back to article Elon Musk's Tesla set to unveil home storage battery

Elon Musk's electric car company Tesla is about to unveil a home storage battery that could compete with the electricity companies as a power source, he said in an earnings call. Musk said yesterday the company has completed the design of the battery. "We are going to unveil the Tesla home battery for use for people's houses …

  1. Kurgan


    A home battery? For what use? How do you recharge it? Why do you need it? Is it basically a 3KW UPS?

    1. Suricou Raven

      Re: WTF?

      I can see two potential niches for it. First, those plagued by frequent power cuts may find a home battery appealing, as it would let them ignore the shorter ones and gracefully prepare for the long ones. It might also be a money-saver, as you could charge it off-peak for use in the day - the youtube tinkerer PhotonicInductction does exactly that, and has run through the calculations to determine it can be economical. Even with the efficiency loss, the price difference is enough to justify operating the battery. The payback time would be poor, I expect - but a lot better than those rooftop wind turbines, and people are suckered into buying those.

      1. Anonymous Coward
        Anonymous Coward

        Re: WTF?

        It might also be a money-saver, as you could charge it off-peak for use in the day

        so you need one of those "cheap off peak" tariffs that cover their arse by charging (pun) almost 30% more for the remaining 18 hours of the day that are not midnight to 6am? (UK figures, other countries may vary)

        please show me the "savings" math here

        during summer you don't need the storage heaters so are paying through the nose

    2. Anonymous Coward
      Anonymous Coward

      Surely you aren't serious?

      You have heard of solar and wind power, right, and how one of the biggest issues with it is you still need to be tied to the grid or have substantial battery storage because the sun doesn't shine / wind doesn't blow 24x7?

      Even if you don't intend to disconnect from the grid entirely, or don't even intend to generate your own power this can be very useful if your utility does time-of-day pricing like California. Top up the battery at night when power is cheap, use it during the day when it is expensive. With the price differentials in California, I'm sure it would pay for itself in a few years.

      This would also be great for Tesla owners, if the design of the home storage battery allows for a faster transfer of power from it to your car, as compared to plugging it in. Depends on how it is wired, series vs parallel, etc.

      There are so many reasons why a home storage battery system, if it is plug and play and more affordable than current solutions, would interest millions in the US alone. The current state of home battery systems for renewable power can be compared to buying a PC in the mid 70s - kits like the Altair, Apple I, etc. versus buying one in the mid 80s when you could just buy a Mac, IBM PC, Amiga with everything you needed and not have to understand how it works to make use of it.

      1. Anonymous Coward
        Anonymous Coward

        Re: Surely you aren't serious?

        Stand-by diesel generators are far more practical than some huge battery for house or business use in power outages or for down times on wind and solar. Battery banks are fine and all but no matter how you cut it, you still need to recharge a battery. I suspect Elon is desperately trying to dupe more gullible people as Tesla continues to lose billions of dollars.

        1. Yet Another Anonymous coward Silver badge

          Re: Surely you aren't serious?

          Slightly more practical then 1000s of backyard diesel generator sets for load peaking.

          If enough people have an electric car plugged in to a smart charger it can charge slowly and cheaply off-peak and then you can have it sell power back to the utility when the game comes on, or it gets hot and the AC kicks in. Cheaper than spinning up a lot of gas turbine peak load plants.

        2. localzuk Silver badge

          Re: Surely you aren't serious?

          Battery storage for homes is a great idea. Where I live, we use very little electricity, making a monthly bill about £25. With a battery like this, and a move to economy 7 or installing some solar panels, we could drop that bill down to £10 or less.

          Imagine it this way - every house in the country has a home battery capable of storing enough power for a day's usage - blips in the power grid would be less of a worry. Load balancing and capacity on the grid would be simpler and the cost of power in general could drop.

      2. Anonymous Coward
        Anonymous Coward

        Re: Surely you aren't serious?

        all great until you run the numbers and realise that the cost benefit scales slam down on the cost side and the same benefit can be had for far far less cost

        I can't work out if Being Green basically destroys the ability to Do Simple Sums, or whether Being Green is simply a natural refuge for self important people who can't actually Do Sums Anyway.

    3. CJ_in_AZ

      Re: WTF?

      Significant parts of the (developed) world are on power plans that the cost goes up dramatically as the "peak usage" (OK, usually averaged over at least several minutes) goes up. When I was living in an apartment, I had the misfortune to be on such a plan (or "scheme", with the American derogatory connotation of that word) where the "peak usage" charge accounted for about half my monthly electric bill. The "come-on" of these plans here in the States is that the per-kWh charge is much lower. So, a battery could be charged when my demand is otherwise low (e.g., wee hours of the night) and provide power when, for instance, I'm doing laundry. Conceivably it could even out the load, even more effectively than a "load balancer".

      Also, the local power company is making noises about adding a $50 PER MONTH "surcharge" for folks with solar power. That can make it more attractive to go "off grid" completely.

      From the perspective of the utility (which, given that asinine surcharge, I'm not currently to sympathetic to, even though I have some "professional knowledge" of) having large batteries on-grid can potentially save some big bucks. "Base load" can cost them as little as $0.016 per kWh (and sometimes even less) "at the fence" of the power station, while "peaking" generators can be well over $1.00 per kWh. The problem today is that really big battery banks needed for a utility are prohibitively expensive, in most cases. There are a few exceptions, where they can avoid putting in, say, 60 miles (100kM) of lines to provide two or three hours of peak power per day a few days a year, when the existing lines are under-utilized much of the time.

      All in all, I'm looking forward to see what Mr. Musk has come up with.

      1. Phil O'Sophical Silver badge

        Re: WTF?

        having large batteries on-grid can potentially save some big bucks.

        Flywheel storage seems more popular for that now, it has a much longer working life than batteries faced with constant charge/discharge cycles.

    4. Anonymous Coward
      Anonymous Coward

      I've already got the system beat.

      I have a duplex (a house with two sides).

      One side is connected to the grid on a 'Time Of Day' tariff where the power is sold to me at one-half price during off-peak times (half the day and all night).

      The other side is connected to the grid on a 'Renewables Reversible' tariff where they pay me double price for my "renewable" power. I have a small solar cell on the roof, for legal-decoration purposes; not even hooked-up to anything.

      In the common basement is a motor-generator set capable of 200A. I buy half-price power and sell them double-price power.

      I'm making $85K a year on the deal.

      That's some "Green Power".

      1. squigbobble

        Re: I've already got the system beat.

        You have a house with 2 grid/mains connections?!

        1. Black Betty

          Re: I've already got the system beat.

          Two separate dwellings sharing a wall, on a single land title. They often share certain features as a commons, ie basement and yard space.

          I suspect a certain amount of lawbreaking, given that he is to all intents and purposes DEFRAUDING an incentive scheme intended to pay for electricity generated from renewable sources, by instead feeding in electricity from an ICE*-generator set powered by fossil fuels. He probably pays a premium of 50-75% over the standard tariff for his fuel and running costs, but still profits on the inflated price he's being paid for the 25 odd kVA "generated" day and NIGHT by his 25W cosmetic solar panel.

          * Infernal Combustion Engine.

          1. Anonymous Coward
            Anonymous Coward

            Re: I've already got the system beat.

            No, he has no generator, he's feeding in power on one side of the duplex, and feeding it out on the other. If the feed-in tariff is higher than the nighttime ToD pricing, he makes money on every kilowatt.

            Definitely fraud, which would be a good reason for him to post AC. But I'll bet it is just a "I wish I did this" rather than "I actually did this". If he actually did it, I hope he gets caught and goes to jail. Idiots like that will give utilities the excuse they're looking for to drop feed-in tariffs entirely.

      2. Anonymous Coward
        Anonymous Coward

        @AC - Re: I've already got the system beat.

        Great deal until the utility decides to audit their systems for the ones feeding them the most power, determines you aren't feeding them renewable power, and refers your case to the local DA for felony fraud prosecution. Likely federal charges as well assuming the utility is getting some federal dollars as part of this deal.

      3. Rick Brasche

        Re: I've already got the system beat.

        careful, as soon as Buffet and a few of the really big "green energy" people know you've released a version of their little secret, you'll end up disappeared.

        Unless it's already too late. :P

      4. This post has been deleted by a moderator

    5. IvyKing

      Who owns Solar City?

      ISTR that there is a pretty tight connection between the ownership of Solar City and Tesla...

      A home battery does make perfect sense for people with solar panels. In California, solar production is essentially zero at 6PM PDT, where peak power consumption occurs 7PM PDT in the summer. This likely to lead to some pretty hefty rates for usage in the 6PM to 9PM time frame, so running off a battery during that time will likely bring significant savings in electric bills especially if the CPUC starts setting rates that have some connection with the reality of providing service. The CPUC and CalISO are already encouraging people to put solar panels on west facing roofs.

      I've been researching batteries for exactly this purpose, and while lead-acid batteries intended for stationary service will do the job, their size is a bit impractical.

      FWIW, the high at home was 33C today.

    6. Anonymous Coward
      Anonymous Coward

      Re: WTF?

      "A home battery? For what use? How do you recharge it?"

      Tsk, Tsk, my friend. If like me you have a team of small Indian boys, pedalling away on bicycles, to power the dynamos used to create your usual electricity supply. Simply connect said dynamos to the rechargeable home batteries. This is obvious! No?

    7. Black Betty

      Re: WTF?

      Combine with rooftop solar for total grid disconnect, or stay connected to the grid and sell your leftovers for whatever pittance you can get AFTER you've accounted for your night time and grey sky needs.

      I suspect, given the way power companies are starting to punish rooftop solar in some locales, that a new service industry might emerge offering a mobile rapid charge service as more and more people elect to abandon their connection to the grid entirely.

      Or form a cooperative with your neighbours. Lots of solar panels on lots of roofs, a big battery bank and just one grid connection per 20-30 houses.

      Affordable high capacity batteries are a real game changer, given their intermittent nature of the most mature renewables. Solar only works during the day, and wind only when wind speeds are neither too fast or too slow. Wave and tidal generators, not tied to rare geographic features, have a bad habit of being smashed to smithereens whenever the weather gets a little too boisterous.

      One beauty of a fully mature portfolio of renewable energy sources is that the idea of excess/underutilised capacity ceases to have any meaning. Since running costs are extremely low, it begins to make sense to do energy intensive things like use desert sunshine to melt Boston's snow and use that to water lawns in Las Vegas.

  2. Anonymous Coward
    Anonymous Coward

    And all because

    ...Tesla need to build battery volume to drive down car production costs. The real (ie wholesale) price arbitrage on electricity over a few hours (less the 25-30% losses into and out of storage) is insufficient to pay the costs of home power storage system like this, but Tesla hope that ill-conceived solar subsidy programmes will mask the harsh realities.

    As the article says, the system has been hawked around utilities and I suspect that they've run the numbers and they don't work except in niche situations *cough, cough, AC and all that*.

    If you can launder the subsidies by using such a system, then you might have some small rationale for using it, but as I understand the rules both microgen and storage must switch off if the mains goes down, so even the theoretical value of UPS is not available.

    1. Anonymous Coward
      Anonymous Coward

      Re: And all because

      Or maybe because there's a market for this, and building volumes for their battery "gigafactory" will make both Teslas and renewable power more affordable?

      What a bastard that Musk is, possibly benefiting from renewable energy subsidies just because he'd be giving a big boost to making renewable energy more successful!

      1. BornToWin

        Re: And all because

        The reason why batteries are not used for many applications is because the energy available is impractical for the cost of the system and maintenance. Stealing money for so called renewable energy is a farce and con game that many profit from including Elon Musk. You're paying for his follies.

        1. Anonymous Coward
          Anonymous Coward

          Re: And all because

          The reason why they're really looking at static storage is that the cost/kWh of batteries has fallen dramatically in the past 10 years, and Tesla in particular emphasizes reducing battery costs. As other people have mentioned, the marginal cost of electricity is stupidly high, due to the need to deal with instantaneous, intra-day and seasonal variations in demand, and that means that battery costs don't have to get too low to be able to used at the margins. Oncor, a Texas distributor, wants to spend $5.2B on installing batteries around the network from about 2018, estimating that as long as prices are below $350/kWh it would lower electricity prices slightly, and obviously, prices would be lowered by more if batteries prices fall more than that (and almost all projections see that happening).

          Right now, because electricity pricing is totally stupid (paying for distribution costs by kWh instead of kW) and solar PV subsidized by net metering, a consumer battery could have a market, especially if they pass marginal pricing on in the consumer batteries.

    2. Anonymous Coward
      Anonymous Coward

      Re: And all because

      Musk is building the new battery factory with a lot of tax payer dollars. He lost BMW and some other potential battery customers so he's spinning to gain sales for his battery factory.

    3. Black Betty

      Re: And all because

      You might be surprised. The Old paradigm of continually managing the energy supply to match the demand is fast flying out the window.

      The new paradigm is matching demand to a continuously variable supply. Even a quite small battery (2-5kWh) in the home in conjunction with a rooftop photovoltaic system, would suffice to significantly limit the amount of time your home has to resort to the grid at all, even when firing up energy hogs like air-con, kettles and vacuum cleaners. Simply trickle charged at off-peak rates that battery combined with an increasingly affordable inverter will let you avoid the worst of premium rates.

      If Elon Musk get battery prices down to a genuine $100-$200/kWh, a few thousand dollars worth of battery and inverter would allow most households to make ALL of their electricity purchases at the lowest available tariff. Even at $400/kWh (looking at < that price right now) such a setup would result in enough savings to more than cover the cost of a new battery every few years. Provide the overcapacity and in all likelihood, electricity providers will happily lease it off you for load balancing purposes. Do your number right, pop on a few solar panels and become a small scale electricity provider yourself with a zeroed power bill and showing a modest profit after amortised costs. Can't argue with that.

  3. Anonymous Coward
    Anonymous Coward

    Count me in, but...

    For us, that sounds wonderful, but that's because we're not on the grid, and the battery bank is a perennial source of grief. However, in the off-grid home context, one of the most hysterical things to read is the "charging regime" from the battery manufacturers, who assume you are on the grid and can therefore charge in an ideal way, and every day. The reality for renewables is that you charge when the wind blows or the sun is shining. That may be predictable in California, but in Northern Europe, not so much. Still, welcome news, as the concepts underpinning the grid need a shake-up

    1. Salts

      Re: Count me in, but...

      We are on the grid, but power here is about 8 hours a day, but when in the day is not so certain, could not agree more about the "Charging regime" not everyone has a reliable on grid electricity supply and affordable lithium tech would make a big difference.

    2. AdamT

      Re: Count me in, but...

      Sure, charge/discharge regime is an issue with battery life. But Tesla now has (a) an ton of R&D on this subject and (b) a ton of experimental data (from the cars themselves) of running batteries at their limits with charge/discharge cycles based on traffic flow and heavy-footedness of the driver. Which might be a reasonable proxy for sun/wind cycles...

    3. Black Betty

      Re: Count me in, but...

      With conversion efficiencies above 95% it's perfectly practical to buffer a delicate high capacity battery bank with a smaller capacity battery that will tolerate high charge rates and also being sucked dry by a joule thief.

  4. noominy.noom

    Lots of interest in this

    I don't currently use any home generating equipment but I keep up on the literature. It is a common refrain in the literature that some form of home storage is necessary to utilize the potential of home generation. That is assuming current or likely near term technology. Yea, you can sell your excess when you have it draw from the grid when you don't but from what I read that is not working well. And of course some people want or even need (geographic issues) to be off the grid.

  5. Ken Hagan Gold badge

    Off the top of my head

    It needs to pay for itself on a timescale less than the period for which you have a reasonable hope of predicting the price of electricity.

    Deployment will be limited to those properties that can retrofit the battery and that itself may be costly if the battery is large. New builds would be fine, though, and that may be a large enough market for starters.

    On the plus side, if this can be deployed widely then it is a game-changer for electricity generation because you wouldn't need power stations that can switch on and off at short notice.

    So, um, what breakthrough in battery technology makes this possible in 2015?

    1. Paw Bokenfohr

      Re: Off the top of my head

      Could conceivably be Liquid Metal Battery, or perhaps a true Lithium Polymer battery, or maybe he's just punting really cheap current tech through economies of scale?

  6. Anonymous Coward
    Anonymous Coward

    Choose one: energy density, durability, power output

    I wonder if what this actually means is "we've managed to make a high capacity battery but it is either too heavy or insufficiently durable for cars, so we want you to use them in static applications to get enough production going to get the bugs out".

    It may not be that of course, but it is basically what happened with fuel cells.

    1. Anonymous Coward
      Anonymous Coward

      Re: Choose one: energy density, durability, power output

      JB Straubel (Tesla CTO, their battery guy) was the keynote speaker at a storage symposium last may (, well worth watching) and at that symposium, talked about how the demands placed on static storage are much less than in a car. As an example he said that their car batteries are rated for 4C discharge, while static storage systems are just C/2 and remarked that re-using the tech they'd used in the Model S was really overkill. (It's not just about the battery, but the power electronics as well, that JB Straubel referred to as soon costing $100/kW.) So, it'd really suggest if they expand the static storage market as they intend to (15GWh/year, 30% of Gigafactory output) you could expect a the chemistry, if not the fundamental manufacturing. If they've found a high-energy-density, low power-density mix that lowers the cost of static storage, I'm sure they'd be very happy.

    2. Matt Bryant Silver badge

      Re: Arnaut Re: Choose one: energy density, durability, power output

      "I wonder if what this actually means is "we've managed to make a high capacity battery but it is either too heavy or insufficiently durable for cars....." The design issues for a static battery are very different to those for a vehicle. I would not want two tons of bulky batteries in a car as it would compromise my car's design, but the same two tons of bulky batteries sitting in the corner of my garage (or in the basement) is much more acceptable. And if Mr Musk is selling it as a bundle with some solar panels (and government rebates and/or off-peak rates) then it is also economically appealing too. I know one technohippy in Cyprus that is already doing this with solar panels and old car batteries so he could go off-grid in the hills.

  7. JeffyPoooh

    Oh great...

    A $100,000 battery for my house.


    1. Black Betty

      Re: Oh great...

      Actually about $4000 or less at Musk's CURRENT prices. Combine with a sub $15k 5 kW solar system to go off grid without sacrificing much in the way of convenience or lifestyle, but with probably enough back from even a pitiable feed-in tariff to justify remaining grid connected just in case.

      With sub $100 per kWh of battery on the cards, staying grid connected is a no-brainer. They'll be installing the battery for you. Even leasing it off you if you choose to own outright more hardware than you actually need. Idling wind generators would no longer be a waste of free electricity. Everybody's battery gets a top up and those cheaply hoarded electrons are ready and waiting at a discount rate for when the ads come on and everyone's kettles sing as one.

  8. Tromos

    Most houses will need four of these...

    ...make sure they're inserted the right way round.

  9. Charles 9 Silver badge

    Color me sceptical...

    It's funny we're not seeing actual specs about these batteries. Nothing about storage capacity, power output, and especially (in terms of payoff factor) working life. If such an announcement doesn't give the details right off the bat, I suspect they're hiding something (because if it really isn't too good to be true, they could tout it as a selling point).

    1. Daniel Hutty

      Re: Color me sceptical...

      "It's funny we're not seeing actual specs about these batteries..."

      Well, not really, when you consider they *haven't officially announced the product yet* ! This was an earnings call; I doubt he discussed the power-to-weight ratio of his cars, either...

      "Funny" (in the "suspicious" meaning of the word) would be if, when they made the official press announcement of the new product, they *still* made no mention of the specs you mention.

      Musk is the CEO, not an engineer working on this particular project, and the article is about a comment he made during the course of an earnings call, not a press release or other written announcement regarding this specific product. That's not the venue for technical details; he's talking to financial types, not techies (or potential customers for the product); an earnings call is about whether his *company* is a decent investment, not about whether any particular *product* is suitable for any particular application.

  10. Anonymous Coward
    Anonymous Coward

    people have already re purposed Tesla batteries to power a house

  11. a_mu



    I've been looking at these from a few suppliers ,

    I have a PV system,

    and what do I do with extra energy, export it , or use it to heat .

    the house base load is around 300 watts ,

    so a battery of 'only' 14 KWh would be fine to cover my background needs assuming 50 % efficiency in the DC:AC,

    And I generate that each day or more 9 months of the year.

    For reference a standard 200 Amp H car battery is around 2 KWh though I'd not use them,

    The batteries in the Teslar are 60KWh if I remember, so more then enough to get me off grid most of the

    1. Anonymous Coward
      Anonymous Coward

      Re: FIT

      "For reference a standard 200 Amp H car battery is around 2 KWh though I'd not use them"

      Indeed. The safe level of discharge for a lead acid battery is around 25-30%; as you go beyond that life starts to get shorter. A nominal 200AH battery is good for 600WH in static use.

      This is one reason why you need such a big battery for a car; another of course is the cranking current. But people are using lithium batteries in cars with around 12-14AH capacity, which is about the real capacity of a 60AH lead acid battery.

      The biggest problem with the adoption of electricity for any kind of off grid use as that all current batteries are bad in at least one significant way.

  12. JP19


    No one can make batteries that cost less than the mains electricity they can charge and discharge in their lifetime so you can't even break even when the electricity to charge them is free.

    Musk isn't going to change that his batteries are bloody expensive. The only way it is going to change is if the price of mains electricity is artificially jacked up much more than it already is for political reasons.

    If you could economically store mains electricity in batteries the generators would already be doing it and they would be doing it on a large scale much more economically than stupid little 'home' installations.

    Musk's home batteries like his cars are for technically illiterate green willy wavers.

    1. Charles 9 Silver badge

      Re: Stupid

      "No one can make batteries that cost less than the mains electricity they can charge and discharge in their lifetime so you can't even break even when the electricity to charge them is free."

      No one can make them YET...unless you can pull an Alan Turing and demonstrate a formal proof that no battery can beat the grid, even if running off environmental power.

    2. Black Betty

      Re: Stupid

      Battery does not have to beat the grid. It has to assist in balancing the load on the grid.

      Practically, to achieve 100% electricity generation from renewables, there is always going to have to be a certain degree of overcapacity in generation simply to compensate for the fact that the wind and sun are inconstant as well as intermittent. But there's also an upper limit how much under-utilisation of generating plant that can be financially tolerated. A small amount of storage can go a long way toward limitting the amount of over capacity needed to meet peak needs.

  13. Anonymous Coward
    Anonymous Coward

    another hype

    finish at least pouring the foundation for the gigafactory before claiming to be "making" batteries that will save the world + dog?

    all these tech blogs giving all the credit before actually accomplishing anything. Nice to be optimistic but now they're three steps away from current reality instead of one or two.

    Of course, find how many tech blog/social media bigwigs are financially attached to Tesla and other Musk projects and we'll see why even the barest hint gets hype to drive up value and increase deposits made on nonexistent product.

  14. Anonymous Coward
    Anonymous Coward

    re: No one can make batteries that cost less than ...

    "No one can make batteries that cost less than the mains electricity they can charge and discharge in their lifetime"

    Hmmm -

    Nissan Leaf battery 24kWh@0.25/kwH (total incl line charges) = $6 * 365 = 2190 *10years = $21,900

    Replacement cost for Nissan Leaf battery (no exchange) $5000.

    Nope looks like we are already well past economic!

    In fact: Nissan Leaf 2012, 11000km = $19,995

    I think I'll just leave it parked outside as a nice battery box, and sell the motor and tyres as spares on ebay

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