Reverse PV Combiner Box?

[AlaskanNoob]

So if we switch instead to the 250/100 SCC and get four of them, we can cut the wires down to 8 wires, preserve the ability to dump 400 amp to charge the battery bank. Now I just have to size the wires for the lower voltage and increased amps to see about that option...

 

[Hedges]

Also note that with a large bundle of 32 wires running that far, you will likely need even larger gauge wire to deal with the extra heat

He's AlaskanNoob
But seriously, there is a derating for conduit loading, but also adjustment up or down for temperature.

 

[rmaddy]

For Four 450/200:

You are looking at 16,000' of wire (32 x 500'). Depending on the Voc and Isc of each string and what you consider an acceptable voltage drop, you might be looking at 10AWG to 4AWG. That's probably somewhere in the range of $8,000-$32,000 just for wire. You might want to lay two conduits where each can handle 16 wires. Run the initial 16 wires for half the cost now and spend the other half and pull them through the 2nd conduit if and when the time comes for the extra PV.

While I was typing that you posted about switching to four 250/100 SCCs. That's half the charge current and half the total wattage. But it's 1/4 the wires. So even if you got eight 250/100 SCCs to match the four 450/200 SCCs, that's still half the wires.

 

[rmaddy]

He's AlaskanNoob
But seriously, there is a derating for conduit loading, but also adjustment up or down for temperature.

Good point but wasn't there just some record high temps in Anchorage (or nearby) recently? Something like 60ºF in winter?

 

[AlaskanNoob]

So to future proof and allow us the ability to double our PV in the future we have options:

a). 2 x 450/200 SCCs and 32 x 8 AWG wires

or

b) 4 x 250/100 SCCs and 8 x 2/0 wires

 

[rmaddy]

a). 2 x 450/200 SCCs and 32 x 8 AWG wires

2 x 450/200 SCCs and 16 x 8AWG wires (not 32 wires - that's for 16 trackers or 4 x 450/200 SCCs)

 

[AlaskanNoob]

2 x 450/200 SCCs and 16 x 8AWG wires (not 32 wires - that's for 16 trackers or 4 x 450/200 SCCs)

I'm adding those extra wires trying to preserve the option of doubling the PV in the future. So 14 of those wires would be plugged in, the rest would just be laid in the trench and unplugged but there in case we added more panels later (and more SCCs).

I know I'm not being clear with my stream of consciousness and sometimes I talk about what I would use now, and what I want to preserve to future proof, so I'm muddying the discussion and making it hard to follow.

 

[WYtreasure]

I see combiner boxes that will take strings of PV and combine them, in parallel, onto one wire. Is there a box on the other side that can split that back into several wires per string to plug into several MPPTs?

Alrighty then,
It's Saturday Night and We're LIVE.
DId you mean to post this in the HUMOR forum?

 

[rmaddy]

I'm adding those extra wires trying to preserve the option of doubling the PV in the future. So 14 of those wires would be plugged in, the rest would just be laid in the trench and unplugged but there in case we added more panels later.

OK, then it's either 32 wires for 4 possible 450/200 SCCs or it's 16 wires for 8 possible 250/100 SCCs. Those two options should handle the same amount of PV.

 

[Hedges]

22kW/400V/8 circuits - 6.875A/circuit
1000' of 12 awg 1.6 ohms
6.875A x 1.6 ohms = 11V
11V/400V = 2.75% drop

I would consider allowing twice that voltage drop (2 strings per wire pair instead of 1) and derating for conduit fill might still be OK. IF not, more PVC conduit for fewer wires per.

Should be $2000 in wire for the live circuits.

 

[AlaskanNoob]

So to future proof and allow us the ability to double our PV in the future we have options:

a). 2 x 450/200 SCCs and 32 x 8 AWG wires

or

b) 4 x 250/100 SCCs and 8 x 2/0 wires

Okay, so option B is definitely out. I don't have $50,000 to spend on wires. Truth be told, after a month or so of posting on this board I'm already on my third marriage and I want this one to last...

 

[Hedges]

Check my math on 12 awg.
What are your PV panel ratings? What series/parallel configuration?

 

[AlaskanNoob]

OK, then it's either 32 wires for 4 possible 450/200 SCCs or it's 16 wires for 8 possible 250/100 SCCs. Those two options should handle the same amount of PV.

The way I calculated it, it would be 8 wires for the 250/100 SCCs because on those wires I could take my 4s3p strings and make them 4s6p and use those same 8 x 2/0 wires.

But there is no way I can afford 8 x 2/0 wires so that's out. I don't have $50,000.

And 32 x 8 AWG wires is also incredibly expensive at something like $14,000. I don't like that number either.

 

[AlaskanNoob]

Check my math on 12 awg.
What are your PV panel ratings? What series/parallel configuration?

Asking me to check math....you asked for it...

I think perhaps "22kW/400V/8 circuits - 6.875A/circuit" doesn't account for the temp correction. 1.23 in my area for possible -20F temps. So taking the SCC limit of 450 and dividing it by 1.23 = 365. 365 / 46 = just under 8. So that's why I went with 7 panels in each string.

For the 450/200s I'd have strings of 7 in series. Bifacial panels with a VOC of 46. ISC is 10.23.

Each of the 450/200's 4 trackers is limited to 20 amps.

Now eight panels like you calculated would just barely go over the max voltage of the unit potentially. I know there is discussion of clipping and whether that is okay or not, but I've just been doing my math to keep it under the 450 of the 450/200. Maybe I'm being too conservative.

 

[Hedges]

The way I calculated it, it would be 8 wires for the 250/100 SCCs because on those wires I could take my 4s3p strings and make them 4s6p and use those same 8 x 2/0 wires.

4s of PV panels?
I thought you were looking at a 600V controller.

For the 450/200s I'd have strings of 7 in series. Bifacial panels with a VOC of 46. ISC is 10.23.

Each of the 450/200's 4 trackers is limited to 20 amps.

7 x 46Voc = 322Voc at 25 degrees C. No more than 386Voc in freezing weather, can sharpen pencil with temperature coefficient of Voc and record cold temperature.

I think you can use longer string, higher voltage lower current.
Up to some conduit fill, you could use 12 awg and have maybe 4.1% loss (only when current at peak)

 

[jeremyee]

Thanks.

I'm essentially trying to figure out if I can run my PV into a combiner box, reduce the wires down to one (or maybe two) and run that the 500 feet to my cabin and then split it back up to feed multiple trackers in multiple MPPTs, OR do I have to have 7 smaller wires running the 500 foot distance to plug into the MPPT.

I'm not sure which would be better, I'm just asking about what can be done. Thanks for that info.

How many solar panels do you have? What is the voltage an wattage? How far from the MPPT controller to the solar array? How amny MPPT controllers or inputs do you have?

these questions will help answer how how many wires and what size wire you will need. All solar controllers (MPPT) have a input wattage and voltage limit.

Example, I have a 800 watt array. This is 4x 12 volt 200 watt panels in series to make 48 volt & 800 watts. That is 17 amps so my wire size is a min of 6 AWG for 60 feet @ 2% voltage drop. I can go up to 10 AWG @ 5% voltage drop but I want to increase my solar array to 1600 watts. So I need to increase the voltage to decrease the amperage. If I run 8x panels that are 12 Volts 200 watts each and put all 8 in series thats 96 volts @ 1600 watts which is 17 amps. The other option is to combine two sets of 4x panels in series, which would be 48 volts @ 1600 watts and teh amps would be 33. I can still use the 6 AWG wire for 60' @ 33 amps but the voltage drop will be 4%.

I hope this example explains the reason for the upfront design before buying all the equipment and wire. See the below link for a wire size calculator.

solar powered calculators, solar panel calculator | Renogy

Renogy's Solar Power Calculator Tool can quickly help to estimate your solar power requirements, calculate the size and cost of an off-grid solar system needed.

www.renogy.com

 

[AlaskanNoob]

Check my math on 12 awg.
What are your PV panel ratings? What series/parallel configuration?

4s of PV panels?
I thought you were looking at a 600V controller.



7 x 46Voc = 322Voc at 25 degrees C. No more than 386Voc in freezing weather, can sharpen pencil with temperature coefficient of Voc and record cold temperature.

I think you can use longer string, higher voltage lower current.
Up to some conduit fill, you could use 12 awg and have maybe 4.1% loss (only when current at peak)

I was looking at 2 x 450/200 SCCs and comparing that with 4 x 250/100 SCCs (which have only one PV input, but take in 70 amps).

 

[Hedges]

4s of PV panels?
I thought you were looking at a 600V controller.

Oh, my bad. Is Victron 450/200 the highest voltage they offer?
Some other brands have 600V SCC. I use 600V GT inverters. there are 1000V inverters.

I was looking at 2 x 450/200 SCCs and comparing that with 4 x 250/100 SCCs (which have only one PV input, but take in 70 amps).

You don't want 250V, even lower. At least stick with 450V and calculate Voc carefully.
I think you can use 8 panels in series not 7, but double check.

Normally I tell people to make one string face SE, another SW, and connect in parallel. They don't peak at the same time, give more hours of production, so better use of SCC and wire. But in your location probably due South is the only thing to consider.

 

[AlaskanNoob]

How many solar panels do you have? What is the voltage an wattage? How far from the MPPT controller to the solar array? How amny MPPT controllers or inputs do you have?

these questions will help answer how how many wires and what size wire you will need. All solar controllers (MPPT) have a input wattage and voltage limit.

Example, I have a 800 watt array. This is 4x 12 volt 200 watt panels in series to make 48 volt & 800 watts. That is 17 amps so my wire size is a min of 6 AWG for 60 feet @ 2% voltage drop. I can go up to 10 AWG @ 5% voltage drop but I want to increase my solar array to 1600 watts. So I need to increase the voltage to decrease the amperage. If I run 8x panels that are 12 Volts 200 watts each and put all 8 in series thats 96 volts @ 1600 watts which is 17 amps. The other option is to combine two sets of 4x panels in series, which would be 48 volts @ 1600 watts and teh amps would be 33. I can still use the 6 AWG wire for 60' @ 33 amps but the voltage drop will be 4%.

I hope this example explains the reason for the upfront design before buying all the equipment and wire. See the below link for a wire size calculator.

solar powered calculators, solar panel calculator | Renogy

Renogy's Solar Power Calculator Tool can quickly help to estimate your solar power requirements, calculate the size and cost of an off-grid solar system needed.

www.renogy.com

I think I detail most of those questions in this thread.

About to spend a lot of money tomorrow on this system (am I making a mistake?)

Planning on buying the bolded * items tomorrow for our completely off grid homestead. Big purchase for us! Just posting this in case somebody sees something glaring with our mix of components who might sound the alarm and prevent me from making a costly mistake. I'm showing the 22KW ground...

diysolarforum.com

This thread was meant to ask just the one question about a fictional reverse combiner box. Which doesn't exist. Likely because electricity doesn't behave like I was imagining. Even so, I'm going to make one and make bazillions of dollars. I'll be sure to post the Kickstarter as soon as I figure out how electricity works and how to get solar to my cabin without paying $15,000 for 32 wires...

 

[Hedges]

I think you could have 8 strings of 8 panels in series, each with 12 awg wire, about 5.6% loss at peak power.
That's about $2000 of wire. use 10 awg, about $3000, to reduce loss.

I'll be sure to post the Kickstarter as soon as I figure out how electricity works and how to get solar to my cabin without paying $15,000 for 32 wires...

Look up "Nikola Tesla" and we'll visit you in the madhouse.