Solar panel wire question

rc626184

So have a ground mount system that is going to be axitec 270w panels 46 of them equal to 12420 watts but will be upgrading to 16kw in later future so I need to size the wire larger. I am not sure if i will go with aps320  invertors or 2 solar edge 6000. The distance from the panels to the house panel is 150 ft. i would really like to put the solar edge in the basement because of its 50 degrees all time and that's what I want. but if I go with solar aps micro invertor i would be running a ac wire to the panel where as the solar edge in the house would be a dc wire . What wire size would i have to run if i had a solar ege in house  for the two solar edges  and how many wires ?  What wire size would it be if i ran a ac wire to house ? tks in advance

mike95490

If you have no shade issues, forget about the micro-inverters, and focus on string inverters.  Better to run the HV DC the long distance, and then the 240VAC from the inverter the short distance to the elect panel.

But you can't guess on this stuff.   Figure out your 16Kw array, how its going to be wired, combiners or multiple DC input inverters.

Use a wire gauge calc for the distance, and see what gauge works out the best with cost vs loss.   Don't forget to include calcs for aluminum wire too, easier to pull than copper, lighter and of course, less expensive.   More care needed to make reliable connections.

rc626184

the hole reason for this post with all the facts i put in was for someone to give a recommended size ... mike im sorry but that does not answer my question other than you recomend using dc wire for long distance. i figured the ac would be better because of the voltage drop  and the size of the wire would have to be huge. but im not sure if my calculations are right hence the post. i will not use alluminum wire because it can not hand high temps as it melts at a much lower temp then copper . Thats why most of them burn up .

BB.

We need to know the input voltage range for the inveter(s) you plan on using... For example, a 600 VDC max input inverter typically needs around 300-400 Volts Vmp-array input... To high, it will shut down (and possibly cause damage) to the GT inverter in freezing weather. Too low for Vmp-array-hot, the inverter may not start or not run efficiently below ~250-300 volts on Hot days (something like 180 VDC minimum to start up is a typical number).

Regarding aluminum--The problem with aluminum is not the absolute maximum operating temperature for aluminum but the mechanical properties of the metal.

When compressed (installed binding screw), the aluminum can get hot and "extrude" from under the (improperly designed) binding screw/system. Then when the joint cools (at night for example), the aluminum contracts and leave a little air gap between the binding surface and the aluminum. The exposed "raw aluminum" (in minutes" developed a insulating oxide which reduces contact area and eventually cycling will increase the joint resistance causing it to overheat and possibly catch fire.

In theory, the newer CU/AL rated connections are not supposed to do this... Or you run your main run with (~3 AWG heavier) AL main cable and use approved compression fittings at each end to convert from AL to Copper pigtails. Aluminum and rated compression fittings (crimped with the correct tools) are very secure and reliable (hermetically sealed) and used on pole to house drops "everywhere" in the US (at least in my region).

If you want to run copper--That is fine (and would be my personal preference). But many have used Aluminum too.

Sending the power longer distances (in terms of residential scale systems)--Does not matter if AC or DC. Running Vmp-array at ~300-400 volts is a lower current than ~240 VAC nominal--So you can use smaller diameter cable and/or send farther distances.

Also--It does depend on what and where you need your power... if you need no AC power near your solar array (no out buildings, no water pumping, etc.), then sending 300-400 volts Vmp-array power is (in theory) the least costly solution. Also, voltage drop and variations do not matter to the GT Inverter--It takes whatever Vmp-array*Imp-array and converts that to your local ~240 VAC (if single phase) power.

If, however, you need 120/240 VAC at the array (out building, etc.), you can run the GT Inverter (or micro inverters) at the array and run a 240 VAC branch circuit from the "house to the out building" so you have your one long run servicing both the GT Array and your local power needs. Note that running long cables of 240 VAC at high current levels (shop tools, GT Solar pushing current back to the home) can end up with voltage drop and voltage "rise" (i.e., the "backwards current flow" from GT solar)... (I.e., if your high line is ~255 VAC and you have a 3% rise or +7.65 volt rise--You are really close to where the GT inverter is supposed to shut down for safety (typcially around 260-264 VAC is shutdown). For folks at the end of the rural power lines, sometimes there is a wide range of AC mains voltage (summer/winter/local processing plants/etc.).

Running DC voltage to the GT inverter at the home removes Voltage "rise" as an issue for the long branch circuit.

I hope this helps--A lot of typing and hand-waving here.

-Bill

rc626184

it kinda does but with the info i be using a common solar edge invertor se6000h and the panels axitec 270 w 31v panel runing a 9 amp each cant you figure that out . see im not sure if that invertor wires in parrel  , series or combination. so im unable to no what the voltage would be for the dc wire . if it were parrlel it would be the 31 as volts stays same but if it were series volts adds .. so i guess im looking for someone that has experience with this type of system and ohms law that would give me a ideal in the differant size wire needed from ac to dc . and what they had recomend . tks tho 

mike95490

Lets play with  8,100w  30 PV panels.  270W  40Voc  31Vmp  8.7Imp (my best guess from your #'s)  This will be "close"

40Voc means max of 13 in a string, 10 gives 400Voc & 310Vmp  Might need 11 panels to fire up a inverter min voltage

3 strings of 10 panels gives 26A @ 310VDC  for 150'

Converted to 240VAC, that's about 33A, and could be done with #8 wire for a short run from inverter to Meter Box

You need 6ga copper wire , 300'   ( x2 for your 150' run)

or  4ga aluminum wire (for the same amps) 300'   price those out, a couple extra bucks for the copper splices (after you pull the wire runs) and you may have to pull a ground wire too.

When you actually select an inverter, you can juggle the numbers a bit, and if it does not get too cold in your climate zone, maybe 15 panels in a string (600Voc) if your inverter can take it.

rc626184

tks mike so you think if i did a 6awg wire from panels to inside house with invertor in house i would be ok . I  was wonsering how many wires would go to each invertor there are two optoins a solar edge rated for 11400 that goets to 15.5max  or 2 of the solard edge that are aroudn 6000 each. so first questions how any wires go to a invertor ? and should i run a ground under the ground ? i do plan on putting in two new grouding rods next to the panels unless they ok just grounding the metal ground mount . whats  your recomomendation. 

Photowhit

Solar Edge has some string sizing tools for down load.

https://www.solaredge.com/us/products/installer-tools

At this point I guess you understand that you would be running higher voltage with a common inverter, than with micro inverters, though DC current.

rc626184

thank you so any comments on my decision to use solar edge in basement and to use axitech panels . i no the panels is a new company but they have great reviews. this is my first system and has been really challenging because most salesman only love their crap and so much to choose from. im opon to anyones opinions if im choosing a good system or junk .

mike95490

I think at this point, you should pause, think, and maybe get the book "Solar Power for Dummies".  Disgusting title, but it really does cover the basics pretty well.   Use the info from here, and from the book, and get a good plan together in your mind, before you spend any money.   Are you planning to install this yourself, or have a professional install it ?

What I have presented is a educated guess based on some numbers from your PV panel.  The actual inverter will drive the final decisions.  Do it all on paper, revise it, and do it over again, till there are no more issues.

Photowhit

rc626184 said:

thank you so any comments on my decision to use solar edge in basement and to use axitech panels . i no the panels is a new company but they have great reviews. this is my first system and has been really challenging because most salesman only love their crap and so much to choose from. im opon to anyones opinions if im choosing a good system or junk .

I don't deal much with grid tied systems. I think current requirements are to have a disconnect that is accessible on the outside of the building, and I think it's integrated into the inverter. Do your research.