16 Panels in Series 525 VDC and 9 Amp

[adobejoe]

I want to connect my 16 210 W panels in series and run high voltage, about 525 VDC, and 9x1.25=11.2 AMP in a single set of conductors to my inverter. This is grid tied. The panels are 150 ft from the shelter where the inverter will be, which is 20 feet from my main panel. The conduit is in the ground, so why would I want to run multiple strings of wire? I am thinking #12 or #14 at this high voltage. I cannot cannot easily site the inverter next to the panels--they are on a bluff, and I do not want the expense. Thoughts? I believe it meets code.

AdobeJoe

[Ungrounded Lightning Rod]

I want to connect my 16 210 W panels in series and run high voltage, about 525 VDC, and 9x1.25=11.2 AMP in a single set of conductors to my inverter. This is grid tied. The panels are 150 ft from the shelter where the inverter will be, which is 20 feet from my main panel. The conduit is in the ground, so why would I want to run multiple strings of wire? I am thinking #12 or #14 at this high voltage. I cannot cannot easily site the inverter next to the panels--they are on a bluff, and I do not want the expense. Thoughts? I believe it meets code.

AdobeJoe

Going over 50V nominal puts you in a tougher part of the electrical code.

You'll save a lot in copper going at the higher voltage.  But 525 VDC @ 9A available is "touch it and die".  And you'll have problems finding switchgear and inverters that can handle such a high input voltage.

[defed]

i can't comment on the safety of doing it, because i don't know enough, but i have just been trying to figure out wire sizes and was directed to a voltage drop calculator such as this:

http://www.nooutage.com/vdrop.htm

[TomW]

Another "gotcha" is most common cable, switches, terminal blocks / etc are only rated to 600 volts. Your stated goal doesn't leave much room for overhead. Events like cloud edge effect may well drive your voltage higher than 600 volts. if you blow a hole through the insulation and an arc gets started at 600 VDC the fun will begin in a spectacular way.

Just something I noticed over the years you should be aware of if you are not already.

Tom

[tecker]

You want to this for what reason

[tecker]

   525 volts at 11 amps is very very dangerous settle for 200 at 20+ .That's still dangerous but it won't hedge on the 600 volt max on the insulation.

[adobejoe]

Correct me if I am wrong, but the inverter house is 150 Feet from the panels, and the conduit is in the ground already. It goes down a steep hill. I can run one set of conductors (+/-) to handle the entire string in series. The other option would be to run two sets of wires (4 wires. 2 at + and 2 at -) with 260 V DC and 20 amps on each. I think pulling two wires in the 1 1/2 " conduit will be much easier then four wires.

AdobeJoe

[TomW]

I think pulling two wires in the 1 1/2 " conduit will be much easier then four wires.

AdobeJoe

You are deciding conductor sizing on the wrong criteria.

They make grease to ease pulling cable. What is the type of cable?

Individual conductors or Romex?

Romex puls hard because it is mostly sheath.

THNN (just individual wires) will pull much easier. Pulling 4 or even 6 thnn  #14 should be fairly easy in 1.5" conduit. Just be sure you have someone to feed in cable on the far end . grease it with some dish soap will make it slip easier.

Anyway. Do it right once and be done with it.

Best advice I can give.

Tom

[tecker]

I't's almost imposable to keep the water out of a ground conduit so make sure there is a grade to allow the water to drain out of the bottom box into some sort gravel or sand etc with such high voltage .IF you get hit by 500 volts dc and that goes across your body you will lock on it .High voltage dc has been abandoned for that reason.

[tecker]

 Last little bit of soap here is an Arc over at higher voltages will put you out of business also . Breakers at both ends of the run .

[birdhouse]

with your 1.5" conduit, you have plenty of room for multiple wire runs.  i recently managed to get (5) #10's through a 1" conduit.  the wire was solid too.  quite the huffing and tugging, but got it though.  it is a 120' and even has a long sweep elbow mid way through the pull.

with your pipe, you should be able to get (4) #8's through pretty easily.  this could get you away from that super high (dangerous) voltage mentioned above.  

adam

[riahserf]

4 #10 should fall in 1.5 conduit... #8 shouldn't be any problem either... but some one feeding will help greatly!!... not just for ease of pulling but to make sure no knots or kinks in the wire go into the pipe.

Something else to think about... pretty sure the max voltage allowed in a house is 250 volts between conductors. My work is mostly industrial & commercial... not sure if there is an exception for "solar" in a residance

[Ungrounded Lightning Rod]

Last little bit of soap here is an Arc over at higher voltages will put you out of business also . Breakers at both ends of the run .

Breakers rated to break DC!  That's a much harder job than breaking AC, which does most of the work for you twice per cycle.

[dnix71]

What is the max voltage the panels are rated for? If they are made to series for higher voltage, it's usually right there in the specs.

This sounds like one of the few times an Enphase micro inverter might make sense. They mount under the panel and make ac directly. They can talk to each other so they can be connected in parallel and have remote monitoring capabilites. Sending 240vac 150' is no problem.

http://www.enphaseenergy.com/products/    Maybe you could email them and ask if they have a model that would work with two panels in series. That would mean you would only need 8. The cost would be comparable to a single 6kw grid-tie inverter.

[BrianSmith]

I would go with at least two sets of wires. 
If you break up the panels into two groups, you should be able to work on one and still have half your power working as well. 
The comments about DC being hard to break are true. 
If something starts burning and carbonizing you can make a lot of fire and plasma type fireworks with DC that will keep going with no alternating current to allow it to stop.

Handle with caution.  That being said, sounds like you are going to be a one man power company pretty soon.    Enjoy.

[don1]

Adobe,

 I don't know if I am reading this right or not.  But how do you get 525 Volts out of 16 -12 or 24volt 210 watt panels?  At 12 volts  you get 192 volts.  Are you confusing watts for volts in your calculations or are there higher voltage panels. 
 Even at 192 volts DC you are likely to be rather stressed  if you come in contact with it.  And it really really hurts. 
 My thought here as others have said would be to beak it into to 8 panel legs.  At 96 volts it's still high enough to get it down the 150 ft hill with out the wire size breaking the bank.
 Please understand that I am confused easily and may not the sharpest pencil in the drawer. So correct me if i'm wrong.  Don.
 

[Rob Beckers]

I'm a bit mystified by all the responses urging not to do it...
As a PV installer we size systems as close to 600V DC as we can. That's normal practice, as it minimizes losses and makes the most economic sense. All the equipment involved is of course rated at 600V, and this does not mean it will fail at that voltage, it means it will continue to work normally at that voltage. Insulation values of 600V rated wire and other supplies is several times beyond the rated voltage (they have to pass hipot testing with a factor of 2 or 3x rated voltage, forgot the exact multiplier). In short, there's nothing wrong with going with such a high voltage. If the components are rated for it code will allow it.

Having said that, this assumes you know what you're doing. Others are correct that this voltage can absolutely kill you. Then again, so can much lower DC voltages (getting zapped by DC is worse than AC). It helps safety-wise to float the DC side, so you have to actually touch both terminals to get zapped (the inverters we use are transformerless, so there's no grounding of the negative lead, a very good thing IMO). Also, and that is very important, string size needs to be such that you stay under 600V DC open-circuit voltage (unloaded) for the absolute coldest temperature that can reasonably be expected for your location. Going over 600V will set a flag in the inverter's permanent memory before it blows (for a 600V rated inverter), and you can wave bye-bye to the warranty. For our climate, with -35C as the minimum (and that means I use -40C for string calculations), the MPPT voltage of the string at normal temperatures usually ends up somewhere in the 350V - 400V DC area.

-RoB-

[Bruce S]

I'm a bit mystified by all the responses urging not to do it...
As a PV installer we size systems as close to 600V DC as we can. That's normal practice, as it minimizes losses and makes the most economic sense. All the equipment involved is of course rated at 600V, and this does not mean it will fail at that voltage, it means it will continue to work normally at that voltage. Insulation values of 600V rated wire and other supplies is several times beyond the rated voltage (they have to pass hipot testing with a factor of 2 or 3x rated voltage, forgot the exact multiplier). In short, there's nothing wrong with going with such a high voltage. If the components are rated for it code will allow it.

Having said that, this assumes you know what you're doing. Others are correct that this voltage can absolutely kill you. Then again, so can much lower DC voltages (getting zapped by DC is worse than AC). It helps safety-wise to float the DC side, so you have to actually touch both terminals to get zapped (the inverters we use are transformerless, so there's no grounding of the negative lead, a very good thing IMO). Also, and that is very important, string size needs to be such that you stay under 600V DC open-circuit voltage (unloaded) for the absolute coldest temperature that can reasonably be expected for your location. Going over 600V will set a flag in the inverter's permanent memory before it blows (for a 600V rated inverter), and you can wave bye-bye to the warranty. For our climate, with -35C as the minimum (and that means I use -40C for string calculations), the MPPT voltage of the string at normal temperatures usually ends up somewhere in the 350V - 400V DC area.

-RoB-

RoB;
 Our main reason for keeping people away from these voltages is as you pointed out in paragraph two. While even 6Vdc can be enough to give you a lethal dose of current at these higher voltages it even easier to get between the terminals and we certainly do not want to read some one has passed away due to working with them.
I am pretty safe saying that 99.9% of the people posting and giving advise do not have malpractice insurance, so it's always better to play safe.

As it seems you are an installer of PVs other may chime in here to ask questions that will range from roof mounts to gridtie.

Are you a certified contractor for these or sub-Contractor that is certified?

The professional installers point of view and information is very much welcomed.

Cheers;
Bruce S

[Rob Beckers]

RoB;
 Our main reason for keeping people away from these voltages is as you pointed out in paragraph two. While even 6Vdc can be enough to give you a lethal dose of current at these higher voltages it even easier to get between the terminals and we certainly do not want to read some one has passed away due to working with them.
I am pretty safe saying that 99.9% of the people posting and giving advise do not have malpractice insurance, so it's always better to play safe.

As it seems you are an installer of PVs other may chime in here to ask questions that will range from roof mounts to gridtie.

Are you a certified contractor for these or sub-Contractor that is certified?

The professional installers point of view and information is very much welcomed.

Cheers;
Bruce S

Hi Bruce,

Many of the technologies discussed here involve dangers; be it working on a roof, on top of a tower, or high voltages. IMO the people contemplating work that involves these dangers should ask themselves if they are up to the job. At the end of the day it's everyone's own responsibility and decision.  All we can do is point out the dangers involved.

Likewise, all we can do is provide accurate technical information as well to those asking, so an informed decision can be made. My reply attempted to do both. What I don't like to see are replies that provide incorrect information (such as the suggestion that insulation will fail at 600V) or that are so generic as to be not very informative  ("don't do it" would fall in that category).

Since you're asking: I'm an electrical engineer by trade, and have been running an RE business for 5 years now. Canada does not have certification for PV installers, nor do they require it (something I would like to see changed, especially since with the Ontario feed-in-tariff many clueless fly-by-nights have emerged). All the installations I'm involved in are done in conjunction with a Master Electrician, and are always beyond code.

-RoB-

[Bruce S]

RoB;
                                                                      !! That is excellent !!
It will be good having more than one person here who is doing the real world work and can jump in and correct things.
OP; apologies to drifting BUT having having someone who is doing the work can be a very good source for input.

Cheers
Bruce S


 

[TomW]

RoB;
                                                                      !! That is excellent !!
It will be good having more than one person here who is doing the real world work and can jump in and correct things.
OP; apologies to drifting BUT having having someone who is doing the work can be a very good source for input.

Cheers
Bruce S


 

Yes, indeed. I also think it is very important to chime in with warnings because we have a range of users from no clue on how a voltmeter works, let alone electricity to people who have run megawatt size power stations.  And I cannot tell from words on a screen who is which.

You wouldn't give an infant your sidearm because they knew how to get it out of the holster.  Improperly handled power systems can be at least as deadly and has a potential for more property damage than a half inch hole thru the wall / roof, too.

Just me I guess.

As Rob says this hobby is well seeded with dangers.

And I believe I said "approaching the rating" of cable insulation? But that is another rant.

Sorry for the additional topic drift.

Tom

[ghurd]

I'm a bit mystified by all the responses urging not to do it...

Having said that, this assumes you know what you're doing.

I know 20Voc DC solar shocks the heck out of me.
Makes me a little nervous telling people to use High Voltage DC if they need to ask basic questions.
(not aimed at AdobeJoe)

If anyone wonders what high voltage DC can do from arguably open voltage solar panels...
have a look at this pic of electronbaby and a high voltage arc...

[Rob Beckers]

TomW, while I don't disagree with what you're saying, I believe the situation here is qualitatively different: We're not talking to children but adults. It is my opinion that it is better to simply inform people of both the technical issues, and dangers involved. With that people can make an informed decision; if this is a job they should be doing themselves, or leave it to the pros. I was very clear that those voltages can kill you.

Nice picture Ghurd! I've not seen any DC arcs close-up yet (knock-on-plastic), customers tend to frown upon such things. I have had the pleasure of watching a spectacular AC short-circuit; in one of my jobs long ago we were swapping out street lights. Since the houses on that street were hooked up to those same lines this was done under power. Not a problem if you're careful. A backhoe had accidentally ripped a power line in one of the streets we were working, and the electrician decided he could cut those (now stripped) phase lines, an cap them. He accidentally shorted phase-to-phase, and this was 380V fused at a thousand or so of Amps (a whole street was on these lines). A spectacular bang, sparks two meters high, and the entire head of his pliers had melted off. The fuse hadn't even blown...

With the use of MC4 connectors on most PV modules nowadays the risk of shorts or shocks has gone down quite a bit. Still, at some point one has to transition from MC4 to regular wiring, and care is needed there (hook everything downstream up first, before plugging in the MC4 connectors to the array).

-RoB-

[Bruce S]

We're not talking to children but adults.. I was very clear that those voltages can kill you.
-RoB-

-RoB-
Unfortunately that isn't always easy to find out. There are people who are part of this forum who, including our daughter who might not have a clue about the dangers, which is why we usually try to be over cautious.
I read your to be clear, TomW's was, as was (I hope ) mine.
Some of the posts that have made it to the old forum and even this one shows that there are those who don't completely think things through.

Having been the recipient of a 660vac shock  and lived to tell about it 32 years ago, I can honestly say it was not fun  , even if it did get me a lifetime DAV income  .

I know we're drifting a lot here but the main common thread is that safety should be first.

Cheers
Bruce S
 

[DanG]

If one is so bold to build a ~600VDC system its complete unlimited liability for any & all incidents. The 800-pound guerrilla here isn't the ~600VDC alone - its our fear the installation would be just another casual system.

I worked 750VDC 1000A  subway car subsystems for 13 years - OSHA or Code Inspectors never visited the manned-facility as all safeties were designed into the system and if the Mechanic screwed up they'd simply be inside-out in 100 milliseconds... So complete was the planning I can't put most of it in print even if I had noticed all the details.

A few details that come to mind:

Things like restricted access - I grew to like the seven-foot fences and three strands of barbed wire ringing the facility. If your panels are on a roof with no access that is a good start otherwise how you going to child-proof ground-mounted racks? How about security against theft, or attempted theft leaving the system partially dissembled when the sun comes up? Its one thing if you burn up some wire and another if you level a house or start a forest fire.

We enjoyed having every last piece of metal being grounded from handrails to fire doors to diamond plate floor panels to the metal grates on floor drains - all being able to throw a fault if voltage leaked.

Weather proof lockable control panels ($$$) with internal barrier guards covering any hazardous voltages so getting crossed up with control voltages won't throw you into the meat-grinder voltages. No insect intrusions, no condensation, no wind-blown snow making into the boxes.

Ya, the topic has drifted - this is the third time I've written this response so I'll hit 'post' before I change my mind...