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

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

    As most of you know Tesla anounced the Powerwall Home Energy Storage batteries to be released sometime this Summer in two models. A 7 Kwh version for Grid Tide Load Shedding, and a 10 Kwh UPS straight Battery Inverter for emergency stand by use. The specs were very misleadinf leaving more questions than answers. Got my curiosity up so did some searching on Tesla Forums and EV forums and got some details, useful details along with follow up PR releases from Tesla and Musk Twitter account. So here is what is known and some of my comments.

    Input Requirements: 180 to 300 volts AC 5 amps circuit operating at 50/60 Hz. This makes is compatible with any countries electrical architecture. Although a 5 amp circuit at 240 VAC in the USA is unheard of as I do not know of any 5 amp dual pole 240 amp breakers on the market. 240 volt circuits are for large loads not small loads of 1000 watts the charger uses. None the less doable but a special order product.

    Nominal Battery Voltage and AH Capacity: 390 volts @ 25 AH for both 7 Kwh and 10 Kwh models. Battery chemistry unknown Lithium at time of writing. Strongly indicates a 108SxP Lithium battery meaning of at least 108 cells give or take up to 5 cells depending on which cathode/anode material they are using from Panasonic. Possible up to 3 parallel strings making it 216 to 314 cells. Best guess is same battery type the Tesla Mega Factory will be producing licensed from Panasonic. The only difference between the 7 Kwh and 10 Kwh models are firmware in the controller limiting how much energy is accessible by the users.

    What Comes Inside The Magic Box: 2 Amp AC 390 Volt DC Power Factor Corrected Charger, BMS, and Liquid Thermal Management with both heating and cooling. OK charger and BMS are no surprise here to anyone except one noted feature. You must provide an Internet connection so Tesla can monitor you. Some people are not going to like that very much. The guise or justification is it can be made to use as a microgrid giving up control to someone else. What was a surprise is Thermal Management for such a low density energy battery. Normally that is only required when high energy density cells are combined with high charge and discharge rates to prevent thermal runaway and resulting fires that come with it. Unfortunately Tesla has not published any specifications on how much energy the thermal management uses. Only thing known is it uses pumps, fans, and an electric heating element. All of it mechanical subject to mechanical failure and uses unspecified power. Only thing that makes sense is to keep the batteries at optimum operating temperatures fo maximum power capacity in both cold and hot climates. My take Red Flag.

    Output: 350 to 450 Volts DC At a maximum of 6 amps (2 Kw) continuous, and 8 amps burst (3 Kw) for unspecified amount of time. OK this is where a lot of questions come in play. What are you the consumer suppose to do with that? You cannot take it to your Grid Tied Inverter because it is made to use a Current Source, not a voltage source of a battery. It can go to a Battery Inverter if you could find one that operates from 350-450 volts. You could also send it to a Hybrid Inverter is one actually existed. Rumor has it that is the next announcement from Tesla offering a line of Hybrid and Battery Inverters. Absolutely Brilliant, create a monopoly market for your product.

    Price Point & Distribution: The 7 Kwh is listed at $3000 and the 10 Kwh is listed at $3500. Both units are the exact same thing, only firmware is different. OK the price is completely BOGUS and good ole fashion Bait and Switch Marketing. Just no nice way to say it. The battery is only available through certified Installation Contractors. Solar City has been named as one of them and their contractor must install the system. Bloomberg reports just to get the battery installed is $7000 and higher. It is speculated Musk is trying to create a monopoly market offering a battery only his company makes Inverters and interface equipment to work with it. At least initially until other manufactures can com eup with some products. But for now Tesla has the whole market exclusively including the distributors and installation. Absolutely brilliant IMHO, reminds me of Rockefeller with Standard oil and Bill Gates with MS
    MSEE, PE

  • #2
    With regard to a grid-tied inverter, SolarEdge is listed as a partner and their design effectively operates from a constant voltage 350-500 VDC source. Probably not a big leap to go from their existing design to a hybrid that supports these batteries, possibly just firmware.


    Edit: Thanks for the objective technical review. I hope this thread can hold a higher bar for civility than the other recent threads on this subject have.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

    Comment


    • #3
      Originally posted by sensij View Post
      With regard to a grid-tied inverter, SolarEdge is listed as a partner and their design effectively operates from a constant voltage 350-500 VDC source. Probably not a big leap to go from their existing design to a hybrid that supports these batteries.
      Not sure about the SolarEdge connection, but Musk is on the board of directors at Solar City who has the exclusive installation rights as of now and more to be announced after roll out.

      I am not saying there cannot be Hybrid Inverters made to wotk with a high voltage current or voltage source, I am saying I do not know of any. Currently that market is 12, 24, and 48 volts. It can be done, just needs to be a demand for it which Tesla has now made. The genius is it appears Tesla is going to offer the equipment in the form of an Inverter to corner the market or a short term monopoly. Perhaps SolarEdge is the company Tesla is teaming with to make the equipment. It would be a brilliant idea. There is a lot more to this than is letting be let out as of now. As an investor signals to me might be time to buy in to Tesla stock, or a great scam Musk is pulling off. Who cares as long as you can make a quick buck.
      MSEE, PE

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      • #4
        That not a monopoly. It's vertical integration.

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        • #5
          Originally posted by donald View Post
          That not a monopoly. It's vertical integration.
          Is that what companies call Monopolies now days? I bet Gates wished he had heard that term 20 years ago when he got busted.

          When it comes right down to it, I don't give a damn what Musk does. If he can pull it off more power to him. He certainly took PT Barnum lesson to heart of A Sucker Born Every Minute. Hell i am sitting here thinking of buying a hundred shares of Tesla Stock. Does not bother me to take money from folks who believe in Global Warming. Hell I own McDonald's stock and never eat there.
          MSEE, PE

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          • #6
            Originally posted by donald View Post
            That not a monopoly. It's vertical integration.
            Pardon?
            [SIGPIC][/SIGPIC]

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            • #7
              Originally posted by Sunking View Post
              Is that what companies call Monopolies now days? I bet Gates wished he had heard that term 20 years ago when he got busted. ...
              'busted' and yet the courts never broke up Microsoft, the way they did Ma-Bell.
              4400w, Midnite Classic 150 charge-controller.

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              • #8
                Originally posted by Sunking View Post
                ...
                Sunking, thank you for digging up details and presenting them without attaching bias.

                Regarding monopoly... Is it still a monopoly if no one is restricted from copying the product, but no one actually does?

                Tesla claims they will not enforce patents with their All Our Patents Belong To You statement, and Musk said basically the same thing about the battery system. That would imply that anyone is welcome to build the additional pieces required to utilize this battery (inverter, etc.). Of course there is the warranty issue if your inverter doesn't meet Tesla's requirement.

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                • #9
                  Sunking, thank you for digging up details and presenting them without attaching bias.
                  Thats funny, after you look past the 5 known points it's all his speculation.

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                  • #10
                    Originally posted by jimqpublic View Post
                    Regarding monopoly... Is it still a monopoly if no one is restricted from copying the product, but no one actually does?

                    Tesla claims they will not enforce patents with their All Our Patents Belong To You statement, and Musk said basically the same thing about the battery system. That would imply that anyone is welcome to build the additional pieces required to utilize this battery (inverter, etc.). Of course there is the warranty issue if your inverter doesn't meet Tesla's requirement.
                    Well if you have followed Musk for any length of time then you know he is no straight shooter, says one thing and does another. Of course I am speculating but it strongly appears like his vehicles is building a proprietary product. The cells used are from Panasonic as I have learned as are the batteries used in the vehicles. Not the same cells used in the cars, but exclusive to Tesla no one else can access or use. That is not exactly sharing. It also took two years investigating how Tesla was able to stay in biz when it was learned the sales numbers were so low. Musk claimed it was superior management skills and money management. Well I guess you can say that but what kept them afloat and to this day is the $35,000 extra profit they receive from Al Bore for every car sold. Musk never disclosed that until reporters figured it out

                    The two pieces as of now that makes this battery in compatible with anything out there right now are the operating voltages and this mysterious Ethernet port required to be connected to the Internet. The operating voltage is no big deal. But it does give Musk and a partner manufacture at least a couple of years head start on the competition by offering equipment ready to go.

                    But this Ethernet thing is troublesome. Having the port is nothing out of the ordinary as it allows the customer access and communication is the customer wants it. But requiring it to be connected to the internet is problematic. Musk will only say it is for giving them the ability to make micro grids. Hogwash! It may have that capability, but there is more to than that. What exactly Musk will not say.

                    So if you have followed Musk for any length of time, then you know he is not very honest and extremely evasive. It would not surprise me one little bit if someday he turns out to be another Bernie Ebbers.
                    MSEE, PE

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                    • #11
                      As far as the $7000 price, consider the install on a typical existing system. There needs to be a grid disconnect, and also branch circuit control. Either an ethernet cable needs to be run, or a wireless adapter installed. Most people should probably add a generator connection too. So I can see $7K, especially at first when there is no direct competition. Early adopters are going to pay full retail on all the work and parts involved in a complete installation. That is just how it is when demand exceeds supply.
                      Simply installing powerwalls for California Tesla owners should keep solarcity electricians busy for a year.
                      Each additional Powerwall should cost considerably less than $7K.

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                      • #12
                        First, I am a novice when it comes to designing solar systems and battery banks so please bear with me. Nonetheless from my understanding, basic electrical calculations are as follows:

                        Watts = Volts x Amps
                        Amps = Watts / Volts
                        kWh = (Amp x Volts) / 1000

                        Amps = Amount of current in a circuit
                        Volts = Strength of current flow
                        Watts = Total electrical power per second

                        For this post I'm going to make an assumption that a "totally off the grid" user uses 20 kWh per day for calculations sake. From that you can calculate amp hours used per day per input volts.

                        20,000 / 120v = 167 Amps / day (Normal Utility Voltage)
                        20,000 / 48v = 417 Amps / day (48VDC Battery Bank)
                        20,000 / 350v = 57 Amps / day (PowerWall)

                        Obviously you're going to need an inverter capable of handling a 350V input voltage to use the PowerWall. I've seen them but their pricey (starting around 10K). In addition you'll need a charge controller capable of handling an input voltage of 350v as well - have not run across any of those for home use but I'm sure they're available. (i.e. I would think that utility scale solar farms have controllers capable of handling high voltages).

                        I would also think that you would have to rewire (and or augment) your existing solar array to provide the higher input voltage required of the PowerWall.
                        Another point of confusion (for me) is on the consumption side of things. I would think based on the calc's at the beginning of this post that amps used by a particular appliance falls as voltage increases.

                        For example, let's say you have an appliance rated at 1000 watts - that would seem to indicate the following:

                        Watts / Volts = Amps

                        1000 / 48 = 20.8 amps with a 48V Battery Bank
                        1000 / 120 = 8.3 amps at normal household voltage
                        1000 / 350 = 2.85 amps with a PowerWall

                        So based on my understanding you would need at least 3 PowerWalls to supply 20kWh per day and that's at almost 100% DOD (which I don't think is feasible even for a LiON battery). Additionally you have no days of autonomy with the scenario above and the real kicker is that I would think you're going to shell out close to 25K before you even get to the solar array side of things.

                        For the sake of comparison a conventional FLA or AGM 48V battery bank would cost about 9K for 1200 amp hours or roughly 58kWh (1200 x 48) / 1000 = 57.6).

                        So if I have this correct, from just the battery bank perspective you're shelling out 9K for 58 kWh as opposed to 9K for three PowerWalls at 21kWh.

                        As I said above I'm still a novice so if anyone finds fault with my calc's and assumptions so please feel free to reply.

                        Thanks in advance

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                        • #13
                          You've got some more to learn about charge controllers and inverters. That aside, your basic conclusion is correct. There are much less expensive options than the Powerwall for someone who wants to take 20 kWh daily off grid.
                          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                          Comment


                          • #14
                            Originally posted by sensij View Post
                            You've got some more to learn about charge controllers and inverters. That aside, your basic conclusion is correct. There are much less expensive options than the Powerwall for someone who wants to take 20 kWh daily off grid.
                            Completely understand that I've got a lot to learn, however I would think that I would need an inverter capable of handling 350v input voltage as well as a charge controller capable of handling a solar array wired to push out at least 350v

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                            • #15
                              Originally posted by RoadGlide View Post
                              Completely understand that I've got a lot to learn, however I would think that I would need an inverter capable of handling 350v input voltage as well as a charge controller capable of handling a solar array wired to push out at least 350v
                              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.
                              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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