Announcement

Collapse
No announcement yet.

Throwing in 12w panel with 100w panel?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Throwing in 12w panel with 100w panel?

    Hey everyone, just had a quick question about a small tent / camping system I'm going to use for a week during an event I'm attending (primitive camping only, limited gen usage though I plan on using my EF100is to recharge in emergency / before dark.)

    My basic (BUDGET) system (modified slightly from earlier ideas) is 2x 6v 215ah golf cart batteries, 100w panel, and an inverter ~1500w cont. (for future expansion). This will be totally fine for LED lights, two laptops, and cell phone recharging every night.

    I was initially going to use two marine batteries (G 27s) buy $/ah is way better for the golf cart batteries - even with a budget system I can't deal with the efficiency and durability differences.. it's worth the $$$ easily. So that's great, but now my 215AH is overkill for my 100w panel to say the least, but hey if I get a cloudy day I can use that extra 80AH over the marine batts on the second night, gen to recharge later.




    I DO however have a 12w mono panel sitting around, theoretically it'd add 10% to the system, but I don't know if it's actually possible.

    I'd obviously have to combine panels in parallel but the Vmp of the 12w is 17.2 and the 100w will be around 18.4, let's say I pull down the big panel to 17.2v (~7%) now we're talking about 93w, plus 12w means total I'm at roughly 105w? Which isn't really worth the trouble.

    I guess my other option is to use the little charge controller I have for the 12w panel, and attach that to the bank in parallel with the new charge controller I get for the 100w panel. I'm concerned about the controllers "checking" the voltage and instead of seeing battery voltage they'll see the charge voltage from the other controller, which I'm assuming would render them unable to decide when to switch between bulk/float charge etc.

    Should I just leave the 12w one behind? I have it so it's obviously tempting to put it to use, I'm just not sure I can though.

    Thanks guys!

  • #2
    You have not said what you are using for a charge controller for the big panel.
    If you are using a PWM type controller or no CC at all you are already losing potential power output from the panel because both panel voltages will be pulled down to the battery voltage anyway.

    If you have an MPPT CC (not cheap, but potentially inexpensive for your purposes), then you will still end up with more power from the two panels together than you would get from just one. The combined Vmp will be between the Vmp of the two panels, but closer to that of the large one. You will not get full power from the smaller panel, but it will help some.

    Depending on how long you will be spending at the camp site, you might actually do just as well bringing in charged batteries and running them down without even trying to recharge them. Or else charging them from the generator with a larger capacity AC charger whenever the generator is being run for other reasons.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by inetdog View Post
      You have not said what you are using for a charge controller for the big panel.
      If you are using a PWM type controller or no CC at all you are already losing potential power output from the panel because both panel voltages will be pulled down to the battery voltage anyway.

      If you have an MPPT CC (not cheap, but potentially inexpensive for your purposes), then you will still end up with more power from the two panels together than you would get from just one. The combined Vmp will be between the Vmp of the two panels, but closer to that of the large one. You will not get full power from the smaller panel, but it will help some.

      Depending on how long you will be spending at the camp site, you might actually do just as well bringing in charged batteries and running them down without even trying to recharge them. Or else charging them from the generator with a larger capacity AC charger whenever the generator is being run for other reasons.
      Thanks for the reply - for some reason I was fairly certain the controller I was looking at was MPPT but now that I looked again there really aren't many options anywhere near the price range of some of the "nicer" PWM controllers. In any event, the 100w panel is going to be using a CC, the 12w one has an older/smaller one as well.

      I'm a little confused though, I thought it was understood that when there was a given decrease in voltage there would be an increase in amperage if the overall power output remained constant? Is that not the case here? If a PWM controller is used, am I still getting 100 watts of potential solar energy (obviously in ideal conditions, etc)??

      Hypothetically let's say I had a PWM controller available for both panels. Would you just wire the panels in parallel and keep them on the newer PWM controller? It has LCD to show incoming volts/amps and usage (not that you can do much with the internal load limits) but it shows KWh used too which is cool.

      I had a nice 30a power supply/intelligent charger on a boat a while ago for the same generator and 3x group 27 batteries that worked great. I'd like to have something similar to recharge the bank in the evening if needed but I think it's a little out of the budget for this trip, they all seem to be around ~120 which isn't bad but not when it's all at once (at the end of the day, I have to keep it cheaper than the hotel options. )

      Comment


      • #4
        Originally posted by EstorilM View Post
        I'm a little confused though, I thought it was understood that when there was a given decrease in voltage there would be an increase in amperage if the overall power output remained constant? Is that not the case here? If a PWM controller is used, am I still getting 100 watts of potential solar energy (obviously in ideal conditions, etc)??
        A common point of confusion.

        An MPPT CC includes a circuit that converts DC at one voltage and current to DC at a different voltage and current. One way to do that is to convert to AC and then go through a transformer. If the intermediate AC frequency is high (usually above 2KHz) the transformer can be very small.
        A PWM CC simply has an electronic switch that connects and disconnects the panel circuit at a high speed using pulse width modulation (PWM) to allow the filtered output to be any average DC voltage required. But the switch cannot change the amount of current that flows, and the panel cannot store up energy while the switch is open to be delivered later when the switch is closed.

        To paraphrase Dereck (Sunking):

        PWM: Current In = Current Out.
        The panel voltage will drop to whatever corresponds to the voltage on the far side of the switch, so the current may be a bit higher than Imp, but never as much as Isc. The voltage drop means less power from the panel.

        MPPT: Power In = Power Out.
        If the output voltage is lower than the input voltage, the output current can be higher to transfer the same amount of power.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

        Comment


        • #5
          Originally posted by inetdog View Post
          A common point of confusion.

          An MPPT CC includes a circuit that converts DC at one voltage and current to DC at a different voltage and current. One way to do that is to convert to AC and then go through a transformer. If the intermediate AC frequency is high (usually above 2KHz) the transformer can be very small.
          A PWM CC simply has an electronic switch that connects and disconnects the panel circuit at a high speed using pulse width modulation (PWM) to allow the filtered output to be any average DC voltage required. But the switch cannot change the amount of current that flows, and the panel cannot store up energy while the switch is open to be delivered later when the switch is closed.

          To paraphrase Dereck (Sunking):

          PWM: Current In = Current Out.
          The panel voltage will drop to whatever corresponds to the voltage on the far side of the switch, so the current may be a bit higher than Imp, but never as much as Isc. The voltage drop means less power from the panel.

          MPPT: Power In = Power Out.
          If the output voltage is lower than the input voltage, the output current can be higher to transfer the same amount of power.

          Great info, and makes sense now - MPPT would definitely be ideal but it sounds like this one should be okay and for $35 I can't go wrong. After the trip I think I'll start piecing together a higher end system one step at a time (should be made a little easier now that I'm using GC batteries).

          One more thing, can you all comment on using DC devices? I think the inverter will be working around 80% efficiency most of the time so definitely not ideal.
          I plan on leaving the batteries, CC, and inverter in the back of the land rover, and running an extension cord ~20' into the tent. This way I can lock it all inside during the day (it's like a week long international horse show sporting event so we will be walking around all day each day). Panel on roof rack, some kinda battery vent, etc.

          I'll have lines from rover into tent for AC power, inverter remote switch (so I can turn it off inside the tent at night when we go to sleep) and DC (for USB, cig lighter, and a weather station thing that has battery state of charge. Probably 10 AWG for the DC. Going to use the loose spiral conduit to keep everything clean. When we are roaming during the day for the event I'll just unplug the rover, lock it and toss the cord in the tent.

          Should I be using DC for the iphones, my forms of light (I'll use LED either way, but I can keep it DC instead of using 120vac LED bulbs) a fan or two for the tent, and the DSLR battery chargers? How much loss would I realistically be preventing if I did this? I could run the two macbook pros off DC too but the adapters are kinda $$$ and probably not worth the few AH I'd save, especially if capacity turns out not to be an issue.

          Comment

          Working...
          X