Did I do my math correct?

[sed6]

so where did you get the idea anyone was encouraging undersized wires?

You gave me that impression because of what you said.
Guda said:
Or rely on a loss of current from a long wire run?
MBR said:
How long is your wire run from your panels to your charge controller

Sounded like you were gonna take that bad idea and encourage it, my mistake.

 

[Craig]

Doesn't matter, no one should encourage him to undersize his wire and burn off extra energy as heat because part of his system (charge controller) is undersized for his system (panels).

I guess you have unlimited funds huge price difference between 2 and 10 Awg

 

[Craig]

At those volts and amps for 120 feet round trip 8 is sufficient and 10 is possible but close to the edge

 

[sed6]

I guess you have unlimited funds huge price difference between 2 and 10 Awg

You must have misquoted me or not understood me or not read the whole thread.

Edit: I think you misunderstood me, I wasn't meaning that wire size and cost and panel location weren't important, they are but that's not what I was getting at. I was worried that MBR was encouraging undersize wire, which he isn't, so all is good.

 

[Guda]

I was planing on doing east, west & up. So I can have power all day. With 4 maybe 2 up then.

http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg. I was rounding up for better conductivity

By pointing the pv in different directions, I'm not as close to the edge & longer power curve. I think...

 

[Forbisher]

At those volts and amps for 120 feet round trip 8 is sufficient and 10 is possible but close to the edge

Actually 4 strings at 8 amps is 32 amps
10AWG is under 3% voltage drop as per that calculator.
Voltage drop: 3.84
Voltage drop percentage: 2.19%
Voltage at the end: 171.16

2AWG gotta cost a lot more than even 8 AWG wire.

http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg. I was rounding up for better conductivity

That chart is not accurate for panel wiring as it is only for 12 volts which requires much thicker wire than the much higher voltage from your series connected panels
Use the calculator i posted.
2 awg would cost a lot and is not needed.

 

[sed6]

By pointing the pv in different directions, I'm not as close to the edge & longer power curve. I think...

Good idea. Different directions will help with the amps but not the volts. My panels make peak voltage very early in the day and then the amps rise as the sun rises.

 

[Guda]

I cant find your post with the calculator. Is there a link?

I can use standard pv wire to connect all the panels & connect it all to the SCC? Or I'll need some bigger wire for that run? I'm not sure what "standard" pv wire gauge is. I'm referring to the wire I was sold with the same connector & wire size of the pv's.

 

[Cal]

Granted, 2 awg is too big (0.35% cable drop). I like to design to 1% drop, but given the long distance, 8 awg (1.4% drop) is a good compromise.

 

[Guda]

Good idea. Different directions will help with the amps but not the volts. My panels make peak voltage very early in the day and then the amps rise as the sun rises.

How many directions are you pointed in? Someone was saying I needed to look up what happens to shaded pv. I really counld not find anything bad. Just stuff how it will reduce the curennt to the lowest pv to the all pv. Thats kinda what I am going for with pointing in different directions.

 

[Craig]

Wire size calculator by voltage

Voltage drop and ampacity for 4/0 to 10 AWG for any voltage. "Chart is based on USCG, ABYC, and UL standards for marine-rated (105°C dry / 75°C wet) wire."

diysolarforum.com

 

[Forbisher]

I cant find your post with the calculator. Is there a link?

I can use standard pv wire to connect all the panels & connect it all to the SCC? Or I'll need some bigger wire for that run? I'm not sure what "standard" pv wire gauge is. I'm referring to the wire I was sold with the same connector & wire size of the pv's.

8 AWG is your best choice.
For the second time and the fields are filled in for you for your system.
Note that the distance is one way.

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

 

[sed6]

8 AWG is your best choice.

Agreed. IF he puts them 60' away in the yard. I'd vote for the roof instead with only a 10' run. For me roof mounting was the shorter distance also, cheaper than rack mounting, more secure from vandals and IMO roof mount looks better than rack mount in the yard.

 

[upnorthandpersonal]

Added those calculators to the Wiki as well: https://diysolarforum.com/ewr-carta/tools/

 

[CoryBaker]

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

 

[tictag]

Not quite sure if your original query has been answered, but I suspect it has.

The only thing I would urge caution is with facing the panels in different directions, unless you are planning to have one SCC for each 'direction'.

 

[Guda]

Not quite sure if your original query has been answered, but I suspect it has.

The only thing I would urge caution is with facing the panels in different directions, unless you are planning to have one SCC for each 'direction'.

I tried to find why that was so, but I could not. Explain ,link? Please thank you.

 

[Guda]

Pretty please

 

[tictag]

You just need to google 'partial shading' but the short version is that if you have a lower voltage panel in parallel with other panels, the output of the string will 'become' the lowest voltage in that string and similarly if a a panel is generating a lower current in a series string, it will 'become' the current flowing through that string. Either way, you lose power from the array as a whole (P=VI).

Why does this matter?

Because if you position your panels in different orientations to the sun (when connected as single array), there will always be times where one string has a lower voltage and/or current, thus you will always be losing power from the array you would otherwise be able to harvest if you either:

1. Orientate all panels in the same direction i.e. South OR
2. Use a separate SCC for each string orientation.

As I said, I found out the hard way having panels on the left-hand-side, right-hand-side and roof of my caravan. Spent months trying to figure out why I never got my full Pmax array output despite favourable weather. Once I learned about the effects of partial shading, I fitted two additional SCCs and I now I get what I would expect (considering that none of them are actually oriented perpendicular to the sun, but there's not a lot I can about that).

This is not new, or rocket science, just google 'partial shading'.

 

[Guda]

That is interesting. I have been looking at inverters that have MPPT in them also. As I add inverters I can rewire & get max power. The Midnite classic 250 might be able to do a better job. But we will see. There maybe a few incarnations of this system. Until I get a 48v battery its going to be 12v.

Much thanks!