bought a chateau in France where he could keep it and drive it.

Here's the PowerPro, $4000 for 14kWh

EG4 PowerPro 48V/280Ah LiFePO4 Battery - UL9540, Heated | Current Connected

Unleash your solar power potential with EG4 PowerPro 48V 280Ah Battery. Reliability, peak performance, and all-weather resilience in one.

www.currentconnected.com

cajocars · Dec 28, 2023

It looks like I need one or more Multiplus II and a Solar Charge controller.

So the solar charge controller will convert PV DC to 48V DC which will then be inverted by the multiplus to be consumed by the loads.
Does this mean an all in one inverter would be more efficient in using solar power as it would convert PV DC power to AC without the intermediate conversion to 48V DC?

Hedges · Dec 28, 2023

Some AIO may convert to 48V, but others have HV DC rail.

There are also AC coupled systems, PV to AC, then AC to 48V battery (or to HV battery).

What is more efficient may depend on whether most PV gets stored in battery for later, or is used immediately.
My primary usage is grid-tie net metering. When grid is down I have more PV than I can use (in summer), so don't care about efficiency.

cajocars · Dec 28, 2023

I

Hedges said:
Some AIO may convert to 48V, but others have HV DC rail.

There are also AC coupled systems, PV to AC, then AC to 48V battery (or to HV battery).

What is more efficient may depend on whether most PV gets stored in battery for later, or is used immediately.
My primary usage is grid-tie net metering. When grid is down I have more PV than I can use (in summer), so don't care about efficiency.

I’ve calculated I’ll produce 76% of the energy I need but only 35% will be used while being produced; the rest will be stored for later use

Which Victron devices do I need for an off grid 12kW system?

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