Choosing Electrical Wire

What voltage does your farm generate?

The inverters are 260 kW at 480v, so 480v

From NEC Table 316-10, 350MCM copper is most closely equivalent to 500MCM aluminum. The cost difference pales into insignificance when compared to a 1MW solar farm and its appurtenances. It ought to take only a 5-minute phone call to get local/regional comparative prices, anyway.

You would think it would be that easy but after 4 hours I come on bended knee to you guys.

Without knowing a lot more about the configuration of this solar farm I could not give you a true knowledgeable opinion. With limited knowledge though I would recommend the copper instead of aluminum. If just for the thermal expansion problem that aluminum has when it heats up. This is why when thinner gauge aluminum wire was used to wire people's homes, the self heated aluminum would expand farther than the hardware anticipating a copper wire expansion. This then caused many loose wire connection that would occasionally through a spark that would ignite something. Most junction hardware today have been redesigned to accept both types of conductors. So it is possible to fabricate your whole facility safely using either wire. But with wire cost likely being a small part of the whole expense and there being a small but real possibility that aluminum could add a hidden problem to this project, I'd choose copper.

I have been able to get some ball park figures off the internet, yes, relibility is a question, but the average is about $7/Lft for 350 MCM Cu and $2.25/Lft for 600 MCM Al. After a few thousand feet the difference adds up and cannot be ignored. Solar farms are not Gold Mines, and if it isnt financially profitable it isnt feasible.

Now the question is cost of direct bury as opposed to using conduit.

The inverter companies say Al is ok with them as they are using compression couplings.

$164 per liner foot, will ship next day on receipt of your credit card details.

Worse, Redfred. The aluminum to copper (or other metal) mechanical connector was never solved for any significant current. The solution for high voltage aluminum cable you see on high voltage towers is a special one, but here it is: a cold weld crimp end on alu, a copper flat bar for termination. The economics on this is for hundreds or more miles. By the time you are done with this for your purpose, copper cable will appear cheap in comparison.!

I think that you ultimately agreed with me that copper is the preferred metal conductor. I thought that there were some spring loaded junctions that were designed to compensate for the expansion. You are likely correct though that these special junctions will quickly eat away any savings one might get from using aluminum. All savings will quickly evaporate when a non-aluminum grade junction gets used on aluminum and ignition occurs.

The special connectors are not that much more than the regular connectors, and most of the equipment in the solar biz is rated for Al already anyway, its the 5 dollars a linear foot difference that is significant.

So no one has any idea of the cost of 600 MCM Al THHN as oposed to direct bury 600 MCM Al, per linear foot?

Dudes???

Copper has really gone up in price lately.

So has Al. $1.00USD per pound for Al cans.

I would get a new engineer.

This is a design issue. The answer is dependent on the price of the acceptable conductors. Surely this is not a DIY project. You are talking about a very significant line item. The approved drawings will need to call the conductor. Would you really ask a customer to pick a conductor? I could go on and on.

Guys, the recomendations for using Al wire are coming from nationally recognized Electrical contracting firms with their own engineers, I always get more than one opinion.

Critisizing someone or firm, you know nothing about is low class and not up to the standards of CR4.

No its not DIY, I hire professionals, and manage construction myself cause giving the managment over to an EPC adds 20% to the cost and its just not in the budget.

I'm sure you are going to get it figured out. You said a small 1.1 MW PV facility in the desert. This is not small. You may have the expertise to engineer this wire run, your question implies that you do not. As for the engineer I was referring to, it is you. That was a little harsh, sorry. Maybe I've got it all wrong and jumped to the conclusion that asking that question on the CR4 forum without any details, and expecting an expert to spit out the answer was unrealistic.

Are you building these inverters, or purchasing them? If you are purchasing them I have found very extensive engineering resources available with your purchase. (Solectria, Satcon) are two I deal with. They will answer your questions. Good luck.

Im an old broke home developer that got suck with some property. In the commercial solar business 1.1 Mw is considered small, in fact anything under 20 Mw is the small catagory for the CPUC, CEC, NREL, etc. Im an organzer, (developer), I do not have the expertise to engineer this, so I hire engineers and consultants, etc. I then double check their answers cause Electrical engineering is not my area of expertise. Sometimes i get a third opinion from CR4, sometimes they give good answers and sometimes the court jesters come out and they dont have a clue.

The suggestion for Al conductors came from a nationally known EPC that is considering partnering with me. (Engineering-Procurement & Construction firm)

I thought the CR4 "experts" opinion on the cost of wire was straight forward, surely one of you guys knows how much 600 MCM Al THHN wire costs a Lft as opposed to the cost of 600 mcm direct bury.

For one thing, prices are quintessentially regional/local, so overseas CR4 members are not likely to have any idea at all of prices around Mojave. For another, CR4 is somewhat more about technical discussion than about economics. If I wanted to know the price of something, CR4 would be among the last places I would ask.

I cannot see at all why you are unable to get at least budgetary prices from nearby suppliers within hours, if not minutes. Is service in California really that bad?

ξ

I agree. If the only thing that Spacecannon wants is a price, then CR4 is the wrong place to come for just a price. Now once he's found the variety of prices one can find for various copper and aluminum wires I would understand asking us here what advantages each type provides so that an informed evaluation of each price can be weighed. But frankly asking us just for a price is rather insulting.

Redfred,

Seriously, if you work with it and dont have any idea on the costs, then you have no business engineering anything with it, I expect an Electrical Engineer would have a clue.

Then you have no idea what an electrical engineer does. A contractor electrician would have an idea of what the wire cable costs. How many threads have you seen here where price quotes were included in the discussions, none that I remember.

Redfred,

I disagree with you, you think only engineers occupy these spaces? If an engineer doesn't have a clue about the cost of materials the "he" doesn't care about his clients, a wildly arrogant position. Everything, EVERYTHING, has to be taken into account when engineering a system, structure or facility. I have seen people ask about prices on things here, why not! Your argument is a fallacy and doesn't hold water.

You seem to be refusing to see anything but your own little problem. So sad.

Yes, any engineer has to work within their budget on a project. An engineer on that project has access to all of the relevant parts and concerns of that project so they can make a sound judgement on where to wisely spend the money to produce a functioning product with an acceptable lifetime. As you've said, "Everything, EVERYTHING, has to be taken into account when engineering a system, structure or facility." When I earlier gave you my opinion that I preferred copper over aluminum I also pointed out that there was not enough information to say which conductor is worth the money. I did try to inform you about a hidden hazard that one finds when using aluminum conductors. Others here have also agreed with me that there are hidden problems that one can find from using aluminum wire. Instead of trying to use my information or granting us more information to help you make an informed choice you just ask for a price quote. Well look at the words in that red bar on the top of the page. They say "The Engineer's Place for News and Discussion®" This space is for Engineers and those who wish to discuss things relevant to Engineering. If you want a price quote, ask a vendor that will take your money.

Give it a break with the criticisms, It was late on Friday and most shops don't deal in 600 MCM Al.

Of course I wouldn't consider prices from out side of US Valid. Inside US would be close enough for comparison.

My recomendation is to us Cu only, 500MCM min in my opinion, I paid $7.35/ft 4 weeks ago, copper is up and down, when I purchased it 2000FT, I was on the phone and email several times a day as it fluctuates every 2 hours. I waited till it dropped to 7.35, it was on the initial inquiry 9.80/FT. I would not use Al for any thing but to make cans with. It should not be used in electrical installations, but then this is my personal opinion. Also the questions are related to runs and multi conductors per phase. Amp ratings, you are talking 1.1MW. 480 3Ph. You may even consider using 1000MCM THHN depending on your voltage drop/distance of cable to reduce the amount of multi conductors. As for price, this is like water. It is in constant flux.

Find several suppliers in your area, the larger suppliers can get better price breaks,

I use 6 different suppliers for products. Each has their specified expertise they deal with and each has better pricing depending on what they deal with. On the 500MCM I was quoted as high as 11.85/ft for 2000FT on the same day I was quoted 7.35 so you know who got the purchase order, and the quote was only good for 4 hours. After that it would have to be re-quoted.

Greetings to Spacecannon,

Asking personal opinions from your comrades in CR4 is a sign of humility even you know the answers. You recognize the importance of one's contribution, comment which may not be applicable today perhaps tomorrow.

We may not give you any prices for your asking because prices vary from places to places, and current prices changes.

But we can give you alternatives to think about to help you choose the the best and most economical option.

We presumed that you have the right choice in cable sizes, factors were considered like ampacity of cable, derating factors, voltage drop. etc. Now you are to decide whether to use the ff:

1. 350 MCM Cu vs 600 MCM Al - bury with conduits.
2. 350 MCM Cu vs 600 MCM Al - direct burial
3. 600 MCM THHN Al Free Air bury in conduits vs 600 MCM Al direct bury

For #1: Both of the two can be used but prices of cable per linear foot will dictate economy.

For #2: Both of the two can be used but prices of cable per linear foot will dictate economy. There will be reduction in material and labor costs.

For #3: Both of the two can be used but prices of cable per linear foot will dictate economy. Consider the costs of conduit installations.

I opt for #2, whichever cheaper in material and labor costs b/w copper and aluminum will be used.

Hope this can be of help.

____________________

"Iron sharpens Iron"

Electiguru62211,

YOU ARE AN HONORABLE AND GOOD PERSON!!!

GA, Thanks for your opinion

Thanks.

____________________

"Iron sharpens Iron"

Out of idle curiosity, where is this proposed installation, and how far is the grid tie-in from any recognizable municipality? Somehow from 480 volts I get a whiff of another Californicated grid folly, probably wrapped up all purty in goobermint subsidies.

tornado,

I cannot answer all of your questions because of NDA concerns, but the tie in is at the corner of the lot, the facility is in a city that will use it, No other rebates than the Federal Cash grant everybody else is gettiing, just adapting to survive, dude.

Just going on past experience 1000KVA transformers had either 7 x 500CU or 7 x 600AL singles.

I've only installed two 750KVA 550V transformers that had a multi cored SWA feeds to the LV board. We used two paralleled 3&½ core 400CU.

350 CU is far too small!

The photo is a "baby" 500KVA trany! 4 x 600AL

cool picture, thanks.

I dont know if 350Cu is too small, all his stuff gets double checked by the EPC and then tripple checked by the Utility Co. , so if he screws up, he has to fix it, and it makes him look bad.

This 1.1 MVA system is subdivided into four parts, each 276 KVA as I recall....

Technically its 5 parcells with a small remainder, 4 260 inverters and 2 small 30s, the 1.1Mw is DC.