Maximum Panels for Solar Boost 50?

On my RV, I have a Solar Boost 50 and currently have four Kyocera 120 watt panels. I believe I currently have the panels wired in pairs (parallel) and in series to provide 24 volts. The controller is set to charge the batteries (660Ah) at 12 volts. If I understand things correctly, my current input is 15Ah at 24V (max).

I want to have the maximum solar input to the controller. Without replacing my current four panels, how much more can I add? I'm looking at adding four more Kyocera 135 watt panels. Is this doable with my controller. If so, I believe wiring will still be in pairs (parallel) and then in series for 24volt input.

If having 8 panels (four 120watt and four 135watt) is possible, what's the best way to wire them? A diagram would be most useful. I'm not positive my current wiring is correct, although all appears to be working fine. I also don't currently use a junction box - wiring is from panel to panel. Would a junction box be the way to go?

Thanks!
Larry

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Maximum Panels for Solar Boost 50?

    What are the specs on the panels?
    for the 120's
    Maximum Power: 120 watts
    Maximum Power Voltage: 16.9 volts
    Maximum Power Current: 7.10 amps
    Open Circuit Voltage: 21.5 Voc
    Short-circuit Current: 7.45 amps


    Specifications for Kyocera KD135GX-LPU Solar Panel
    Max Rated Power (Pmax) 135 Watts
    Voltage at Max Power (Vmpp) 17.7
    Current at Max Power (Impp) 7.63 Amps
    Open Circuit Voltage (Voc) 22.1
    Short Circuit Current (Isc) 8.37 Amps

    the controller looks like these are it's specs
    Output current rating..........................50A
    System voltage ..................................12/24VDC nominal
    Max. PV Open circuit voltage ............57VDC
    Max. battery voltage...........................57VDC
    Output current limit.............................50±2A
    Volt meter full scale range .................60.0V
    Volt meter accuracy ...........................±0.3% full-scale
    Current meter full scale range ...........±60A
    Current meter accuracy .....................±0.5% full-scale
    Acceptance voltage ...........................13-16/26-32V typical
    Float voltage.......................................0-2/0-4V <Accept.
    Equalize voltage.................................1V/2V >Accept.
    Power conversion efficiency ..............97% typical @ 40A
    Temperature compensation
    Lead-Acid............................-5.0mV/°C/cell
    NiCd....................................-2.0mV/°C/cell
    Current consumption
    Standby...............................30mA typical
    Charge on ...........................150/90mA typical
    Cabinet dimensions ...........................10”Hx8¾”Wx3½”D
    Remote display module .....................14½”Hx4½”Wx1¾”D
    Storage temperature range ...............-40 to +85°C
    Specified temperature range .............0 to +40°C
    Extended range...................-40 to +60°C
    (will operate but may not meet specifications,
    see technical bulletin #100206)

    Looks like the new panels are pretty close to the old ones within 10% anyway
    your 2 pair of existing panels are well under the rating on the controller. You want to keep the MAX voltage under the 57 volt rating and 2 pairs is doing that. Now can you use all the extra amps produced by the new panels. So each pair is putting aout about 15Amps max, sounds like the controller is a bit undersized, Other will pipe up here and give a better explanation than I can.
  • System2System2 Posts: 6,290 admin
    Re: Maximum Panels for Solar Boost 50?

    Larry,
    I believe you should be able to add 4 more panels with your current Solar Boost 50Amp controller, the math goes something like this:

    660ah battery bank needs 5 to 13% to charge (33 - 85.8 amps) @ 12v
    your current panels put out 15 amps max @ 24v not counting losses
    4 new 135 watt panels should put out 16 amps max @ 24v not counting losses
    puts you around 31 amps max @ 24v. You could probably add 6 new panels and be ok! (if you have the room) that would put you around 40 amps [email protected] 24v total not counting losses.

    On a minimum I would fuse the + side of all panels with an in-line fuse, fuse the + side at the batteries, and if you are using an inverter, fuse the + feed. A fuse between batteries is also a good idea, a short in the battery bank can easily cause a fire.

    I am a new to solar but have been reading alot :) , please correct me if I am wrong.
    Rickie
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Maximum Panels for Solar Boost 50?
    zmanky wrote: »
    Larry,
    I believe you should be able to add 4 more panels with your current Solar Boost 50Amp controller, the math goes something like this:

    660ah battery bank needs 5 to 13% to charge (33 - 85.8 amps) @ 12v
    your current panels put out 15 amps max @ 24v not counting losses
    4 new 135 watt panels should put out 16 amps max @ 24v not counting losses
    puts you around 31 amps max @ 24v. You could probably add 6 new panels and be ok! (if you have the room) that would put you around 40 amps [email protected] 24v total not counting losses.

    On a minimum I would fuse the + side of all panels with an in-line fuse, fuse the + side at the batteries, and if you are using an inverter, fuse the + feed. A fuse between batteries is also a good idea, a short in the battery bank can easily cause a fire.

    I am a new to solar but have been reading alot :) , please correct me if I am wrong.
    Rickie

    Actually he has 4 panels, wired in pairs so max output is 15 amps. 2 strings of 2 panels if I read it right. The series wiring of 2 panels gets the voltage up and then paralleling the 2 strings gets the amperage up. He could probably add two more strings of 2 on that controller. (actually even more I think)
  • System2System2 Posts: 6,290 admin
    Re: Maximum Panels for Solar Boost 50?

    Dave,
    I agree, Larry asked if he could add 4 new panels, my answer is yes, he should be able to add at least 6 more 135 watt panels, or 3 more pairs of wired in series.
  • System2System2 Posts: 6,290 admin
    Re: Maximum Panels for Solar Boost 50?

    Thanks Dave and Rickie,

    You've both confirmed what I've been thinking. Your projected 31amps @ 24V is also in line with my thinking, so I guess I'm on the right track.

    My only hesitation now is how to properly and efficiently wire these 8 panels. I know I can figure it out, but am not sure my way is the most efficient.

    Larry
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Maximum Panels for Solar Boost 50?

    Let's see, 14.2 Volts @ 50 Amps (maximum output from charge controller - not really related to output from panels) = 710 Watts @ 80% efficiency = 887.5 Watts peak array.

    Existing panels 480 Watts ... subtract from 710 ... leaves 230 Watts.

    Add two 135 Watt panels = 750 Watts @ 80% = 600 ... divide by 14.2 Volts charging ... 42 Amps max.

    So it comes down to an issue of efficiency. How well can you keep the panels oriented towards the sun, what temp they'll reach, how much line loss ...

    Two more panels should be no trouble. Four more might be a waste of money (controller simply won't make use of the extra Watts) unless you're habitually in less-than-ideal insolation conditions, which is often the case when camping.

    At any rate, your existing array is a tad undersized for 660 Amp hours of battery.
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