Can't figure out charger/invert size needed

[IP4]

Hi - I'm trying to plan an off-grid system and have run into a problem with selecting an inverter/charger.

The system needs to handle 22 kWh per day (most days won't need that, but just being safe). I plan on using 48v for everything, with LiFePO4 batteries.

Based on that usage, this site says I'll need 24 x 365 watt panels. My own calculations are roughly the same. A 365 watt panel has a max output of 10.62 amps.
So, 24 panels x 10.62 amps = 254.88 amps. But I can't seem to find a charger/inverter that can handle that many amps. For example, the largest Victron on this page (Quattro 48/10000) can only handle 200 incoming amps (assuming I'm reading this correctly).

What should I do? Thanks!

 

[John Frum]

Hi - I'm trying to plan an off-grid system and have run into a problem with selecting an inverter/charger.

The system needs to handle 22 kWh per day (most days won't need that, but just being safe). I plan on using 48v for everything, with LiFePO4 batteries.

Based on that usage, this site says I'll need 24 x 365 watt panels. My own calculations are roughly the same. A 365 watt panel has a max output of 10.62 amps.
So, 24 panels x 10.62 amps = 254.88 amps. But I can't seem to find a charger/inverter that can handle that many amps. For example, the largest Victron on this page (Quattro 48/10000) can only handle 200 incoming amps (assuming I'm reading this correctly).

What should I do? Thanks!

The inverter part is sized to for the maximum continuous load and the maximum instantaneous load.
The charger part is sized to charge your batteries in the amount of time that you choose.

See my signature for the load question.
22000 watt hours / 51.2 nominal volts = 429.6875 amp hours
That is how many amp hours you need to replenish daily.
Will your inverter/charger be connected to mains power or a generator or no ac input?

 

[robby]

Panels in series you add the voltages and panes in parallel you add the currents/Amps.
So if the panels are rated at a Vmpp of each panel is 36 Volts and the Impp is 10.62 Amps then 12 of them is series is 12 x 36V = 432 Volts and because they are in series the Amperage does not change so its 432V at 10.62A.
If you parallel two strings of 12 panel in series the you get 432V at 21.24 Amps

Another big consideration is the Voc or (Voltage the panels produce "Open Circuit" or with no load).
Your panels might have a Voc of 41V and when you do 41v x 12 panels = 492V. This would blow an MPPT rated for 450V so you have to get a charge controller or Inverter that can handle the Voltage and current. the panels produce.

Is there a reason why you picked Victron? What kind of budget do you have for an Inverter and batteries?
I am using a Solark 12K but that might be more than your willing to spend. As an example a typical good Inverter will do 420 to 450V input and 20Amps with two strings. You need to see what the Start voltage is for the Inverter but lets say it's 125V. So 125V is the absolute minimum combined Vmpp we would want on the system and a 425V Inverter MPPT might say it's max voltage will be 450V.

12 Panels is 492V so that is to big. If we settle at 10 panels we get 10 x 41Voc =410V which is pretty comfortable spot to be in and the loaded voltage will be 10x36V =360V which is good because we are not going to close to the 425V limit and we are high up from the 125V start voltage.

So 10 Panels in series would be 360V and the current would be 10.62A so that array would produce 360x10.62 = 3823W of power. If you make two of these string and use 20 panels you will have 7646W of power. The inverter would have two strings of MPPT inputs so you would plug each string in one input and 4 panels left over. You could add 6 more panels and make another set of 10 with the extra 4 and then parallel two strings together if the Inverter can handle 22 Amps of current but given your usage I think a 7.6Kw array is more than enough.

 

[John Frum]

But I can't seem to find a charger/inverter that can handle that many amps. For example, the largest Victron on this page (Quattro 48/10000) can only handle 200 incoming amps (assuming I'm reading this correctly).

The inverter only draws the dc current that it requires.
10000 ac watts / .85 conversion factor / 48 volts low cutoff = 245.098039216 service amps.
I wonder if you are talking about an mppt charge controller.

 

[IP4]

The inverter part is sized to for the maximum continuous load and the maximum instantaneous load.
The charger part is sized to charge your batteries in the amount of time that you choose.

See my signature for the load question.
22000 watt hours / 51.2 nominal volts = 429.6875 amp hours
That is how many amp hours you need to replenish daily.
Will your inverter/charger be connected to mains power or a generator or no ac input?

Hi smoothJoey - there will be no mains power or generator. It's 100% solar.

 

[John Frum]

Hi smoothJoey - there will be no mains power or generator. It's 100% solar.

An inverter/charger is composed of an automatic transfers switch, ac2dc charger and an inverter.
The first two functions are not useful in your setup.
Although for a system of this size you probably won't be able to source a decent discrete inverter.
Sound like you need an mppt solar charge controller.

 

[IP4]

Panels in series you add the voltages and panes in parallel you add the currents/Amps.
So if the panels are rated at a Vmpp of each panel is 36 Volts and the Impp is 10.62 Amps then 12 of them is series is 12 x 36V = 432 Volts and because they are in series the Amperage does not change so its 432V at 10.62A.
If you parallel two strings of 12 panel in series the you get 432V at 21.24 Amps

Hi robby. The conversions of parallel vs series always get me. I need to really read up on that.

So you're saying the Quattro 48/10000 charger inverter can handle all 24 panels if I connect them the way you described?

Also to clarify: as far as watt usage at any moment, I don't expect it to ever be more than 4500 (on the rare occasion).

 

[IP4]

An inverter/charger is composed of an automatic transfers switch, ac2dc charger and an inverter.
The first to functions are not useful in your setup.
Although for a system of this size you probably won't be able to source a decent discrete inverter.
Sound like you need an mppt solar charge controller.

I thought the Quattro is an MPPT charger combined with an inverter. Is that right?
Also, I don't expect to ever draw more than 4500 watts from an inverter at any given moment (and that much would be rare, but still possible). I should have mentioned that in my first post.

 

[John Frum]

I thought the Quattro is an MPPT charger combined with an inverter. Is that right?

It does not include solar charge controller functionality.
Do you need 120VAC or 120/240VAC or something else?
Said another way, what country do you live in?

 

[IP4]

It does not include solar charge controller functionality.
Do you need 120VAC or 120/240VAC or something else?
Said another way, what country do you live in?

120VAC, for US - thanks!

 

[John Frum]

120VAC, for US - thanks!

That is a huge pv array for 120VAC.
Let me ask another way, are you planning on powering your house?
If yes, does your house have an existing panel?
The vast majority of residences in the united states have a 120/240VAC split phase panel.

 

[robby]

Hi robby. The conversions of parallel vs series always get me. I need to really read up on that.

So you're saying the Quattro 48/10000 charger inverter can handle all 24 panels if I connect them the way you described?

Also to clarify: as far as watt usage at any moment, I don't expect it to ever be more than 4500 (on the rare occasion).

See my post update.

 

[IP4]

That is a huge pv array for 120VAC.
Let me ask another way, are you planning on powering your house?
If yes, does your house have an existing panel?
The vast majority of residences in the united states have a 120/240VAC panel.

I'm planning on powering a cabin off-grid. None of this exists yet (not even the cabin or the land for the cabin) but I don't want to buy anything until I am sure of all details.

 

[John Frum]

I'm planning on powering a cabin off-grid. None of this exists yet (not even the cabin or the land for the cabin) but I don't want to buy anything until I am sure of all details.

What is our largest draw ac load?

 

[OffGridInTheCity]

Hi - I'm trying to plan an off-grid system and have run into a problem with selecting an inverter/charger.

The system needs to handle 22 kWh per day (most days won't need that, but just being safe). I plan on using 48v for everything, with LiFePO4 batteries.

Based on that usage, this site says I'll need 24 x 365 watt panels. My own calculations are roughly the same. A 365 watt panel has a max output of 10.62 amps.
So, 24 panels x 10.62 amps = 254.88 amps. But I can't seem to find a charger/inverter that can handle that many amps. For example, the largest Victron on this page (Quattro 48/10000) can only handle 200 incoming amps (assuming I'm reading this correctly).

What should I do? Thanks!

I have a 13kw pv array off-grid system. In my case - I went individual components.
1) Charge Controllers - I use 3 x Midnite Classic 150 charge controllers, each one maxes out at 4500kw PV in and 86a out at 48v. Each one is connected to a common bus at the battery control box, so I can generate up to 258a @ 48v of charging.

The thing about charging batteries is not the amount of PV coming in but rather the size / specifications of the battery. In my case, my battery is big enough to handle 300a of charging. I didn't see how big a battery you plan - but this will be key.

2) Inverters - I use a pair of AIMs 48v@12,000w inverters and cooperate with grid thru ATSs. These AIMS do have the ability to accept 240v input with a max 120a of charging @ 48v. BUT these are actual 'chargers' (rather than charge controllers) and cannot invert and charge at the same time.

--------------
These days, all-in-ones are popular and look quite good. I have an MPP Solar 3048 in my trailer and it's running *very well*!! But again, you can only charge what your battery will allow

 

[IP4]

See my post update.

Thanks! That helped. I just picked Victron as an example. I don't have any equipment yet and am just planning. I just know Victron has a good reputation but they're pricey. Pricey is ok because I want to avoid "cheap" items, but of course I'd like to save as much money as possible since this setup will cost a lot no matter which brand I go with.

 

[IP4]

I have a 13kw pv array off-grid system. In my case - I went individual components.
1) Charge Controllers - I use 3 x Midnite Classic 150 charge controllers, each one maxes out at 4500kw PV in and 86a out at 48v. Each one is connected to a common bus at the battery control box, so I can generate up to 258a @ 48v of charging.

The thing about charging batteries is not the amount of PV coming in but rather the size / specifications of the battery. In my case, my battery is big enough to handle 300a of charging. I didn't see how big a battery you plan - but this will be key.

2) Inverters - I use a pair of AIMs 48v@12,000w inverters and cooperate with grid thru ATSs. These AIMS do have the ability to accept 240v input with a max 120a of charging @ 48v. BUT these are actual 'chargers' (rather than charge controllers) and cannot invert and charge at the same time.

--------------
These days, all-in-ones are popular and look quite good. I have an MPP Solar 3048 in my trailer and it's running *very well*!! But again, you can only charge what your battery will allow

Thanks! For batteries, the same calculator suggested 34447 watt-hours (718 amp-hours @ 48V), LiFePO4. My envelope math was similar.
As far as the all-in-one, I'm totally flexible at this point since I have no equipment and am just planning. If I can do something better and/or less expensive but still good quality, I'm all for that.

 

[OffGridInTheCity]

Thanks! For batteries, the same calculator suggested 34447 watt-hours (718 amp-hours @ 48V), LiFePO4. My envelope math was similar.
As far as the all-in-one, I'm totally flexible at this point since I have no equipment and am just planning. If I can do something better and/or less expensive but still good quality, I'm all for that.

It depends on the actual LifePo4 specs of course but let's say you do 16s7p of 100ah for 700ah@48v. Assuming you can charge each cell at 50a then 7p * 50a = 350a max charging.

On battery size. I run a 13kw PV array which generates 18,000kwh/year on an 81kwh battery bank and have a yearly average of 38% DOD to be able to consume 100% of the PV generated. By extrapolation, your 9kw PV array is about 70% of mine leading to a 57kwh at 38% DOD for a similar experience. If we take the 38% and double it to 76% (e.g. 80%) DOD we can cut the battery size by 50% to the 29kwh range.

So I'd say a 34.5kwh battery will do it and you might be able to go a bit smaller - 16s6p of 100ah cells instead of 7p for 30kwh battery bank to be able to use all the PV. 6p * 50a = 300a max charging.

In any case - I'd say you're right in the zone with your sizing

 

[IP4]

What is our largest draw ac load?

The largest individual item is a microwave at 1470 watts AC, but would only run 30 minutes a day.
The mini-split Air Conditioner would run at 1060 watts AC for 10 hours a day in the summer, making it by far my largest consumer.

 

[robby]

Thanks! That helped. I just picked Victron as an example. I don't have any equipment yet and am just planning. I just know Victron has a good reputation but they're pricey. Pricey is ok because I want to avoid "cheap" items, but of course I'd like to save as much money as possible since this setup will cost a lot no matter which brand I go with.

Take a look at the Sol-Ark 8K or 12K
Sol-Ark
Since your not using any Well Pumps the 8K should be perfect fit for you system. If you want a bit more than go with the 12K.
These units manage loads very well and are very easy to setup and overall just work with very little user intervention. Having 240V is going probably to be very handy to have as you don't have to be limited to just 120V appliances.

If this is out of your budget range then at a significantly lower price take a look at MPP series line of Inverters like the LVX6048. If you really just want to stick with 120V then MPP also makes Inverters that will do that.