Splitting PV at the inverter?

[Tulex]

Can the feed for the solar panels be split at the inverter to use 2 MPPT?
I've got to run around 100 feet, so would like to do it in one set of wires. Sol-Ark 15K will only do 6.5kW / MPPT | MAX 500VOC PV 26A self limiting.
The panels I'm looking at are 450W 41.25V (Voc) 34.67V 12.98 amps, max 1000V system voltage.

So can I put 24 of these in series and split it at the inverter into 2 of the MPPTs? 24 is 990V, holding at 13 amps.

As I was typing this, I looked up cable, I guess it's not that expensive, but why run 2 if it can be split.

 

[rodrick]

No 2 separate strings the mppts will fight each other

 

[meetyg]

Can the feed for the solar panels be split at the inverter to use 2 MPPT?
I've got to run around 100 feet, so would like to do it in one set of wires. Sol-Ark 15K will only do 6.5kW / MPPT | MAX 500VOC PV 26A self limiting.
The panels I'm looking at are 450W 41.25V (Voc) 34.67V 12.98 amps, max 1000V system voltage.

So can I put 24 of these in series and split it at the inverter into 2 of the MPPTs? 24 is 990V, holding at 13 amps.

As I was typing this, I looked up cable, I guess it's not that expensive, but why run 2 if it can be split.

No, I don't think you can do it that way.
You are exceeding the max VOC of the MPPT inputs, because of the 24 panels being in series.
Even a single string of 12 panels is pushing the VOC limit of your MPPT input.

 

[Ampster]

As mentioned above there is no practical way to split the voltage. It is much simpler to physically split the arrays into two strings. I understand 100 feet of wire seems like a lot but it will already be at a high enough voltage the loss will be minimal. It is usually the cost of the trenching and conduit that is expensive.

 

[Tulex]

Thanks guys.

The part that sucks is that the amps doesn't drop, so still the same size wire for both runs.
I used this site to size the wire. https://unboundsolar.com/solar-information/voltage-drop
Sol-Ark says 12-10 Awg wire (I don't know what size will actually fit), but at 100 feet, even 10 awg loses 8%. That's a lot.

 

[rodrick]

Thanks guys.

The part that sucks is that the amps doesn't drop, so still the same size wire for both runs.
I used this site to size the wire. https://unboundsolar.com/solar-information/voltage-drop
Sol-Ark says 12-10 Awg wire (I don't know what size will actually fit), but at 100 feet, even 10 awg loses 8%. That's a lot.

I think your calculations are off 10 panels is 412 volts at 13 amps 14 gage would only be a 2% drop the big problem is going over the 500 volt mark when temperature drops. 10 panels in series per mppt will be max maybe 9 if it gets really cold there

 

[zanydroid]

Looks like OP put in Voc instead of string voltage.

Also you can always upsize the run and transition down to the size that the terminals accept, though you want to use robust splice connectors for that, like Polaris style.

 

[Tulex]

I think your calculations are off 10 panels is 412 volts at 13 amps 14 gage would only be a 2% drop the big problem is going over the 500 volt mark when temperature drops. 10 panels in series per mppt will be max maybe 9 if it gets really cold there

Is the increased voltage just from the panels, or does the wire also play into it?
This makes it really hard to put a large array on one inverter unless you use parallel/series with the panels, but then you drive the wire size up from doubling the amps.

 

[Tulex]

Looks like OP put in Voc instead of string voltage.

Also you can always upsize the run and transition down to the size that the terminals accept, though you want to use robust splice connectors for that, like Polaris style.

You are correct, that's what I get from doing calcs after my bedtime.

 

[rodrick]

Is the increased voltage just from the panels, or does the wire also play into it?
This makes it really hard to put a large array on one inverter unless you use parallel/series with the panels, but then you drive the wire size up from doubling the amps.

You would make 2 series strings of 10 panels and run them on 2 separate lines to your 2 mppts 4 wires total in your run from pv array to mppts

Remember you are dealing with high voltage at this point it can kill you be careful!!!

 

[Tulex]

You would make 2 series strings of 10 panels and run them on 2 separate lines to your 2 mppts 4 wires total in your run from pv array to mppts

Remember you are dealing with high voltage at this point it can kill you be careful!!!

Right, but it's still a balancing act. The Sol-Ark 15K has 3 MPPTs, 4 connectors at each one, so 2 stings each. But, each MPPT can only handle 500 Voc and 26 amps. I'm looking at buying a pallet, which is 31 panels usually. Not only is the price about $.15 a watt cheaper, but I want to put in as much as I can to take advantage of what the inverter can do. If I run 2 strings to each MPPT, that's 6 sets of wire, so 1200 feet.

 

[Ampster]

If I run 2 strings to each MPPT, that's 6 sets of wire, so 1200 feet.

Unless I am missing something, isn't there a max Wattage of 6500. 26 Amps at 500 volts is 13000 Watts. You can do it but there will be a lot of clipping.

 

[timselectric]

Right, but it's still a balancing act. The Sol-Ark 15K has 3 MPPTs, 4 connectors at each one, so 2 stings each. But, each MPPT can only handle 500 Voc and 26 amps. I'm looking at buying a pallet, which is 31 panels usually. Not only is the price about $.15 a watt cheaper, but I want to put in as much as I can to take advantage of what the inverter can do. If I run 2 strings to each MPPT, that's 6 sets of wire, so 1200 feet.

Correct
That's how you can get the most out of it.

 

[Tulex]

Why would you need 6 sets (pairs) of wires. You could save wire by paralleling them at panel location instead of at SolArk. It is the same electrically but a lot less wire. I am assuming either way the strings are within voltage specs.

When I look at the larger panels (450 watt or larger), I'm seeing either higher Voc (in the 50v range), or higher amps (13+ range). So, if I parallel some of these at the panels, I could be going over the 26 amp limit.

 

[timselectric]

If all of the strings are in one location. You could combine them in pairs at the array. An only run one set to each MPPT, as @Ampster suggests.
I would compare prices of the two different sized conductors. And see what is more cost effective.
don't forget to add the cost of combining them.

 

[timselectric]

When I look at the larger panels (450 watt or larger), I'm seeing either higher Voc (in the 50v range), or higher amps (13+ range). So, if I parallel some of these at the panels, I could be going over the 26 amp limit.

The 26 amp limit is what the MPPT can draw. Not what you can connect to it. You will rarely get full output from the panels. Overpaneling helps on cloudy days.

 

[Tulex]

In reality, I know the cost of the wire, regardless of how I end up doing it, is just a small part. It's just that I haven't cut corners anywhere. So, this is adding up to way more than I expected. Just looking for a small win. Yes, I'd like some cheese to go with the whine.

 

[Tulex]

The 26 amp limit is what the MPPT can draw. Not what you can connect to it. You will rarely get full output from the panels. Overpaneling helps on cloudy days.

This is something I definitely didn't understand. So that is what self limiting is? Through whatever you want at it, it will just simply use up to the limit.

 

[timselectric]

This is something I definitely didn't understand. So that is what self limiting is? Through whatever you want at it, it will just simply use up to the limit.

Solar panels are just like the grid. You don't have to use everything that's available. Doesn't matter if you plug in a hair dryer or a phone charger. You only draw what is required. The difference is that you want to use all available with solar. And you don't when paying for the grid.

 

[timselectric]

But.......
VOC is a hard limit. Do not go above it.
Voltage is pushed. Amperage is drawn.