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Tesla Powerwall, The Specs, Numbers, and Implementation Absolutely Brilliant

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  • #16
    Originally posted by sensij View Post
    Almost any grid tied inverter is capable of 350 V. The SolarEdge inverters that will be used with the Powerwall (per press reports) actually run at 350 V nominal. A 3 kW SolarEdge inverter costs a bit over $1k. The inverter will probably handle the charge controller function, or it will be built into the Powerwall itself. No reason to believe a standalone controller will be required.

    Off-grid is not the target market for this.
    That much I understand, and I know the PowerWall is not necessarily intended for "off the grid". However if money was not necessarily the object I'd rather hang 6 of these units (which from my understanding are basically maintenance free) as opposed to having a huge bank of FLA's and the commensurate maintenance.

    Like I said, I'm still learning.

    Thanks for pointing me at grid tied inverters. I hadn't even thought of that. I'll have to research that approach as I have seen grid tied systems with battery backup so I would think that you could use such an inverter off grid as well

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    • #17
      Originally posted by RoadGlide View Post
      However if money was not necessarily the object I'd rather hang 6 of these units (which from my understanding are basically maintenance free) as opposed to having a huge bank of FLA's and the commensurate maintenance.
      Once you understand the economics and what you are asking for you might care, and care a lot.

      Buying power from the utility toady's average is about 12 cents for all you can possible waste and want. In TX the more you use, the less expensive it gets down to 6-cents per Kwh.

      You wanna go-off-grid with batteries? Nothing will make your battery supplier happier. For Pb (lead acid) batteries just in battery cost alone, no equipment, you are looking at 55 to 75 cents per Kwh in a very limited daily supply.

      Want the convenience of lithium? You battery man is really going to fall in love with you. You now get to pay $1 to $2 per Kwh.

      So tell me which price would you pay for a Kwh?

      12-cent
      55 to 75-cents
      $1 to $2


      Does it matter what it cost now?
      MSEE, PE

      Comment


      • #18
        Originally posted by Sunking View Post
        Once you understand the economics and what you are asking for you might care, and care a lot.

        Buying power from the utility toady's average is about 12 cents for all you can possible waste and want. In TX the more you use, the less expensive it gets down to 6-cents per Kwh.

        You wanna go-off-grid with batteries? Nothing will make your battery supplier happier. For Pb (lead acid) batteries just in battery cost alone, no equipment, you are looking at 55 to 75 cents per Kwh in a very limited daily supply.

        Want the convenience of lithium? You battery man is really going to fall in love with you. You now get to pay $1 to $2 per Kwh.

        So tell me which price would you pay for a Kwh?

        12-cent
        55 to 75-cents
        $1 to $2


        Does it matter what it cost now?
        Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

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        • #19
          Originally posted by RoadGlide View Post
          Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.
          Do you understand what off grid life style is?

          Most think of off grid as a direct replacement for grid connect, its not really,

          Grid connect gives you as much as you need whenever you want it unless there is a power failure,

          Off grid gives you some of the power some of the time, you stress over what you can use when.

          Off grid you generally dont have electric kettles, toaster and cant just light up the workshop and do a bit of welding or run a compressor anytime.

          Think carefully about the lifestyle you want to lead then way up the pros and cons of grid or offgrid.

          Comment


          • #20
            Originally posted by RoadGlide View Post
            Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.
            When we were shopping for land, most properties I looked at were like that.

            In the end we decided to live 'in-town', so hooking up to the grid was cheap. Now we wish we could go more than a week at a time with continuous power.
            4400w, Midnite Classic 150 charge-controller.

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            • #21
              used with GTI

              I think I know the answer, but will this battery with an inverter allow GTI to stay on in the event of a power outage?
              SHF produces something besides manure!

              Comment


              • #22
                Originally posted by Bala View Post
                Do you understand what off grid life style is?

                Most think of off grid as a direct replacement for grid connect, its not really,

                Grid connect gives you as much as you need whenever you want it unless there is a power failure,

                Off grid gives you some of the power some of the time, you stress over what you can use when.

                Off grid you generally dont have electric kettles, toaster and cant just light up the workshop and do a bit of welding or run a compressor anytime.

                Think carefully about the lifestyle you want to lead then way up the pros and cons of grid or offgrid.
                Have thought carefully about going totally off the grid. Right now I use about 23 kWh per day in a house that is not nearly as efficient ( all electric appliances etc.) as the one I am designing which will incorporate gas fired appliances (dryer, oven, water heater, radiant heat, etc.)

                A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits. Another 5k for a generator and I won't have to worry about cloudy days. In other words I could install an off grid system w/ generator backup for about 30k after tax credits i.e. half of what the utility company wants just to bring power to my house.

                Of course I won't be able to fire up a tig welder in the middle of the night (If I needed to I could always fire up the generator). However I don't see any issue with using it during the day as the above array should be able to provide the necessary power while at the same time still charging my battery bank.

                Comment


                • #23
                  Originally posted by RoadGlide View Post

                  A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits. Another 5k for a generator and I won't have to worry about cloudy days. In other words I could install an off grid system w/ generator backup for about 30k after tax credits i.e. half of what the utility company wants just to bring power to my house.
                  What tax credit?
                  MSEE, PE

                  Comment


                  • #24
                    Originally posted by RoadGlide View Post
                    A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits.
                    I can only assume you are thinking 48 volt battery with two 80 amp charge controllers. A 1200 AH battery is a bit to small with 9000 watt panel. You would be adding water weekly and splashing electrolyte everywhere. You cannot replace electrolyte and that destroys the battery. Minimum size required is 1500 AH, and that only gives you 14 Kwh per day usable.
                    MSEE, PE

                    Comment


                    • #25
                      Originally posted by RoadGlide View Post
                      Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

                      With new construction you will be able to do a very nice solar install. Storage choices really are not relevant at your stage of planning, except to get a rough estimate of cost. In a new house I would do a budget set of batteries for the initial purchase. That would have you making the choice of a better battery system after 2020. If utility scale storage does "take off", there will be some really nice choices for off grid storage in five years.

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                      • #26
                        Originally posted by Bala View Post

                        Off grid you generally dont have electric kettles, toaster and cant just light up the workshop and do a bit of welding or run a compressor anytime.

                        ......
                        Or pull out the iphone and press the "GEN" button.
                        There's not a lot of off grid being built in California that can't easily run an electric kettle or toaster without the generator.

                        Comment


                        • #27
                          Originally posted by RoadGlide View Post
                          Have thought carefully about going totally off the grid. Right now I use about 23 kWh per day in a house that is not nearly as efficient ( all electric appliances etc.) as the one I am designing which will incorporate gas fired appliances (dryer, oven, water heater, radiant heat, etc.)

                          A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits. Another 5k for a generator and I won't have to worry about cloudy days. In other words I could install an off grid system w/ generator backup for about 30k after tax credits i.e. half of what the utility company wants just to bring power to my house.

                          Of course I won't be able to fire up a tig welder in the middle of the night (If I needed to I could always fire up the generator). However I don't see any issue with using it during the day as the above array should be able to provide the necessary power while at the same time still charging my battery bank.
                          I don't believe you can get any FED tax credit for an "off grid" system. You better check with your CPA on that one.

                          Also whatever you have estimated to build your off grid system I guarantee you have forgotten something and it will cost you more. You will also be spending a lot of time baby sitting the batteries.

                          There are a number of people on this forum that live totally off grid and they might jump in and provide you with some costs and details of their systems.

                          Comment


                          • #28
                            Originally posted by Sunking View Post
                            I can only assume you are thinking 48 volt battery with two 80 amp charge controllers. A 1200 AH battery is a bit to small with 9000 watt panel. You would be adding water weekly and splashing electrolyte everywhere. You cannot replace electrolyte and that destroys the battery. Minimum size required is 1500 AH, and that only gives you 14 Kwh per day usable.
                            Sunking - not quite sure of your calculations, specifically where you get 14kWh usable. From my understanding a 1500 Ah bank @ 48V gives me 72kWh per day. Assume your 14kWh usable is being based on a 20% DOD.

                            The way I am looking at it is that the array will be able to provide all the power I need on a typical day while at the same time charging up my battery bank and thus I would have 14kWh after the sun goes down and very little worries.

                            I do see your point on a larger battery bank though.

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                            • #29
                              Originally posted by SunEagle View Post
                              I don't believe you can get any FED tax credit for an "off grid" system. You better check with your CPA on that one.

                              Also whatever you have estimated to build your off grid system I guarantee you have forgotten something and it will cost you more. You will also be spending a lot of time baby sitting the batteries.

                              There are a number of people on this forum that live totally off grid and they might jump in and provide you with some costs and details of their systems.
                              I'll check with my CPA but from what I understand you can qualify for the tax credit if conventional power is available but you elect not to use it. There is utility power available at my site but they want 60K to bring it my home.

                              Understand that I may be underestimating total cost however I have a contractor background and will be doing most of the work myself hiring out subs where appropriate.

                              As far as babysitting the batteries - this is my retirement project so I should have enough time to make sure they don't get fubared.

                              Comment


                              • #30
                                Originally posted by RoadGlide View Post
                                I'll check with my CPA but from what I understand you can qualify for the tax credit if conventional power is available but you elect not to use it. There is utility power available at my site but they want 60K to bring it my home.
                                Well worth the price, and I doubt your neighbors will not pay one penny for your system. Stand Alone Battery systems do not qualify last time I checked.
                                MSEE, PE

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