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  • #46
    Originally posted by Sunking View Post

    Because you are not doing it correctly. Math does not lie or make mistakes. Only humans do that.
    I did not factor in the 'Hi' watts usage on the powermeters. It seems the "HI" is maximum/peak watts used at any given time.
    Solar Newbie Learning Fast!

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    • #47
      1st Solar Sketch.jpeg
      Up for scrutiny is my sketch for the new system. I have left out a battery output meter.
      I also drew the input/outputs to batteries in pencil, as I am not sure whether the cables are connected that way for the two banks.


      Solar Newbie Learning Fast!

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      • #48
        Not sure I understand your PV wire sketch. Text at top says 48V 24.7A
        Is that the rating for each panel, or each string?
        For a MPPT controller to work well with a 48V battery bank, you need to supply at least 1.5x battery voltage, up to 2x battery. So 73V of array would be the least, up to 96 for the best efficiency in the Controller. Going higher voltage may be desired if you have long runs ........
        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

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        • #49
          You need to wire your panels as 2 strings of 3 panels to get your voltage high enough to charge a 48 volt bank.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #50
            Originally posted by Mike90250 View Post
            Not sure I understand your PV wire sketch. Text at top says 48V 24.7A
            Is that the rating for each panel, or each string?
            For a MPPT controller to work well with a 48V battery bank, you need to supply at least 1.5x battery voltage, up to 2x battery. So 73V of array would be the least, up to 96 for the best efficiency in the Controller. Going higher voltage may be desired if you have long runs ........
            Is that because of loss/resistance in cable & length?
            Solar Newbie Learning Fast!

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            • #51
              Originally posted by Hiro View Post

              Is that because of loss/resistance in cable & length?
              For two reasons.

              1. It takes a minimum of 64 volts to charge a 48 volt battery.
              2. Yes higher voltage means lower current, smaller less expensive wire, and less losses. Some of the newer charge controllers can input as much as 600 volts to charge a 12 volt battery. On paper it is possible to input 600 volts @ 1.67 amps, and output 12 volts @ 80 amps.

              Battery panels are are low voltage and cost 2 to 6 times more than higher voltage Grid Tied panels. MPPT controllers have two huge advantages over PWM.

              1. It allows you to use much less expensive GT panels. GT panel wattages go up to 300 watts. Lot smaller wire, and less racking and material cost. With PWM controllers you MUST USE expensive battery panels.

              2. Efficiency. MPPT controllers convert at around 95 to 98% efficiency. At very bet PWM with Battery panels is 66%. It takes a 300 watt PWM system to equal a 200 watt MPPT system. Price break is 200 watts. A 200 watt MPPT system cost $200 to $500. A 300 watt PWM sytem will be $600 to $800. That is just for the panel and controller. With PWM wire, racking, and material cost will be higher.

              All one has to do is match equipment up. For you it looks like you are using GT panels. You want to wire them up 3 x 2 because your CC can take 150 Voc. Looks to be a match. Need more details like panel and CC manufacture and model numbers. With only 2 strings means you do not have to use fuses. 2 x 3 will not work and if it did requires expensive fuses. So stop and make sure you got things right from the start. Otherwise I wil beat the crap out of you for being stupid wasting your money and my time. Trust me neither one of us will be Happy if you phuck this up. .
              Last edited by Sunking; 02-24-2017, 12:02 AM.
              MSEE, PE

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              • #52
                I wont be building anything until I have everything right and I understand everything. I've always been one to have the right tool for the job and know what I'm doing before I do it. Otherwise, I ask. The only place I can say I wing it in is Love, cos lets face it understanding women is another level to Solar...

                Back on topic.
                My father had a friend text me his panel specs and I just found out his panels are
                IMG_9393.JPG
                I spoke with him for about half an hour, explaining insolation factors, wattage, usage. Knowing his usage exactly not ad hocking things... When I told him his daily consumption could be as high as 5.8kWh. He didn't believe me, he said its impossible with the argument that My Mother has a (12 250W panel) 3kW GT system and she hardly pays anything, but her bill averages $215 per quarter and she uses split system alot, incandescant lighting, TV. Her water & cooking is gas!
                I told him you're misunderstanding something. She isn't using up to 3kW per day cos its a 3kW system... Sydney gets 2.36kWhm2 which calculates to 7kWh at best plus some trickling outside of this peak period.
                When he heard his area has just 3.0kWhm2 he again didn't believe me. He also needs a battery bank 5x his usage, calculating 20-25% charge depth practices. He fell silent then said we will discuss it when he comes to Sydney.

                I'd like to Thank you blokes for getting me this far. So much still to know and its exciting.

                Solar Newbie Learning Fast!

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                • #53
                  These panels are not what your diagram shows. From the opening statement your father has these right? Now we are talking about a different system you are building right? Hope so. I don't feel like reading this whole 4 page string to clarify. Read it once but a comment at a time.
                  The main reason I suggested wiring 3s2p is the 250 watt panels you show are more than likely 60 cell, grid tie panels and not 24 volt (nominal). Their voltage isn't high enough to properly charge a 24 volt battery. In your case (48 volt) 2 series wired panels don't produce high enough voltage. 3 series wired panels will work with an MPPT controller.
                  The pictured panels are high voltage/low amperage thin film panels. Definitely need an MPPT controller with them and parallel wiring. Series wiring would produce a voltage out of the range of most MPPT controllers. At 100 Voc they would cook many MPPT controllers as not all have a 150 volt open circuit limit.
                  2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                  • #54
                    Originally posted by littleharbor View Post
                    These panels are not what your diagram shows. From the opening statement your father has these right? Now we are talking about a different system you are building right? Hope so. I don't feel like reading this whole 4 page string to clarify. Read it once but a comment at a time.
                    Yes, we are talking about a whole new different system. I didn't know they were 100V. When he sent me this picture yesterday, I told him they are high voltage and we cant use these for the proposed 48V system. He said why? I mentioned these can only be strung in parallel, not series for the same reasons you noted.

                    My whole agenda on this forum is to learn about solar, how electricity works, how to make it work efficiently, safely and cost effectively while imparting what I learn and know to my Father so he recognises that this is much more technical than he assumes.

                    All the info I have on the best type of Panel is that it is 24V 250w GT. I am assuming and calculating a 24V panel has a Vpm of 30.8V with an MPPT should draw the right amount of voltage from the Panel array. My research of GT (Grid Tie) is that this is for Homes connected to the Grid. How does Grid Tie work in a Stand Alone Solar PV System?

                    I'll make it clear. None of the parts he bought; Panels, batteries, inverter, CC will be used in my system. They wont work!

                    I could make a smaller 500W 24-48V system for an automaric water or bore pump with the current items he has.
                    Solar Newbie Learning Fast!

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                    • #55
                      To the unknowing person these panels being touted as 24 volt panels may seem plausible. In reality a 24 volt nominal panel as we know it is typically a 72 cell module with a Vmp of around 36 volts and a Voc of about 44 to 46 volts. These numbers are standard test condition numbers. The panels are tested in lab conditions using a 1000 watt per square meter test light and at 25 degrees Celsius. The reason your panels with a Vmp of 30.8 wont work is as the panels heat up in real world conditions their cell temps will rise considerably higher than 25 degrees Celsius. The voltage will drop to the point where it isn't high enough to properly charge and equalize a 24 volt battery bank. This works both ways, when panels get extremely cold the voltage rises and systems need to take this into consideration so as to not over volt the controller in cold conditions.

                      For GT panels to work in a off grid scenario you use MPPT controllers and series wire panels to a higher voltage, (1 1/2 to 2X) than your nominal battery voltage. When you are pushing this a long distance to your controller you can use higher voltage, up to your controllers limit, to keep amperage low and minimize voltage drop over long distances.
                      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                      • #56
                        Originally posted by littleharbor View Post
                        The main reason I suggested wiring 3s2p is the 250 watt panels you show are more than likely 60 cell, grid tie panels and not 24 volt (nominal). Their voltage isn't high enough to properly charge a 24 volt battery. In your case (48 volt) 2 series wired panels don't produce high enough voltage. 3 series wired panels will work with an MPPT controller.
                        The 6 panels of 24V 250W 3s2p makes 76V 1500W 16.48A. In terms of voltage in a 48V Battery Bank 1 1/2x is minimum, would 2x be ideal? If so, then another 2 panels would be ideal, if this were to prolong battery life. Despite the fact off grid battery systems have a general life span of 5yrs in good conditions.
                        3s2p also means I can use 20A circuit breakers.
                        Solar Newbie Learning Fast!

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                        • #57
                          Originally posted by Hiro View Post

                          The 6 panels of 24V 250W 3s2p makes 76V 1500W 16.48A. In terms of voltage in a 48V Battery Bank 1 1/2x is minimum, would 2x be ideal? If so, then another 2 panels would be ideal, if this were to prolong battery life. Despite the fact off grid battery systems have a general life span of 5yrs in good conditions.
                          3s2p also means I can use 20A circuit breakers.
                          Depends on the specs of your charge controller and your battery bank size.

                          The amp rating of your controller is based on the output amps. The max Voc. rating is calculated using the minimum temperature expected for your area. If you are thinking of running 4s2p That probably wont fly as your panels are in the 36 Voc. range,. Four in series at STC would be something like 144 volts, add cold temps to that and out comes the magic smoke. 1 1/2 times nominal battery will work but if you want to go 4s2p you can use a Midnite Solar Classic 200 or better yet a Midnite SL 200,solar only charge controller.

                          Your proposed battery bank, at 420 Ah would like to see from 5 to 13 % charge rate. 5%, or 21 amps, being only good for intermittent ie; weekend use. Any full time off grid scenario wants to see 10-13% so 42 to 55 amps would work best. Charge voltage needs to be set accordingly for flooded or VRLA, (AGM) batteries. Stay away from Gel batteries. They don't work well in off grid situations.
                          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                          • #58
                            The property will never have services installed there. So we need this system to work exclusively as stand alone.
                            I would rather not add 2 more panels.
                            You're right, the panels I have sighted are 37.9 VoC (151.6V 4s2p) 30.4 Vmp. That doubles the price of the CC to handle two more panels...

                            Charge rate needs to be 10-13% 46.2 Amps of Battery Bank 420 Ah. At that amperage I would need to use #6 cable instead of #10.
                            Voltage needs to be 1 1/2 of Battery Bank Voltage @72V, 113.7 VoC, 91.2 Vmp.
                            This wasn't mentioned before.

                            My charge rate is too low at 24.7A when it should be 46.2A with 420Ah BB.
                            How can current be increased other than changing cable size?

                            I am noticing some discrepancy here. My MPPT draws panel voltage at the optimum 30.4V (91.2V) which makes 113.7 VoC. 1500W / 91.2V = 16.4A. That is the actual current, lower than the stated 24.7A.
                            Am I interpreting the stats correctly?
                            Last edited by Hiro; 02-26-2017, 06:02 AM.
                            Solar Newbie Learning Fast!

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                            • #59
                              Originally posted by Hiro View Post
                              My research of GT (Grid Tie) is that this is for Homes connected to the Grid. How does Grid Tie work in a Stand Alone Solar PV System?
                              There are two very good reasons to use MPPT Charge Controllers.

                              1. It allows you to use much higher voltage GT Panels. Low voltage battery panels cost some 2 to 5 times more watt than GT panels.

                              2. 95% efficient vs 66% of a PWM controller.

                              MSEE, PE

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                              • #60
                                "quote"
                                I will write it all down again
                                AC for 4hrs @ 106w = 424w
                                Fridge 24hrs @ 32w = 768w
                                2 lights 6hr @ 20w = 120w
                                TV 4hr @ 63w = 252w
                                Tools 1hr @ 750w = 750w
                                Charger 2hr @ 90w = 180w
                                Washer 90min @ 50w = 75w Cold wash
                                Radio 2hr @ 50w = 100w

                                The first item on this list is an air conditioner, right? Do you know what the BTU rating is? Because about the smallest residential window unit available is 5000 BTU and they use 450 to 500 watts while the compressor is running. At 4 hours with a 50% duty cycle that's 1000wh or 1kWh which only adds a little over 500wh to your total, but the problem is the surge amperage. The surge can be 4 to 5 times the running amperage. I don't think a 1000 watt inverter can handle that much surge. But I do know someone who runs a 5000 BTU A/C on an 1800 watt inverter. Food for thought.
                                3.6 kw PV, Classic 150, Radian GS4048A, LFP 195A

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