Tesla Battery

ZakarumeZakarume Solar Expert Posts: 143 ✭✭
If money was not an issue. Would you get this Tesla Battery that has come out? What is your opinion on it? Good or Bad? Does anyone how much watts you would need to recharge the battery bank to full?
1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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Comments

  • BB.BB. Super Moderators Posts: 26,768 admin
    I moved your post to the New Battery Tech forum...

    But asking the question to you--What is your power storage needs (how many kWatt*Hours per day, how many days of storage) are you looking for?

    What else interests you? Longer battery life, small/lightweight, no servicing needed? High surge current/fast charge? Just less "work" vs lead acid?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 4,202 ✭✭✭✭
    What is interesting, is even giving this away, for current off grid users, you would have to include the peripherals, Since they run at such a high voltage, you may not be able to reconfigure your array to charge it, your charge controller won't work, and you have to go out and buy a new inverter....
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Something about the TESLA Power Wall. Its not a true, "Lithium". Discharge isn't where the performance of Lithium batteries should be, and there isn't anything appealing that says I would want to own it VS any older battery technologies.
    Lead Carbon technolgy is suppose to blow Lithium out of the water in regards to discharge, safety, capacity, and specific gravity.

    Asking if money wasn't the issue....... Even if it was the cost of a AGM 12V battery bank, I still wouldn't want a TESLA Power wall, because the discharge isn't there. Applying basic mathmatics on discharge we come to find out a power wall is reverse engineered in regards to voltage, reducing amp hours and selling the batteries to the consumer on a kWh, rather than an amp hour. So lets not fool ourselves, not disregard the reverse engineering and see what we are working with in regards to equal discharge and efficiency.

    1 powerwall=12 volt battery bank
    2 powerwalls=24 volt battery bank
    3 power walls=36 volt battery bank
    4 power walls=48volt battery bank
    5 power walls= 60volt battery bank

    It would take 4 power walls to equal the kWh/power distribution/delivery/capacity that a 48Volt AGM battery bank can already deliver at half the cost.
    Don't care to consider that a Lithium has a lower level of resistance for charging, its discharge doesn't make it an appealling piece of equipment.

    I would rather own LiFePO4 with a 12V BMS that allows me to use standard CC,and inverter equipment that is already available and disposable on the market, and coupling that equipment with a natural gas generator, and or solar its a better bang for the buck storage system.

    TESLA power wall is "dirty" lithium chemistry that requires an extreme safe gaurd, that limits its discharge, that isn't paying for efficient technology, thats paying for a level of safety that no matter the condition can not be reduced in price, even if money wasn't the issue.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Why are there so many threads about this same thing?
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Why are there so many threads about this same thing?

    It's investors exercising their rights to freedom of speech. LOL
    Either that or people that don't understand off grid technology has been around before the grid was built.
    Most of this stuff is investors pumping advertising on the web. It's not just this forum, seems to be a flooded internet problem.
  • BB.BB. Super Moderators Posts: 26,768 admin
    GM is looking for secondary uses of old Chevy Volt batteries:

    http://www.informationweek.com/it-li...d/d-id/1321077
    General Motors may not be the first company you think of when you hear the world recycling, but the auto giant has done just that by taking used batteries from its Chevy Volt electric vehicles and deploying them to power an enterprise data center at its Milford Proving Ground in Michigan. The company is tapping into the energy left in batteries from first-generation Volt models by employing five of them at the data center, which feed the administration building's circuit breaker panel, working in parallel with a new solar array and two wind turbines.
    Assuming that the Chevy Volt batteries are replaced when they hit 80% of original capacity--Then the re-using in a data center (and possibly later as solar RE batteries for home use?) is an interesting idea.

    But now you get into supply and demand--Will the number of ex-Volt battery packs match the secondary usage market? Will the batteries be cheap because supply exceeds demand, or will they be expensive as demand exceeds supply (of course, then you can always move some new battery banks directly into the secondary markets if the price can justify it).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • pleppikpleppik Solar Expert Posts: 62 ✭✭✭✭
    You can pretty much tell which generation someone belongs to by their opinion of Tesla. (There are news articles about that). The CEO of Tesla is in his fourties I believe. As long as you are 40 or younger you will like Tesla. That's not a joke, it's what is happening.

    Tesla is a bandwagon of new comers consumers with absolutely no engineering experience, that are tree hugging, into being green liberals.

    There's a certain delicious irony in that juxtaposition....

    Personally, I don't understand why people seem to get so wound up and emotional about Elon Musk's companies. Maybe it's because both the successes and failures have been so spectacular that people just can't help getting sucked into the drama.

    At the end of the day, Tesla is just a company. The PowerWall is just a product which is not yet shipping, and so it might or might not live up to the marketing. Elon Musk is just a smart guy who took some big risks, got really lucky, and made a ton of money.

    I think it's a little silly to identify yourself by whether you like/dislike Tesla and Musk.

    It's not like we're talking about Apple and Steve Jobs here.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    There you have it Zakarume, this thread is already too hot to touch. I recommend hitting Google and YouTube to form your own opinion.

    FYI, the first time I heard about Tesla was watching a video of their electric car beating a Dodge Hellcat in a 1/4 mile drag race!
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    BB. wrote: »
    GM is looking for secondary uses of old Chevy Volt batteries:

    http://www.informationweek.com/it-li...d/d-id/1321077


    Assuming that the Chevy Volt batteries are replaced when they hit 80% of original capacity--Then the re-using in a data center (and possibly later as solar RE batteries for home use?) is an interesting idea.

    But now you get into supply and demand--Will the number of ex-Volt battery packs match the secondary usage market? Will the batteries be cheap because supply exceeds demand, or will they be expensive as demand exceeds supply (of course, then you can always move some new battery banks directly into the secondary markets if the price can justify it).

    -Bill



    I completley missed your post BB.

    So there is a high demand for the Mercedes/Daimler Lithiums, in Europe the Daimler Lithiums have been on the market for about 5 years now. Tesla won't have a market in Europe, Australia, Asia or Africa.

    I think its great what Chevrolet is doing, Chevy would of had to spend more money in dump recycle fee's because most battery recycling plants do not know how to handle Lithium batteries, yet there are safety risks for proper disposal, as alot of lithiums still contain alot of electrical power, and there are risks of thermal runaway explosions. I think its great to know that as long as for an R.E application that a heavy discharged load isn't required, installing these recycled lithiums in series/parrallel have served the purpose. It also is a better way of extinguishing the service life of the lithiums so they can be properlly disposed in the future, by having a higher depletion.

    There is a "test market" 100% e car only sold in California, and Oregon called the chevrolet spark( E car built by Chevrolet and AC delco), The E car surpasses the Nissan Leaf at, as well as the BMWi3 at 108MPGe. This car is only being bought by consumers on a very small level so as not to take the risks, that tesla test markets at. If the Spark meets its consumer testing demands, there ar eplans to release the Chevy Bolt, with double the storage capacity, of the spark.

    The Chevy Spark recieved a 5 star review on car and driver. Runs a faster 1/4mile time than its slugglishly slow gasoline counter part.
    http://www.caranddriver.com/chevrolet/spark-ev


    I find it ironic that in the same month, Chevrolet press released they are moving forward with the Chevy bolt production line for 2017/2018, Elon Musk press released the power wall. There is alot of talk in the stock market that Elon press released the power wall because stock prices would of plummeted on the hype that Chevrolet will be able to release the Chevrolet Bolt, before Tesla can meet the release of the giga factory, and the TESLA 3, which are slatted for late 2018/2019.

    Car and Driver has stated it may even put TESLA out of business, and Car and Driver has tested alot of Cars, including the TESLA S and X models.
    http://www.caranddriver.com/news/che...-and-info-news

    Chevrolet in my mind is doing all the right concious decisions, that TESLA is not, which is test marketing on levels that don't affect the general public, or steal money by lying to people about product lines that aren't tangeable.
  • BB.BB. Super Moderators Posts: 26,768 admin
    For discussions about Musk, the man and the promoter, we have a thread for that:

    Elon Musk and his Powerwall/Companies

    It can be difficult to separate the man from his products when he works so hard to inject himself into all discussions, but let us try.

    The original poster asked about the hardware--Please keep this thread about those questions.

    I have moved some of the other posts to the Elon Musk thread.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,330 ✭✭✭✭
    I am just going to pipe in here about Chevy's lithium technology from a users point of view with 2 Volts in the stable..

    We just crossed year 4 with the original Volt we purchased (#2140 off the assembly line). The car has lived up to every expectation we had, so far the battery shows no signs of degradation and the estimated range remains consistent at 42-45 miles per charge in spring and fall, same as day one. I think the engineers have done the due diligence to keep Chevy from getting hit with a bunch of battery warranty claims. While I have no hard stats on the battery warranty claims, there are several forums of Volt owners out there and only a very few have been reported, mostly for BMS issues and a couple of internal cooling leaks. I have heard of no cell failures and certainly no battery fire issues other than the stupid one from the crash testing. That on they T-boned the car enough to get a leak and then set it upside down in a yard, the fire started 3 weeks later.

    I think Chevy is going to have a real winner in the Bolt, we may have even bought one for the around the area travel. Elon has a definite problem in the lower end of the market.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Refurbished 6Ah Prius Nimh's are being sold for under $1800 each, (2) Prius 6.5Ah battery packs in parallel is 1/3 greater in potential discharge than what TESLA is offering one power wall for at $3500.

    However neither Tesla, Prius NiMh Batteries, or Chevy lithium Batteries have after market support that is reasonably priced at this time.

    I believe with the way Tesla has conducted business with proprietary chargers for their cars and not using the universal J1772, the company is going to run into more problems down the road, just as iPhone sales with apple have been declining over the years with use of proprietary equipment.

    Chevrolet, which has stayed away from proprietary devices will probably find ways to recycle lithium cells and break them down to a 12v~48v platform that is more universally friendly for the end user. It's just the way they have done business.

    Until that point has been reached though and until the equipment is available for any.

    I recommend sticking with Stark Industries LiFePO4 12v BMS systems, or using RC car LiFePo4 10Ah packs and building a custom battery bank.

    I believe Schnieder electric makes a MPPT lithium/NiMh charger, but the price tag is 3 times more than a standard MPPT charger.
  • AmpsterAmpster Registered Users Posts: 22
    Something about the TESLA Power Wall. Its not a true, "Lithium". Discharge isn't where the performance of Lithium batteries should be, and there isn't anything appealing that says I would want to own it VS any older battery technologies.
    ..................

    Newbie here. Trying to learn some of this new terminology. What is "true" Lithium. I have LiFEPO's and am wondering are they "true" lithium?
  • BB.BB. Super Moderators Posts: 26,768 admin
    Lithium is the reactive metal in the battery (lots of stored energy, very light, high current output).

    However, there are so many ways to make the battery and compound the electrodes/electrolyte/etc., that a lithium battery of type A has very little in common with type Q battery.

    You need to read the specifications closely to figure out which is correct for your needs.

    For off Grid solar, LiFePO4 (lithium iron phosphate) seems to work pretty well & fit our needs. However there are significant variations in that chemistry/construction too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 4,827 ✭✭✭✭
    there are some quite long threads here with lots off good info...Topic is well covered with lots of thoughts and data..Search LiFePO4 and lithium and happy reading.
     
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    West Chilcotin, BC, Canada
  • AmpsterAmpster Registered Users Posts: 22
    Thanks, in the meantime I did do some searches and the only thing I found with regard to "true" was my original post and the one that I quoted. As explained by others and in the various posts on the subject, Lithium describes an overall category of Lithium ion batteries. So it appears that "true" Lithium is just an adjective with no meaning with regard to Lithium batteries. The ones in my VW conversion contain iron (FE) phosphate (PO) and some Yitrium. Others contain one or more of Nickel, Cobalt, Manganese, Aluminum to name just a few. Each combo seems to have application to different uses. Even the few car manufacturers differ on which one is the best. Each of them think they are using the best chemistry.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Ampster wrote: »
    Newbie here. Trying to learn some of this new terminology. What is "true" Lithium. I have LiFEPO's and am wondering are they "true" lithium?

    What makes any intelligent discussion about lithium so hard is that most users don't know the difference between the chemistries, much like not knowing the difference between a flooded lead-acid and a sealed agm. Both are lead, so we treat them the same right? Nope. :)

    LiFePo4 is at the bottom-of-the barrel when it comes to energy density, size, high-current handling, etc compared to ALL OTHER lithium chemistries, such as those in your laptop, Nissan, or the Tesla battery. They do NOT use lifepo4, and concentrate on very small size and very high current capabilities, along the lines of handling 10C or more!

    In fact, they are on the next rung above the high quality "pure lead" agm in capabilities.

    The question is from a solar housebank standpoint - do we NEED that capability? NO because we don't design systems intended for EV's. Should we be paying even higher prices than lifepo4 for that extreme capability we'll never utilize? No.

    BUT, lifepo4 being at the bottom end is actually a blessing from a safety standpoint. Iron-phosphate is one greedy little molecule that does not like to give up oxygen, one of the main ingredients of fire. And, due to the chemical structure, you can abuse them with far greater latitude than you can with ANY OTHER lithium chemistry that the commercial EV'ers use.

    I'm not saying that abuse is tolerated. You will hurt cells with abuse, but catastrophic events take far more effort than with non-lifepo4 chemistries. Consider with lifepo4 going beyond 4v will make your cells swell, possibly vent, but to make it catastrophic, you need to go to 30v or so. ALL OTHER lithium chemistries typically top out at 4.2v per cell max. What happens when you take them to 4.5v or just a little higher - catastrophy.

    Consider this - at the small end of the spectrum, lifepo4 motorcycle powersports batteries like Shorai, Braille, Antigravity and the like are about 3 inches away from your butt-cheeks. You basically sit on top of them. You would NOT want to do this with ANY other lithium chemistry.

    So, using lifepo4 from our diy standpoint gives us a little more latitude when dealing with minor errors than it would with anything else.

    In the end, our usage patterns and solar housebank design has very little to do with EV concerns.

    Unfortunately, much of the input about solar housebank use with lifepo4 comes from outside our application, like commercial EV'ers, model-airplane enthusiasts, and cheapskates buying used / damaged goods and hacking it all together with duct-tape.

    We are a lonely little bunch us solar / lifepo4 users. :)
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Ampster wrote: »

    Newbie here. Trying to learn some of this new terminology. What is "true" Lithium. I have LiFEPO's and am wondering are they "true" lithium?


    The TESLA lithium (Li-NCA) Nickel Cobalt Aluminum, is a very unstable battery composition. It offers the highest discharge rate, but with higher discharge comes greater temprature with that discharge.

    So in order for TESLA to honor the warranty of the PowerWall, and to avoid thermal runaway, (which happens from thermal expansion of the aluminum plates in the battery, due to high discharge, and rising temprature). TESLA chose to incorporate a regulator on the BMS (battery management system) that will not allow the PowerWall to discharge at its highest rate (like a true lithium battery should), instead tesla wants you to buy more power walls daisy chained to double the discharge, while maintaining a safer battery.
    What makes NCA extremely dangerous is aluminum. When aluminum reaches melting point at the cellular level, it releases both hydrogen, and oxygen seperatley (NOT H20, "water"), Nickel as well releases oxygen when it reaches melting point so the combined oxygen to hydrogen when combined with temprature exceeding 1200*F on the cellular level causes a reaction that is like a mini bomb domino effect.

    The large 70kWh and 90kWh banks that come on the tesla are relatively safe in regards to demand to the discharge the car requires, however once you install a 1/9 scale version in to a home the demands for discharge are increased by 90% or according to how the engineering breaks down between the "watered down home use", and the much larger battery bank car version.

    TESLA builds the bank larger than it should for the cars so thermal runaway doesn't occur, but when the banks are broken down in 1/9th scales it increases the probablility of thermal runaway, so a BMS which I would assume is the same on the TESLA (per 10kWh bank), would mean you would need a minimum of 70kWh to get the potential dischareg you are really desiring from a lithium battery.

    Now liFEP04 is the safest, and best technolgy for RE applications. It may be heavier in density than NCA, but there is minimal regulation for the BMS which actually makes it a much more universal lithium battery on the market that can deliver a better discharge with much less needed BMS safegaurds.

  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
  • AmpsterAmpster Registered Users Posts: 22
    Thank you Solar Powered, that was a good read. Now I understand what you may have been trying to convey when you said the Tesla batteries were not "true" Lithium. For future readers benfit, the article calls them "less common".
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Ampster wrote: »
    Thank you Solar Powered, that was a good read. Now I understand what you may have been trying to convey when you said the Tesla batteries were not "true" Lithium. For future readers benfit, the article calls them "less common".



    NO the BMS to powerwalls doesn't allow powerwalls to be a "true lithium battery". The battery can only discharge 40% of its capacity in one duration, rather than 90%discharge in 1 duration. The battery is limited in how it performs.

    NCA unfortunately is becoming more of a "common" battery, because the manufacturing processess are becoming less expensive.
  • AmpsterAmpster Registered Users Posts: 22


    The TESLA lithium (Li-NCA) Nickel Cobalt Aluminum, is a very unstable battery composition. It offers the highest discharge rate, but with higher discharge comes greater temprature with that discharge.

    So in order for TESLA to honor the warranty of the PowerWall, and to avoid thermal runaway....... TESLA chose to incorporate a regulator on the BMS (battery management system) that will not allow the PowerWall to discharge at its highest rate (like a true lithium battery should), instead tesla wants you to buy more power walls daisy chained to double the discharge, while maintaining a safer battery.
    What makes NCA extremely dangerous is aluminum. When aluminum reaches melting point at the cellular level, it releases both hydrogen, and oxygen seperatley (NOT H20, "water"), Nickel as well releases oxygen when it reaches melting point so the combined oxygen to hydrogen when combined with temprature exceeding 1200*F on the cellular level causes a reaction that is like a mini bomb domino effect.

    The large 70kWh and 90kWh banks that come on the tesla are relatively safe in regards to demand to the discharge the car requires, however once you install a 1/9 scale version in to a home the demands for discharge are increased by 90% or according to how the engineering breaks down between the "watered down home use", and the much larger battery bank car version.

    TESLA builds the bank larger than it should for the cars so thermal runaway doesn't occur, but when the banks are broken down in 1/9th scales it increases the probablility of thermal runaway, so a BMS which I would assume is the same on the TESLA (per 10kWh bank), would mean you would need a minimum of 70kWh to get the potential dischareg you are really desiring from a lithium battery.

    Now liFEP04 is the safest, and best technolgy for RE applications. It may be heavier in density than NCA, but there is minimal regulation for the BMS which actually makes it a much more universal lithium battery on the market that can deliver a better discharge with much less needed BMS safegaurds.
    There appear to be a number of contradictions or misunderstandings in what you are saying. For the purposes of discussion I will agree that the NCA as a Lithium chemistry is more unstable than LiFePO. However, the most unstable chemistry is Lithium Polymer or LiPo's that are most often used by hobbyists and are the source of many spectacular fires and bomb like situations that you must be referring to. Yes, NCA, it is the same chemistry as in some laptops and yes indeed there have been fires with laptops. .
    You corrrectly mention that the BMS in the Powerwall limits the discharge rate of the 10Kwh powerwall to 2k. That would be a discharge rate of 0.20C (2/10). However you go on to say that the battery packs in the cars are relatively safe. Yet a P85 Model S when accelerating is consuming 300kWs of power which is 4C.

    How is the Powerwall at 0.2C less safe than a car that is accelerating and drawing 4 times the capacity of the battery (4C)? I think your explanation suffers from the assumption that you make about the power restrictions for the car and the Powerwall being the same.They are NOT the same. In fact the car does the opposite that you assume. You go on to say that the demands for discharge are increased by 90% "according to how the engineering breaks down...." What is the "engineering" that your are basing your argument upon? If I want a back up system that will deliver 1kWh for 8 hours the Powerwall will do that and even accomodate a 2kW surge. That is the engineering that works for me.

    I am just looking for clarity and understanding based on the same facts.You appear to have a great deal of experience that we all can benefit from. I am glad to see that we agree that LiFePO is the safest technology for RE applications. That is what I ultimately settled on for my system.
  • BB.BB. Super Moderators Posts: 26,768 admin
    In general, a car pulling 4C is going to do it for 10 seconds... The average home may draw 2-4 kWatts for many hours per day. So the actual amount of heating between 10 seconds and 4 hours is a factor of ~360:1

    More or less saying that the amount of heat generated in the bank at 4C for 10 seconds is not near as much as 0.2C for many hours. Self heating of the bank is much less in short term use.

    4C loading on a "home" would mean you run out of battery juice in 15 minutes. A 0.2C discharge is 5 hours to "flatten" the battery bank--So, for home use, we need more Watt*Hours of storage vs what a typical car would use (home powered for several days vs a car that is "empty" in three hours of driving). The larger WH storage, even if peak current is limited, is still large enough to support the relatively small "average peak" power needs of a home.

    Not the the Tesla design is bad or wrong--Just not the same as we would define for use with a home.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AmpsterAmpster Registered Users Posts: 22

    NO the BMS to powerwalls doesn't allow powerwalls to be a "true lithium battery". The battery can only discharge 40% of its capacity in one duration, rather than 90%discharge in 1 duration. The battery is limited in how it performs.........
    Are you saying that the 10kWh Powerwall only has 4kWhr of usable capacity? What is your source for that claim? Yes you are correct, the Powerwall is limited, and that limitation is what makes it safer than bare unregulated NCA cells. My Outback inverter can limit the amount of kWhrs (via an Amp setting) that I can draw from my LiFePO pack. How is that any different than what the Tesla BMS doesin the Powerwall? I only draw at the most 40 Amps from my 480Ahr LiFePO pack so that now makes my pack NOT a "true" Lithium pack because I am conservative in how I exercise my pack. How does that make a pack unsafe or uneconomical?

    I am asking these questions because I think they will bring clarity to the discussion. You appear to have a great deal of experience that we can all benefit from. We do agree that LiFePOs are the safer chemistry.
  • BB.BB. Super Moderators Posts: 26,768 admin
    I don't like the term "true Li Ion" battery bank/pack/system... There are lots of design and manufacturing choices made in any product. If it is done correctly, then we don't really care if it is a 10kWH battery running at 50% of capacity (say 40% to 90%) state of charge--Or it is 5kWH battery bank at 100% of "operational capacity" when looking from the outside when looking at operational specifications. It is only what we can use (safely/reliably).

    Just like Lead Acid batteries... We say that nominally we run from 90% to 50% cycling for an XYZ AH battery bank... We really only use ~40% of the lead acid battery life for long life and good performance. Can you discharge to 20% state of charge--Yes, but it will probably not last as long. Can you use the 90% to 100% state of charge every day--Yes, but the battery bank will be less efficient and also probably not last as long (plus there are not enough hours in a solar day for most people to run 50% to 100% SOC on a lead acid battery bank).

    We don't worry about if this is a "true Lead Acid Battery system"--It is just how we make optimum use of the batteries.

    LiFePO4 batteries have some definite advantages over Lead Acid--But cost is not one of them. And many people end up "murdering" their battery banks (before batteries die of old age/cycle usage)... There is a real concern over the cost of replacement if/when we murder the battery bank (through our mistakes, sometimes through the mistakes of our kids/guests, sometimes even mfg. errors). Lead acid tend to be much cheaper, so mistakes are not as draining on our bank accounts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AmpsterAmpster Registered Users Posts: 22
    PNjunction wrote: »

    What makes any intelligent discussion about lithium so hard is that most users don't know the difference between the chemistries, much like not knowing the difference between a flooded lead-acid and a sealed agm. Both are lead, so we treat them the same right? Nope. :)
    ..............
    We are a lonely little bunch us solar / lifepo4 users. :)

    I came into the stationary storage market from the EV perspective. My first E bike used AGMs and I quickly discovered the limitations. My first pack died because I didn't float charge it while it went unused for a couple of months. Many E bikers use LIPOs because of the energy density but the risk of burning down my apartment was too great so I migrated to the safer LiFePOs. I evolved into converting an old VW to electric and got my first real EV grin. I still drive the VW occasionally but our family's main transportation are a Chevy Volt and a Smart ED. I am on a TOU rate with Southern California Edison with solar on the roof. I am able to benefit from TOU rates because I can shift a good portion of my loads to the super off peak rates. As a result I am a net consumer of kWhrs but run a negative bill. At true up at the end of my relevant period it all washes out and that is the sweet spot as far as I am concerned.

    About six months ago SCE changed the timing on the TOU pricing to more reflect their demand curves. That stranded some of my solar production and meant that the early evening uses would now pay $0.37kWhr after the sun went down. It looked like I would still break even on my NEM agreement but since I am in an all electric home I wanted the flexibility use electricity in the early evening hours. I also wanted protection on further shifts. I had not considered the opportunity to also do some rate arbitrage at that time.

    I bought an Outback Radian and for a test I reconfigured the pack in my VW conversion to power the inverter in order to gather some data on usage so I could build the right size pack. I seriously considered pieces from old Chevy Volts and salvaged Tesla packs which came in units that could be configured for my 48v inverter. Ultimately I found 24k in Voltronnix used LiFePOs that tested to 95% of original capacity. My solar system uses Enphase inverters so there was no way to charge from my solar production. I call my system AC Coupled but that is technically not correct since the inverter never feeds the grid. In fact I am of the opinion that I do not need SCE's permission for the inverter because everything I am doing is behind their meter.

    I currently run my critical loads that average 800 Watts from 9am until 10PM which is part of my off peak rate period and all of my on peak rate. I then charge my pack during the super off peak rate which is also when I charge my cars and run my water heater. I use a timer and programmable voltage switch which control a 48v charger. I charge my 16 LiFePOs to 55.2V (3.45 per cell). Apparently according to another poster that makes my cells NOT true Lithium because I am not utilizing their full potential. LOL. The great thing I discovered about stationary storage is you don't have to run your cells at high C rates.

    So that is how I evolved from the EV space into the stationary storage space. There is a great deal of knowledge on this site about the care and feeding of Lead Acid batteries. I actually found that more complicated than figuring out a high voltage cutoff for my Lithiums. I think there will will be a slow transition from Lead Acid to Lithiums for the housebattery market. For the large commercial market, Lithiums seem to be the choice that pencil out for commercial and utility level users. In fact the cost of some utility level storage systems is competive with gas peaker plants.

  • AmpsterAmpster Registered Users Posts: 22
    BB. wrote: »
    In general, a car pulling 4C is going to do it for 10 seconds... The average home may draw 2-4 kWatts for many hours per day. So the actual amount of heating between 10 seconds and 4 hours is a factor of ~360:1

    More or less saying that the amount of heat generated in the bank at 4C for 10 seconds is not near as much as 0.2C for many hours. Self heating of the bank is much less in short term use.

    4C loading on a "home" would mean you run out of battery juice in 15 minutes. A 0.2C discharge is 5 hours to "flatten" the battery bank--So, for home use, we need more Watt*Hours of storage vs what a typical car would use (home powered for several days vs a car that is "empty" in three hours of driving). The larger WH storage, even if peak current is limited, is still large enough to support the relatively small "average peak" power needs of a home.

    Not the the Tesla design is bad or wrong--Just not the same as we would define for use with a home.

    -Bill
    Maybe the car analogy wasn't very good. I wanted to stick to the same analogy the original poster was using. I saw his point as that the PowerWall was less safe than the car because of some unclear math. I see it just as safe as the battery in a Tesla. I would agree that a 10kWH Powerwall won't get you very much power in a stationary storage situation. In my home I only use 800 Watts per hour but occasionally have peaks of 2kWhrs. in 10 hours that is still 8kWhrs and I wouldn't want to use any 10kWhr pack to do that regardless of the chemistry. I understand the design of the PowerWall has no appeal to the majority of us here. I think that is especially true among us that are invested in 12-48V hybrid inverters. If they are successfull in building them at the $350/kWhr price, they will have a big impact on the market. For a new solar customer who wants some battery backup or load shifting capacity they offer some value. That will mean more affordable options for housebattery systems.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Ampster wrote: »
    Are you saying that the 10kWh Powerwall only has 4kWhr of usable capacity? What is your source for that claim? Yes you are correct, the Powerwall is limited, and that limitation is what makes it safer than bare unregulated NCA cells. My Outback inverter can limit the amount of kWhrs (via an Amp setting) that I can draw from my LiFePO pack. How is that any different than what the Tesla BMS doesin the Powerwall? I only draw at the most 40 Amps from my 480Ahr LiFePO pack so that now makes my pack NOT a "true" Lithium pack because I am conservative in how I exercise my pack. How does that make a pack unsafe or uneconomical?

    I am asking these questions because I think they will bring clarity to the discussion. You appear to have a great deal of experience that we can all benefit from. We do agree that LiFePOs are the safer chemistry.

    According to TESLA's advertising of the 10kwh powerwall within the first hour peak discharge(or surge discharge) is 3000watt peak, after 1 minute the discharge drops to 2.5kWh's continuos.

    Those are shame full numbers for TESLA to advertise because a standard AGM 12v bank can easily discharge that rate at literally half the price.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    This means the power wall can deliver 2.5kWh for roughly 3.5hours maximum.
  • AmpsterAmpster Registered Users Posts: 22
    Okay we agree that the Powerwall has a 10kWhr capacity. (your math 2.5kWhr for 3.5 hours) It has a maximum discharge of 3000 watts for one minute. I agree the price is higher than the equivalent in AGMs (half the price). Another reason why you or I would not buy it is the 350V DC bus. We would lose too much power going back and forth through a DC to DC converter. The only Inverter that can handle that Voltage is the Solaredge inverter with power optimizers.
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