Hi first post

john61ctjohn61ct Registered Users Posts: 24 ✭✭
Newb but learning fast.

Tapatalk doesn't work here? Android suggestions?

I need to use semi-flexible panels, and want to use PWM controllers; please take both as givens for now, don't try to convert me.

Please confirm: I'll get closer to panels' rated power by buying ones with a lower voltage, I guess more 'traditional' that could in theory be hooked up directly to the bank.

If so, and my bank is 12V, what is the lowest voltage I should use, and can expect to find? Should I look for "60-cell" or some other number

And same question for 24V.

For the latter, does hooking two 12-volt panels in series expand my range of choices?

Cost-effective sources on the flex panels, in smaller sizes and quantities would be appreciated. Not sketchy please, not looking to take risks on getting seconds to save 3%, looks like $2/w delivered is market ballpark?

Comments

  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    With PWM controllers you want a Vmp of about 18v to charge 12v. Double for 24v. Wiring in series (eg 36v for 12v bank) doesn't help as the "extra" voltage can't be used with a PWM controller.

    Battery charging voltage (should be) temperature controlled unless bank will always be at room temp. Normal absorb voltage will be around 14.5v, higher in low temps.

    Choice of voltage depends mainly on loads and distance from array to bank.
    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
  • littleharbor2littleharbor2 Solar Expert Posts: 1,605 ✭✭✭✭
    Most cost effective approach would be to use 72 cell ie: 300+ watt frameless "semi flexible" panels for a 24 volt system. They would be 24 volt nominal voltage and wouldn't cost you much in lost power due to voltage mismatch into a PWM controller. You could series wire 12 volt panels for 24 volt but that will cost you quite a bit more per watt in the end.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 540 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • PhotowhitPhotowhit Solar Expert Posts: 5,592 ✭✭✭✭✭
    john61ct said:
    Please confirm: I'll get closer to panels' rated power by buying ones with a lower voltage, I guess more 'traditional' that could in theory be hooked up directly to the bank.

    If so, and my bank is 12V, what is the lowest voltage I should use, and can expect to find? Should I look for "60-cell" or some other number

    And same question for 24V.

    For the latter, does hooking two 12-volt panels in series expand my range of choices?

    Cost-effective sources on the flex panels, in smaller sizes and quantities would be appreciated. Not sketchy please, not looking to take risks on getting seconds to save 3%, looks like $2/w delivered is market ballpark?
    Closer to rated power would first depend on charge controller, with a MPPT type voltage is less relivant, but requires incoming voltage of about 40-50% above charging voltage to work effectively. In general you will produce more current/effective charging with a MPPT type charge controller. ... but they cost more.

    With a PWM (cheaper controller) 60 cell panels would not be effective, you would want 36 cell panels for 12 volt charging or 72 (or 2-36 cell in series) for 24 volt charging.

    2 - 12 volt panels in series would only be effective for 12 volt charging with a MPPT type charge controller. It would be fine for 24 volt battery bank with a PWM charge controller.

    Amazon has some flex panels in the $1.35 a watt range, they have an easy and reliable return policy. I know nothing about these and don't recommend flexible panels as a rule.

    https://www.amazon.com/DOLSS-120watt-12volt-Flexible-Bendable-Solar/dp/B01M0O0NN0/ref=sr_1_2?ie=UTF8&qid=1489278078&sr=8-2&keywords=flex+solar+panels
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mcgivormcgivor Solar Expert Posts: 3,844 ✭✭✭✭✭✭
    Most cost effective approach would be to use 72 cell ie: 300+ watt frameless "semi flexible" panels for a 24 volt system. They would be 24 volt nominal voltage and wouldn't cost you much in lost power due to voltage mismatch into a PWM controller. You could series wire 12 volt panels for 24 volt but that will cost you quite a bit more per watt in the end.
    Agree with that, a 60 cell panel wil not work effectively with either voltage, 12 or 24V on a PWM system, too high for 12V too low for 24V. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @Estragon said:
    > With PWM controllers you want a Vmp of about 18v to charge 12v.

    Wouldn't it be more efficient to get one lower, output will never go above 13.8V, also no temp comp, being an LFP bank. Big wires to minimize voltage drops.

    ----
    > @littleharbor2 said:
    > Most cost effective approach would be to use 72 cell ie: 300+ watt frameless "semi flexible" panels for a 24 volt system. They would be 24 volt nominal voltage and wouldn't cost you much in lost power due to voltage mismatch into a PWM controller. You could series wire 12 volt panels for 24 volt but that will cost you quite a bit more per watt in the end.

    As I mentioned, I need to use smaller panels, 30-50w, maybe max 100w if they're narrow, in order to get a larger total, space constraints. Recognize higher costs.

    ----
    > @Photowhit said:
    > Closer to rated power would first depend on charge controller, with a MPPT type voltage is less relivant, but requires incoming voltage of about 40-50% above charging voltage to work effectively. In general you will produce more current/effective charging with a MPPT type charge controller. ... but they cost more.

    Again, please treat PWM and flex as givens in this thread.

    > you would want 36 cell panels for 12 volt charging or 72 (or 2-36 cell in series) for 24 volt charging.

    Thanks

    > https://www.amazon.com/DOLSS-120watt-12volt-Flexible-Bendable-Solar/dp/B01M0O0NN0

    The 21" may turn out OK, but 51' doesn't fit.

    More to the point, 20-22.8V would waste a lot more watts in PWM context, right?

    I'm hoping more for 15-16V? 30V for nominal 24?

    ----
    > @mcgivor said:
    > Agree with that, a 60 cell panel wil not work effectively with either voltage, 12 or 24V on a PWM system, too high for 12V too low for 24V. 

    Turns out the physical dimensions don't work for me, too heavy also, but these look like they might work otherwise?

    http://www.ebay.com/itm/282022835546

    Good value too.

    I've read that there are some Chinese flex mfg that will do custom layouts, e.g 4x15 or 5x12 rather than these 6x10. But they likely want large qty, and I hear sometimes anti-dumping fees at customs can be brutal?
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @Photowhit said:
    > Closer to rated power would first depend on charge controller, with a MPPT type voltage is less relivant, but requires incoming voltage of about 40-50% above charging voltage to work effectively. In general you will produce more current/effective charging with a MPPT type charge controller. ... but they cost more.

    Again, please treat PWM and flex as givens in this thread.

    > you would want 36 cell panels for 12 volt charging or 72 (or 2-36 cell in series) for 24 volt charging.

    Thanks

    > https://www.amazon.com/DOLSS-120watt-12volt-Flexible-Bendable-Solar/dp/B01M0O0NN0

    The 21" may turn out OK, but 51' doesn't fit.

    More to the point, 20-22.8V would waste a lot more watts in PWM context, right?

    I'm hoping more for 15-16V?
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @Estragon said:
    > With PWM controllers you want a Vmp of about 18v to charge 12v.

    No 15-16V possible? Max output is 13.8V, no temp comp, LFP bank and stout wires.
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @littleharbor2 said:
    > Most cost effective approach would be to use 72 cell ie: 300+ watt frameless "semi flexible" panels for a 24 volt system.

    Need small size panels 30-50w, maybe 100 if narrow enough. Space issues, jigsaw puzzle tiling required.

    Yes I know more per watt.
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @mcgivor said:
    Agree with that, a 60 cell panel wil not work effectively with either voltage, 12 or 24V on a PWM system, too high for 12V too low for 24V. 

    http://www.ebay.com/itm/282022835546

    Too big and heavy anyway.

    I've read some Chinese flex mfg can do custom layouts. Wonder what qty required?
  • PhotowhitPhotowhit Solar Expert Posts: 5,592 ✭✭✭✭✭
    john61ct said:
    > @Estragon said:
    > With PWM controllers you want a Vmp of about 18v to charge 12v.

    No 15-16V possible? Max output is 13.8V, no temp comp, LFP bank and stout wires.

    I don't think you will find them under 17 volts, and likely under 17.5 volts. I think you are correct and 16 would work for your application, voltage sinks with higher temperatures, so you might see if you can find NOCT (Normal Operating Cell Temperature) values for one of these flex panels.

    Unfortunately they are being made for the masses, who generally have lead acid batteries which need 14.5 and 15+ for equalizing.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.BB. Super Moderators, Administrators Posts: 31,771 admin
    Mass production is usually the more cost effective solution... You will get more bang for the buck with a high volume Vmp~18 volt panel vs a custom made 16 volt panel.

    Also, you have not spoken about the use of the system... In general, for properly charge a lead acid battery in a hot climate, you need Vmp~18 volt (36 cell) panels because hot panels (100F+ day) will drop Vmp by ~20% (18 volts Vmp * 80% Vmp drop for hot panel = 14.4 volts--About the optimum charging voltage for an AGM battery in a 75F environment--excluding wiring/controller losses).

    Also, semi-flexible panels can have their own issues. Glass mounted crystalline cells can last >20+ years (assuming nothing shatters the glass). Flexible panels (plastic) seem to have a 1-5 year life in any sort of permanent outdoor environment.

    Also, many flexible panels are thin film (not crystalline silicon) and are about 1/2 the efficiency of crystalline panels (you need 2x the area for the same amount of electrical power).

    There are hybrid flexible panels (crystalline cells in a "bendable sheet")--But they are not usually very rugged (don't walk on them, don't drop stuff on the panels). And probably have less than a 5-7 year maximum life too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john61ctjohn61ct Registered Users Posts: 24 ✭✭
    > @Photowhit said:

    > Also, you have not spoken about the use of the system... In general, for properly charge a lead acid battery in a hot climate, you need Vmp~18 volt (36 cell) panels because hot panels (100F+ day) will drop Vmp by ~20% (18 volts Vmp * 80% Vmp drop for hot panel = 14.4 volts--About the optimum charging voltage for an AGM battery in a 75F environment--excluding wiring/controller losses).

    From my second post: output will never go above 13.8V, also no temp comp, being an LFP bank. Big wires to minimize voltage drops.


    > Also, semi-flexible panels can have their own issues

    Yes, and I will need to make the best of them, as I said twice now they are a given. But thanks for the details.
Sign In or Register to comment.