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  • need help sourcing correct components

    Hello, my brother and I are new to solar and are trying to put together 600-900 watts of panels for our small cabin. We will only be running 3kw a day maximum (typical day should be around 1.5-2 kw). I see people selling a bunch of nice panels, inverters, and charge controllers for cheap on Facebook and want to make sure what I get works together. Also I will be getting deep cell gel batteries for storage (most likely Renogy as amazon has a good deal on them). I saw a vector max 3000watt inverter for cheap and looking to pick that up. Also a sunpower 305 watt panel (will post pic of specs). And then also want to know what charger I should get.

  • #2
    Several quick suggestions:
    - The Vector Max 3000W inverter is a Modified Sine Wave inverter. If you're hoping to run refrigerators/freezers, or other appliances, I would HIGHLY recommend a pure sine wave inverter. (Yes, that will cost more, but you'll be happy you got one.)
    - Just for a benchmark, running a chest freezer and a standard 'fridge, I average 4KWh/day usage. Better oversize--you'll never regret it.
    - Keep in mind that even if you have 900W of panels, they will only produce close to that if it's completely sunny. Cloudy days will produce 1/10 that or less; it's really amazing how little power gets generated in less than ideal conditions. I'd recommend getting more panels than you think you'll need--you'll never regret it
    - I would highly recommend an MPPT charger...though keep in mind that there are some cheap "MPPT" chargers on eBay that are actually PWM chargers (which lose a lot more power than a true MPPT charger.)
    - What system voltage are you planning to go with? I assume you're thinking about going with a 12v system; for small systems, that will be OK. However, if you want to be able to upgrade in the future, I'd suggest going with 24v. (To change the voltage, you'll have to replace the inverter--so you want to make a long-term decision when buying one!)
    - I'm also assuming that you're going with an off-grid system (it's a lot of fun to hear people talk about a power outage, and you say, "What? I didn't notice.")

    How much are you looking at paying for the SunPower panels? (If you divide the wattage by the price, you can get a "price per watt"; a good price is less than 80 cents/watt. I can get panels for around 50 cents/watt, though I did pay 80 cents/watt for my first ones. Just didn't know any better!)

    EDIT: While I have no personal experience with them, there are some "hybrid" units that incorporate both an MPPT and inverter in the same case. They're not the cheapest at $700, but it might be more cost effective to get an all-in-one unit rather than an inverter and an MPPT that each cost about the same as the "hybrid" unit. Reviews on Amazon are middling; again, I will note that I do NOT have any experience with them. Had I known of them when I was building my system, I'd probably have bought them.
    Amazon: https://www.amazon.com/MPP-SOLAR-Inv.../dp/B078746PG3
    eBay: https://www.ebay.com/itm/2400W-24V-1...l/254240090199 [NOTE: It may be "split-phase CAPABLE", but you'll need two units to get that.]
    These are 24vDC inverters (2,400W), and have a built-in 80-amp MPPT (which should be good for up to around 2,000W of solar panels).

    Other members are welcome to chime in with experience on these units--if they are good idea, or if they're a terrible idea.
    Last edited by NochiLife; 07-08-2019, 07:24 PM.

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    • #3
      2000 Wh/day requires about 10KW of batteries and probably 1000W of panels with an MPPT charge controller, depending on location. Use 48V at 200AH, 12V is bad advice because you'd need to use parallel batteries to get the 800AH needed, adding a lot of cable complexity and ensuring early battery death from unequal charge/discharge rates. I assume you mean AGM (sealed lead acid) and not Gel. AGM batteries costs more and gives fewer cycles than flooded batteries and don't allow you to measure specific gravity for state-of-charge estimation, a useful capability for someone starting out with their first system.

      The inverter you mentioned is a cheap modified sine wave inverter, with the money you'll be spending I'd go for a quality pure sine wave inverter around 1000W if that'll handle your loads. And of course one that runs on 48V.

      There are some assumptions here and it's best if you take a look at this sticky and work through it yourself to see what you come up with:
      https://www.solarpaneltalk.com/forum...battery-design

      Last edited by sdold; 07-08-2019, 08:00 PM. Reason: Added link

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      • #4
        Thank you guys for the info. I am in rainbow, ca on a south facing flat. The average peak sun here for solar is 5.5 hours year round. Also all my appliances are propane (fridge, stove, water heater). The only things being used on the solar would be my internet router (about 5-10 watts, two TVs (80 watt and 100 watt), two Xbox ones (230 watts max), 2 phone chargers (10 watts), 2 MacBook chargers (170 watts) and 4 fans 65 watt fans (only 2 running regularly). I am sorry for the long reply as I am living without power and my data ran out the other day so had no internet.

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        • #5
          The panels will be just under 50 cents a watt. They are model spr 305 wht u. I want to upload a pic of the specs but won't let me so here they are:
          peak power 305 watts
          voltage 54.7
          current 5.58
          open circuit voltage 64.2
          short circuit current 5.96
          maximum series fuse 15

          Comment


          • #6
            I really like that all in one system, I'm going to look more into that. Thanks nochi.
            Sdold I was thinking of getting batteries similar to this but different voltage:

            https://www.amazon.com/gp/aw/d/B01KN...1WR?th=1&psc=1

            Comment


            • #7
              Originally posted by Mcmullen7242 View Post
              The panels will be just under 50 cents a watt. They are model spr 305 wht u. I want to upload a pic of the specs but won't let me so here they are:
              peak power 305 watts
              voltage 54.7
              current 5.58
              open circuit voltage 64.2
              short circuit current 5.96
              maximum series fuse 15
              Under 50c/watt--you're doing really good . Congrats.
              ONE NOTE: These panels have a relatively high voltage, which can cause a slight problem with the typical 150v MAXIMUM limit on most MPPTs (the all-in-1 system maxes out at 145v). Typically, the higher the voltage running into the MPPT, the better, as less power will get lost in the wiring. THE PROBLEM: with the panels' Voc (open circuit voltage) at 64.2v, you can only run TWO panels in series (= 128.2 Voc). Your options are to go with an even number of panels (2,4,6, etc.), or put all three in parallel (which...um...will go beyond the "maximum series fuse" rating of 15A).

              Originally posted by Mcmullen7242
              Thank you guys for the info. I am in rainbow, ca on a south facing flat. The average peak sun here for solar is 5.5 hours year round. Also all my appliances are propane (fridge, stove, water heater). The only things being used on the solar would be my internet router (about 5-10 watts, two TVs (80 watt and 100 watt), two Xbox ones (230 watts max), 2 phone chargers (10 watts), 2 MacBook chargers (170 watts) and 4 fans 65 watt fans (only 2 running regularly). I am sorry for the long reply as I am living without power and my data ran out the other day so had no internet.
              Kudos on your energy conservation; it's the things that can't be turned off (like a 'fridge) that can cause energy headaches on an off-grid system. Basically, if you end up being low on power, turn something off. Or just go to bed

              I might put a personal "plug" in for a deal on eBay for truly unlimited data through a "back door" AT&T hotspot plan (for use with an external hotspot, not a phone). I wasn't sure if it was just a gimmick or not, but for $4, the seller sent me the instructions...and it works. I have to admit that I went through about 35GB the first month...no "slowdown" or anything else like that. The recurring monthly bill (from AT&T) is $35.08. You will need an AT&T compatible hotspot (I like the AirCard 770s...it supports all the bands), and make sure you have AT&T coverage in the area. https://www.ebay.com/itm/AT-T-Unlimi...t/292830364708

              Comment


              • #8
                Originally posted by NochiLife View Post

                Under 50c/watt--you're doing really good . Congrats.
                ONE NOTE: These panels have a relatively high voltage, which can cause a slight problem with the typical 150v MAXIMUM limit on most MPPTs (the all-in-1 system maxes out at 145v). Typically, the higher the voltage running into the MPPT, the better, as less power will get lost in the wiring. THE PROBLEM: with the panels' Voc (open circuit voltage) at 64.2v, you can only run TWO panels in series (= 128.2 Voc). Your options are to go with an even number of panels (2,4,6, etc.), or put all three in parallel (which...um...will go beyond the "maximum series fuse" rating of 15A).


                Kudos on your energy conservation; it's the things that can't be turned off (like a 'fridge) that can cause energy headaches on an off-grid system. Basically, if you end up being low on power, turn something off. Or just go to bed

                I might put a personal "plug" in for a deal on eBay for truly unlimited data through a "back door" AT&T hotspot plan (for use with an external hotspot, not a phone). I wasn't sure if it was just a gimmick or not, but for $4, the seller sent me the instructions...and it works. I have to admit that I went through about 35GB the first month...no "slowdown" or anything else like that. The recurring monthly bill (from AT&T) is $35.08. You will need an AT&T compatible hotspot (I like the AirCard 770s...it supports all the bands), and make sure you have AT&T coverage in the area. https://www.ebay.com/itm/AT-T-Unlimi...t/292830364708
                That's funny you brought that up about the hotspot on AT&T, I actually just started doing that a few months ago and I've been going through 100-200gb a month with my brother and it's been great. Thanks for looking out though man. The propane appliances definitely cost me a lot up front but I didn't want to deal with that on solar and always having to be worried about the lights going out. I mainly will just be using the solar for entertainment and non necessities. Thanks for the info on the panels, saved me a big headache. I'll look into some charge controller and that can handle it and then go for a separate charger and inverter system. I want to be able to upgrade as time goes on so willing to spend money on the right inverter up front.

                Comment


                • #9
                  Maybe a little misunderstanding...I'm not sure what "big headache" I saved you from. Pretty much all MPPT units (that I'm aware of) top out at 150v, so my statement was intended more as "just so you're aware when wiring the system up", and not "there's a problem here." Technically, Morningstar Corporation does make a 600v MPPT, but I don't think it's worth the extra cost...especially not in a smaller system. My Morningstar TS-MPPT-60 has a maximum of 150v; I'm running a 3x4 configuration (dozen panels, but they're a much lower voltage), with a 120voc rating. Works fine.

                  I really don't understand the reason for the "maximum series fuse" rating, though I'm sure it's there for a reason. You will obviously need a DC-rated breaker to disconnect the solar panels (NOT to be confused with an AC-rated breaker--it is considerably harder to "break" a DC arc, and the breaker has to be designed to handle a high DC voltage), but if you ran two separate lines from the three panels, you'd probably be fine. (Gurus who understand how this works are more than welcome to correct me here ). I used a 400vDC-rated tandem 63A breaker to simultaneously disconnect both solar and battery lines from the MPPT (so if the MPPT tripped the battery breaker, solar would also be disconnected).

                  I briefly glanced over the Internet, and really couldn't find too much about the all-in-1 units: people either like them or they dislike them. As I mentioned, I personally have no experience with them--but with the little loads you're planning on running, you should be just fine. Those units can also be paralleled for expansion in the future. Definitely cost effective if they work...and definitely a waste of money if they don't .

                  Comment


                  • #10
                    [QUOTE=. I used a 400vDC-rated tandem 63A breaker to simultaneously disconnect both solar and battery lines from the MPPT (so if the MPPT tripped the battery breaker, solar would also be disconnected).
                    .[/QUOTE]

                    MPPT controllers really need to be connected to the battery bank FIRST so that they can boot up before PV input is added. This tandem breaker should have the individual sides separated so that upon energizing the controller the PV isn't simultaneously energized.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      Originally posted by littleharbor View Post

                      MPPT controllers really need to be connected to the battery bank FIRST so that they can boot up before PV input is added. This tandem breaker should have the individual sides separated so that upon energizing the controller the PV isn't simultaneously energized.
                      Technically, you are completely correct. However, in the Morningstar Tristar TS-MPPT manual, it states the following on page 27:
                      A disconnect is required for the battery and solar circuits to provide a means for removing power
                      from the TriStar MPPT 150V. Double pole switches or breakers are convenient for disconnecting
                      both solar and battery conductors simultaneously.
                      MOD NOTE - The above double pole suggestion was from an OLD manual and has been removed from current manuals. It is not recomneded to use dual breakers for the CC in and out.

                      It does go on to talk about "turning the battery disconnect on first, then the solar", but that's assuming that they are separate.

                      Actually, the Tristar spec would really like the controller to be put in "disconnect" mode before turning off the battery breaker. I concluded that there was no way a solar breaker would ever trip (because a solar panel's "maximum power point amps" is from a breaker's point of view the same as "short circuit amps"), and using a tandem breaker would make it shut the solar off IF the MPPT breaker tripped for whatever reason. (And yes, if you read the manual, you'll notice that my 63A breaker is less than the recommended 75A breaker...but as it has a 60A output current limit, I don't see why that breaker should trip [it hasn't.] Also, 63A was the biggest size I could buy...)
                      Now, that being said, I did have a Tristar explode on me (trying to change the configuration settings, and yes, in disconnect mode each time I cycled power--just one time there was a orange flash and a "pop" three seconds after I turned it on [after completing it's power-up cycle]); fortunately Morningstar was gracious and replaced it VERY quickly under warranty.
                      Last edited by Mike90250; 07-20-2019, 05:21 PM.

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                      • #12
                        Actually, the Tristar spec would really like the controller to be put in "disconnect" mode before turning off the battery breaker. I concluded that there was no way a solar breaker would ever trip (because a solar panel's "maximum power point amps" is from a breaker's point of view the same as "short circuit amps"), and using a tandem breaker would make it shut the solar off IF the MPPT breaker tripped for whatever reason. (And yes, if you read the manual, you'll notice that my 63A breaker is less than the recommended 75A breaker...but as it has a 60A output current limit, I don't see why that breaker should trip [it hasn't.] Also, 63A was the biggest size I could buy...)
                        The breakers for charge controllers are to protect the wire, in case the controller shorts out. Use wire large enough to handle your projected amps, and protect the wire with a breaker.

                        What is the "disconnect mode" ? Is that a term for removing the solar power before shutting off the controller ? Simultaneous breaker action is odd, generally all MPPT controllers want solar to never be applied unless battery is connected.




                        Powerfab top of pole PV mount (2) | 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

                        Comment


                        • #13
                          "Disconnect" mode (at least in the case of the Tristar MPPT) is where the MPPT internally shuts down, and is not using the solar at all. At least according to their tech support, the basic reason for "batteries first, then solar" (or simultaneous) is because their switching regulator cannot regulate down far enough with no battery load, to avoid overvoltage of the output circuitry. Thus, if its powered on solar, but no batteries, the output voltage will rise beyond the maximum rating, damaging the unit. But if it's in internal "disconnect" mode, the MPPT is shut off anyway. It's like a "power switch" controlled via MODBUS.

                          EDIT: when the one Tristar MPPT blew out, it tripped the (then) 70A breaker I had on the batteries. Breakers are literally lifesavers!
                          Last edited by NochiLife; 07-12-2019, 11:40 AM.

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                          • #14
                            So, all good when disconnecting the Tristar. What about CONNECTING? Is the internal circuitry such that you can simultaneously flip the battery and PV? That is what I was referring to.
                            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                            • #15
                              Sorry I missed your question...however, it's worth noting that if the documentation would recommend a tandem breaker, the only option is a simultaneous "on" upon power-up. At least on the Tristar, it goes through approximately a 3-second boot-up procedure before turning the MPPT on. Tech support didn't frown on it when I talked with them, and it didn't void the warranty--after all, it's suggested in the manual.

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