PV to Aluminum wire vs. Copper...

System

Hey Everyone,

I was wondering about using copper vs. aluminum wire when coming from our PV's to our power center. I have been pricing out copper lately and to say the least, it is rediculous. We would spend the same on copper that we would for more than twice that in aluminum.

I had read back a while ago that using aluminum on dc power can lead to faster corrosion of the wire. Is this true?

Thanks,
Matt

niel

Re: PV to Aluminum wire vs. Copper...

you could use it, but you'd just about need twice the wire so you really wouldn't save on its usage. aluminum has more resistance than copper is the reason. it also expands and contracts more than copper so bad connections can develope if not done correctly. aluminum gage for gage breaks easier than copper and using aluminum means galvanization if connected to copper only connections. you're just not going to get around the cost of good wires so save yourself some hassle and get the copper unless somebody gave you the right size aluminum wire.
as to dc causing more corrosion, i haven't ever heard of this one and moreover, i've never heard that running ac into it would do this either for if done right there isn't any corrosion. wires will tend to corrode or rust left exposed to moist air though so don't confuse this with the power running through them. dissimilar metals like copper to aluminum will cause this corrosion or galvanic reaction as will all dissimilar metals tend to do this. i hope this sets you straight.

BB.

Re: PV to Aluminum wire vs. Copper...

Not a clear yes or no answer... Legally, using the correct connectors/parts/anti-corrosive compound to join everything together, Aluminum is fine--but, of course, you knew that.

Some issues:

You will need, roughly, two American Wire Gauges larger Al wire vs Cu wire (10 awg copper would be, roughly, equivalent to 8 awg Al in rated current). So, you may also need larger conduit/wire trays to run the cable.

Aluminum is more sensitive to how you install it. You should sand the wire ends (to remove oxide layer) and use an approved anti-corrosive compound.

Connectors need to be Al rated (or Al/Cu rated).

The best Al connectors are compression/cold forming type connectors--requires a special crimping tool to apply.

Al wiring will probably tend to run a bit cooler, and may have less resistance (lower power loss)--especially since you can afford larger wire gauges.

Check with your local building department/code... Some will not allow anything smaller than 6 awg to keep it out of home wiring (10 and 12 awg Al would be equivalent to 12 and 14 awg for Cu).

Here is a link with some suggestions and more links to read (end of link 2):

http://www.hsb.com/thelocomotive/Story/FullStory/ST-FS-ALUM.html Reducing the Risk of Aluminum Wiring Hazards, Part 1
http://www.hsb.com/thelocomotive/Story/FullStory/ST-FS-ALUM2.html Reducing the Risk of Aluminum Wiring Hazards, Part 2

Basically, there is, probably, slightly more risk of failure with Aluminum wires (apparently, in the smaller gauges) and the newer aluminum alloys have resolved many of the issues with older aluminum wiring (1960s-1980's+).

For myself, if the wire is in a damp area, I don't have sealed compression fittings, and/or it would be difficult to access the connections for inspection and repairs--I would probably go all copper.

If, I have the correct tools and components for Al/Cu wire, and the price is just a killer (project would not be done without aluminum wire)--I would probably use Al wire and components and just cross my fingers. Make sure that all wiring is properly supported (no vibration or bending motions to loosen connections or work harden the wire).

-Bill

System2

Re: PV to Aluminum wire vs. Copper...

Funny, it seems that I should just go the copper route. The cost when compared to the entire system is negligible and I really don't want to deal with an oops on the alum.

Thanks all,
Matt

System2

Re: PV to Aluminum wire vs. Copper...

Just a bit of info from Nova Scotia Canada.
Here, electricians are now using mostly aluminum from the mast head through to the meter base and into the main panel. It's about 1/3 the cost, (here) even with the larger guage required. Example, a 100 amp entrance always used #3 copper, now using #2 Aluminum. #6 copper is replaced by #4 AL.
Seems that sometimes they go two guage larger, while other times, just one guage. All approved by the inspectors. Of course the meter base etc has different terminals for copper only, vs CO/AL.
Wayne

Roderick

Re: PV to Aluminum wire vs. Copper...

Speaking to corrosion in general, my experience with open-air relay contacts many years ago was that DC was much more conducive to corrosion. I think that's because the current goes only one way, and the current flow allows one side to get corroded. If AC went across the contacts, they seemed to be self-cleaning.

An experiment with electrolysis can give you an idea of what's happening. Take two bare copper wires, connect them to a battery or solar panel, and immerse them in some salt water. Both wires will bubble, one with oxygen, and one with hydrogen. After a while, you will see that one the wires has an oxidation layer, and actually isn't conducting very well. The other wire will look really shiny and clean. If you reverse the direction of the current, the opposite will happen. Since AC keeps reversing its direction, you would be cleaning each terminal about half the time.

ggunn

Re: PV to Aluminum wire vs. Copper...

niel wrote: »

you could use it, but you'd just about need twice the wire so you really wouldn't save on its usage.

Au contraire. For a long AC run in a large system, the difference in cost between copper and aluminum for the same voltage drop can be tens of thousands of dollars. I know this is an old thread (maybe the relative cost between Cu and Al is a lot different now), but I found it searching the web for the advisability of using aluminum for long AC runs. I've found nothing definitive yet. Even John Wiles (I emailed him) doesn't take a position.

mike95490

Re: PV to Aluminum wire vs. Copper...

I've got several 1,000 foot runs of aluminum 240VAC wire on my property, some is #4 ga 400' to my well pump.

Use approved interfaces to the copper, and use the "goop" on them and it should be fine.

Pierman

Re: PV to Aluminum wire vs. Copper...

On a similar thought, I have set my panels about 200' from my inveters and batteries. The copper sizes out to be a MCM250 at a price pushing $4000.00 I have a roll of 1/0 aluminum steel core over head cable I had leftover from a elevated water tower lighting rod grounding. If I am reading things correctly from the mfg, this cable has a circle mil of about 100,000 and good for 240 amps. The MCM250 copper has a circle mil of about 250,000 good for 600 amps. I am considering using 3 cables bundled together in a sealed conduant to cross the 200 ft. I would need 4 conduants each with the 3 cables to make this happen. The cable is bare, but I'm thinking that I would heat tape the last 2 ft on each end and crimp lugs on both ends so it can be bolted in at the connections. I know this is uncoventional and won't pass code, But is their any reasons that I'm overlooking, why it would not work. Thanks for you thoughts.

Cariboocoot

Re: PV to Aluminum wire vs. Copper...

Pierman, welcome to the forum.

Could you give us some details on the specs of your array? You say "inverters and batteries" so I assume this system uses a charge controller. It may be a good idea to run the array at a very high Voltage, even such that you'd use a Xantrex XW 600 MPPT 80 controller. 200 feet @ high Voltage should not require extremely large wire.

Example: maxed out XW controller would be 5 kW array. That would be <18 Amps @ around 300 Volts. 10 AWG would work for that wire run with minimal loss. You could probably use 8 AWG, 240 Volts, 20 Amps, and a MidNite Classic 250. A lot easier to deal with than 1/0 aluminium.

NorthGuy

Re: PV to Aluminum wire vs. Copper...

Pierman wrote: »

On a similar thought, I have set my panels about 200' from my inveters and batteries. The copper sizes out to be a MCM250 at a price pushing $4000.00 I have a roll of 1/0 aluminum steel core over head cable I had leftover from a elevated water tower lighting rod grounding. If I am reading things correctly from the mfg, this cable has a circle mil of about 100,000 and good for 240 amps. The MCM250 copper has a circle mil of about 250,000 good for 600 amps. I am considering using 3 cables bundled together in a sealed conduant to cross the 200 ft. I would need 4 conduants each with the 3 cables to make this happen. The cable is bare, but I'm thinking that I would heat tape the last 2 ft on each end and crimp lugs on both ends so it can be bolted in at the connections. I know this is uncoventional and won't pass code, But is their any reasons that I'm overlooking, why it would not work. Thanks for you thoughts.

Looks like you're oversizing your wires.

I'm thinking about adding a new array 300ft from the power room. When I did the desing, my choice was between #6 and #4 wires for 3.5kW 150V controllers, or #10 wire for 5kW 600V controller.

Cariboocoot

Re: PV to Aluminum wire vs. Copper...

NorthGuy wrote: »

Looks like you're oversizing your wires.

I'm thinking about adding a new array 300ft from the power room. When I did the desing, my choice was between #6 and #4 wires for 3.5kW 150V controllers, or #10 wire for 5kW 600V controller.

Great (Canadian) minds think alike.

gww1

Re: PV to Aluminum wire vs. Copper...

I have thought about this alot and still seem to be ending up "weakly" in the same place. I also am running a 200' run and trying to do it to fill two fm80 charge controllers. I am doing not quite 90 volts from the pv. I am only going to start with 2820 watts worth of panels but like the ideal of being able to expand to the max of the charge controller with a less then 3% line loss. It was explained to me that lots of times you to not get full panel rated output and your losses are less except at full output.

It has been suggested that I could maby get buy with as low as 6 awg wire. That losses might not be bad enough to worry about.

I came up with either 1/0 awg or 2/0 awg copper for a les then 3% line loss.

My quandry is that when I price wire, mostly on ebay, but also in stores and other sites, I find the 4/0 gage direct burial aluminum wire is cheaper then even the small copper and believe it or not it is even cheaper then the 1/0 and 2/0 aluminum wire. That is even before the conduit that would have to be used with the copper. 2 awg copper cost more then double the 4/0 direct burial aluminum.

It seems to be easier to get copper fittings then aluminum. I keep thinking with the 4/0 aluminum, for the price, I can pretty much do anything I want later with out worry about line loss but I trust copper.

As I have found no salvage wire yet that might be cheaper I think I am going to have to buy new. I have a guy at work that has about 100 foot of 1/0 3 wire aluminum but I am afraid to try using it in any way cause I would have to splice it underground and I wouldn't trust the slice.

I still have no ideal what to do when I think about it. I will probly buy the 4/0 direct burial wire in full lenght with no splicing untill I go into the building with a pig tail of copper. I welcome you to call me stupid in my plan cause I really don't know what is best. I have been adviced by a couple of you and then I look at the prices and end up back where I started. Advise me one more time please.

Thanks
gww

gww1

Re: PV to Aluminum wire vs. Copper...

Also If I go with smaller copper am I correct in that it needs to be stranded not solid. What does the insulation code need to be "thw,thhn..." ?
Thanks
gww

Vic

Re: PV to Aluminum wire vs. Copper...

Hi gww,

Yes wire in conduit should be stranded.

Some definitions of dire ratings:
http://www.southwire.com/support/BldgWaCDesig.htm

Good Luck, it is never easy, Vic

gww1

Re: PV to Aluminum wire vs. Copper...

Vic
Thanks, no other thoughts or preferances?
gww

vtmaps

Re: PV to Aluminum wire vs. Copper...

gww1 wrote: »

I also am running a 200' run and trying to do it to fill two fm80 charge controllers.

If you have two charge controllers, they can share a battery bank, but they cannot share an array. You will need two runs of cable, one for each array/controller.

--vtMaps

gww1

Re: PV to Aluminum wire vs. Copper...

vtmaps
Yea, about 800' of wire.
thanks
gww

ggunn

Re: PV to Aluminum wire vs. Copper...

gww1 wrote: »

Vic
Thanks, no other thoughts or preferances?
gww

FWIW, we have gone over to aluminum for all long AC runs for the commercial installations we design. Fear of aluminum stems from experiences 40 years ago before alloying changes made it much safer to deal with.

gww1

Re: PV to Aluminum wire vs. Copper...

ggunn

Thanks, that helps calm my fears a bit.
gww

Pierman

Re: PV to Aluminum wire vs. Copper...

NorthGuy wrote: »

Looks like you're oversizing your wires.

I'm thinking about adding a new array 300ft from the power room. When I did the desing, my choice was between #6 and #4 wires for 3.5kW 150V controllers, or #10 wire for 5kW 600V controller.

I have 29 Kyocera KC175gt panels ( 1 was damaged during installation. I'm hung up trying to find a similar replacement. I'm open for any sujestions on this one. I have emailed Kyocera with no response.) I had it sized by an licensed electrician and he sized it for 250 MCM copper. Today, I was able to buy 360' of aluminum 4/0 three conductor with a ground direct burial for $2.00 per ft. I'm now thinking I'm going to use two conductors bonded together for the positive and the third conductor with the unshielded ground bonded for the ground. I will have enough to make two separate cables to feed the 2 MX60 inverters

Thanks

inetdog

Re: PV to Aluminum wire vs. Copper...

Pierman wrote: »

Today, I was able to buy 360' of aluminum 4/0 three conductor with a ground direct burial for $2.00 per ft.

You are probably OK, but confirm that the grounding conductor is actually 4/0. Some special purpose cables have a reduced size ground.
Indeed 2 x 4/0 aluminum should do the same job as 250kcmil copper, only better.

If you can find a panel that fits in the same space and has Imp within 5% of your Kyoceras (but not lower!) and Vmp anywhere within 10% or so in either direction, you will probably be OK substituting it.
Depends on how many panels you will be putting in your series strings. ( 6 strings of 5 versus 10 strings of 3) You will have smaller matching problems if you are using strings of 5, but that is probably above the Voc limit of the MX60 CC.

You might be able to just redesign for 7 strings of 4 panels and keep number 29 as a spare. But if you get cold temperatures that could still drive Voc too high.

NorthGuy

Re: PV to Aluminum wire vs. Copper...

Pierman wrote: »

I have 29 Kyocera KC175gt panels ( 1 was damaged during installation. I'm hung up trying to find a similar replacement. I'm open for any sujestions on this one. I have emailed Kyocera with no response.)

If the voltage of 2 panels in series is enough for controller/batteries combinations, and you believe your wire is think enough for the current produced by 7 parallel panels, you can build two uneven arrays 7x2 and 5x3. Otherwise, you would need to leave out 2 panels and go with 4x3 and 5x3.

Pierman wrote: »

I had it sized by an licensed electrician and he sized it for 250 MCM copper. Today, I was able to buy 360' of aluminum 4/0 three conductor with a ground direct burial for $2.00 per ft.

I've always trusted laws of physics more than licensed electricians. Oversized wires will not hurt you, and you've got a really good price.

Pierman wrote: »

I'm now thinking I'm going to use two conductors bonded together for the positive and the third conductor with the unshielded ground bonded for the ground. I will have enough to make two separate cables to feed the 2 MX60 inverters

You will need two positive and two negative wires (one positive and one negative for each MX60).

Pierman

Re: PV to Aluminum wire vs. Copper...

inetdog wrote: »

You are probably OK, but confirm that the grounding conductor is actually 4/0. Some special purpose cables have a reduced size ground.
Indeed 2 x 4/0 aluminum should do the same job as 250kcmil copper, only better.

If you can find a panel that fits in the same space and has Imp within 5% of your Kyoceras (but not lower!) and Vmp anywhere within 10% or so in either direction, you will probably be OK substituting it.
Depends on how many panels you will be putting in your series strings. ( 6 strings of 5 versus 10 strings of 3) You will have smaller matching problems if you are using strings of 5, but that is probably above the Voc limit of the MX60 CC.

You might be able to just redesign for 7 strings of 4 panels and keep number 29 as a spare. But if you get cold temperatures that could still drive Voc too high.

WOW! Thanks for the advice. Not much if a cold temp problem around here except for the heart of winter and that usually mild. Im in no mans land, below the upstate of SC and above the central part.

I never considered an odd number of strings. I thought that both inverters needed to be balanced with the same voltage and amperage. If I were to use the 7/4 panel arrangement, I would be feeding one MX with 4 strings of 4 and the other MX with the 3 of 4. The panel are rated for a max of 23.6 volts and 7.42 amps each. So a string of 4 would give me 94.4 volts at 7.42 amps??? The 4 strings combined would give 94.4 volts at 29.68 amps for one MX and the string of 3 would produce 94.4 volts at 22.26 amps for the second MX. The voltage would not change,only the amperage??? Am I getting this correct?

The original design was for 10 strings of 3. Five to each MX. Each string goes through a 10amp breaker. Do you think the 10amps will still work with the string of 4?

Thanks for your thoughts!

Cariboocoot

Re: PV to Aluminum wire vs. Copper...

For the record neither GT inverters nor OG charge controllers need to be identical on the amount of panel on their inputs nor on the size of the output. Both produce current @ Voltage and the Voltage is more-or-less determined "externally", so more than one of either feeding the same circuit will work together without any problem (aside from circumstances which would lead to exceeding current maximums for the circuit).

Man I am getting tired of having to add in caveats on every generalized statement I make. It seems some people have nothing better to do than bring up every minute exception they can think of just to "prove the moderators wrong". :roll:

vtmaps

Re: PV to Aluminum wire vs. Copper...

Cariboocoot wrote: »

Man I am getting tired of having to add in caveats on every generalized statement I make. It seems some people have nothing better to do than bring up every minute exception they can think of just to "prove the moderators wrong". :roll:

Power systems can be very unsafe if installed or designed improperly. You/we are giving some folks enough information to be dangerous to themselves and others. It is good that you include the caveats. Especially since you are a super moderator.

--vtMaps

ggunn

Re: PV to Aluminum wire vs. Copper...

Pierman wrote: »

WOW! Thanks for the advice. Not much if a cold temp problem around here except for the heart of winter and that usually mild. Im in no mans land, below the upstate of SC and above the central part.

Go to weather.com and enter your zip code. Select "monthly" on the panel on your left and select "averages" from the buttons at the bottom. Check the "record low" button and set the units as "metric" (both up at the top). Find the lowest dark blue dot; that represents the all time low temperature Centigrade for your location.

Calculate the number of degrees below 25 degrees C that temperature is, and use that number to correct Voc for your modules at that temperature; somewhere on the data sheet it will show a temperature coefficient for Voc in %/degree C (or rarely in mV/degree C). Multiply that number by the number of modules in a string and compare it with the maximum DC your inverter or charge controller can accept.

From there on it's a risk assessment. The conservative approach is to set your string length so that Voc can never reach the DC max even if the record low is reached again.

One other thing: some gear has a "black box" recorder that keeps track of the maximum DC voltage it has ever seen. If you subject it to overvoltage and even if it survives, if and when you submit that equipment for warranty work for any reason, they may check that register and void your warranty irrespective of when it happened or whether or not the problem at hand has anything to do with overvoltage.

rmurray43

I had a PV system installed two years ago.  It’s a modest 4kw system with micro inverters on a 220v line on a 20A breaker.   After about 11 months of operation, the system went dead.   The electrician checked the main connection under the solar panel on the roof where, inside a box on the roof that the aluminum trunk lines connect to the connection to the distribution wire.   The connection was completely cooked.  They replaced it and two days ago it failed again.   I’m suspecting the same failure.   I noticed some large fluctuations in power the day of the failure.  I’m thinking this is a weakness of the aluminum to connector.   The expansion coefficient of AL is much different than other metals, and this connector goes through a lot of temperature change through the day.   Last year it failed in July.  This year August.  They should be coming out this week to fix it again.   Any advice?   I was told in electrical engineering school that AL contacts have to be tightened periodically to avoid this.  That was 40 years ago.  Anti-oxidation paste? Redundant connections?  Any comment would be appreciated 

Dave Angelini

take a picture when they are there. Need to see what they used.

My comment would be to replace the aluminum wiring if it is not  really hard.  Why would they use aluminum for this 20a circuit?
Are they still in business?  I thought not.