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  • How to wire properly, Tesla batteries, Combiner, Inverter, Panels

    Title basically says it all!

    I am having a rough time figuring this out, or maybe I am just over thinking. I am not quite sure lol. Here is what is going on. I am going to be doing everything electric, tankless water heater (this one will be a problem for the system I’m thinking), mini split a/c/heat. Cooking and all.

    i am planning on either doing 21 305 watt sunpower panels at 64.2 open circuit VOC, 54.7v max power voltage, 5.58 amp max current, 5.96a short circuit.

    or doing 21 345 watt Hanwha QCell panels. 9.64a short circuit, 47.46 open circuit voltage, current max power 9.09, 37.93 max voltage power.

    so here is where my problem goes... most combiners im seeing do 150v or 300v... I’m completely confused and do not know where to go with combiners or if I even need one lol.

    I honestly don’t know where to do fuses as it seems every panel is suppose to be fused? Or is this the point of the combiner?

    most charge controllers seem to go from 300v up to 500-600v, (saw one at 900v for a 10kw system). But then I get even more confused lol, because if I do say 3 strings of 7 panels that’s going to exceed the voltage on any of them no matter what panel I choose... even if I do it by the strings that’s 280 a string or so if I do 40v or 420 if I do 60v...

    most inverters I’ve seen accept one positive and one negative from the PV system... so I was like ok maybe I combine those 3 strings at the combiner and then run those 3 strings into one string into the inverter... but that just won’t work cuz we go past the voltage limits...

    basically I’m trying to figure out the best way to set this system up, and I’m driving myself crazy trying to figure out how I’m the world to wire it

  • #2
    Well it deleted half of what I said lol

    Comment


    • #3
      So I guess to add on, going to be 6 Tesla batteries with about 14.4kwh of usable energy... 340sq ft living space, and 120 storage... 9000 btu mini split for 120 square ft, 18000 btu for 340 sq ft... something that worries me is the tankless water heater will have probably a 14-18kw surge turning on... most inverters have a 6000-10000w surge, so that leads me to believe I will have to have two inverters... who knows lol like I said I’m driving myself crazy

      forgot to also add, I have 3.8k in the Tesla batteries, around 2200 in the solar panels, and would like to keep the inverters within a 1-2k range if possible

      tesla batteries are 24v, going to be hooked up as a 48v system
      Last edited by Brandon8791; 03-24-2020, 03:53 AM.

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      • #4
        Have you calculated your total loads? Have you compared the loads of a heat pump water heater vs a tankless water heater? What about refrigeration and cooking?
        I would start with figuring out loads first before I worry about where to put fuses. The choice of inverter will determine the string sizes so no need to worry about that now either.
        .
        Last edited by Ampster; 03-24-2020, 11:57 AM.
        9 kW solar. Driving EVs since 2012

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        • #5
          I have not calculated any loads as it’s a new build, but I’m more than certain everything is going to be well overkill. I havnt looked into a heat pump water heater. I was mostly concerned on how to do all the wiring from the panels to the inverter, with doing fuses, and figuring out the combiner box and such... going to be running 120/240 so I’m guessing I need a split phase system.... I basically want to run this system exactly like it would be hooked to the grid

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          • #6
            So there are two things,

            the tankless water heater is significantly cheaper

            Ecosmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology https://www.amazon.com/dp/B0047V0KSU..._qtJEEb5D22CW2


            $366 compared to

            https://www.homedepot.com/p/Rheem-Pe...-303419574-_-N



            $1299...

            so that’s atleast $900 difference... plus tax... so say $1,000.
            and then tanked water heater would take up a lot of space, when we already have very very little space.... it would however eliminate needing possibly three inverters though I’m thinking... lol this is going to be fun.

            im not to worried about water hardness as we are doing a rain catching system that will be going through 7 levels of filtration before reaching a water heater.

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            • #7
              What about refrigeration & cooking? In a new build it is possible to estimate loads and that would drive the inverter size.. I understand you are concerned about wiring, but my question was meant to get you to focus on loads first because that will drive inverter size. Then you can decide how many kWhrs of batteries and how many panels you need to charge those batteries.
              As you said, you are driving yourself crazy worrying about some details that are distracting you from the big picture. After you figure out what loads you are going to have, then the next task would logically be how often and when you will need those loads.
              9 kW solar. Driving EVs since 2012

              Comment


              • #8
                I have to say your problems in large part stem from you being very misinformed. Let's break it down step by step.

                most combiners im seeing do 150v or 300v... I’m completely confused and do not know where to go with combiners or if I even need one lol.

                Yes, you need a combiner. It holds the breakers so that fuses are not needed. You need breakers (or fuses) whenever you have more than two strings of solar panels.

                most charge controllers seem to go from 300v up to 500-600v, (saw one at 900v for a 10kw system).

                No, most reasonably priced charge controllers top out at 150VDC. There are however several manufacturers that make high voltage controllers, but please be aware that they are high-end products that are priced accordingly. Expect to pay 1200-1600$ for any of the following....

                Magnum Energy PT100 (300VDC)
                Outback FlexMax 100 (300VDC)
                Schneider XW-MPPT80 (600VDC
                MorningStar MPPT60 (600VDC)

                But then I get even more confused lol, because if I do say 3 strings of 7 panels that’s going to exceed the voltage on any of them no matter what panel I choose... even if I do it by the strings that’s 280 a string or so if I do 40v or 420 if I do 60v...

                When wiring up your panels you need to pay attention to the highest "open circuit" voltage the panels may ever produce. Then you need to compensate for cold temperatures. The voltage goes up as the temperature goes down. In the winter, the panel's VOC can raise to destructive levels. Use a string calculator to determine what that would be. I like midnite's found at http://www.midnightsolar.com/ You also need to pay attention to the maximum current all of your strings are producing. Depending on the controller, as the voltage goes up, the maximal amperage they can handle goes down.

                most inverters I’ve seen accept one positive and one negative from the PV system... so I was like ok maybe I combine those 3 strings at the combiner and then run those 3 strings into one string into the inverter... but that just won’t work cuz we go past the voltage limits...

                NO, NO, NO!!! The inverter is NEVER connected to the PV or the combiner. The PV is always connected to the charge controller, the charge controller is connected to the batteries, and the batteries are connected to the inverter. The charge controller MUST be properly connected to the batteries, and booted up BEFORE PV current comes in to charge the batteries.

                would like to keep the inverters within a 1-2k range if possible

                Dream on! Dude, you're talking about a high end high power system. Just the charge controller alone is going to be in that range. Inverters in that range are in the 3000-5000$ range.

                9000 btu mini split for 120 square ft, 18000 btu for 340 sq ft... something that worries me is the tankless water heater will have probably a 14-18kw surge turning on

                The water heater is a resistance load, it's likely to have little or no surge. The 9000 BTU air conditioner will. If it runs at about 900 or so watts, expect it's surge to measure about 4X higher, or about 3600 watts. Most of the high end inverters should handle that.

                You really should pay someone to design a system for you, because you really have no clue what you are doing. Whatever you slap together is likely to be grossly mismatched, perform marginally, and fail quickly.

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                • #9
                  I appreciate you being nice about the situation lol, I was honestly basing it off of how my moms house is being billed on electric (since all her stuff is electric). And she is anywhere from 1400-2000kwh a month in a 1600 sq ft house. So I figured if we did around 600-800kwh a month for a 460 sq ft area, everything electric I would be good...

                  ive bought an inverter microwave which we cook I’d say 5% of our food... might be used 2 times a day if that for 3 minutes (1250watt)...

                  we have a 21.5 cu ft French door stainless steel refrigerator which I think said uses around 420kwh yearly...

                  the stove is a 5 burner, glass top... it’s a new stove 2019 Frigidaire stainless steel, forgot it’s energy usage.

                  we bought a oster toaster oven so we could cook our pizzas and cookies or anything really in it instead of using the stove oven to cut down on electric.... other than that, we have a 65 inch LED smart tv (thank god its LED), which is used a good 6 hours a day. Same goes for the surround sound receiver which is a pioneer elite SC-85 (says 330 watts on the back) because it uses class D technology so it’s suppose to be super efficient... then we have our router and modem... a business printer which will rarely be used... a MacBook Pro laptop which will probably be used 3-6 hours a day... and a 8 camera 4K security camera system with night vision. Which will run 24/7.

                  heat and air will be going basically 24/7 I’m assuming, not sure really, I think mini split systems run constantly which is actually better for electricity usage. (Just what I’ve read about mini splits).

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                  • #10
                    Originally posted by Brandon8791 View Post
                    ...................

                    heat and air will be going basically 24/7 I’m assuming, not sure really, I think mini split systems run constantly which is actually better for electricity usage. (Just what I’ve read about mini splits).
                    That is not the quantitave answer that would provide much accuracy in sizing a system, How have you tested that 600-800 kWh a month estimate? Are you on the grid now? One example of loads is your minisplit at 1kW an hour, running just one minisplit 24/7 is 8700 kWhrs in a year or 700 kWhrs per month.
                    Based on the adjectives you have chosen to describe quantitative things like loads my only advice is you are going to need some very large inverters powered by lots of batteries and charged by many square feet of solar panels.That would end up costing lots of money, How to wire those up is the simple part.The hard part is striking a balance between system size and energy conservation.
                    9 kW solar. Driving EVs since 2012

                    Comment


                    • #11
                      I’m just really needing an idea of how to get this system up and operating... I have a general idea which I’ve went over, but I’d feel more comfortable if there was a walk through or something Of that nature....

                      as far as the inverter/charge controller, I understand you can buy them separately, however most systems I have seen have them built in together... accepting pv inputs, outputs to battery, and then output to the house. Therefore it must be a charge controller/inverter in one...

                      as far as the comment of I don’t know what I’m doing, give me some credit, because I atleast, have a general knowledge or idea of what’s going on... 95% of the population doesn’t even understand how solar works. We all come to forums to learn and grow together, so why basically call me an idiot? Cuz that’s how I take it. As far as the other info on combiner and fusing I appreciate that info... as far as the water heater load, I remember when we put the water heater into my moms place, we measured the KW being pulled from the water heater... when you very first kicked the hot water on, it pulled like 22000 watts, then settled down to about 6000 when the water reached it’s temperature. But hers is a 29kwh tankless heater... might will most likely be a 18kwh...

                      also, as far as if I’m on grid no, not yet. This place is not finished being built yet. I’m debating on doing grid, or doing off grid... if I do off grid then I continue down this path, on grid then I lose about a $1,000 or so to get it hooked up.

                      as far as calculating the 600-800 kWh number, I’m basing it off of my moms place... say 1.2kwh a sq ft... her house is 1600 sq ft... at 1.2kwh that’s 1920kwh a month... well she is usually at 1200-2000kwh depending on summer or winter...

                      again I’m OVER building the system on purpose because I’m going to have over 30k in products sitting in the 120sq ft area... so 460sq ft x 1.2kwh is 552kwh... I’m estimating 600ish which is still safe... not only this, but there is only going to be one dual window throughout the whole place... it is a Low E window as well, so energy efficient.... the walls are 2x6 with r19 insulation, floor is r10, with dual sub flooring, roof is going to end up being around r60 when completed... so it should be very well insulated... one door leading outside (not exposed to outside elements.) 8 ft roof all around... all led recessed lights, I mean I’m going super energy efficient. I’m sure someone will have something to say about it, but I’m pretty proud of it myself considering I’m only 22

                      Comment


                      • #12
                        Originally posted by Brandon8791 View Post
                        I’m just really needing an idea of how to get this system up and operating... I have a general idea which I’ve went over, but I’d feel more comfortable if there was a walk through or something Of that nature....

                        as far as the inverter/charge controller, I understand you can buy them separately, however most systems I have seen have them built in together... accepting pv inputs, outputs to battery, and then output to the house. Therefore it must be a charge controller/inverter in one...

                        as far as the comment of I don’t know what I’m doing, give me some credit, because I atleast, have a general knowledge or idea of what’s going on... 95% of the population doesn’t even understand how solar works. We all come to forums to learn and grow together, so why basically call me an idiot? Cuz that’s how I take it. As far as the other info on combiner and fusing I appreciate that info... as far as the water heater load, I remember when we put the water heater into my moms place, we measured the KW being pulled from the water heater... when you very first kicked the hot water on, it pulled like 22000 watts, then settled down to about 6000 when the water reached it’s temperature. But hers is a 29kwh tankless heater... might will most likely be a 18kwh...

                        also, as far as if I’m on grid no, not yet. This place is not finished being built yet. I’m debating on doing grid, or doing off grid... if I do off grid then I continue down this path, on grid then I lose about a $1,000 or so to get it hooked up.

                        as far as calculating the 600-800 kWh number, I’m basing it off of my moms place... say 1.2kwh a sq ft... her house is 1600 sq ft... at 1.2kwh that’s 1920kwh a month... well she is usually at 1200-2000kwh depending on summer or winter...

                        again I’m OVER building the system on purpose because I’m going to have over 30k in products sitting in the 120sq ft area... so 460sq ft x 1.2kwh is 552kwh... I’m estimating 600ish which is still safe... not only this, but there is only going to be one dual window throughout the whole place... it is a Low E window as well, so energy efficient.... the walls are 2x6 with r19 insulation, floor is r10, with dual sub flooring, roof is going to end up being around r60 when completed... so it should be very well insulated... one door leading outside (not exposed to outside elements.) 8 ft roof all around... all led recessed lights, I mean I’m going super energy efficient. I’m sure someone will have something to say about it, but I’m pretty proud of it myself considering I’m only 22
                        I am concerned that you intend to take up this large endeavor without the electrical experience that you will need to install it efficiently and safely.

                        I plead for you to find a solar expert in your area and get their help to install your system. Yes it may be expensive but it will be a safer installation.

                        I also implore you to not expect to get detailed installation information from the internet. It is not worth your life should someone give you incorrect or unsafe data.

                        Comment


                        • #13
                          Get a gas range and a tankless gas water heater. Propane for both will cost pennies.

                          Driving a 18KW tankless electric water heater will require you 3 x 5000$ inverters and you'll be pulling almost 400 amps from a 48V battery system. Good luck with that. You'll burn your house down.

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                          • #14
                            I may end up seeing if I can get a non profit or volunteer solar installer to take a look over it, and offer some guidance. Gas or anything Besides electric is out of the question.... I may end up doing a typical tanked water heater, that just wasn’t the goal, due to the power pulled from a tankless heater. I do love a tankless heater but it might just not be feasible with this system.

                            as far as amperage draw, 1 Tesla battery can handle around 800 amps drawn for 10 seconds... I’ll end up having 6 of these together... which would 5400 amps for 10 seconds... a house runs on 200 amps, so these will NEVER be stressed

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                            • #15
                              Originally posted by Brandon8791 View Post
                              .............

                              as far as amperage draw, 1 Tesla battery can handle around 800 amps drawn for 10 seconds... I’ll end up having 6 of these together... which would 5400 amps for 10 seconds... a house runs on 200 amps, so these will NEVER be stressed
                              You are correct a Tesla battery can take that kind if short term discharge. Check you math though because if I understand your configuration you are only going to have three in parallel. Also the Amperage of your panel is based on 240 volts which is 48,000 Watts. That translates to 1000 Amps at 48 volts.

                              Of course yor statement about the Tesla battery ability to handle large discharge currents assumes the BMS is actively managing it particularly with regard to temperature and the cooling system. What are your plans to limit discharge, control temperature and monitor the battery with appropriate LVCs and HVCs? What kind of BMS are you considering? I am not emphasizing balancing here but rather monitoring.

                              Don't misinterpreted my comments about using the Tesla batteries. I own and drive two of them totaling 130 kWhrs. As my current Nissan pack ages and I assess the need for more capacity I will probably consider used Tesla modules.
                              Last edited by Ampster; 03-25-2020, 01:27 AM.
                              9 kW solar. Driving EVs since 2012

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