Wiring-series v. parallel or?

hillsidehillside Posts: 35Registered Users ✭✭
Need wiring advice--am upgrading our backup solar power and will have approx. 940 watts.
24 volt system
SRNE 40A MPPT  controller
Cotek 3000W 24V. pure sine inverter
4- 208 AH 6V GC batteries Would like to replace these with something in the 300AH range in the future. 350-370AH too much?

Have one 5 yr. old Trina 230w, (removed 4- 70W panels which the installer added a 20Amp. Midnite Solar combiner box).
Now adding 3 new 235W panels, however, the final panel, as delivered, is 255W.  They will take it back if necessary and switch to 235W
Under 10% difference...an issue?

This setup is primarily for powering the washer/dryer a couple of times a week, and on occasion, a mini fridge of 1.5amps or small TV. 
Washer is 9 amp and propane dryer is 6 amp.
Wiring in series, parallel, or a combination is the question.

So, here's what I've read elsewhere...do you agree?
Series produces more voltage for larger appliances while parallel produces more amps for charging batteries faster.
Series only gives less battery life but produces more power in volts, but less amps.  (Battery life is very important here due to shipping cost.) And is subject to power loss from tree/house shading. Not an issue here. But thick clouds are.

Series and Parallel combined...a good balance of watts and amps and extends battery life.
An MPPT CC will lower the volts but raise the amps.

I'm trying to get the professional installer to do the wiring but the office wants to send an "installer" to do the job. Last time this happened the installer got the wiring wrong and the owner came and did it right.
Adding to the mix is, he doesn't speak English. My Spanish is ok but not for specifics like this.

In this area (central Caribbean) finding expert advice is difficult.
Climate is typical Caribbean, lots of sun and can be hot. Much like the southern US in summer.
So far, series/parallel combination seems right. What do the experts think?

If I go series/parallel combination, what size wiring do I need? It's about 24 feet  from the panels to the CC.


Comments

  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    hillside said:
    Have one 5 yr. old Trina 230w, (removed 4- 70W panels which the installer added a 20Amp. Midnite Solar combiner box).
    Now adding 3 new 235W panels, however, the final panel, as delivered, is 255W.  They will take it back if necessary and switch to 235W
    Under 10% difference...an issue? 
    I wouldn't worry about it, I would be more concerned that all panels are 60 or all panels are 72 cell panels and the same type poly crystalline or mono crystalline.

    hillside said:
    This setup is primarily for powering the washer/dryer a couple of times a week, and on occasion, a mini fridge of 1.5amps or small TV. 
    Washer is 9 amp and propane dryer is 6 amp.
    Wiring in series, parallel, or a combination is the question.
    I can't speak to loads with out a lot more information on solar insolation, panel orientation, parasite loads, length of time running loads...

    hillside said:
    So, here's what I've read elsewhere...do you agree?
    Series produces more voltage for larger appliances while parallel produces more amps for charging batteries faster.
    Series only gives less battery life but produces more power in volts, but less amps.  (Battery life is very important here due to shipping cost.) And is subject to power loss from tree/house shading. Not an issue here. But thick clouds are.

    Series and Parallel combined...a good balance of watts and amps and extends battery life.
    An MPPT CC will lower the volts but raise the amps.
    Pretty much, loads run off batteries so ignore any mention of loads and ignore the person suggestion there is a connection.

    A watt is a watt if you are using a MPPT type charge controller. Likely you will HAVE to run 2 strings in series and 2 2 strings in parallel to fit under the charge controllers guidelines. Look in the instruction manual.


    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    edited September 19 #3
    hillside said:
    Need wiring advice--am upgrading our backup solar power and will have approx. 940 watts.
    24 volt system
    SRNE 40A MPPT  controller
    Cotek 3000W 24V. pure sine inverter
    4- 208 AH 6V GC batteries Would like to replace these with something in the 300AH range in the future. 350-370AH too much?

    You can probably get away with 350ah for a backup system IMHO.

    Have one 5 yr. old Trina 230w, (removed 4- 70W panels which the installer added a 20Amp. Midnite Solar combiner box).
    Now adding 3 new 235W panels, however, the final panel, as delivered, is 255W.  They will take it back if necessary and switch to 235W
    Under 10% difference...an issue?

    Check the specs.  If voltage & amperage is within 10%, probably close enough.

    This setup is primarily for powering the washer/dryer a couple of times a week, and on occasion, a mini fridge of 1.5amps or small TV. 
    Washer is 9 amp and propane dryer is 6 amp.
    Wiring in series, parallel, or a combination is the question.

    So, here's what I've read elsewhere...do you agree?
    Series produces more voltage for larger appliances while parallel produces more amps for charging batteries faster.
    Series only gives less battery life but produces more power in volts, but less amps.  (Battery life is very important here due to shipping cost.) And is subject to power loss from tree/house shading. Not an issue here. But thick clouds are.

    Series and Parallel combined...a good balance of watts and amps and extends battery life.
    An MPPT CC will lower the volts but raise the amps.

    Assuming the appliances are running off the AC output of the inverter, I don't think it matters much how the panels are wired.  You generally wire in series to reduce the size of wire needed to keep voltage loss acceptable.

    I'm trying to get the professional installer to do the wiring but the office wants to send an "installer" to do the job. Last time this happened the installer got the wiring wrong and the owner came and did it right.
    Adding to the mix is, he doesn't speak English. My Spanish is ok but not for specifics like this.

    In this area (central Caribbean) finding expert advice is difficult.
    Climate is typical Caribbean, lots of sun and can be hot. Much like the southern US in summer.
    So far, series/parallel combination seems right. What do the experts think?

    If I go series/parallel combination, what size wiring do I need? It's about 24 feet  from the panels to the CC.

    You could try various combinations using an online voltage drop calculator (eg www.calculator.net)



    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Posts: 35Registered Users ✭✭
    Thanks for the replies. So, it looks like series is the best way. I'm going to print these and try to work with the owner to do the install (speaks English).
  • oil pan 4oil pan 4 Posts: 751Solar Expert ✭✭✭✭
    What's the input voltage limit on the mppt?

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • mike95490mike95490 Posts: 7,901Solar Expert ✭✭✭✭
    hillside said:
    Need wiring advice--am upgrading our backup solar power and will have approx. 940 watts.
    .........
    So, here's what I've read elsewhere...do you agree?
    Series produces more voltage for larger appliances while parallel produces more amps for charging batteries faster.
    Series only gives less battery life but produces more power in volts, but less amps.  (Battery life is very important here due to shipping cost.) And is subject to power loss from tree/house shading. Not an issue here. But thick clouds are.

    Series and Parallel combined...a good balance of watts and amps and extends battery life.

    ..........
    Total BS is what you typed.  Whoever gave you that information is a fraud

    * Battery life is determined by depth of discharge and rate of recharge.

    * Wire panels in series for use with a MPPT controller

    * Wire panels in parallel for use with a PWM controller. (you may need to have some panels in series to have proper recharge voltage for battery, 12V battery needs 19V panels)

    *  Generally over 300 watts, MPPT is a better choice for less cable losses, management, and lower equipment costs

    * If you have medium clouds, expect no more than 10% of panel rated output.  Voltage will remain the same, but AMPS vary with the brightness of the light.   MPPT controllers are better at harvesting in cloudy conditions.  With heavy clouds, expect to run the generator a lot, PV will not keep up and with out recharging you will destroy your batteries.

    Build and run the system with golf cart batteries, to prove it out, and when they fail in 1-5 years, you will hopefully have learned enough to let the next, expensive set of batteries last longer.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    Okay, I believe you speak English, and I will feel free to be a bit rude, since you DIDN'T bother to look up the specs for your charge controller. Since you didn't hold it close enough to the computer for me to read, I'll assume that it's this 40 amp SRNE MPPT controller. I looked up some specs for it (other's asked too!);

    http://www.srnesolar.com/product/detail/177.html



    So a maximum of100 volts AND a working range of Battery voltage + 2 volts to 75 volts.

    With 4 panels in series, you can fry the controller quite nicely... As I said before, likely you can run 2 strings in series with 2 panels in each string...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • hillsidehillside Posts: 35Registered Users ✭✭
    Jeez, thanks for the last two kind comments. Just the kind to expand beginners participation
    Do you know what time zones are? I generally post during daylight hours.
    Photo, I said it was the 40 amp CC in the 1st post. I DID bother to look it up. And was trying to keep the post brief.
    And you're saying series wiring will fry the CC but no one else mentions it.
    Mike, Photwhit agreed in post #2 with what I typed ("Pretty much") So maybe you two should have at it.
    The first set of "solar batteries" lasted between 2 and 3 years.
    There are not a lot of choices in batteries here. Having them shipped a couple thousand miles costs a bit. Like a lot.


  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    I'll mention that 4 in series will likely fry the controller too.

    Most likely, your panels will have a Voc in the low 30v range. Even in your warm climate, 4 in series will put you over 100v.

    For a 24v nominal system voltage, I'd wire them 2 in series for ~60Voc, and 2 strings in parallel for ~15a. Distance is reasonable, so 10awg wire would likely do the job. I'd get standard mc4 extentions which are normally 10awg.

    I'm making some assumptions about panel specs etc though, so you should work through it with actual numbers.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Posts: 35Registered Users ✭✭
    edited September 20 #10
    Thanks Estragon,  mvp, most valuable post...the Voc. is listed as 36.8
    I have several small, stand alone solar setups on the property, for electric gate, home water pumping, bathroom lights and fan.
    Simple stuff. To me, it's not worth going all solar due to hurricanes, tornadoes and lightning strikes. The lightning is frequent in summer and everyone has stories of losing electronics. My neighbor has had 2 strikes go into a screened window and hit the floor. He only lost the tv and dish receiver.
    I didn't have time to take down the solar panels last year and luckily they stayed in place thru 140 mph winds and 3 feet of rain. (not on the roof)
    So I stay in beginner's corner. Anything smaller? You got a kiddie pool here? :) :)
    (The 235W Hanwha)



  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    You can do things to reduce the probablility of catastrophic lightning damage, but in a lightning prone area, you can't eliminate it entirely (at least not in a cost-effective way).

    I'm in a bit of a valley, with trees on ridges on three sides, and a lake on the fourth. Makes for some winter shading issues, but makes it unlikely lightning will find me a tasty target.

    Others on the forum have much more experience dealing with the issue, so if interested you might want to start a thread on that topic.

    I can only imagine 140mph winds and 3' of rain, but in my travels in that part of the world, it looks like the landscape is adapted to handle it to the extent possible.

    How does Voc of 36.8 compare to the old Trina panel?

    As this is a backup system, how long would it be expected to last in an outage?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • hillsidehillside Posts: 35Registered Users ✭✭
    You're right, the landscape handles it well for the most part but landslides were everywhere esp. where roads were made in steep hills.
    We had quite a few fruit trees blow down but a house built with concrete blocks and cement  is the way to go. Still, with a plywood and steel roof, it was a concern, but it stayed together. A single screw lifted up 1/2".
    Old Trina panel is 37 V rated. And the one 255w panel is 37.8. If we get a sunny day I'll measure the Trina. Lots of cloud cover lately.
  • BB.BB. Posts: 27,883Super Moderators, Administrators admin
    Need to be clear that these are Vmp (voltage maximum power) voltages for both panels... Not Voc (voltage open circuit) or a mix of Vmp/Voc specifications.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillsidehillside Posts: 35Registered Users ✭✭
    Thanks, Bill, 30.1 and 30 for the older Trina, 30.5 for the one that is 255watt.
    " As this is a backup system, how long would it be expected to last in an outage?"
    Would use this for the small mini fridge, a fan for overnight use on hot days/nights,  washer/dryer, all the while keeping an eye on charge level. Have a gas 3000w Honda EU for house power otherwise.  Love it.  :)

  • BB.BB. Posts: 27,883Super Moderators, Administrators admin
    edited September 21 #15
    That is fine to parallel (30 volts +/- 10%, = +/-3 volts from low to high panel)... Similarly, series connected panels should have Imp matching to within 10%.

    Not quite sure where the system is located... The amount of sun depends on local weather conditions... You can use a site like this to figure out how much sun such a system will receive:
    http://solarelectricityhandbook.com/solar-irradiance.html

    For example, Aruba, fixed array (see next post for table--formatting issues):

    The typical off grid AC power system will produce:

    4x 235 Watt panels * 0.52 off grid system eff * 6.44 hours of sun (September) = 3,148 Watt*Hours (average day September)

    Realistically, your base load should be around 50% to 65% or so of "predicted amount"...
    • 3,148 WH per day (Sept) * 0.50 base load fudge factor = 1,574 WH per day
    That is pretty close to what a pretty efficient refrigerator could use (~800-2,000 WH per day--Depending on brand/model/local room temperature/etc.).

    On days with "poor weather", don't run other optional loads... On clear/sunny days, you can run the other optional loads (washing machine, etc.) .

    Several notes:

    One is that Vmp~30 volt panels are not high enough voltage to quickly/fully charge a 24 volt battery bank... You need Vmp panel voltage in the range of 35-40 volts for a PWM type charge controller.

    For a MPPT type charge controller, you need >40 volts for an "efficient" installation. Or, 2x of your Vmp~30 volt panels in series, 2x parallel strings (for example). Details matter (charge controller specifications, etc.).

    The other note is the 3,000 Watt AC inverter... These can take 20 watts or more "just turned on"... 20 Watts * 24 hours per day = 480 Watt*Hours--A significant amount of your daily harvest. Some inverters have "sleep mode" which can reduce energy usage... But many/most frost free refrigerators do not work well on "sleep" mode (defrost timers do not work correctly).

    Getting a Kill-a-Watt type energy meter can help a lot in understanding the daily loads (lots of different brands and models--120 VAC vs 240 VAC and such).

    https://www.solar-electric.com/kiacpomome.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Posts: 27,883Super Moderators, Administrators admin
    edited September 22 #16
    Try the table again:

    Angochi
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 78° angle from vertical.
    (For best year-round performance)

    JanFebMarAprMayJun
    6.76
     
    7.07
     
    6.96
     
    6.24
     
    6.53
     
    6.75
     
    JulAugSepOctNovDec
    6.83
     
    6.63
     
    6.44
     
    6.43
     
    6.41
     
    6.36
     
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillsidehillside Posts: 35Registered Users ✭✭
    Wow, thanks so much for that. Will check solar city site. We're probably similar to Aruba..(PR)
    We have been turning the inverter off at nights--what a difference it makes.
    Got the kill-a-watt.
  • hillsidehillside Posts: 35Registered Users ✭✭
    Hello, I'm back again with a couple stupid questions.....have zero confidence in the company I'm dealing with, mainly because I cannot talk to the actual owner/installer, who, 5 years ago put a Midnite Solar 20A combiner box on the original system.  (515W, 24 volt, 3000w inverter)
    Now, with 4 panels at roughly 900 watts, they (owner's wife, knowledgeable but that's debatable) are telling me I need a higher amp combiner box, like 60 amps.Yet, I read here, (link to follow) that on small systems like this a combiner is not even needed.
    That's question 1..do I need one?
    Two, written above by Estragon, "For a 24v nominal system voltage, I'd wire them 2 in series for ~60Voc, and 2 strings in parallel for ~15a. Distance is reasonable, so 10awg wire would likely do the job. I'd get standard mc4 extentions which are normally 10awg."
    When you say two strings in parallel for ~15A,  I'm not sure what you mean. Isn't a string 2 panels or more? If the first string is in series, that leaves 2 panels?
    The run from the panels to the CC is 24 feet, and from there to the batts. is about 5 ft.
    Appreciate the help. Thanks



  • jmbjmb Posts: 12Registered Users ✭✭
    Two serial strings in parallel.  So, hook two panels in series you have a "string" and you then hook it in parallel with the other "string."
  • BB.BB. Posts: 27,883Super Moderators, Administrators admin
    As "jmb" typed... Two panels in series, and the two sets of series panels connected in parallel--Then connect to charge controller Vpanel input.

    You can use or remove the combiner box... If the combiner box has circuit breakers, it is nice to leave the box in place. You can turn off the breakers (solar panels) to work on the controller. And if you need to diagnose a solar array problem, you can turn off breaker A and see how much string B is generating... And turn off breaker B, and see how much current string A is generating (looking for bad panel, poor wiring, etc.).

    You really only need a combiner box if you have 3 or more strings in parallel. Basically, the fuses/breakers prevent two "good strings" feeding a bad/shorted panel/string (3 strings in parallel is just over the requirement for needing a combiner box with fuses/breakers).

    If you have a choice (and can get a good price), using a combiner box with circuit breakers is nice. You can turn power on/off at will (for debug/servicing). And if for some reason a breaker pops--You don't have to find a spare fuse.

    Also, the modern "touch safe" fuse holder has a design issue. If you simply pop the fuse holder open under load, it is very possible for the fuse holder to arc and ruin the holder/cause a fire. Do not use the fuse holder to "turn off" solar power when working on the system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    Lets go to basics on definitiions;

    2 or more, solar panels wired + to - is a string, this is called wiring in series. This gives you the 2x the voltage of a single panel at the amperage of the smallest amperage panel.

    2 panels or strings or panels wired - to - and + to + is called wiring in Parallel. This gives you 2x the current of a single panel (or string of panels)

    Your wiring should look like this;
    Image result for Solar panels in series and parallel

    I don't know what combiner box you are referring to, I checked Midnites' smallest combiner box, MNPV3, and it is rated for 3 input strings with breakers and 60 amps, They also make a MNPV2 that is also rated for 60 amps. As others have said if you have 2 or less strings of the same, or roughly the same amperage there is no need for a combiner box;



    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • hillsidehillside Posts: 35Registered Users ✭✭
    Photo, cannot thank you enough. The combiner box is 5-6 yrs. old and if I find anything interesting about when I open it up I'll post.
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