Great source for learning about string configurations?

softdown

Proper string configuration has been my stumbling block for a month now. I am on my fourth book covering PV solar. Two were intro type books. About all I have found is a couple paragraphs saying things like you can connect panels either in series or in parrellel. With a schematic showing some panels connected in series or in parrellel.

That does not qualify one to string up 18 panels with a Voc 44.8. I believe that I can do four strings with each string having two in series and two in parrellel. That uses 16 panels and leaves out two. Or I can do an ultra safe approach of nine strings with two in series. My Outback FM80 will likely be destroyed by HyperVOC if I run three panels in series and the temp falls under -20 F. Which it does on a regular basis, temps hit -12 yesterday morning.

I have a Midnite MNPV6 combiner box. Not a huge deal to buy a MNPV12 combiner box. Then I could safely add six panels if I pointed three to the east and three to the west. "Virtual tracking" allows one to employ more panels without cooking their MPPT charge controller.

I would be happy to buy another solar book if it really made string configuration a 'do-it-yourself' project. I have helped wire a few houses and believe that I have enough savvy to someday wire up my strings. So far, I have 20 pairs of 25' 12 AWG MC4 solar wires. Think I can trade those for 10 AWG with a 20% restock fee. Also have four 4 into 1's and one 2 into 1 which I can return for a couple more weeks. They combine 12 AWG into one 10 AWG wire. I am comfortable with a 1-2% line loss. Maybe better than having many hundreds of dollars in wires that "scrappers/theives" are likely to steal. I mention that because I have been "hit" many times.

My goal today is to make some progress on the string configuration. I want to do it right. Even if I have to "bite the bullet" a bit. Their are no "solar inspectors" in this region. This area doesn't even exist according to "the system". But it is a solar paradise. Dry and extremely sunny at 7800' elevation.

EDIT: realized that running future series strings with three panels/each on the east and west sides is not readily doable. I think eighteen 190 watt panels (what I have) is plenty for a couple people.

softdown

Re: Great source for learning about string configurations?

I wouldn't be offended if a Good Samaritan told me what to do. But I didn't want to ask the board to solve a complex (for me anyway) problem for me.

I've run a couple very simple solar banks for a few years. But the string configuration pretty well eludes my grasp to date. Probably something to do with getting 18 Voc 44.8 panels through a six string combiner and into a 150 volt charge controller.

2twisty

Re: Great source for learning about string configurations?

At what voltage is your system? If we know that, we can help you plan the array dimensions.

mike95490

Re: Great source for learning about string configurations?

Most MPPT controllers have a website with a string calculator on it. Enter your panels, series, parallel, whatever, and it adds the watts, volts and low temp Voc and tells you what is in the acceptable range.

softdown

Re: Great source for learning about string configurations?

2twisty wrote: »

At what voltage is your system? If we know that, we can help you plan the array dimensions.

48 volts for the future battery array. The Outback FM80 is rated for 150 volts though it is designed to shut down for self protection somewhere between 142 and 145 volts.

I can not do three panels in series. That would deliver about 135 volts but a -25F morning introduces a multiplication factor of about 1.23. Midnite Classics are designed to cope with the resulting Hyper VOC, Outbacks are not.

softdown

Re: Great source for learning about string configurations?

mike95490 wrote: »

Most MPPT controllers have a website with a string calculator on it. Enter your panels, series, parallel, whatever, and it adds the watts, volts and low temp Voc and tells you what is in the acceptable range.

Outbacks string calculator is pretty bad unless you know something that I do not. Midnite has a nice string calculator but it is designed to employ Midnite Classic charge controllers....which can handle Hyper VOC that pushes voltage over 150. I'll try to dig up the link for the Midnite string calculator.

EDIT: Here is the nifty Midnite string calculator; http://www.midnitesolar.com/sizingTool/

BB.

Re: Great source for learning about string configurations?

Remember, (I believe) that the Midnite controllers still shutdown when in "Hypervolt" mode--So do not plan on operating during those events.

-Bill

softdown

Re: Great source for learning about string configurations?

BB. wrote: »

Remember, (I believe) that the Midnite controllers still shutdown when in "Hypervolt" mode--So do not plan on operating during those events.

-Bill

Their string calculator yields these numbers for a 48 volt battery array:
Classic & Classic Lite Charge Controller Selection
150 200 250
Max Operating Voltage 150 200 250
Max Non operating VOC (HyperVOC) @ 48V Nominal Battery Voltage 198 248 298

I think they may be the only ones designed to cope with Hyper VOC.

Outback is certainly a great name. Unfortunately the combination of my high panel voltage (44.8 Voc) and very cold weather (-32F) has me dancing on the edge of frying my charge controller with three panels in series. At 7800 feet, I also get more solar power than most.

If I had 16 panels, I could do strings of four with two in series and two in parrellel. But I have 18 panels that I would like to use.

Vic

Re: Great source for learning about string configurations?

soft ...

IMO, you should not really consider using the MC4 paralleling connectors on your strings. Seems that you might be trying to use your MNPV6 Combiner box. But you really need a breaker on each string of two PVs.

Seems that you have no real choice. Even with the Classic CC, the string voltage would be too high. This would reduce the CC efficiency, and you would find that the Classic would be Resting, waiting for the input voltage to diminish during coldest weather, again in my candid opinion.

So, seems that using strings of 2 PV, into a Combiner that has positions for nine or more breakers would be a good setup for your situation.

Just my opinions. Good Luck, Vic

BB.

Re: Great source for learning about string configurations?

That has been an ongoing problem on the forum for years. There are some "higher Vmp voltage" solar panels that don't really work well with standard 140-150 Volt Vmp MPPT charge controllers and 48 volt battery banks.

For places with extremes in temperature, you need almost a 2:1 range for Voc:Vmp (Voc-cold:Vmp-hot) to work correctly over the entire range.

When I did the calculations a few times in the past to help people, it works out that a Vmp~100 volts (STC) will give you a Voc-cold (very cold regions) of ~140 volts. That means panels that are Vmp~50-70 volts, cannot be put in series for charging a 48 volt battery bank and are not high enough voltage to charge a 48 volt battery bank (that typically needs a ~70 volt Vmp-array minimum for proper output voltage in hot conditions to charge a cool battery bank--such as high deserts).

Panels with Vmp>~36 volts are less common now--But where very common with various thin film panel manufacturers a few years back. Usually, crystalline silicon panels were 60 or 72 cell panels (Vmp ~30/36 volts)--Usually for Grid Tied solar arrays (the high volume stuff).

Quite a few of the GT inverters today do not really have that wide of array input voltage range (between start voltage, MPPT range, and Voc-cold/non-operating). You have to be very careful to get that exact number of panels that will run the controller (and not violate the warranty) over the 4 seasons.

Another problem with Thin Film panels was that their Vmp/Voc was a few volts higher when new, and degraged over ~6 months exposure to sun... You have to design for both for proper operation (new and after "burn in" of the solar panels).

-Bill

softdown

Re: Great source for learning about string configurations?

Vic wrote: »

soft ...

IMO, you should not really consider using the MC4 paralleling connectors on your strings. Seems that you might be trying to use your MNPV6 Combiner box. But you really need a breaker on each string of two PVs.

Seems that you have no real choice. Even with the Classic CC, the string voltage would be too high. This would reduce the CC efficiency, and you would find that the Classic would be Resting, waiting for the input voltage to diminish during coldest weather, again in my candid opinion.

So, seems that using strings of 2 PV, into a Combiner that has positions for nine or more breakers would be a good setup for your situation.

Just my opinions. Goof Luck, Vic

Thanks Vic. I believe that you are likely correct. But it sure would have been nice to use my 6 string combiner box and my 4 into 1 connectors. One guy did assure me that I could make strings with six panels in each string (via series and parallel) but my instincts yielded caution lights.

Sometimes it is best to gather a few professional opinions before doing important stuff. This board is just fantastic to date.

2twisty

Re: Great source for learning about string configurations?

Why not strings of 2? If he has a VOC of 44.8, that puts him at 89.6V for 2 panels in series. That should be plenty to charge a 48V bank, right?

So,9 parallel strings of 2.

BB.

Re: Great source for learning about string configurations?

Yep, two series panels should be fine in all temperatures and conditions (of course, do your own due diligence with the string calculator).

The drawbacks to two (vs 3 panels) include more breakers (one per string when three or more parallel strings) and "lower" Vmp-array -- Which means heavier/more expensive copper wire from array to charge controller+battery shed.

Midnite does offer higher voltage charge controllers. However, as they go up in rated voltage, their rated output current goes down (higher voltage FETs probably have lower current rating/higher internal resistance).

As always, do several paper designs (for example 2 vs 3 series panels with different Classic 150 vs 200 volt controllers), and see which one "wins" for your needs.

In general, the lower Vmp-array voltage will be "more efficient" for the MPPT charge controller, but more costly for copper wire (larger diameter for higher current).

Until you run the design, it is difficult to say which will be best for any particular project (need to know wire run length, ratings of panels, size of array, etc.).

-Bill

softdown

Re: Great source for learning about string configurations?

BB. wrote: »

Yep, two series panels should be fine in all temperatures and conditions (of course, do your own due diligence with the string calculator).

The drawbacks to two (vs 3 panels) include more breakers (one per string when three or more parallel strings) and "lower" Vmp-array -- Which means heavier/more expensive copper wire from array to charge controller+battery shed.

Midnite does offer higher voltage charge controllers. However, as they go up in rated voltage, their rated output current goes down (higher voltage FETs probably have lower current rating/higher internal resistance).

As always, do several paper designs (for example 2 vs 3 series panels with different Classic 150 vs 200 volt controllers), and see which one "wins" for your needs.

In general, the lower Vmp-array voltage will be "more efficient" for the MPPT charge controller, but more costly for copper wire (larger diameter for higher current).

Until you run the design, it is difficult to say which will be best for any particular project (need to know wire run length, ratings of panels, size of array, etc.).

-Bill

If the combiner box is mounted on the roof top (current plan) then 25' wire runs will work. I have 20 pairs of 25' MC4 solar wire. There are 18 panels that are 190 watts/panel (though it looks like they have also been called 180 and 185). The 25' MC4 wire to the combiner box are all 12 AWG. An asst stole my roll of 8 AWG TMMT along with everything else he could fit in his "clothes" bag (sorry but this gets my blood roiling everytime I think about it). I'll either use 10 AWG or 8 AWG to run to the charge controller I think. Probably use PVC conduit to protect it. Either that or drop the wires straight down (about six feet) to the charge controller.

Alaska Man

Re: Great source for learning about string configurations?

There are calculators for sizing wire too.

I had to use 2 panel strings with the Midnight 150 for the same reasons. It's Butt cold round here.


I mounted the combiner box on the outside of the wall I hung the Controller on. My run is about 8".

softdown

Re: Great source for learning about string configurations?

Alaska Man wrote: »

There are calculators for sizing wire too.

I had to use 2 panel strings with the Midnight 150 for the same reasons. It's Butt cold round here.


I mounted the combiner box on the outside of the wall I hung the Controller on. My run is about 8".

Cold in Alaska's interior? Your credibility remains unchallenged. I flipped some buckets with ice a month ago. Ice has not melted yet. Sure is pretty up there.

Alaska Man

Re: Great source for learning about string configurations?

softdown wrote: »

Cold in Alaska's interior? Your credibility remains unchallenged. I flipped some buckets with ice a month ago. Ice has not melted yet. Sure is pretty up there.

They say it's God's Country.............. God darn hard and God darn Cold. (G) rated version.

As of late, I've been thinking about moving to Utila Honduras. I hear it's nice this time of the year.

softdown

Re: Great source for learning about string configurations?

Alaska Man wrote: »

They say it's God's Country.............. God darn hard and God darn Cold. (G) rated version.

As of late, I've been thinking about moving to Utila Honduras. I hear it's nice this time of the year.

Aye, it is the roughest part of the year. My area is the coldest in the continental US I hear. I move from cold to colder to coldest. Anything much over freezing feels alright.

westbranch

Re: Great source for learning about string configurations?

One day at or around -40 (same in both C & F) makes everything above that feel like Spring!

softdown

Re: Great source for learning about string configurations?

I think that is 10 degrees colder than anything that I have endured. Sometimes Canada is hard to compete with. But I have "bragging rights" around most of these soft 'Muricans.

Alaska Man

Re: Great source for learning about string configurations?

-25°F right now. Heading out with dreams of women in bikinis in my head.

And the Good Lord said, "This too shall pass" or was that my Ol'e Lady?

Peace Gents.

softdown

Re: Great source for learning about string configurations?

Since USE-2 wire with MC4 connectors will be employed, it makes sense to get a 12 breaker combiner box that already has MC4 connections built in.

I have seen smaller combiner boxes, on Ebay, that were thusly equipped. Does someone know a good source for a 12 breaker combiner box with MC4 connections built in? I checked Ebay, Amazon, and our sponsor of course - http://www.solar-electric.com/catalogsearch/result/?q=combiners.

I wouldn't ask but I have to run pretty soon. Won't have easy internet for a few days. Would be nice to get this item squared away.

Alaska Man

Re: Great source for learning about string configurations?

http://www.amazon.com/Midnite-Solar-Mnpv12-Photovoltaic-Combiner/dp/B007CBNOK8

softdown

Re: Great source for learning about string configurations?

Alaska Man wrote: »

http://www.amazon.com/Midnite-Solar-Mnpv12-Photovoltaic-Combiner/dp/B007CBNOK8

Oh yea....I have probably found at least twenty sources for a 12 breaker combiner box. Interesting to see that Outback also offers them with a polycarbonate face and a great price.

I want one with the MC4 connectors already in place. Without all kinds of other fancy gear like lightning arrestors. Those go for over $600 when they get fancy.

I may ask for a bid at this stage. See what happens... Sometimes it is much easier and possibly more economic to let the "experts" do the buying and labor.

softdown

Re: Great source for learning about string configurations?

This would be almost perfect if it was nine string instead of eight string. Also prefer circuit breakers over fuses, think they are better.

http://www.solar-electric.com/misomnsoarco5.html

Vic

Re: Great source for learning about string configurations?

soft,

For smaller systems, the Pre-wired Combiners can make sense. Perhaps the reason that you are not finding more than an eight position MC4ed Combiner, is that things get messy with too many ins and outs, and that takes quite a lot of space on/in a box.

And, since you mentioned using conduit for the cable runs to the Combiner (this is the Code and "correct" way to do it), that exiting the conduit with the PV cables is a bit of an issue, without an exit into a box of some sort ... then each cable needs to exit yet again to get into the MC4s on the outside of the Combiner.

Agree that the link from AK man is the Combiner that I would use. This allows the PV cables to enter the Combiner inside the conduit, and you can directly wire these cables into the breakers and busbars.

Know that you already have MC4 extensions, but once cables enter a conduit box, a transition to THWN/THHW (etc) building wire could be made as it is easier to pull, and is quite a lot smaller in diameter than is the PV cable.

Just my opinions. Good Luck, Vic

softdown

Re: Great source for learning about string configurations?

This looks like a nice item for five strings:
https://www.powell.com/e2wItemQuickSearch.aspx?searchText=1954283-1&searchcondition=true&searchType=K&WT.z_cid=sp_POWELLELECTRONICSINC._20120425_buyNow&TE_cid=POWELLELECTRONICSINC.-1420576101283

Two of them is more than I wanted to spend....of course.

softdown

Re: Great source for learning about string configurations?

Vic wrote: »

soft,

For smaller systems, the Pre-wired Combiners can make sense. Perhaps the reason that you are not finding more than an eight position MC4ed Combiner, is that things get messy with too many ins and outs, and that takes quite a lot of space on/in a box.

And, since you mentioned using conduit for the cable runs to the Combiner (this is the Code and "correct" way to do it), that exiting the conduit with the PV cables is a bit of an issue, without an exit into a box of some sort ... then each cable needs to exit yet again to get into the MC4s on the outside of the Combiner.

Agree that the link from AK man is the Combiner that I would use. This allows the PV cables to enter the Combiner inside the conduit, and you can directly wire these cables into the breakers and busbars.

Know that you already have MC4 extensions, but once cables enter a conduit box, a transition to THWN/THHW (etc) building wire could be made as it is easier to pull, and is quite a lot smaller in diameter than is the PV cable.

Just my opinions. Good Luck, Vic

Thanks Vic, I hope that I said conduit for the run to the charge controller. That is what I have in mind unless I drop the feed almsot straight down to the charge controller.

I can wire and people think I do pretty sharp work. But I always feel like it wasn't 100% and always fear that it will malfunction. I'd really prefer a pro to wire up the combiner box. As far as splices...I really don't like electrical splices unless there is just one in one box. Then I still don't like them.

softdown

Re: Great source for learning about string configurations?

Reckon I will go with several, small pre-wired combiners that are fused. Just don't feel like wiring up a big combiner box these days.

Alaska Man

Re: Great source for learning about string configurations?

I must be missing something........ I ran my MC4 into the combiner box, cut off the clip, stripped the wire, and connected the positive to the bottom of the breaker and negative to the negative bus bar.

Easy Peasy.

softdown

Re: Great source for learning about string configurations?

You aren't missing anything. I just have too many other irons in the fire right now. Too many to name right now. A big one is the guy who slammed into my car at a red light. His insurance company adjuster is extremely elusive. The Holidays are very awkward for getting important stuff done. Now I have a medical issue three weeks later that probably is not accident related.

Though 18 panels, using nine strings, is more cumbersome than a smaller amount. We all have things we feel comfortable with and other things that we don't.

Alaska Man wrote: »

I must be missing something........ I ran my MC4 into the combiner box, cut off the clip, stripped the wire, and connected the positive to the bottom of the breaker and negative to the negative bus bar.

Easy Peasy.