Victron 250 / 60 or 150/60? *same amount of panels*

MK2

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Hello people. I am going to buy my first ever MPPT unit.
I know victron isn't the cheapest around but from what i understand it's good quality.

But what model should i go for?

I will have 4 panels (<400w each)
Voc: ~50V
Vmp ~40V
Isc ~10A
Imp ~9,4A

Battery today will be a lifepo4 8S type (25,6V) and in next year when 8 more arrives it will be a 48V system at 280Ah

If i do my calculations right i will have 1 possible scenario for the 150/60 model and 2 different scenarios for the 250/60 model. i will round of voltages and amps just for easier overview

150/60:
2s2p:
Voc ~100V
Isc ~ 20A

250/60:
2s2p:
Voc ~100V
Isc ~ 20A

4s1p:
Voc ~200V
Isc ~10A


The price of the different victron models is not very big in difference. I will upgrade to more panels in the future (then 250/60 will be more benefitial) but for now, is the any upsides of running a 250 vs a 150? how will higher voltage behave on a cloudy day compared to lower voltage? I am trying to make a well judged call here on what mppt voltage range to choose.
I live in Sweden so in the winter we have very little sun and in the summer we have very long days (sun rises at 4am and sets at 11pm even).

So again, to not lose focus of the question:
Higher voltage lower current or lower voltage and higher current?
 

sunshine_eggo

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Before you think I'm losing focus, your question is too simplistic. :)

The 60A is the OUTPUT/charging current. You need to check the controller for its input current specifications. They are often different for Victron and typically lower than output. The two give the exact same MAXIMUM amount of charge power - 60A * 28 = 1,680W or 60A * 3,360W

In reality, the only reason to buy the 250 is if you NEED the higher voltage for your planned array. Your array is sized based on your available solar and loads. If you plan to significantly over-panel the array, the 250 gives you more flexibility as it lets you keep the PV input current lower. A 4S5P array would be quite acceptable - 8kW on a system limited to 1680W (24V) or 3360W (48V) output.

MPPT efficiency drops off 1-2% at higher PV voltage due to inefficiencies in converting the larger voltage difference to battery voltage, but that is usually offset by reduction in wiring losses operating at higher voltage and lower current.

The two will likely not perform significantly different with the same panels in the same conditions.
 
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MK2

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Before you think I'm losing focus, your question is too simplistic. :)

The 60A is the OUTPUT/charging current. You need to check the controller for its input current specifications. They are often different for Victron and typically lower than output. The two give the exact same MAXIMUM amount of charge power - 60A * 28 = 1,680W or 60A * 3,360W

In reality, the only reason to buy the 250 is if you NEED the higher voltage for your planned array. Your array is sized based on your available solar and loads. If you plan to significantly over-panel the array, the 250 gives you more flexibility as it lets you keep the PV input current lower. A 4S5P array would be quite acceptable - 8kW on a system limited to 1680W (24V) or 3360W (48V) output.

MPPT efficiency drops off 1-2% at higher PV voltage due to inefficiencies in converting the larger voltage difference to battery voltage, but that is usually offset by reduction in wiring losses operating at higher voltage and lower current.

The two will likely not perform significantly different with the same panels in the same conditions.
Thank you for that lovely replay!
U woke me up on that point, i did ignore it at first but one you mention it now i see that 250 allows 35A input and 150 allows 50A input.

150/** allowes max 150 (less since it's Voc) 50A and that is 7500w
250/** allowes max 250 (less since it's Voc) 35A and that is 8750w

Both controllers are capable of a lot more than i might be planning on using. my 4 panels at the moment is just to test and try solar before i invest more. i desire somewhat in the 5kwp array in the future and a larger battery pack for offgrid (where i live grid is unstable, frequent times without power and working on the grid and i am so so tired of it. going offgrid is probably not going to pay off in years but that fact to be independant is worth a lot to me).

But okay! so the answer to my original question is that in my first scenario it wouldn't matter much. Right now i am "forced" to run a 24V system but i am going to upgrade to a 48V system as soon as i can. This is kinda one of the reason why i am looking at victron since it seems easy to change in the future, if i buy a all-in-one unit i will be locked to either 24 or 48V. sure it's cheaper than buying mppt + inverter (i already have 2 inverters, 48V 2500w/5000w and 24V 3500w/7000w from my boat).

But thank you a lot for information! it was very useful!
 

rmaddy

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With the MPPT SCC you need at least 5V of PV over system voltage for charging to start. When you have the 48V system (51.2V) you basically need at least 57V. You get that with either 2S2P or 4S.

There is a (small?) advantage with the higher voltage of the 4S vs 2S that allows it to start producing some charging current with less sun. I don't know how much more charging you might get during the course of a day between the two.

I have 3 panels in series that gives me about 120V on my 24V system. I start to see non-zero charging current the moment the sun is on the horizon in the morning. It's tiny at that point but I'm getting some. It quickly climbs as the sun gets a bit higher. If I had lower voltage I wouldn't see any charging until a little later in the morning.

Do keep in mind that if you started out with 48V then you could actually use a 150/35 with your 4 400W panels (4 x 400W / 48V = 33A).

The 250/60 does give you a lot more options. You can go 3S or 4S and once you are at 48V you can have up to 2900W of panels.
 

rmaddy

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150/** allowes max 150 (less since it's Voc) 50A and that is 7500w
250/** allowes max 250 (less since it's Voc) 35A and that is 8750w
This doesn't seem right. The max panel wattage is basically your system voltage times the max output current of the SCC. So with a **/60 on a 24V system you can have up to 1440W and on a 48V system you can have up to 2880W. This ignores some slight "over paneling".
 

MK2

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This doesn't seem right. The max panel wattage is basically your system voltage times the max output current of the SCC. So with a **/60 on a 24V system you can have up to 1440W and on a 48V system you can have up to 2880W. This ignores some slight "over paneling".
Oh so i should not look at those numbers. if i get it right the 2 mppt controllers can in and output the same amount of watt, but circuit breaker on the 150 is at 50A and 250 is 35A.

So in my scenario what happens if i put 4P on both controllers? 40A, will the 250 turn off or how does this "over paneling" works? when i read the data sheet on victrons homepage 1a states that "If more PV power is connected, the controller will limit input power".

As far as i understand it you may never over-voltage a system. i need to take in concideration that my system have to run at low temperatures with increased voltage. so in that sense the 250 have a wider Voc range and that is benefitial but how shall i think when it comes to feeding the controller. is it safe to feed it with 5kw even if the output is only 4kw on the /70 model? (5kw on either controller as long as u stay below max Voc).

How shall i think so i don't burn things out of stupidity? I understand that with my current 4 panels it doesn't really matter how i do as long as i stay under Voc, the current on them is 2 low to be a problem. This is more of a question for the future when i want to scale up.

I have so many questions thou, but i don't want to insert more questions here than nessassary, one question at a time.

How to think with safe input PV arrays? is oversizeing okay, does the mppt prevent dangerous over-input?
 

Bud Martin

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Notes from 150/60 spec sheet: page 56
2) A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array.

If you look ar the Victron spec sheet notes regarding to the input current, that has to do with the max current it can handle of the PV input polarity is reversed because it has the protector at the input of the PV, that calculation you made has nothing to do with SCC power can provide to charge the batteries.
The SCC will PULL the power up to the maximum power it can charge the batteries from the panels, the panels do not force power to the system, that is why you can have more panel power connected to the SCC than the max charger power.
I.E. your home AC outlet can supply 120VAC up to 15A (1800W of power available), but you plug a small 60W lamp into outlet, are you then be drawing 1800W of power? Of course not.
 
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MK2

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Notes from 150/60 spec sheet: page 56
2) A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array.

If you look ar the Victron spec sheet notes regarding to the input current, that has to do with the max current it can handle of the PV input polarity is reversed because it has the protector at the input of the PV, that calculation you made has nothing to do with SCC power can provide to charge the batteries.
The SCC will PULL the power up to the maximum power it can charge the batteries from the panels, the panels do not force power to the system, that is why you can have more panel power connected to the SCC than the max charger power.
I.E. your home AC outlet can supply 120VAC up to 15A (1800W of power available), but you plug a small 60W lamp into outlet, are you then be drawing 1800W of power? Of course not.
Very interesting with the manual! "2) A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array. "
If you check the short info on victronenergy you get this
2) A PV array with a higher short circuit current may damage the controller

I have been using that short version, maybe i need to dig in to the manuals of them both instead of them short information sheets they provide. it was much more clear to me when u shared that link to the full usermanual, especially when they said slightly different information with crusial information difference.

I have not made any calculations on output or battery charging what i know of, i just made some calculation of pv array input but now when i understand more i think that i can actually put a lot of panels in paralell, but since the controllers will only be able to utilize a certain amount of it, everything provided over that is a waste (at least when it comes to money invested in panels).

I will make a basic analog to how i see it, i am used with cars. let's say how the car produce power.
The engine is the controller and the fuel pump is the solar panels.
The fuel pump can pump a lot of fuel but depending on what engine you are feeding you will only be able to use a certain amount of it. So if i oversize with a lot of panels i might reach a scenario where i produce max output from dusk to dawn.


But in my current scenario i believe it works like this:
24v system: 1200w input max
battery 7,1kwh (max cont dischargerate 1C, 7,1kw output).
inverter 3500/7000.

During production hours:
Input - output (on the inverter) = storage or drain from the battery
(if i use 200w cont i will store 1000w, and if i drain 2000w i will use 800w from the battery).
Is this a correct way of thinking?
 
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kuranaga

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you do not need 250V. the only reason I would go for the 250v version would be if you consider the 250v mppt to be more sturdy e.g. to a sporadic peak due to nearby lightning etc
 
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