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kittysmitty
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# Posted: 26 Feb 2023 09:31
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Thinking about re configuring my current system at the camp.I don't have the spec on my panels at the moment but a general question in regards to Maximum System Voltage. In running panels in series, I'm good voltage wise if the Voc of the panels added together is less than the maximum system voltage?
And second, looking at other panels the Maximum System Voltage could be 600VDC, 1000VDC or some at 1500VDC. My panels are 12VDC and about 10 years old. Any Guesses what the Maximum System Voltage might be. Thanks
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Peewee86
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# Posted: 26 Feb 2023 10:05
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The quantity of panels that you have would be a requirement for anyone to give you an approximate guess. I have seen the VOC of 12 volt panels can range between 17 and 21 volts. Without some additional information anyone’s guess is is not going to have much accuracy. Is there a manufacturer’s label on the back of the panels?
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kittysmitty
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# Posted: 26 Feb 2023 10:29
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I'm not where the panels are. There were labels, but could be faded or gone. My question is regards to Maximum System Voltage and it's definition.
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Nobadays
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# Posted: 26 Feb 2023 16:16
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Not really enough information/context here.... but I'd venture to say "Maximum System Voltage" is going to depend upon the maximum voltage of your Solar Charger Controller. You don't want to exceed that voltage... usually represented like - 80/150 or 30/100.... meaning 80 amp output/ 150vdc maximum input or 30 amp output/100vdc maximum input.
My understanding is never exceed either the rated amps ( on your input side by paralleling panels) or maximum voltage by seriesing your panels.
As Peewee said, without knowing your panels/ system no one can offer much clarity.
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ICC
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# Posted: 26 Feb 2023 17:50 - Edited by: ICC
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Quoting: Nobadays "Maximum System Voltage" is going to depend upon the maximum voltage of your Solar Charger Controller.
For those of us with small systems that is generally going to be what sets the maximum voltage. Another consideration can be the maximum voltage rating for connecting wires. That is where the 600 volts figure most likely comes from. 600 volts is a common max voltage for NEC-approved wire that will be found in residential and commercial construction.
NEC rules allow PV systems with up to 600 volts on 1 and 2-family residences. 1000-volt systems may be installed on a commercial building. 1500-volt systems may be used in a utility-scale system, not installed on a building but free standing.
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ICC
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# Posted: 26 Feb 2023 18:10 - Edited by: ICC
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One further thing. Cold temperatures raise the voltage output a silicone solar wafer can produce, and high temperatures lower the voltage. So, the NEC rules specify that a panels rated maximum voltage (Voc) be multiplied by 1.25 to cover that, plus multiplying a second time by 1.25.
The conductors must be oversized by 25% for any conditions under NEC rules. Plus the temperature factor of 1.25 must be accounted for. It is easiest to simply use 1.56 as a multiplier and just do it once.
The amps don't change with temperature, but panels at higher elevations can have increased amp output due to the thinner and probably clearer air equaling more sunlight reaching the solar cells.
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Peewee86
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# Posted: 26 Feb 2023 22:44
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I will take one more shot at answering this. kittysmitty’s original question sort of answered it self.
Maximum system voltage is the sum of all series panels VOC. That is the definition.
For example, if a person has 4 panels in series and they are each rated at a VOC of 20 volts that would maximum system voltage of 80v. No one can answer what that number is for the OP’s system without more information.
Each current carrying component of the system will need to be rated above the maximum system voltage. As ICC stated above, electrical codes use a multiplier to determine a safety margin. A properly sized solar charge controller will have a voltage rating of the maximum system voltage plus a safety margin.
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ICC
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# Posted: 26 Feb 2023 23:43
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It seems to me that kittysmitty must have read some of the info from the NEC regarding max system voltages as the numbers quoted in the OP match the ones in the NEC.
The maximum practical system voltage will be lower than the NEC allowable maximum in part because the vast majority of charge controllers that are likely to be used in small residencial or cabin systems are going to be well under the 600 volt figure.
Morningstar has one, Schneider has one and they cost about $1200 and $1800 respectively. So while one could series connect several panels to make 300 or 400 volts and by some definitions have a 300 or 400 volt system it would not necessarily be usable with average hardware.
It could also be unsafe to series connect older panels together to produce such high voltages as the panels will have a manufacturer's spec'd maximum. Check the labels if possible. Otherwise I would guess that series connecting most older panels would be safe when limiting the maximum voltage to 150 volts which is a common enough maximum spec on many charge controllers used in small cabin systems. BUT, the spec sheet for any controller should be consulted and the maximum voltage being used for calculations must have the cold weather factor applied as well as the NEC 25% figure.
The major league charge controller manufacturers usually have spreadsheets or online calculators available for their own brands of controllers. That makes it easy to enter all the input variables and make special allowances tailored for minimum temperatures for specific locations and get recommendations how to connect panels in different series/parallel arrays. It makes no sense to use -45 F temperatures for system calculations for a location in southern AZ, for example. Many AHJ will allow the use of the climate/location adjusted low temperature instead of the NEC listed 1.25 multiplier.
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gcrank1
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# Posted: 27 Feb 2023 08:19
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All this stuff is discussed in depth over at:
diysolarforum.com
You dont have to join to read it all, and like here, there is a wealth of threads from just getting interested to advanced.
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offgrididaho
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# Posted: 27 Feb 2023 12:28
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Couple of quick things to add that might help big picture thinking:
Charge controllers are rated for maximum voltage in, if you already have a controller you need to figure the maximum voltage it can handle and arrange panels in a series / parallel combination that doesn't exceed the max voltage.
Most larger panels these days are 48v, three in series is just shy of the 150v, but panels can put out more than the max voltage they're rated for (under specific conditions, usually very sunny colder days) so leave a margin for error. For example, if you have three 48v panels in series I would not get a 150v charger controller, go 250v... 150 is cutting it too fine.
Higher voltages allow for smaller wire, less expensive and easier to run and can also make the system more efficient.
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gcrank1
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# Posted: 28 Feb 2023 10:02 - Edited by: gcrank1
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Ime, 12v for small/starter systems with up to a 1500W inverter. Ive done multiple 12v builds and rebuilds, lol, figuring out how this all plays out.
24v is the step up for over 1500W inverter, maybe up to 4000W? I havent done 24v yet...knowing what I do now that would be my choice for cabin life.
48v looks best for pretty much emulating grid power after inverting.
The wiring/fusing sizes are the issue with lower voltage. To 'properly wire' 12v for a 4000W inverter is unrealistic.
12v-small
24v-mid
48v-big
Pick which voltage works for your future needs/wants.
There are lots of online calculators for your 'energy audit'
The biggest expense will likely be storage (bat bank).
How much money do you have to invest into elec power? I discovered quickly that I CANT afford the system it would take to do all my 'wants' but I could take care of my needs.
Solar aint cheap.
Solar is labor intensive in building, can also be intensive in trouble shooting/maintaining.
You need some redundancy/spares in case of system failure; perhaps a way to reduce the system to bare-bones for necessities only.
All this is why designing, building and knowing your system is important compared to paying someone to build you a 'turn-key' system and leave.
And a back-up generator, even if small, is good to have.
Wiring the cabin for 120vac and running off the gen was my first good step.
Then figuring how to make my bat bank inverted to 120vac gave me quiet elec power and experience in how much I could realistically power.
Figuring how to charge that bat bank (solar and/or otherwise) was last. But you have to be able to recharge the size battery you choose. Having a huge bat and only room for 2 solar small panels will kill the bat.
12v panels is just a nominal rating. If you wire multiples together parallel you stay at '12v nominal', really more like 18-21v (you must have about 50% more panel output voltage than the nominal battery voltage to actually charge the battery).
If you series wire the panels you get higher voltages.
Scc are rated for the max input they can take. You dont want to crowd that rating! Ive used a 20% buffer factor for cold and sunny day spikes.
You juggle the series and parallel wiring of the panels (array) to stay within the max scc voltage input capability.
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kittysmitty
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# Posted: 1 Mar 2023 08:17
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Thanks Folks for all your comments. This was what I was looking for, just some "theory". This is a system that started out 15 years ago and has evolved. The panels are pole mounted about 15 feet high, but I'm getting tired of cutting down trees to give them better sunlight. The camp roof will be re shingled in the spring and I will then roof mount. Just doing some early research. I know I will have to upgrade some components, but want to do my homework.
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Brettny
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# Posted: 1 Mar 2023 10:43
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In theory higher voltage means less line loss to the CC. How ever I have found that wireing 235w pannels in series caused less input to my batteries due to shading. Pannels in series dont like shade because the whole array acts as if it's one pannel.
12v pannels can be prety limiting alone but even if you dont get bigger pannels wire them up with MC4 connectors and play around with series vs parallel wireing of the pannels. MC4 branch connectors and connectors alone are very cheap.
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Steve_S
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# Posted: 1 Mar 2023 13:45
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I would say a Re-Roof is an Opportunity and should be seen as such. I would suggest that you consider a Tin roof as opposed to shingles for longevity, especially if you want solar panels on the roof.
Depending on where you are, you may also be eligible for Tax Rebates and possible credits etc and that would certainly be worth considering, especially if it takes the bite out of the upgrade/repairs. Every penny saved is precious these days...
There are several different types of solar panels out there now and there are several with designs to get around shading issues and in low light conditions, as I previously mentioned the Hyundai Shingled Solar Panels are incredibly good with Shade & Low Light but they are only now finally appearing in North America.
Given that this is a Cottage (Part Time) property, the equipment you already have may or may not work, partly due to age and the limits of what was available 15 years ago. It would be beneficial if you gave us the information about the various pieces of gear that you have at present... Make, Model & Version as applicable for the Solar Charge Controller, Inverter & Panels you currently have.
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