Published on May 1st, 2015 | by Zachary Shahan


Tesla’s Home Battery Offering In Context — Pricing Much Lower Than Expected

May 1st, 2015 by  

I think one of the lessons of the day is to trust Elon Musk. When he said approximately a month ago that Tesla would be announcing a “major new product line” on April 30, he wasn’t using the term “major” in a light way. [Full Disclosure: I’m long (very long) TSLA.]

As someone who follows the battery industry very closely, I know that there are a lot of startups and large corporations looking to get a huge chunk of the battery storage market for themselves via their own innovations, competitive advantages, and perhaps even breakthroughs. It made me a bit cautious in getting excited about Tesla’s announcement. Furthermore, while the market is expected to grow in leaps and bounds, it’s still a tough financial sell for the huge majority of homeowners in the developed world.

However, I have also read on a number of occasions that Tesla has the lowest-priced battery packs among all electric car manufacturers, and that the scale of production it would gain from the Gigafactory it is building with Panasonic would enable even deeper price cuts. However, it was hard to figure out how all of that might translate to the stationary storage market, and allow it to compete in this market (where home storage is still dominated by low-cost lead-acid batteries, and grid storage can be provided via flow batteries and other technologies).

Yes, there were pilot rollouts of Tesla’s batteries pegging them at about $13,000 for 10-15 kWh systems. I didn’t want to base any guesses off of those prices, as I knew they could be far higher than the commercial products (they seemed far too high given the estimated per kWh price of Tesla’s car battery packs). Indeed, they were. Here’s the key statement on price from Tesla on price: “Tesla’s selling price to installers is $3500 for 10kWh and $3000 for 7kWh. (Price excludes inverter and installation.) Deliveries begin in late Summer.

Tesla Home Storage Powerwall

Unfortunately, that leaves out the inverter and installation costs, but still, this is a very low price for lithium-ion battery packs. “Nothing remotely in these price points,” Elon reportedly noted at the product release last night (or early this morning, my time).

As an example, a company I love — Sungevity — just this week announced a partnership with Sonnenbatterie. The price isn’t finalized, but it is expected to start below $10,000. “Below $10,000” certainly doesn’t make it sound close to $3,000. However, a CleanTechnica reader and advisor has noted to me, “One other thing on the comparison with Sonnenbatterie, last I saw, their system includes the three-phase inverter ($3,000–5,000?), with fifteen-year warranty, so the price comparison might be seen as an apple and oranges kind of thing.” [Note: I’m going to reach out to these companies as well as several other battery storage companies for a follow-up article featuring their comments.]

Price is the key, and that was the big question mark for me in whether or not this was a “major” announcement or just another announcement. Obviously, I think the price makes it a major announcement, as do the people in attendance who exploded with applause, said “What?!,” etc. Jump to 8 minutes in here:


The presentation continues here:

Other benefits include the fact that this is wall mounted (and can even be mounted on an exterior wall) and can be installed by just two people in half an hour to an hour.

But getting back to price, is the indicated price really going to attract buyers. I posed the question to three of our readers who have been living off the grid for years and know the ins and outs of these systems quite well.

“For someone wanting freedom from the grid, this is probably still too expensive an option unless they can get it qualified under the federal tax credit and the California storage rebate,” Offgridman notes. (My understanding is that a customer can’t claim both.) “Even for SolarCity customers, it isn’t practical yet unless they have to worry about peak charges and/or high utility rates. You notice how he said in 5–10 years it would be part of every SC system. I think that he is admitting that the economics are still pretty tight, unless you are willing to pay for backup for grid outages.”

And that’s still not taking into account some of the competition from non-lithium-ion battery companies. “For straight-up comparison on price per kWh, it’s looking like Aquion expects to hit $250 within a year or two. Now, with theirs, there is a bigger space and weight to consider, but for people with the extra room, it might be enough of a price difference to deal with that,” Offgridman added.

“It is good that Tesla is getting the prices down on lithium, and I hope it will be even more so after the Gigafactory, right now this doesn’t excite me too much.”

Update: Vensonata, another long-time off-gridder, was clearly more excited: “The battery price is unmatched by anyone else including the best lead acid. I estimate the 7 kWh pack at delivering for 13.7 cents per kWh. That is with all inefficiencies included. Working with solar, lithium is ideal because it does not need full recharge. Lead acid does need full recharge and that has been its weak point for off grid.”

Tesla has reportedly been using the product in-house for ~1 year. Furthermore, it has landed partnerships with several major companies in and out of the battery space, including Target (perhaps also Walmart, unless someone mixed up the two), Amazon, AES, Southern California Edison, EnerNOC, SolarEdge, and more. That’s yet another sign that this is a competitive product. Furthermore, it has seemingly been dominating contracts under California’s Self Generation Incentive Program.


What makes Tesla’s battery storage option so great? “The integration at the system level is the big differentiator,” Tesla CTO JB Straubel stated.

“Our goal here is to fundamentally change how the world uses energy,” Elon added.

And don’t estimate the power of influence, excitement, branding, and superb communication skills — all things that Elon and Tesla seem to excel at.

You can find out more about the product on Tesla’s Powerwall page or on the press page about the announcement.

Related: Tesla’s Competitive Advantages — 5 Big Ones

Images by Tesla

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

Tags: , , , , , ,

About the Author

is tryin' to help society help itself (and other species) with the power of the typed word. He spends most of his time here on CleanTechnica as its director and chief editor, but he's also the president of Important Media and the director/founder of EV Obsession, Solar Love, and Bikocity. Zach is recognized globally as a solar energy, electric car, and energy storage expert. Zach has long-term investments in TSLA, FSLR, SPWR, SEDG, & ABB — after years of covering solar and EVs, he simply has a lot of faith in these particular companies and feels like they are good cleantech companies to invest in.

  • Joe Viocoe

    Yes, I saw that. That is good info. Always great to have real numbers. Thanks.

    • JLM Energy, Inc

      Sure…glad you found what you needed…just checking back in.

  • eveee

    Nice link, thanks. The Solar City link just says they will engineer an off grid system for you and give you a quote. Thats similar to BAU for off grid systems. Not much turnkey right now. The author nails it. Solar City is making it clear that they will respond aggressively to utilities turning down users that want solar by providing a solution that makes them independent of the utility. For those that thought utility death spiral was just PR, watch what happens in the next three years in Hawaii. The utility will have to do something like EON in Germany and split and divest the stranded asset central FF generation side. Its going to hit big. The utilities that survive will be transformed. The ones that don’t transform won’t make it.

    • hhl

      what surprises me is that the hawaii utility themselves are not aggressively moving into solar/wind/storage and reducing the cost of power. If a residence can be cost competitive with the utility they are doing something very wrong.

      • eveee

        hhl – it’s only surprising if you think utilities are thinking of the good of all, not their narrow, entrenched, entitled self interest. The PUC and rate rules incentivize them to take advantage of rate basing, that is, amortize a lot of capital intensive central generation and encourage demand to pay it off. That is backfiring as consumers conserve. When demand sags, central generation gets mothballed and the system demands ratepayers pay for unused, stranded assets. This system needs reform or maybe it will just become obsolete as conservation and distributed renewables take over.

  • heinbloed
  • vensonata

    This comment section is so long now that I hope I am not wasting my typing fingers but here is one more clarification about the battery “without an inverter”; When you purchase a rooftop solar system it is complete, including an inverter. You calculate the cost per kwh by the total system installed cost and then a formual tells you the cost per kwh. So today you might get a system installed for $3 per watt peak production. This translates at 3% interest to something like 9cents kwh (depending on the solar resources of your area). The battery can be calculated independantly, at say 9cents kwh. Now you are basically independant. So how much are you paying for electricity? 50% at 9 cents kwh. 50% at 18cents kwh (night time use over the year is about 50%) So your overall rate is 13.5 cents kwh. Not bad. Already beats the grid in many places. But how realistic is this to run a house? Well houses in Vermont are averaging 6000 kwh per year, in Georgia 15,000kwh per year. You see? But lets say there many examples of modern thoughtful houses which use a total of 7000 kwh per year and they are all electric! So your yearly bill is: 7000x 13.5 cents = $945. Significantly less than average. You see it is the combination of efficiency and solar plus battery that makes it possible. Now is there some extraordinary savings involved for the average on grid person? No. But perhaps this merely being an “option” changes everything about your relationship to an anonymous utiltity bill arriving monthly.

    • Offgridman

      Just to let you know, you are not the only one coming back and following up on this.
      Also to add something about how this can change people’s relationship with the utility.
      15-20 years ago I remember reading a story about an older woman that got evicted from her home after deciding that increasing power bills would not fit in her budget so she had it turned off. As I recall she had made accommodations such as a propane refrigerator and stove and etc.
      Tried a quick search to find it, but a new story from February of last year turned up, which said that Florida homes are still required to have connections to electricity and water by law. In this case she had solar, but they were following up on the eviction because she had made free use of the city sewer system getting her water from collecting rain.
      Another story that I heard but have been unable to verify, is that in Texas even if you don’t get a meter installed you still get charged a minimum fee on the property taxes for maintenance of the wires that pass by your property.
      While they usually aren’t as strict about this type of thing in rural areas (part of my reason for retiring out here) some parts of the US are crazy enough (cities especially) that even if you should be able to provide for all of your electricity there will still be some sort of a payment required for the utility.
      Unfortunately we have allowed our utilities to become such large monopolies that they can influence regulatory matters like this in their own favor.
      While I am very much a peace loving left over hippy at times it is necessary to wonder if we will ever get the changes needed without a revolt against our corporate and political aristocracy.

      • vensonata

        Yes, I remember reading about that Florida case. It would make a good movie, a horror movie. Big Brother and all that. These attitudes are from another era when they were trying to keep people from throwing their excrement out the window into their neighbours yard. Understandable. But many, many bylaws are about to be revised, so many it will make our heads spin. My head is already spinning even though I try diligently to keep up.

        • Robert Haylar

          Earlier, Vensonata, you made some calculations, arriving at $0.12kwhr. Using average US tariffs and consumption, that is about right.

          Perhaps you also calculated the number of cells in the 10kWhr unit? Allowing for the vague specifications, you should have arrived at more or less 800 cells. And why is that?

          How to design a Powerwall.

          1) Start Here
          Keeping what has been developed for the car, makes economic sense. That suggests, that like the car, the battery should be 400V. Allow the nominal voltage of each cell to be 4.0V, A series string of 100 cells gives 4*100= 400V.

          2) Charging and discharging currents.
          Perusing the Panasonic 18650B data sheet reveals that cell losses rise substantially at high currents. Those losses lead to poor round-trip efficiency numbers – that’s not going to look good. The losses also give rise to heat, and shorter cell life.
          From the chart provided in the datasheet, a charge and discharge rate of around 0.2C mitigates the above undesirable characteristics.

          3) Output Power
          Calculate the number of parallel strings. 0.2C translates to

          about 0.625A charge/discharge current. Try 4 strings. The discharge current will then be 4*0.625A = 2.5A. Maximum power output is then
          Volts*Current =400V*2.5A = 1KW.

          4) Capacity
          The datasheet says 12.2Whr per cell.

          Number of cells = Series String* Parallel String
          = 100*4 = 400Cells
          Capacity = 400*12.2Whr = 4.88kWhr

          5) Cell Stack weight
          0.045Kg*400 18Kg

          So far:

          Voltage; 400V

          Power Output; 1kW
          Capacity; 4.8kWhr.
          Efficiency around 96%. ( Simply what the cell does at 0.2C)

          Weight of Stack; 18kg

          1KW power output is noticeably low. It would invite “can’t boil a kettle” remarks. How about 2kW? That’s sounds more respectable. “most won’t want more”. Go with that.

          To arrive at 2KW, double the number of strings. Resulting in around 800 cells. No too heavy. This porridge is just right.

          Ta da!
          Around 10WK/2kW. But, cycle life of NCA cells is poor,

          Market it for “occasional use”

          Go cap in hand to Panasonic. “What else d’ya have in 18650 size, Mister?” NMO lasts longer, but has lower capacity.
          Same size…volume production presently lower then the NCA. Material costs are lower, though. Doable.

          Do much the same calculation as above, and the results is 8KWr. NMO has a greater cycle life, but even then, charge and discharge current must be minimized if that is to be preserved. Hence, retain the 2KW output.

          All of the above is good for Tesla, but the customer gets the shaft.

          Power output unusually is low. Why is that important?

          You can’t use the stored energy, unless you can output it.
          The faster the better. The battery “saves” you money – the more you energy you cycle through it, the faster you get your money back.

          What if the battery took 3 days to charge? Useless. Throughput will be really low. The same applies to discharge rates, because you can only recharge what has been discharged. 2KW power output makes this battery one of the least useful on the market. All of the competition, who all have higher power output, better it.

          Cell manufacturers make cells in all shapes and sizes. Not for fun, but because no single cell design best fits all applications. Tesla are a one-horse outfit, who use the same cell for everything, whether it fits the application or not. That is how they appear to “thrash the competition” – but only you don’t look too closely at the real economic value of the Powerwall.

          Only Tesla use 18650 cells to make storage batteries, because in the real market place, don’t suit the application. Tesla use what suits them, and their Gigafactory ambitions.

          Perhaps Mr Shahan would kindly ask Telsa to deny any of the above. I will more than happily fend the ensuing BS.

          • eveee

            Why does it matter what the kw rating is in a grid tied application? What you want is energy in and energy out, and long cycle life. Even in off grid, more energy is needed than power. A typical solar application could be an 8 hour day in the summer. A 2kw rating could get 16kwhr. The battery is rated at 7kwhr. If anything, there is room to lower the power/energy ratio in that application.
            The only application that can possibly benefit from a higher power/energy ratio is peak shaving. But that can be aided by demand management, which is also a possibility with the PowerWall. And demand management is cheaper than batteries any day for peak shaving.

            How is 2kw going to limit a 7kwhr battery to a 3 day charge? That doesn’t add up.
            The numbers for how the pack is built seem about right except the cell voltage is too high. The number of cells in series is more likely 110, with V open circuit about 3.6V fully charged and resting.
            You make a great point of showing how its constructed, but fail to show how its unsuitable for its intended market. Maybe packs with more power and less cycle life are less suitable than the PowerWall. Then there is the not so little matter of cost.
            Who else is offering complete packs including DC, charge controller, BMS, and cabinet at $300/kwhr?
            Balqon offers 36kwhr for 18,350. But no warranty advertised. Its nice because its LiFePo. Thats a good, robust chemistry. That comes to $509/kwhr.

            Its more like a 0.5C equivalent with charge at 18kw. Scaled to PowerWalls 7kwhr, that comes to 3.5 kw, a bit more than the PowerWall, but not a lot, and the PowerWall peak rating is 3.3kw.
            And the Balgon unit is more expensive. And no DC-DC.
            So clearly the PowerWall delivers more for the money.
            FYI, the cell size has nothing to do with the C rating. So I don’t know what you are on about cell size about. For all I care, they are shaped like a football. Tesla doesn’t care either and has said as much. Don’t care about chemistry. Don’t care about package. Care about cost and performance. I can live with that.
            Go look at every one of A123s batteries with the same chemistry. Same with Winston. Its the same no matter what the size or shape as long as the chemistry is the same. You can have a 40A or a 20A or a 200A battery. Same C rating. Cell size won’t help the power/energy rating one bit.

    • eveee

      Here is your inverter.

      ” The pricing options consist of a nine-year lease plan at $5000, or the customers can buy the battery pack for $7,140 flat.

      Furthermore, the $5,000 lease plan include installation, electrical inverter, maintenance agreement, and a control system.”

      • Robert Haylar

        When you lease, you don’t own. Dependent upon where you live,

        any subsidies or rebates from using home storage, go to the owner.
        Make sure you find that out.

        • Robert Haylar

          Like Mr Shahan, I should declare my interests. I am a power electronics engineer, batteries too. But, in specialist fields that are not at all connected or in competition with any of the competing home storage manufacturers.
          However, I do have one vested interest. I dislike con-men other card sharps.
          It’s easy to make money if you are dishonest, and prey upon the weak. Hyperbole and marketing have pushed this ridiculous Powerwall, to the point that it will cost many who can’t afford it.

          Like I said, Tesla can respond.

          • eveee

            I don’t get the con men comment. What exactly is hidden in an announcement that shows the cost of a complete system, various vendor relationships, options for leasing or full purchase, etc?

            If you listened to the investor calls, you would hear Elon Musk saying its not economical for most users in the US. It took JB Straubel to point out, that it is economical for Germany and Australia. And it is economical for Hawaii.

            So if anything Musk understated. Most of the response dollar volume is for utilities.

            They profit at anything under $350/kwhr according to an ERCOT study and can replace gas turbines at a break even of $842/kwhr.


            And Musk stated a lot of people are buying them because they want them, or they want emergency back up, not on energy economics.

            I don’t see evidence to support the con-men comment.

          • Robert Haylar

            Because, for example, the 8kWhr/10kWhr capacity is a forced choice – a consequence of the characteristics of the employed cell.

            Because of the cell’s characteristics, to obtain a plausible, let alone useful power output, a large number of cells are required, resulting in a large capacity. It’s rather like the joke about a software bug being a ‘feature’

            Other manufacturers choose a cell that is appropriate to the task, because they need to compete. Telsa rely upon hyperbole. Do you have any idea of the worth of their patents, or do you simply assume that because of the patents, their battery must be something special?

            Some battery patents are ridiculous – a washer, a piece of wire etc. Even those that are not so trivial, offer no advantage over what is already in use.

            If may or may not be possible to profit from home energy storage – that is not the point, but the role that the battery plays in obtaining that profit. The Powerwall’s limited output makes that all but impossible.

            How do you calculate the return on the battery? You calculate the cost per kWhr by totaling the accumulated energy, and divide the result by the time you are willing to wait for a return.

            The result, the cost per kWhr, is therefore related to energy/time. Power = energy/time. A storage battery must also provide adequate power output, or it will not be an economical proposition.
            No matter what Straubel says of any country or system, there are batteries that will better the Powerwall given the same conditions. The large capacity is sucker bait.

            Comparing batteries using only the storage cost kWhr, is like comparing the cost and financial viability of an aircraft and a car, by comparing their volumes.

            There is no single “lowest Kwhr” cell cost, because cells can be high power, high energy, high discharge rate etc.Telsa have the lowest cost Kwhr, if and only if, you are interested in their cell alone. And only they are using that cell in any significant quantities.

            When Telsa’s cell price is compared with other cells suitable for home storage, they are not a bargain.
            Tesla are rolling the dice on their borrowed Panasonic cell, but that cell is dated technology, even now.
            They need to find some other means of disposing the huge planned cell production. Any means will do.

            “As Musk himself said, just because the economics of
            the battery don’t make perfect sense it “doesn’t mean people won’t buy it.”

            To paraphrase – “the battery makes no sense, but we are Tesla”

          • eveee

            It appears you have not responded to a single substantive issue I raised.

            1. 3 days to charge – math is wrong

            2. Grid tied solar doesn’t need more than 2kw .

            3. Studies show utility storage is profitable at over $350/kwhr.

            The numbers are against you.

            But your last comment is a lot of talk and no numbers. But even the talk can be deconstructed.

            More of the same unsupported mud slinging. What hyperbole? Specifically.

            “here are batteries that will better the Powerwall given the same conditions”

            Which battery, and which conditions?

            “When Telsa’s cell price is compared with other cells suitable for home storage, they are not a bargain.”

            Show us the numbers.

            I say you have sour grapes. Heres the evidence. You slung a lot of trash at Tesla saying they are con men and duping people into believing their batteries are economic.

            Then you quote Musk as saying,

            “As Musk himself said, just because the economics of
            the battery don’t make perfect sense it “doesn’t mean people won’t buy it.”

            That statement is taken out of context because it refers to many US residences that are connected to the grid in low electric rate areas and is true.

            But your use of that quote is a direct contradiction of your assertion that Musk is trying to hide the fact that Tesla batteries are not economic (in some areas).

            If he’s a con man, he really blew it right there.

        • eveee

          There are two price plans, 5k for 9 year lease, and 7140 for an outright buy. Choose.

  • Mike333

    I think we’ve just stumbled across the “problem” with average.

    The average city may see sub-second power outages, the more rural you go, with the more trees along your power line route, the “average” outage increases probably at the square of distance from the base station.

    Secondly, the older and smaller the “rural” community the less upgrades to the electric infrastructure are installed: Capitalism.

    ( And I’m just in the outer suburbs. )

    A backup battery system alone, without solar, I would need a 10 day backup for peace of mind. But with a solar roof, probably just a maximum of a 2 day backup. I don’t know the output on cloudy days though.

    • vensonata

      Mike, get a subscription to Home Power Magazine. All this stuff has been elegantly worked out by thousands off off gridders with decades of experience. It is easy as pie these days, comfortable as well.

    • RobS

      The problem isn’t averages it’s that your envisioning a scenario nobody in the know thinks this system is good at managing then thinking you’ve had a gotcha moment when you show the system isn’t good at handling it. Genuinely when was the last time you had an outage lasting longer than 6 hours? How many have you experienced in the last 10 years? Now tell me are you really willing to pay ~$30,000 to have 2+ days of backup? My guess is that storage would be used once every 2-3 years, whilst you are likely to have a 1-2 hour outage 3-4 times a year which you can render irrelevant with just a $3-5,000 investment. Battery backup is a very expensive way to completely protect against highly unlikely events, if you are going to do it at least size the system for dramatically reduced power demand so it keeps the fridge and a few energy efficient lights running and your phone and tablet charged.

      • neroden

        Answers to your questions, Rob, for me:
        — last year
        — 3 times in the last 10 years

        Grids in the rural areas often suck.

        • RobS

          So my guess was right on the money that it’s an approximately one in three year event. So the only question is whether avoiding the inconvenience once every three years is worth the additional $25,000 I’d be waiting for prices to come down a little more personally and I’d also be thinking that my fridge and LED lights use about 3kwh a day and my iPad about 0.05kwh so as long as I don’t run my desktop washer/dryer/dishwasher etc then I could stretch half the storage a Lon way be enacting deep efficiency measures temporarily during the outage.

        • eveee

          35kwhr/day? Yikes thats high. Average is 10kwhr or so, but varies with location. The hotter, the more. Some off grid places go as low as 5kwhr/day or lower. What is it, the air conditioning?

      • eveee

        Rob – Thats right. It depends on the application. Your scenario is emergency backup power for grid outages to avoid spoilage, wasted time, computer problems, or lost business opportunity.

    • neroden

      Correct, Mike. The more rural you get the more unreliable the grid is. Batteries for off-grid or simply for blackouts will be more popular the more rural the area.

    • NDPTAL85


      Strongly consider wind turbines instead. You can get 1700watt turbines on eBay for $500 a pop. (I strongly recommend Missouri Wind and Solar) That’s $5,000 for 17kW.

      You could either take what ever you were gonna spend on solar and spend it on wind (for a lot more energy generation) or cap your wind spending at $5k and build a massive battery bank.

  • labattfartoui

    I wish they would have included V2G integration with the powerwall. Besides that, this is pretty groundbreaking. First, because it’s now the only home battery company that anyone can name (besides nerds like us). Second, because power companies and their lackeys in government, like SRP in AZ, are playing tricks on solar users with demand charges, and we can expect to see more of this in red states across the country. In ten years even SRP grandfathered systems will be hit by demand charges, so there’s a huge market for battery backup right there.

    This is the disruption we’ve been waiting for in the solar world, and it’s kinda sexy, to boot. I want four of the 10kW units in my man cave.

  • MorinMoss

    Anyone with rooftop solar in Hawaii is going to want at least 1 pack, maybe 2.
    And would break even in 3 – 5 years, depending on install & inverter cost.

  • Jason hm

    That price is a throwdown if musk can deliver volume in a timly manner it’s going to change the groundwork of the entire industry. Just off the top of my head I would say Tesla pricing is more than 5 years ahead of anyone else, It’s going to put a lot start ups out of commission.

    • GCO

      Hmm, no. Companies selling LiFePO4 packs have been offering them at 300~400$/kW⋅h for some time already. I bought some Balqon/Winston at 1$/Ah last year, so ~330$/kW⋅h.
      The only thing new about this battery is that it wallmounts (assuming a strong enough wall), and there is a Tesla logo on it (so it generates ton of press, not all of it deserved IMHO).

      • vensonata

        Yes, the Balqon are in that range. I personally wrote to the Ceo and said “are you sure you want to sell them for that?” Balqon’s reputation is shaky, there is some definite loopiness going on there. However Winston batteries, which was also teetering on bankruptcy seems to have recovered and “may” be producing good quality 5000 cycle lifepo4 yttrium batteries now. Let us pray it is true. But man, the battery world is simply mysticism when you get down to it.

      • eveee

        Except that price does not include DC-DC. I just looked on their site and the 36kwhr is about 18k now. So its $500/kwhr on a comparative basis. The batteries are lower. But we are comparing whole packs in cabinets. I don’t think anybody compares right now. None that have advertised prices you can find by searching that I know of.

  • Michael Anderson

    Great artical. How about a comparison of the actual useable kWh’s of the competiting systems? It’s important for us to understand how much usable power these battery systems and how the discharge cycles impact the lifespan of the units.

  • Jane Martin

    Thanks Elon Musk, thanks.

  • Burnerjack

    So at the end of it all, my only question is this: If I buy everything outright (not so big on PPA’s), what would be a realistic breakeven time period? When I think green, I think of the folding kind first.

    • vensonata

      Depends on grid rate. The math is a little jelly like. Hawaii, Germany, much of Europe, New England perhaps, maybe California… make dollar sense.

      • Burnerjack

        Yeah, definitely “fuzzy math” is involved, what with changing rates (spelled ‘rising’ I’m sure) and falling solar prices. When I try to put realistic numbers to it the break even period always seems to be way out, like 15- 20 yrs. To compound the fuzziness, one reader posted what would happen if you invested that purchase price in the stock market. I don’t remember the outcome exactly, but I do remember his post going by the historic averages of market return compounded annually. According to that post, the market investing scenario was a much greater financial benefit. Of course when siting the stock market, “past is not prologue. Fuzzy indeed.

        • vensonata

          Yes, invest in solar or the stock market or savings account? That is often the economists thinking. The thing is, if you put the money in a savings account hoping for compound interest don’t forget, that interest is required to pay your utility bill. So the interest does not compound, it is withdrawn every month and your principal just sits there being eaten away by inflation and, guess what…rising utility rates!
          The stock market: you must go long and you must know what you are doing, then yes maybe a better investment than solar. But it is always, always, always a gamble. If you want a reliable, peace of mind investment which provides you with necessities of life, go solar.

          • Burnerjack

            All true. As far as the stock market vs. solar goes, the axiom “A bird in hand…” comes to mind. Still a struggle though…

    • Larmion

      1) Do you live in an area with an extremely large gap between peak and off-peak electricity rates? Think 30 cents and more per kWh.

      No: continue to (2)
      Yes: batteries might make sense. Check with a local installer to see what price they charge.

      2) Do you have solar panels (or a small wind turbine)?

      No: batteries don’t make sense for you.
      Yes: continue to (3)

      3) Can you feed any excess generation back into the grid at a reasonable rate where you live (net metering, value of solar tariff, feed in tariff or a similar arrangement)?

      No: batteries might make sense. Check with a local installer.
      Yes: batteries won’t pay for themselves at current cost.

      • Joseph Dubeau

        very good.

      • eveee

        Larmion – You might add,
        are power outages frequent, or cause damage. Does the cost of spoilage or damage exceeds X, based on payback calculation plus storm damage?
        Yes: Batteries might make sense for you. A calculation must be performed to assess payback.
        No: batteries don’t make economic payback for you.

  • vensonata

    I have recalculated kwh for the 7 kwh battery. I believe now that it is the 10 kwh battery only discharging to 70%. If it is good quality lithium ferrous phosphate (lifepo4) it will get a full 5000 cycles at 100% depth (really 70%) That mean 5000×7=35000kwh at least . Multiply by 92% round trip efficency and you get 32,200 kwh. Cost $3000. Price per kwh is therefore about 9cents. I had previously calculated 13.7 because of inadequate info on the chemistry and structure. 9 cents kwh blows away every other battery available to the home today. In combination with PV at $3 watt installed it would be 17cents kwh for stored electricity and daytime solar would be 8cents. So a house producing most or all of its electricity from PV plus Tesla storage would have an average kwh price of about 12 cents kwh. That beats the grid in many places. Until we get exact cycle figures from Tesla we can only make these educated guesses.

    • GCO

      LiFePO4 is less energy-dense than most other Li chemistries, so I doubt that’s what Tesla is using here.

      Cost figures which don’t including charge controller, inverter etc are somewhat pointless; the battery isn’t usable without those external components. Installation will be another significant expense.

      Call me cynical, but I can’t help but think that Tesla omitted all this from its announcement on purpose, to attract more attention by making the system look much cheaper than it’ll end up being.
      Just like its “price after rebates and gas savings” (the way Tesla thinks it’s adequate to shows its car prices minus 17~23k$)…

      • vensonata

        Virtually all batteries are sold without inverters. What if you decide to use straight DC? Many RV’s and Yachts and cabins don’t invert. They use DC appliances. Again I can’t say about the charge controller…I have given an example of a lifepo4 solar BMS which absolutely dispenses with a preceding charge controller. The BMS is the charge controller! See Electrodacus on youtube for full explanation and availability. lifepo4 is the standard chemistry for stationary batteries, it has no heat issues and can have cycling up to 10,000 times as in the Sony battery. Elon said the chemistry in the stationary battery is different than the car so Panasonic would easily provide a high quality lifepo4 to be packaged by Tesla at their Fremont factory until they get into the gigafactory. Again, I have all the “other stuff” already, as do most off grid places, who would be particularly interested in this battery.

        • eveee

          vensonata – Yes. I heard Elon say in the video that it comes with a DC-DC converter ready for solar. Is that the 10k or 7k? Anyway, that would be the conversion from solar to battery voltage. Thats significant.
          I agree that the inverter may need to be more customized to the application and local use.

      • eveee

        Tesla would need to be in the inverter business to offer battery plus inverter. It would be great it they would partner with inverter companies or buy one to provide a complete package. Needs to be turnkey just like solar city, not standalone. My guess is, Elon just did not want to wait.

  • Doug Cutler

    Yah, the byline is a kicker, alright. People should click the link.

  • BigWu

    A couple of technical questions unanswered by the Powerwall website:

    1) There are two options: 10 kWh “weekly cycle” and a 7 kWh “daily cycle” yet there’s only one product weight listed. This implies that the packs contain the same number of batteries and, presumably, the 7 kWh daily cycle version is software limited to charge-discharge between 15-85% to maintain longevity. Is this the case? If so, why the price difference?

    2) a single pack is rated for 2 kW continuous power. If PV connected and the grid is offline, is the home’s total power draw limited to 2 kW or to the PV output + 2 kW? The latter would allow full air conditioning load and/or EV charging.

    ROI notes:
    In addition to saved food and peaceful powered enjoyment during a grid outage, there is the ability to work from home (and bill time) during a grid outage. If that’s a viable option (it is for me), this alone could pay for the unit with just a few outages over the ten year lifespan.

    • GCO

      Re 1) Might be marketing (people expect to get more if they pay more), or Tesla anticipates more wear and abuse, and therefore warranty claims, with the 10 kW⋅h option, and prices it accordingly.

      2) It’s entirely dependent on the rest of the system, which isn’t included with the battery.

      Re keeping food refrigerated and/or working from home during a rare but prolonged outage: I absolutely see the value of solar, not so much batteries.
      A properly insulated and relatively full fridge should stay cool enough overnight anyway, and a modern laptop would also provide hours of runtime after dark (plus, it could also be charged from the car).

    • eveee

      Yes. Thats a pretty good observation. Thats what one would expect. The same happens with hybrids like the Volt. It has almost a 20 kwhr battery pack, almost as much as a Leaf. Yet the battery only range is only a little over half as much as the Leaf. Thats because they must limit the charge/discharge to a fraction of total capacity to accommodate a very high number of charge/discharge cycles.

  • Jason hm

    So that pack must be filled with like 900 panosonic 18650’s for $3,500 jeeze people are going to crack em open just for the batteries. You cant buy high quility 18650’s for $4 not even at wholesale.

  • vensonata

    To summarize in brief: who will buy these batteries. RV, yachts, cabins, off grid, security minded with a bit of cash, tinkerers. That happens to be about 10 million customers in the U.S. Now the larger formats. Walmart, Ikea, Costco, home depot, etc etc. For peak shaving, back up. Now you are actually talking more profit than Tesla car sales, because of the simplicity of manufacturing and shipping. Just the light weight kills lead acid competitors through shipping costs. Get your money out of Lead acid batteries and lead mines soon! That market is going the way of the Dodo.

    • vensonata

      And one other factor to ponder. PV is cheap these days. Still half the price perhaps of Battery power. That means it is better to overkill the PV and be modest with storage. This is the opposite of a few years back when PV was gold. If you are off grid two days storage and 8 kw of PV is better than 5 days storage and 3kw pv. Your generator use, if any, should be less than 40 hours per year. These are just rules of thumb but it is an entirely different formula than was appropriate even a few years back.

      • Interesting. Something that hadn’t even crossed my mind.

      • BtotheT

        I’d do 3 days storage minimum personally due to the recent cloud pattern spurts(though it depends how close you are to a body of water) but couldn’t agree more otherwise. I’d probly throw a 1kWh Bergey Excel in there to supplement/diversify as well.

        • vensonata

          Yes, it needs somebody good with math to calculate the ratio of PV to Battery. The bigger the pv the more it produces on those heavy cloudy days and its price per kwh is dropping all the time. But now batteries are catching up. My new estimate of the Tesla 7kwh battery is 9cents kwh. PV at $3 watt installed (including inverter) works out at about 8-9cents if you factor in 3% lending rate not the 7.5% that is often part of the calculation. So now get out your super computer and tell me just the right balance for the micro climate one is in. All this would be very handy and I find it incredible that it is not instantly available in a 100 places on google, but no, just us amateurs using pencils and napkins.

          • neroden

            If you have the roof space, put in as much solar as possible and size the batteries strictly for nighttime use.

  • Jenny Sommer

    I am a bit disappointed expectations where that the storage would be part of solarcity installations, yet cheaper but instead catering to offgriders it would feature advanced swarm battery management software ultimately making it into a GW scale grid battery.
    Are there any plans?

  • mikgigs

    well, there is no inverter, which makes it little bit frustrating for use

    • eveee

      Yes there is an inverter. It’s offered by solar city as a package with power wall as 5k 9 year lease or as a buy.

  • anderlan

    Hawaii has 30 cent electricity. Tesla’s battery price is very competitive and if they sell them in HI they will sell plenty. They totally answer HECo’s issues cited when they refuse to hook up more solar.

    • Yeah. The Hawaiin utilities looking to block solar, cut compensation, etc., are now screwed. And there are plenty of other places where this is the case. And this is just the beginning.

      Curious to see how the Hawaii market responds in the coming year or two.

    • Bob_Wallace

      The situation in Hawaii may change fairly quickly. With plans to install a lot of renewables Hawaii should start cutting back on expensive imported oil.

    • GCO

      Hmm, this will depend on the price of the rest of the system: PV (and/or wind), charge controller, inverter, and installation (incl permitting etc).
      Hardware for standard 48V systems already isn’t cheap, but at least it’s readily available from many vendors and installers know how to handle those; not so Tesla’s one-of-a-kind 350~450V Li-ion pack.

      I doubt that the cost per kW⋅h will be very interesting after you include everything, even compared to today’s 30c from the grid.

      • eveee

        Its not intended for 48V use. Its intended for inverter use. With an inverter, it comes out to about $5500. The economic details get tricky. How much is needed for how many days? Grid tied or off grid?

        At 30c/kwhr, a 7000kwhr/year home becomes $2100/year in bills and rising with inflation. If one considers the utility bill rises with inflation and if that rate matches interest, you can add up the some of utility bills at present value for an equivalent. Interest is a bit more than inflation, usually, but not much.

        If so, we can compare approximately with the first cost just by summing the utility bill. The error is just the difference between inflation and interest.

        At $4/w solar installed, a 3kw system is 12k. If the storage and inverter are $5500, the total system is $17,500. In ten years the utility bill comes out to $21.000. So if the system lasts that long and meets the needs, it could break even in 10 years or less and be economical.

        By those numbers, Solar plus Storage is right at the place where early adoption turns to rapid adoption and market turnover to a new technology.

        So it does look interesting compared to todays grid in Hawaii.

        The storage is not the big difference. Its the cost of solar. That could be improved by BOS. In Australia its only $2/watt, with similar utility rates. Solar is taking off there. Its taking off in Hawaii already.

        The case with storage is how much value does it add.

        If you can really go off grid with 10kwhr and a 3kw solar system, the utility is in for a some real competition.

        Somebody else has concluded it come out to 30c/kwhr, and he’s not a solar fan.

        Of course, he’s sour because its cheaper not to go off grid in Texas.

        • GCO

          If you can really go off grid with 10kwhr and a 3kw solar system

          then you’re certainly not using 7 MW⋅h/year.

          My family uses barely more, we get about as much sun as Hawaii [link], yet we’d need 15+ kW of PV to go through December/January.

          Residential solar is a no-brainer these days in many places. Adding storage though is unlikely to be economical, and certainly isn’t environmentally-friendly, so I don’t see much value today except maybe when configured as whole-house UPS in areas with very frequent outages.

          • eveee

            You see what veneonsta and others do. They have a gas generator and solar plus battery. It’s best not to rely on only one source. It makes it expensive.

  • I love that this convo turned into some useful energy efficiency information sharing. 😀

    Also news to me, btw, but I don’t know much at all about dryers.

    • Will E

      Siemens -Bosch cool freeze, induction cooking, wash dry.
      all 5 star energy saving. super important. real cleantechnica.
      Its the combination that makes the profit.
      and about the energy wall, its the idea that every house will have a energy wall along with solar PV
      and connected to the grid by software.
      cooperation Tesla-Lichtblick Hamburg, Germany.
      all energy walls will unite to one big storage wall.
      exelent idea, thats why I like Tesla so much.

      • Agreed. We got essentially the most efficient appliances on the market for our place — stove, fridge, dishwasher, washing machine. But we decided not to get a dryer, keep line drying, so I don’t really know anything about them.

        • Will E

          Ok, In short, its heatpump technic. really super cleantechnica.
          and want to show people that you can keep all comfort in a fossil free house with zero energy bill.

  • Note: I updated the article to include a response from Vensonata about the offering.

  • Poirot’s Shadow

    It doesn’t really matter what the energy input source of the PowerWall system is. The most important consideration of the PowerWall is that, in volume, it can make the grid more efficient, reducing the requirement for expensive reserve power-plant capacity that might be employed for a couple hours, or in certain cases minutes, a day. I don’t know if this constitutes grounds for Musk’s rather sanguine estimates that ‘2 billion power-packs (the rack-size units) is not an impossible number.’

    Some sort of a data feed, that allows owners/operators to automatically dispatch power if the wholesale KWH price reaches a set point fixed price is the next logical step. The ideal market for this technology is somewhere like the Caribbean, with very expensive grid rates, $.30kWh running expensive diesel generators.

    Does this solution work in countries with reliable cheap grips? What does the cell degradation curve look like? How does this translate into 10 years, with a 10 year extension? Is the efficiency rating of 92% of the inverter for AC-DC only, is it the same in the reverse direction—if so, then is actually 84% efficient on converting energy from & back to the grid. Don’t get me wrong, it’s a great piece of evolution UPS tech, but Tesla need to disclose more data about it, if an acquisition is going to be made on a purely calculated rational basis.

  • darth

    Anyone know if these are programmed to reduce demand charges? In VA solar PV is limited to 10Kw. Over 10Kw you have to pay a demand charge, like a commercial property. This effectively removes all incentives to install > 10kw systems. If the battery can reduce peak demand, that would add significantly to its value and make larger solar arrays economical here.


    “and superb communication skills… [a thing] that Elon and Tesla seem to excel at.”

    That’s pretty much the only thing I would disagree with. I find Musk to be an absolutely terrible public speaker. He just sort of stutters and stumbles though presentations. If he worked on improving that even a little bit, I think it would help product release (or any type of) presentations a lot.

    • Bob_Wallace

      Elon has a certain boyish nature and informality that I think adds to his appeal and credibility. He doesn’t come off as someone who has polished their sales pitches in order to push product on the rubes.

      • Exactly. People freakin’ love that.

        • Philip W

          I like it, too.
          His stuttering sometimes makes it hard to follow for me and then it can get annoying, but that’s just the way he is.

          (still easier to understand than some korean CEO *cough*Samsung*cough*)

          • I love the stuttering, but stuttering aside, he’s much more enjoyable to listen to because he talks to you like a friend, not like he’s a salesman. Some may call it “polished” what most CEOs have, but I think it’s safe to say that, in the day and era, people want to be talked to in a very down-to-earth way, and don’t so greatly value polished, manicured, corporate speak — in fact, I think that is a big turnoff for the average person. Perhaps greatly valued by some of those who have been trained in it, but not the masses.

          • Philip W

            Yeah I wouldn’t have it any other way.
            When he talks I don’t see a salesman, I see an engineer.

          • Yeah.

    • RobS

      I agree that by traditional measures he is an abysmal public speaker but I actually think that in some ways it is endearing, it makes this billionaire tech genius who could easily come across as arrogant, out of touch and pompous seem remarkably grounded, ordinary and human. he doesn’t come across as a car salesman with a slick pitch, but a passionate and refreshingly human whiz kid who’s letting you in on what hes been inventing in his basement

      • Exactly. I’ve been planning to write an article about this for a long time, just never get to it.

  • harisA

    For someone who has gone solar, I see no reason for residential storage system at all. Maybe when solar penetration is above 25-20% than it may make technical sense.

    • Bob_Wallace

      It depends on how much you pay for electricity and how much credit the utility gives you for what you send to them.

      There are places where residential storage makes sense. Australia is a clear example.

      Storage makes sense for some businesses because their rate is based not just on amount consumed but their highest peak use. By storing some lower cost power that they can use to service their peaks they can lower their overall rate.

      • harisA

        I forgot to mention that my experience is in San Diego and SDG&E is indeed a huge battery:-)

        Our Solar penetration rate is at 3% of total power and we do not have time of use residential pricing.

        In third world countries, where power is gone 50% of the time this is a perfect product.

        • dgaetano

          Currently SDG&E net metering caps at 5% customer penetration. So probably in a year or two. Also time of use pricing is coming to California in the next couple years.

          It’s great that you’re net metered (I say that honestly, not sarcastically), but by 2020 that’s probably going to be the exception not the rule.

  • Larmion

    You’re welcome, but that is a very expensive model :O

    I bought a top of the line Siemens for about $1000 and that’s including 21% sales tax. It even automatically cleans it secondary lint trap, unlike this one. Are they always that expensive in the States?

    But they are great. Apart from the electricity saving, they also deposit their heat in the form of hot water rather than venting it straight outside. In the winter, you can recycle that heat by simply allowing the water reservoir to cool before emptying.

    • Mike333

      US business practice is to price out these models for the average consumer, until forced to sell by government regulation.

      Some fucking MBA thinks it’s more profitable to soak anyone green, then to fix the planet.

      • GCO

        The blame falls squarely on that “average American consumer”, who doesn’t look beyond upfront / purchase price.
        This turn anything but cheap inefficient appliances into specialty low-volume items, further exacerbating the price difference with higher-quality products.

        No miracle here, you get what you pay for. Well-designed, long-lasting, energy-efficient appliances command a premium, but it’s absolutely worth it in the long run in my experience.

        (That said, my dryer is still an old “dumb” model. I almost never use it, as most of the year, anything I hang outside is bone-dry only hours later. And smells fresh.)

  • Philip W

    So the upgrade from 7 to 10kwh is 500$ which translates to ~167$ per kwh. Can we assume that Tesla is close to producing batterys at that price? That would be amazing.

    • Bob_Wallace

      Apparently Tesla was paying Panasonic $180/kWh last October.

    • dgaetano

      This is just a guess on my part, but I suspect the they’re both 10kWh units. The daily use one is only letting you go to 70% Depth of Discharge. 10 years of daily cycling at 70% DoD is doable for lithium batteries. (also note that the power output of both boxes is the same)

      If this is the case then they’ve simplified it for the masses, called the one pack a 7kWh pack and lowered the price a little (people expect to pay less for a smaller number). That also means it’s $300/kWh.

      If you cycle the 7kWh unit every day for 10 years you’re paying $0.12 per kWh of storage, which is really impressive.

      • Joe Viocoe

        Good point. With stationary, weight isn’t important, so no need to take away cells if you’re trying to provide more cycles.

      • vensonata

        Dgaetano, you are brilliant! Those are very good explanations for what is going on. You get an A plus! You have run the numbers too for the price per kwh. You get 12cents kwh. I will raise that to 13.7 cents because of the 92% efficiency factor. But that price, 13.7cents, beats all lead acid batteries, (the best price being for “forklift” industrial at about 14 cents kwh). They also require shipping and inverters.
        The only other battery that needs to be compared with Tesla is the Sonnenbatterie from Germany. The inverter is built in. And the Sony “olivine” battery they use has 10,000 cycles to 100% depth of discharge. (I know, it sounds incredible) also a 20 year warranty. We do not have a price for that battery, though they now have an office in California. You do the math for that one!

        • vensonata

          I have now recalculated price per kwh. 9cents kwh! The 7 kw is 70% DOD, which on quality lifepo4 will have 5000 full cycles and more.

          • dgaetano

            Wow. And this is as expensive as these batteries are ever going to be, imagine how cheap they’ll be a dozen years from now when you replace the first one.

            All sorts of crazyness is supposed to happen with California rates in the next couple years. I’m waiting to see how that goes while I overhaul my house power usage (changing gas appliances to electric) and eventually install battery backed solar. Exciting times 🙂

      • Admiral Reality

        “If you cycle the 7kWh unit every day for 10 years you’re paying $0.12 per kWh of storage, which is really impressive.”

        Makes sense. That’s about how much I had calculated.

        I guess I’m lucky to live near hydroelectric plants which generate a cheap $0.07/kWh off-peak and $0.14 peak. This battery won’t make sense for me until it’s at least half the current price (or until I install solar panels, whichever comes first).

        I absolutely love the idea however and having this thing become a house-wide UPS during blackouts is enticing… but even that last scenario is rare. I get one or two blackouts a year and they last usually less than an hour… and they often happen when I’m not even home or at night… also my alarm clock is my smartphone so there’s not a time where I can blame the alarm getting reset because of an outage.

        I hope this product does well. I want the price to come down. Electricity in Ottawa or Montreal region is not an area where you can save a whole lot of money.

        • Right, a place like yours with $0.07/kWh off-peak and $0.14 peak from hydro is probably one of the last places this will make sense… beyond the user benefits that are not financial.

      • GCO

        Remember that this price is for the battery only. Depending on the exact application, one would need to add charger, inverter and installation, which would easily more than double the total cost.

        Still a good deal compared to e.g. lead-acid for off-grid or backup purposes, but not so much to save on utility bills…

  • ADW

    One item I am not seeing in the comments is in New England many people are installing Nat Gas fired back up generators as the cost is now around $6 – 9,000 depending on the size and how much of your home you want to power. For me I have two small Honda gas units I chain together to run 6 circuits.

    I need to do some math, but I expect I could replace the gas fired generators with this and have 2-3 days back up power for my six circuit sub-panel.

    It would always be there and ready when I am not home, I no longer need to have extra gas tanks on hands, no longer need to risk them not working because the injectors are clogged and gunk.


    • Joe Viocoe

      New England is indeed better positioned for gas as a backup. Perhaps bloom boxes could be used too.

      Folks need to understand that NOT every geographic location has the same economics. Sunnier places will have the advantage, as will places with more expensive electric utilities or less natural gas resources.

      Tesla should not wait until 100% of Americans can benefit, the market is large enough at this point

    • NDPTAL85

      New England has lots of wind. You can get 1700watt wind turbines on eBay for $500 a pop. Thats 17kW for $5000.

      Something to consider.

  • vensonata

    What a pleasant surprise at last nights battery announcement. The price is far better than I had hoped. I will be ordering 1 or 2 of these as I do not foresee much significant decline in prices for the next few years. I am already off grid and so these are the perfect batteries for solar. They “hover” without damage, unlike lead acid, which I have used for 15 years.
    Who will the market be? RV’s, Sail boats, including yachts, cabins, off grid houses, off grid resorts (there are many) off grid ranches. Next, the well off who like a back up and who have PV. And of course suddenly PV makes more sense as a back up. Just that market is huge. As for “grid defection” not likely…for a while! But the stakes in that game just got higher, with little drops of sweat starting to appear on receding hairlines of grid execs.

    • Thanks for the info. 😀

      Yes, it’s something people aren’t talking about much, but I’ve been thinking about it: This sort of thing will make utility execs think twice before pushing for rooftop solar fees, removal of net metering, or PV penetration limits.

  • Matt

    I still think that the stationary battery market will develop as follows:
    – Corp/industry to shave peak charges. Think TESLA use at charging stations. I know that a amusement park in Ohio (not open in winter) but they pay a fee all year based on they highest 15 min use in summer. Or did when I did a tour there years ago.
    – Utilities, to cut use of their peak plants and freq/phase regulation
    – RE generators to prevent curtailment and move when they sell
    – Hospital campus (or other that must stay up) and want smooth power. Yes even in US power is not clean every where. Mixed with local RE you can micro grid and be stable.

    As for homes:
    – For grid connect (in US) most would buy these as insurance. So if grid goes down they can run at reduced power usage from their PV. Not expecting pay back.
    – The less stable your grid, or if you have PV and no net meter.
    – I think that electric pricing to homes (even TOD pricing) is not yet staged to prove a way to justify these system on cost savings alone. At least in US.

  • Kyle Field

    With EVs, this has to change…or get smarter…or something. Average EVs have a 24kwh pack, MB B-Class is ~40kwh and Teslas are 60/70/85kwh so if those owners are putting more miles on their cars and charging at night, they are going to have more solar on the roof and I would think need a larger wall pack. I get that ideal state means they charge during the day but the simple fact is that most people who have cars (at least in the US) have them to drive to work (during the day). I’m not sure how this integrates or makes sense with the new product line.

    • Steven F

      Assuming they are driving to and fom work 8 hours and 2 hours driving they will not fully dischaarge a testla battery on a typical day. You would need to 3 hours of driving plus 8hours of work to fully discharge the tesla battery in one day, That is a 13 hour day. Very few people would do this on a regular basis.

      The solar could charge up the wall battery during the day and then that power would be used to charge the car at night. Yes it would problably require a larger solar array. but if you can afford a Testla you likely have enough space on your home for a larger solar array.

      • John

        Can they not offer a powerwall with a detachable battery pack for the EV. Plug in the battery, drive the car to work, go home, swap batteries and repeat….

        • Bob_Wallace

          Batteries are really heavy.

          Your idea might work sometime in the future if Wh/kg keeps improving.

          • John

            The battery in the tesla isn’t that heavy. They did a presentation where a guy swapped out the battery on stage, no big deal. It doesn’t have to be the full size of the powerwall, just a detachable piece

          • Bob_Wallace

            1200 lb/544 kg for the 85 kWh pack.

            “Some guy” didn’t just swap out a battery pack on stage. (Did you watch the swap?) Some guy didn’t just snatch out the battery and walk it offstage.

          • Bob_Wallace

            Here. Watch the video….


          • John

            Fair enough, you need a machine to do the swap, I thought the guy on the other side of the car was doing it, but that’s the camera man. Thanks for immediately going to aggressive and condescending though, there isn’t enough of that on forums.

          • Bob_Wallace

            Er, “immeidately”.

            I’d say that after I told you that the batteries were very heavy and you tried to tell me that they weren’t I gave you some data and got a bit sarcastic.

            You haven’t had the opportunity to enjoy my “aggressive and condescending”. ;o)

            BTW, I thought I had posted a video of the onstage batter swap taken from an “looking under the car” angle. I’m not seeing it now. I’ll try with this commment.


  • Mike333

    Unless I’m reading my utility bill wrong, the 15kWh pack is just 12 hours of electricity for my house. I thought they’d be selling a 300kWh pack, which would have been a 10 DAY backup.

    What happened?

    • Larmion

      Reality happened.

      But why would one want a 10 day backup? A 15kWh (or even 10kWh) pack is plenty to get you through a minor blackout or through an overcast day. It’s also plenty for arbitrage. In other words, it does what is promised.

      It might not be enough for full offgrid living, but then again nobody who cares that much about the environment would use 11000kWh a year.

      • bink

        there is no abritrage high enough to pay that off in a reasonable time period

        • Larmion

          Correct. As I said above, I neither believe there is an environmental or financial case for home battery storage for most people.

          In a debate, however, it’s common courtesy to stick to the initial premise, which was that a 15kWh battery pack is too small. That’s not true, at least not for the purposes the pack is advertised for.

      • Mike333

        My worst case winter storm in Pennsylvania was an 8 day outage. Typical winter outage in the last 10 years is probably just 1 day.

        • Larmion

          It rarely makes sense to dimension a system based on a black swan event like an 8 day outage. You would pay several times more for capacity that will only see use once in a decade.

          As you say, a typical outage lasts a day or even less. That can easily be bridged with a 15kWh pack if weather isn’t too extreme.

          • Mike333

            Well yes, during a neighborhood outage you aren’t usually doing laundry, running the dryer.

        • eveee

          You need more heat than light for an 8 day outage in a Pennsylvania winter. But your refrigeration needs shouldn’t be that bad. 🙂

        • Ronald Brakels

          Mike, a generator can see you through periods of prolonged grid outages. Or here in Australia, thanks to the low cost of rooftop solar, we now have the option of doing without generators for off grid installations and simply installing enough solar panels to see us through periods of bad weather. Generators are now optional extras.

          • Mike333

            Yes, I was forced to buy a gas generator, it’s no picnic.
            It uses about 20 gallons a day, that mean running to a gas station every day. And it stinks, and is loud, like a diesel is parked outside your house. Very hard to sleep.

            But, it does keep the heat on, and so the pipes don’t freeze and crack.

          • eveee

            I just looked at the SolarCity site and saw the same things you just said. Its real. The noise, smell and refueling are less than ideal with the gas backup. This is why I think long term storage for heat, not electricity, is a major potential market in areas with winters like Germany or Pennsylvania.

        • Mike333

          I made the mistake of thinking ONLY of battery backup. But with solar on the roof the size of the battery can be greatly diminished.

      • Rita

        For me it is 5500 kWh per year, heat included, with no back up at all. !0 kw system would be enough for 2 days if I turn the heat off in winter.


      • Mike333

        You’re right, I’d only need a 10 day backup if I don’t have any solar. With the right size solar, I probably only need a 2 or 3 day backup max.

        • eveee

          If you increase efficiency, you need less storage, less solar. Its worth it. Its usually your cheapest dollar.

    • Kyle Field

      average US home usage is 11kwh/day…

      • Mike333

        I’ve got electric range, hot water heater and electric dryer. The average homeowner in the US is probably hooked up to natural gas.

        • Mike333

          Also a wife and 2 teenagers. What’s the average home have, in people?

        • Kyle Field

          those take you to triple the national average per day? I have an electric dryer and our 4 person house uses less than 8kwh/day even with that.

        • Mike333

          And I don’ve have an EV yet.

        • Larmion

          Wouldn’t reducing energy use (i.e. an efficient condensing heat pump dryer) make more sense than a bigger battery pack here?

          Until a few years ago, I lived with my parents in a large home with 4 people – as you do. We use 2700kWh a year, with an electric range (but no electric hot water heating).

    • vensonata

      All the packs are linkable. You can have as much as you want. The next size up is 100 kwh which would be about right for an off grid resort or hotel with 35 guests. Remember Lithium discharges to 80% or more so you get by with a smaller bank than lead acid at 50% discharge.
      But let me give you a real example. We run a 10,000 sq ft house off grid with an average occupancy of between 12 – 24 people. We have an 11.4 kw pv array and a 40kwh AGM maintenance free lead acid battery bank. That battery never discharges below 50% meaning slightly less than 20 kwh are available. We are at latitude 51 in Canada with cloudy winters. And yet only between November 21 and January 21 do we run a generator to charge the battery bank. The total hours of run time last year was 40. At 2.5 liters per hour of diesel about $100 for the year. Now if I had even two Tesla packs at 10 kw each that would give me 16kwh, very close to what I need. In fact because of the superior efficiency and the ability of lithium to “hover” at less than a full recharge (lead acid should be fully recharged each time, or accelerated degradation takes place) it would probably do me for the next ten years. At $3500 a piece it would mean $2 a day for battery storage. Not enough for a starbucks latte. And split that cost between 15 people and you have about 14 cents per person per day

      Now I should say we have all the conveniences, including 4 computers, l.e.d. lighting, 300 ft well pump, in house pressure pump, electric boilers, microwave, induction electric cooking, etc. What we do not have is electric air con, or heat. However there is enough overproduction through summer that air con and indeed electric water heating and even electric vehicle could easily be run. So that is an introduction to what can be done off grid with batteries.

      • eveee

        Interesting. The mystery of it goes away when you realize that you are using a mix of solar, storage, efficiency and backup generator. Keeps your fuel use down. If you could do fermentation and make ethanol, it would depend on how much waste you had, that would be another. Its remarkable how similar that is to large grid studies for renewables. And you notice how solar matches air conditioning loads, too.

      • So here’s my Q: If you needed to replace your batteries this summer (or were just starting this lifestyle), would you get a couple of Tesla batteries or something else on the market?

        • Bob_Wallace

          I’d wait and see. I’m not an early adopter. I prefer to see how products actually perform before I buy in.

          That said, last summer I payed $2k for 16.2 kWh of lead acid batteries. My original thought was to hold them to 80% or better (use only the top 20% max) in order to make them last 4,000 cycles. That means I have only 3.2 kWh of usable storage.

          Now I’m thinking I’ll take them down to 50% in the winter and shorten their cycle life to, perhaps, 2,000 cycles. (In the summer there’s never the need to go below 80%, there’s always good sunshine the next day.)

          That would let me skate through an extra day or two of limited sunshine and reduce my generator use. Five years from now I expect to be able to get some very much better batteries for under $3k, perhaps under $2k.

          Hopefully this year I mount another kW or two of panels. I now have 1.2 kW. That and better storage should pretty much eliminate my generator use which has been running about 300 hours per year.

          • Which company are you going with for the panels?

          • Bob_Wallace

            No idea at this point. I’m going to start by seeing what sort of deal local installers will give me and what they are using. I have somewhat of a unique situation since this is a non-permit installation and I just want someone to wire the panels down to a second floor deck level. I’ll take it on to the inverter. I want to rework my existing ground mount panels, turn one half east and one half west to get a longer solar day.

            If the installers don’t give me a good price then I’ll have to start digging into panel price and quality. And look at size/weight. I’m going to have to build scaffolding to get onto the roof and will probably have to wrestle them into place by myself.

          • vensonata

            Bob, you can also just hand rotate a ground mount pole array, it take 5 seconds in the morning and afternoon. I did that for 8 years. In the summer you will get 50% more juice. Now I don’t need to because of vast over production. The roof mount is definitely easier with scaffolding (just did it in November on metal standing seam roof with s clips). Ladders are not good. Make sure if you use s clips you make a jig to get precise mounting placement before you add the panels. Rent the scaffold man, building is too much trouble. And don’t fall off the roof, we need you healthy!

          • Bob_Wallace

            I built on a rock ridge. It would take a serious machine to dig a hole and I’d have to tear up a lot of fence and landscaping to get to the spot.
            It’s also a place that gets some very strong wind. (We set most of the roof rafters, braced them as one normally would, and had them blow off that night. Some of the 20′ 2 x 6s ended up 100 yards from the house. I had to Tyvek/Barricade the house three times. The first two times the wind stripped it off the first night after installation. Third time we used wood strips to hold it down until time to install siding

            I’ll contact you via email about the clips for standing ridge. That’s how I want to attach – no roof penetrations.

            I want to know more about the jig. I assumed that by attaching the end sets and stretching a line I could get things lined up. But there could be things I don’t know – I’ve only used racks to date.

            The clips I looked at did not seem to need critical spacing. Just get them all on the same ridge and a few inches from the end of the panels. The installation I saw on line used two clips per panel side. I figured I’d go three and perhaps add a wind barrier on the upwind side so the wind can’t get under the panels.

            Building a scaffold is easier for me than lifting scaffold section ends. I can stand 2x4s, tie the inside set to the house then build off them. I’m going to use some long 2 x on the outside and add a safety rail.

            What I need to do is to figure out how to use the clips to build a ‘standing board’ for an upper run of panels so I don’t have to work off a roof ladder.

            And I always use a harness and safety line when I’m up over eight feet. I also tie my ladders to the building.

            If you’ve got pictures of your installation I’d love to see them.

          • vensonata

            A standing board is definitely a good idea which we eventually used. The clips are stout and take the weight, it is a bonus scaffold. I just sent some pics to you…I think…this Ipad stuff is a little tricky for me. Check your email, if not I will figure out how to do it right. Good to read up a little advice on the jig idea. Try a site called, I think, Solar Pro for an article on s-clips. They are a very good solution but can be finicky until you figure out your spacing system.

          • Bob_Wallace

            Got them. Thanks.

            I’m guessing the mounting jig could be made of 1×2 with diagonal bracing.

          • eveee

            Wow. With that kind of wind, a turbine sounds like it would produce good power.

          • Will E

            I did it myself 3 years ago and its a lot of fun doing it and super easy, plug and play, where do you live, i come over and help :))
            try Alibaba to get some prices, all companies are very friendly and pleased to help and send all over the world.

          • Zooba

            So with lead-acid you get 8.1kWh of energy capacity at 2,000 cycles, but with the Powerwall you get 10kWh at 3,600 cycles (it comes with a 10 year warranty). So money-wise they’re nearly on par with the Powerwall being maybe like 25% more cost efficient. But the Powerwall is also a fully integrated, no-maintenance system. Is there something I’m missing here?

          • I think you’ve summarized it well. The Powerwall, of course, is also hung on a wall and much smaller.

        • vensonata

          I would definitely get 3, 7 kwh packs. I paid $8000 for AGM maintenance free 40 kwh bank in November 2014. That is just the raw cost of the battery. They cannot be discharged below 50%. So in reality I have 20 kwh available. They only discharge to 50% in winter about 50 times per year. The rest of the year between 10% and 20% night time discharge. So the tesla batteries would have 21 kwh available and cover 97% of my needs. They would cost $9000 but last perhaps 15 years or more. My AGM will last, if lucky, 8 years. The math is plain…Tesla wins hands down. I will, in fact probably buy two 7kwh packs right away since they can hover in partial charge and save the life of my AGM as deeper back up. Fortunately I already have double inverters so the Tesla will go into one inverter and be charged by 4 kw PV array (already in) and the AGM will remain being charged by an 8 kw PV array (already in). They should be best buddies I think. Bring on the new age!

          • GCO

            The Tesla pack sits between 350 and 450 V depending on SoC and (dis)charging current.
            What charge controller(s) and inverter(s) will you use?

          • vensonata

            Where do those numbers come from? I would need some specs and advice from the company itself to decide on how to charge it. I have two solar charge controllers available with mppt etc. I would hope it would not be complicated. The outgoing inverter at present handles an 800 amp hour 48volt battery bank. Again I plan to use already existing equipment. Let’s hope it is not rocket science. Tesla must have considered ease of installation and compatibility with easily available equipment….. unless I have to drive my battery to a super charger station to get a refill!!!

          • GCO

            Basic specs are on the Tesla page linked at the bottom of this article:

            Tesla must have considered compatibility

            I’m afraid that this is not at all the style of the company, no.
            For 48V-friendly lithium packs, you’ll need to look somewhere else, e.g. Balqon.

          • vensonata

            Ah yes, dear Balqon. So simple, so easy. Surely, surely Tesla can manage this. This is a topic for some real discussion for sure. Anybody out there that can be credibly definitive?

          • Offgridman

            Please let me know when you find something out. With the internet connectivity and being pre-designed for daily or weekly cycling it was also my concern that it would be hard to get these to work without a grid tied inverter. Hearing different would definitely raise my excitement level. 🙂
            My generator use was under ten hours this last winter, maybe closer to five, and that mainly because I chose to use the chainsaw on some cloudy days when having some free time, instead of waiting for the sunshine.
            Since you are closer to moving on something like this and in a similar situation the information will be appreciated, hopefully I am at least five years out from needing to do anything, but it is good to be prepared.
            Also, just out of curiosity, with the dual inverters, is that for separate loads and circuits, because one is pure sine wave for the electronics, or some other reason?

          • vensonata

            Dual inverters were for our early expectations of heavy power draws but more importantly for bulk charging with the 12 kw kubota diesel generator. Combined the inverters 8.8 kw. Pv array 14 years ago was small, just 1.8kw, the batteries were 80 kwh flooded lead acid. Now the pv is 11.4kw and a downsized agm bank of 40kwh. High powered generator charging is no longer important since the massive solar handles almost all needs.
            Your generator run time is amazing, you are within 1 percent of pure renewable. Congratulations. What we find out though is that the last 1-3% is the most expensive to go pure on! Your fuel cost is trivial, gen run time trivial. A larger battery is more expensive. It is the law of diminishing returns on off grid systems. I will get there though. We need examples of 100% solar off grid in less than perfect climates as motivators for the world.
            It has taken 24 hours for my brain to absorb the implications of this Tesla battery. And I am sure new insights will arise as more info comes in. But here is one thing I realized last night…the 7 kwh battery is just the 10 kwh battery discharging to 70%. So all 7 kwh are available at each cycle (100% D.O.D)

            The battery chemistry is different than the car battery Elon said. I presume it is quality lifepo4. That means 5000 cycles at 7 kwh mimimum. All told, average price per kwh 9cents! But still an inverter is required but it need not be anymore than 3 kw. Since the battery can’t discharge at any higher rate. The details of how to go from battery at 350volts dc to AC120 is unknown but here is my guess. JB Straubel said “the voltage is 400 VDC so the efficiency is greater and the wires are thinner. There is a built in DC-DC inverter” I presume that inverter brings the voltage down to 48 volts. If not, it would be strange!

          • Offgridman

            Thank you for the info and explanation, I got curious when you talked of having two, but the evolution of the system through the years makes sense because my experience has been similar.
            Part of my lack of excitement over the Tesla battery packs is just due to how well they can be used in straight offgrid systems. Because of being designed to work with the SC grid tied solar it seemed that the DC input and output could be at a high voltage that would need a grid tied inverter to access, and not usable by the 48 volt ones you have already.
            Now possibly there is a way around this as I see from one of the other comments that SC has made an offer to its customers in Hawaii that it may be possible for some of them to go totally offgrid. But for me that brings up the question of if the economics will seem good without the comparison to the high per Kwh price that people there have to pay for grid supplied electricity?
            Last of all, thank you for the compliment about being so close to independence from the grid, but there are some qualifiers. We still use some propane for cooking, supplemental water heating (through a small instant on heater), and the clothes dryer when it rains to much to hang them out. In the future I want to replace this with home produced methane for the cooking, big enough storage that the solar thermal will cover the hot water all of the time, and either a heat pump clothes dryer, or converting the current one to natural gas (methane again).
            We do have the advantage of a milder climate than you do, and the house and systems are still a work in progress, which with the ongoing improvements in efficiency for appliances and etc will probably continue to change.
            The main difference in cutting down on the generator use has been that we aren’t just straight solar. The small wind turbine doesn’t contribute much of a percentage from this time of year on through the summer, but for those weak solar months of November – February it made the difference between having to run the generator or not. This of course with the ability to load shift (laundry, vacuum, wood cutting, etc) to when the power was available, since I am semi retired, has made it possible.
            This to could change, with the way panel prices over the past decade and now storage are dropping, and the new high efficiency heat pump water heaters and clothes dryers are becoming affordable it may be easier to go straight electric on just solar when the turbine wears out. As you said it is a job in itself just keeping up with all of the changes.
            There is still too the transportation issue, to be totally independent will require some long range EV’s that suit our requirements, but they are looking more likely in the next couple of years also, so will just have to see what happens.
            Have a great day.

          • vensonata

            Ya, we still need propane as well. But propane used directly instead of from a distant coal fired electric plant is 80% efficient vs. 30% for grid electricity. Basically we can eliminate all propane 6-8 months year but deep winter we need it for domestic hot water. we can also just use wood heat of course.

    • eveee

      Sounds about right. Numbers make it out to about 900 kwhr a month. You won’t get ten day backup with ordinary residential use. Residential use is too high and battery costs too high for that. Off grid places use less, with more efficient appliances, and air conditioning is too much load. An off grid user might use less than 500 kwhr a month. Ask Offgridman.
      These systems are not for taking the average suburban residence off line. They are for temporary emergency back up, load leveling for TOU and peak demand, and storing rooftop solar for high rate times.
      During a temporary emergency, you probably won’t be running a hot tub and air conditioner. Your biggest power need will be for the refrigerator. Which brings up another interesting point. A California company is adding extra coolant to refrigeration systems to store “cool”. A retrofit of an existing refrigeration system supplies thermal storage. Thats very convenient.

    • John

      One thing not mentioned here is that in a future system with a significant distributed storage component, the overall load on traditional generation and transmission is way down. The net effect is less outages, so it’s not fair to comment on the inclusion of battery technology in a house, with a totally unchanged system environment.

  • Admiral Reality

    Like I said in a previous article about the Tesla Home Battery (Powerwall), even at US$3500 (probably CAN$4000+) it doesn’t make sense for a lot of people unless they have solar panels.

    In Ottawa, Ontario, Canada, I pay $0.07¢ off-peak, $0.14 peak. I will never break-even even if store enough off-peak energy to reduce peak use to zero. I would be saving roughly $10/month on electricity by reducing my peak and mid-peak to zero.

    Even if the price of electricity doubled, it would take close to 20 years to break-even. And by that time Li-ion batteries will be ancient, inefficient technology not to mention that it will have burned through many cycles and the battery itself won’t be storing 10kWh.

    That said, I still hope this product does well and drives the price of Li-ion batteries down even further. And this product makes infinitely more sense to those who have a PV system (which I fully intend to get within the next 5 years.)

    • I do think the assumption is that it be paired with solar.

      • mike_dyke

        I agree Zach. When PV is generating most is during the day when I’m out at work and demand is low so the excess is wasted as far as I’m concerned. In the evening my demand goes up and I’d like to use more of that excess I generated earlier at $0.00 cost rather than get it from the grid at peak prices.

      • BigWu

        Paired with solar, these make perfect sense. The avoided losses of refrigerated food alone would cover the cost (we have to clean out our fridges one to two times a year here due to extended power outages).

        I’ve just run the numbers for my home using actual production and usage data for the past two years. With one of these and the 10 kW of PV already on my roof, I could keep my home lit and food cold during even the longest period of cloudy/rainy days we’ve had since the array was installed two years ago (IOW, a single unit pays for itself in saved food losses).

        With two units, we could keep our home humming along as usual so long as we ran the air conditioning during daylight hours (not a problem at all since our home is very well insulated).

        I’d have to charge the car at the office in either case, sure, but that’s no big deal.

        • Jenny Sommer

          Wouldn’t it be cheaper and even more economical to avoid a stash of food worth 200-400$ in your fridge?

          • Calamity_Jean

            “Wouldn’t it be cheaper and even more economical to avoid a stash of food worth 200-400$ in your fridge?”

            Maybe so, but who wants to go grocery shopping two or three times a week? Depending on the size of the family, $200 is just a week’s worth of food.

          • Jenny Sommer

            Are you serious? Just checked my fridge, 5 people, +-60€ including 3kg asparagus.
            200$ is more like 3 weeks of fridge food.

          • Calamity_Jean

            Well, I do live in a fairly pricey area (Chicago), but, yeah, I’m serious. If a multi-day outage caught us right after we had bought the week’s groceries and we had to throw out everything in the refrigerator, we’d lose at least $75 worth of food, and that’s just for two people. If my husband and I weren’t semi-vegetarian it would be more.

        • John

          5 months since you posted, but gotta ask…. 10kW on your roof already??? What sq ft is your roof? Can you tell me the spec? Number of panels; Manufacturer and make of panels; Inverter size and spec.
          System size in Ireland (yea, i know, not as sunny as some places) is generally offered between 1.5 and 5kWp. 10kW would be commercial level

      • Jenny Sommer

        It doesn’t even make sense with solar panels.

        Are there plans to manage these as a GW scale swarm battery? Like a decentralised grid storage plant. Providing more services than just storing solar energy.

        This would have been the chance to make good on all the promises on car2grid.
        If Tesla/SolarCity could make money on them by providing ancillary services (you have visited Younicos and know what their software/storage is capable of) to the grid they could install the battery for free and even lower costumer rates.

    • David

      You should contact me about the solar and storage options we can offer in Ontario that would address the resiliency and not just trying to beat time of use rates in a home that has limited load.

  • Larmion

    A lot of talk about price, but there’s one thing not discussed a site called CleanTechnica should at least mention: the green case (or lack thereof) for home battery storage.

    Batteries are a clear positive in off-grid applications or where blackouts are common as they will mainly displace diesel generators. In isolated, small island grids there is also a good case to be made if insuffucient hydropower or biomass is available for load balancing.

    But for those living on a stable grid, the case for at home storage still seems extremely weak.

    In a grid covering a wide geographic area, there is little need for the load-balancing abilities of a battery pack. Between the remarkable stability of wind output over a wide area and the significant amount of dispatchable renewables (and natural gas) available on such a grid, the need for batteries for storage is far from obvious.

    That leaves frequency regulation, but that requires only limited capacity and happens before the meter, not after.

    Contrast this with the significant embodied energy of a battery pack and the thesis of Agora Energiewende and other think tanks dealing with the energy transition that strong grids, not batteries, are critical to dealing with variable renewables, starts to make an awful lot of sense.

    • bink

      Larmion, I agree with you in regards that there is no real business case for residential but your comment “dispatchable renewables?” is some phrase that you just made up. Without some form of storage that facilitates demand or shifting wind and solar are variable.

      Go around this country and you will find mostly that wind (late night) and solar (day) do not meet system peaks. That is where storage is important not only to the developers but the utility.

      Never could figure out why they are selling 5 cent wind just to energize the grid in low consumption periods and not hold it for peak. For instance the average peak demand charge in Texas is $36.00/kW, that is a heck of alot better pricing for their energy than 5 cents /kWh, ignorance I guess

      • Larmion

        Dispatchable renewables is not a made up term. It refers to renewable energy sources that are, well, dispatchable. So which ones?

        – Hydropower plants with reservoir, which can increase or decrease output as needed by adjusting how much water is let through. They can ramp up and down faster than any fossil fuel plant.

        – Plants running on biomass. Biogas plants (coupled to an AD unit) in particular can ramp extremely quickly, as they are essentially gas turbines. Solid biomass burners (much like the coal plants they share so much technology with) are slower to adjust, but with decent weather forecasting they’re fast enough.

        – Geothermal plants are usually used for baseload for economic reasons, but can ramp up and down if needed.

        – Solar thermal power plants can store molten salt in what is essentially a big thermos. That allows them to produce electricity up to 18 hours after sunset if needed.

        So now onto your second point: wind and solar do not meet peaks. That depends on where you live.

        In hot climates, demand peaks are mainly driven by AC. That means solar peaks precisely in sync with peak demand.

        Offshore winds usually peaks during daytime, whereas onshore wind peaks at dawn and dusk, especially in winter (precisely when demand is highest in cooler climates). The nighttime peak you mention is typical for continental climates.

        Since you mention Texas: inland, wind peaks at night. Along the gulf coast (and offshore), wind peaks in tandem with demand. Hence the very healthy profit margins of farms in the Galveston area, for example.

        • bink

          First of all you mentioned wind and solar without specification

          Secondly stop pulling stuff off the top of your head –

          “In hot climates, demand peaks are mainly driven by AC. That means solar peaks precisely in sync with peak demand.”

          That is such a bogus statement, solar does not meet peak in Central Florida (winter or summer) nor Central New Mexico

          Thirdly, Offshore wind is practically non existent in U.S. and the system demands i refer to do not match wind almost anywhere in US (peaks don’t happen at dawn nor dusk)

          Fourth, Solar Thermal molten salt is a joke, way too expensive

          Fifth, yeat you did make up a phrase and come with facts

          • Larmion

            – Where do I mention wind and solar without specification? Nowhere.

            – A daytime peak can be observed in California, in the Middle East, in southern Spain and in most other areas I have recently seen data for. Exceptions will no doubt exist.

            – Would you please stop being so US-centric? Offshore wind is common in Europe. A peak at dawn and dusk is widely found in temperate maritime climates, i.e. Western Europe and parts of Asia (which account for a far greater portion of the global population than the US). It also occurs in some tropical areas, though to a much more limited degree.

            – So, in a list of four renewable energy sources (two of which, hydro and geothermal, are cheaper than both fossil fuels and variable renewables) you choose to focus on just one of those four? And despite solar thermal’s relatively high cost, it is doing well in arid climates with weak grids, where its ability to do to do load balancing makes it extremely valuable (Chile, South Africa).

            If anyone is making up ‘facts’ here, it’s you. Or rather, you are debating in a deeply dishonest manner by cherry picking specific locations and conditons that match your argument.

          • bink

            where are we? and stop trying to change the debate when your statements are shot down (you talked about wind and solar in your original blog, no mention of any other technology)

            It is the rule and not the exception, yes California has two system peaks and solar doesn’t meet either of them.

            Stop with the solar thermal just because someone convinced some uninformed person in Chile, South Africa to put one of them up.

            See how you keep adding things to the debate

          • Larmion

            – Where are we? I’m in Belgium. You’re in the US. I’d say we are all in the world.

            – I did talk about other renewables (i.e. “In isolated, small island grids there is also a good case to be made if
            insuffucient hydropower or biomass is available for load balancing.”) and did not use the word solar.

            – Again, you are focussing on solar thermal without commenting on biomass, hydro or geothermal. Perhaps because both biomass and hydro are anything but small scale and all three are cheap and proven?

            – Okay, so it’s the exception. Let’s take some large economies with significant solar penetration and see if it holds up:


            US East Coast:



            How odd. Grid operators and researchesrs around the world aren’t aware of your wisdom on solar not meeting peak demand. Set up a consultancy, quick!

        • Michael Han

          Solar absolutely does not peak precisely with peak demand in California, or anywhere really. Peak demand tends to be from 12pm to 8pm, while peak solar tends to be from 10am-3pm or so. AC absolutely affects a huge part of peak demand, but it hardly corresponds precisely with peak solar. Heat sticks around and doesn’t magically disappear as the sun begins to set. Plus, when people start going home that’s when they tend to start turning on their personal AC systems to cool down the house, as well as when they start turning on their other appliances (lights, televisions, computers, electric stoves, etc). There is overlap, but not a big one. That’s been a big problem utilities have had with solar, and it’s also why my utility SCE is changing my peak times from 10am-6pm to 12pm to 8pm, so they don’t have to pay me peak rates for the solar power my system generates.

          • Rita

            With all of that , energy efficiency comes in, to lower demand.Once demand is lower, peak demand is easy to meet. 😉


    • BigWu

      “But for those living on a stable grid…” is the key.

      I live in “the political capital of the free world” of what is, ostensibly, the most advanced economy on the planet. Yet we lose power for days at a time due to wind and ice storms multiple times per year. In 2012 a derecho left us powerless for 11 days in the heat of the summer (100+F, 38+C).

      And these regular events pale in comparison to the outages caused by hurricanes (Sandy in the financial capital of the world, Ike in the energy capital of the world). Both of these events left millions stranded and without power for days to weeks in the heat of the summer with no way to refuel their generators nor gasmobiles.

      For my home, the PowerWall translates to direct annual savings in excess of $400 (based on 15 years of experience) for refrigerated foods I wont be losing. This alone pays for the unit. Add to that the ability to run my heating/air conditioning and charge my car during the day (I have 10 kW of PV) and keep the lights and refrigerators running at night and I’m absolutely sold!

    • eveee

      Yes. For utility grid, German sources say storage is not needed for another ten years. The need for storage awaits higher renewable penetration that todays.

      The home and commercial markets are much different. In places like Germany, Hawaii, and Australia, electric rates are so high that storage can be justified on savings.
      In the average grid tied US residence, electricity is still too cheap to make an economic sense. But there is another angle. Spoilage and emergency backup. Supermarkets are looking at thermal storage for that reason.

      • Ulenspiegel

        Sorry, in Germany you have a stable net, therefore, it does not make sense to store your PV electricity as long as you get a nice FIT.

        If you produce for 13 cent and you get “only” 12 cent FIT then feeding-in excess geneartion makes much more sense than investing in battery systems.

        • eveee

          Thanks. I will take your word for it. I was reading in some literature that in some cases, battery storage might make sense in Germany. By all means, fill us in on the details.

          • Ulenspiegel

            Don’t get me wrong, there is a real offgrid market in Germany too (a very small one), however the counterpart of an US market for private gridtied back-up systems is not found in Germany.

            FYI I read about this aspect in this discussion the first time. 🙂

            Gridtied battery systems are hobby, not business. 🙂

            From discussions on the photovoltaic forum, a battery makes only sense in Germany when costs of production + storage is lower than 23 cents, as you pay taxes for your consumption.

          • eveee

            Thanks. Every place is different. Every utility and area has a different way of billing and different costs. Its surprising how little uniformity there is. I didn’t know you pay taxes for own consumption in Germany.

          • But there is a battery storage incentive in Germany that would cover much of the cost of a Tesla battery, no?

          • Ulenspiegel

            Yes, but I do not assume that it would survive a dramatic increase of storage system installations. 🙂

            I see a sustainable situation when a kWh of battery storage costs less than 200 EUR, then even a separate billing of power (kW) and energy (kWh) could be survived by a residential custumer without further subsidies.

            If we think about investment efficiency (saved CO2/EUR, then other fields are IMHO more attractive than batteries, therefore, I am no friend of large scale storage support programs.

          • heinbloed

            There have been around 16,000 batteries installed in Germany in the last few years, only around 6,000 received subsidies.

            The majority of battery owners use the pocket calculator and work out them self that it makes sense to go ahead without filling in forms and being controlled by some agency.

    • Aku Ankka

      I agree with you mostly, but aside from big picture optimality, there are local financial reasons to possibly prefer local storage: asymmetric pricing.

      If you have net-metering where consume/produce part is calculated over long (enough) time period, like annually, or even monthly, there is probably little reason to store electricity, since price you pay does not change, unless you can buy cheap, time-shift to lower (i.e. charge at night, use during day, IF utility has time-based pricing — not many do, for residential customers).

      But if there is no net-metering, or it is calculated on hourly basis, and utility only pays bulk-rates for your production, calculus changes. You still pay consumer rates for electricity, but are compensated with much lower bulk rates. If this is the case, it is conceivable that you should reduce amount you use from the grid; and do this by temporary storage.

      This is a game theory problem in that the best solution depends on actions of other players, politics and so forth. The more self-centric utilities actions are (they do have valid financial short-term reasons to dislike full net-metering, at least in some geographic regions), the more likely it would actually be to encourage self-consumption.
      And to prevent rise of self-consumption they may need to suck up and offer a reasonable compromise for net-metering balance.
      Given that self-consumption is ultimately a big existential threat — whereas sub-optimal net-metering is more of an optimization/balancing problem — I think that battery storage is a good bargaining chip for distributed PV, more than anything else.

      • Agreed. I think the biggest effect from this could genuinely be one that we don’t see… the avoidance of a potential change. To be specific, as you state, it could keep utilities from implementing strongly anti-solar policies.

  • Raja Bob

    $500/kWh for the PowerWall, or you can buy an off lease 2012 LEAF for $583/kWh with the added benefit of being able to drive it around if you like.

    • Joe Viocoe


      And it can stay home, charge up on solar while you’re sitting at work

      • Kyle Field

        That’s the big challenge…how to leave the car at home to charge on solar while at the same time getting to work. Charging at night/at work seem to be the two big use cases that we need to hit. Can’t wait for a Tesla universal EV smart charger…that would give them the keys to the kingdom in terms of building the infrastructure to intelligently manage grid level storage.

        • eveee

          Challenge? Charge it at work. Your rooftop solar doesn’t know where its electrons go and doesn’t care. If some of them wind up in a Tesla parked at a nearby dentist office…
          Its not everywhere yet, but neither is solar. its coming though.

          • Aku Ankka

            This assumes net-metering scheme where you offset retail prices with PV, and calculated over long enough time period (year, f.ex; and not hourly).
            That is the case in many places; but not everywhere, and even where it exists, utilities would want to change it. As a setup, it is often a sub-optimal deal for them.

            In absence of net-metering with long-term calculation, you “sell” your PV-generated electricity at market/spot prices, which usually are a fraction of retail price. And then you buy electricity from grid at higher retail prices. So even if you produce as much as you consume, you end up paying some amount.

            Electricity storage really only helps if pricing schema is asymmetric and you can either replace more expensive from-grid electricity, or time-shift production vs consumption (or selling).

            So it is definitely true that for some markets storage makes more sense than for others.

          • eveee

            You are making things way too complicated. Its a perq at work. Plus, we already have utilities pushing it in various ways. Can you say ducks belly? Thats all you need to know. Excess solar fills up the EVs.

          • Aku Ankka

            As opposed to you making things sound… nonsensical? Pushing what? Perq… ?

            I am sorry but understanding the way electricity pricing works for prosumers is a fundamental criteria that determines cost of one’s electricity bill. And from thereon also points to whether or not battery storage could help lower the costs. It would, in, say, Australia. But not, for example, in most US states.

          • eveee

            So does it make sense to buy a battery pack to store your own solar PV output and then transfer that energy to the battery pack in your car?

          • Aku Ankka

            Not if your car happens to sit there at exact moment when your solar PV produces energy. That would just waste energy for transfer, plus cost of battery.

            But if you commute and car stays at home mostly/only during time when sun does not shine, it could make sense. Whether it does, at all, depends on which is cheaper overall: selling PV electricity to the utility during day and buying during night, or, producing and (mostly) storing during day and consuming rest of the time.

            In all likelihood, no, it does not make sense to buy battery at this point if the only/main use is to be able to charge your EV during the night.

          • eveee

            A perq is free, so thats the best option.

            The afternoon utility rates may reflect the low or negative wholesale rates or not. IMO, they will soon.

            Your scenario depends on the exact nature of the net metering from your utility and state. Its a complicated set of conditions based on the net metering rates and the TOU rates charged. I doubt its the same formula for even two neighboring utilities.
            But think about this. If you sized your solar for net metering the way you are supposed to, and then you add EV, you will have more net demand than generation. And you will be paying the utility rate whenever you charge. That could be at retail.
            To avoid that you have to increase your PV.
            With net metering, do you get paid higher wholesale according to TOU? or do you get a fixed amount? Do you pay TOU? Or do you pay a fixed amount?

            Can you show the numbers how that works for your utility?

          • Aku Ankka

            It would not work for my utility, specifically, since net-metering is still very beneficial (due to low penetration) at this point.

            But I think we are agreeing in the basic thing: costs and benefits heavily depend on pricing scheme, and that (a) schemes vary a lot and (b) will keep on changing and (c) in many cases are not well balanced for all parties. Examples of (c) vary from states like where I live, where we have full net-metering and production-based compensation, to something like Spain/Italy with actual punitive fees (imposed or propose) for rooftop solar.

            Beyond that, all am I saying is that AVAILABILITY of battery storage is a good thing and has potential to become relevant. Not that it is guaranteed to, just that it is possible, depending on multiple things: from utilities policies, changes, to further advanced in battery technology and integration. Without option of storage, customers have less leverage in negotiations and discussions.

          • eveee

            Battery availability gives you options instead of being at the mercy of a monopoly. That’s power. What Tesla realized is that utilities slowness can be exploited as an opportunity. That’s where startups succeed.

          • Aku Ankka

            Actually this new article here:


            is quite relevant:

            “But, “after just four days,” said Walter, “I was very disappointed about that system. Because it produces a lot of energy by day, (it) is going to the grid, and in the evening I came back, I have to buy it back by night.” But Walter was even more disappointed that he “had to pay more for the electricity he bought back from the grid than he got for the electricity he’d sold to it.””

            and says is much better than I could.

          • eveee

            Yes. Thats a demand management system. He still loses efficiency if he goes from solar to battery to battery compared to direct to battery. He’s talking about how utilities don’t pay him as much for solar in the afternoon as he pays for electricity in the early evening.

            The underlines what I said. It would be cheaper for him to buy an EV, charge it at work, and use the EV battery as vehicle to grid in the evening. That is, if utilities price solar according to the afternoon price dip they get due to excess solar.

            Right now EV users just charge at night and use during the day. A typical EV has enough capacity to commute to work and supply the peak demand at home in the evening with V2G.

            So what difference would net metering have to EV charging? If the solar is sized right so that the PV covers EV demand, is there any?

            Net metering is about the solar, not the car or charging time.

            You can expect there to be changes in the near future. Utilities are shifting to TOU because of excess solar in the afternoon.

            Right now, rates don’t reflect it. If they did, you would be charging your EV in the afternoon already.

            Instead, the utilities in California are still complaining about the ducks belly, the dip in the afternoon, saying solar causes that.

            Yet they still charge a premium for electricity in the afternoon.
            Thats why I say the TOU premiums are out of sync. They should be encouraging afternoon charging with lower rates, not discouraging it.
            Thats what happens when retail doesn’t follow wholesale.

            There are many different and complicated net metering plans. Some buy at wholesale, sell at retail, some give value of solar rates. There is no simple one size fits all net metering. It varies state by state and utility by utility.

          • Kyle Field

            This specific case represents 2 of the 3 primary use cases for powerwall (using solar production during day to offset night usage and “peak shaving” where the battery is charged when power is cheap (or free from solar) and used when it’s expensive (or rather, costs money in this case)).

            The other use case is for off grid usage… I don’t think it will actually payout in many cases but the concept is breakthrough…especially when we think about it at scale with 1 million of these deployed in a smart network…and used as a utility scale battery. The future is [almost] here, folks.

          • eveee

            It will pay out in places like Australia and Hawaii. Especially for Hawaiians that have been denied solar by the utility. Utility death spiral is a possibility there. SolarCity has a micro grid plan, too. In Australia, utilities are urging some customers to go off grid. Solar City is there to assist. Thats whats revolutionary about this. Utilities now have competition, and are not pure monopolies anymore.

          • Kyle Field

            Yes…these are niche scenarios and I agree Powerwall will likely see traction in these markets…but that’s not going to change the world. This tech will ride the huge volume required for EVs to a place where it is cost effective and more than that – but makes sense for most or all consumers. Tying a V2G EV in is the next logical step for disaster coverage, etc…

          • eveee

            Yes. It’s a mix. Forcing one solution is impractical.

          • Kyle Field

            The reality is that employers aren’t going to give away power….period.

          • eveee

            Better look at this. 80% of workplace charging is free. Google is the largest, and gives 4 hours free. See the pie chart page three.


            Why wouldn’t they? its a really cheap perq. 4 hours of a level one charger? Maybe 6 kwhr. $1.20?
            Google spends more on their in house restaurant perq. Medical insurance is way more.

            Long term. There are going to be chargers everywhere. Some a small pay fee. Some a low fee or free, as a business inducement.

          • Kyle Field

            That’s what the govt is incentivizing…not what “business as usual” will look like. As EVs and their chargers become more mainstream…with 90% of employees driving EVs, we suddenly move into hundreds if not thousands of dollars/day in power consumption.

            Google’s business model and work perks are anomolies…not the norm.

          • eveee

            Yes. We are in an early period. Tho not all or most future charging will be free, it makes sense for businesses to offer some limited amount of free charging as an incentive for shoppers. IMO, you will see some, but not the 80% we now have.

          • Bob_Wallace

            Companies that want the best and brightest are likely to give away power. Companies that want happy employees are likely to install charge outlets and charge reasonable fees for employees to use them.

            Predatory companies like Walmart are likely to view employee EV charging as a new profit center and add a healthy percentage onto the actual cost.

          • Kyle Field

            True…the other factor is scale. As EVs become more and more mainstream, the expectation that workplaces offer EV charging at retail rates will become the norm.

            I could see free charging being a perk much like free food is at some employers though this would still be the exception vs the rule.

        • Jenny Sommer

          Get 2 EVs…

          • Kyle Field

            Working on that 🙂 Need more range from our second vehicle to make the 150+ mi round trip to my in laws house which we do 2x per week in the summer.

      • jammer

        Not after you factor in the cost of an inverter. Solaredge 3kW inverter, which will work for the 10kWh backup battery or 7kWh solar battery, costs about $1k. That’s $450/kWh and $571/kWh, respectively.

        Then there’s installation cost.

        Not that it isn’t worth it if you have unreliable power.

        • cleantech

          Why is everyone missing very important components of the system. THE INVERTER and the CHARGER. The Powerwall is a high-voltage battery. So a grid tie inverter like Solaredge will not work. You *may* be able to use a modified grid tie invert to dump power from the battery to the grid. But it would require substantial modifications to control the discharge and not to discharge the batteries too far etc. Then you need to charge the Powerwall. That is a high voltage charge controller that as far as I know no one make since traditional systems are limited to 48VDC. So now you are looking at a custom high voltage battery charger/Inverter. Now granted a high voltage battery architecture should be more efficient but currently there is no standard equipment to support it. Maybe Tesla will provide that but the pricing of that system is as critical as the battery pack.

          • Bob_Wallace

            If Tesla is going to be selling the batteries I suspect they’ve figured out a good inverter solution.

            Don’t forget the tie in to SolarCity.

          • GCO

            That seems reasonable, but if Tesla indeed already came up with a package including inverter etc, then it’s quite disingenuous, misleading even, to only disclose the price of the battery. By itself, except for a few motivated hobbyists, it’s useless.

          • I assume it’s because they are selling through outlets where you just buy the battery (look at the Tesla links on the bottom of the article) and if they are going through multiple installers (seems like they will), the installers are handling that side of it.

            But, yeah, it would have been nice to see a full example

          • vensonata

            They must have a built in BMS (Battery management system). With Pv it is just plug and play through the solar Charge controllers which any off grid system has. If they don’t have an inverter then your rooftop pv array will run straight in to your batteries and the BMS will stop when full. The Bms must act as a charge controller. Then the inverter will convert for household use. By the way off grid inverters work like this: You can use AC to charge your batteries either from a generator or grid input (there are two ports so either source can be used) your PV comes in through a charge controller directly to your battery in DC. That will probably be taken care of by the built in DC to Dc inverter which JB Straubel specifically mentioned in his description. When leaving the battery the same inverter converts to AC directly for your house and/or exports to the grid. Off grid inverters are a little more expensive than grid tied. About 20% more. I will use my present inverters for the Tesla battery since I have dual inverters already, no added expense. Most modern inverters have Lithium battery chargeing configuration built in.
            Lastly, remember that the google million dollar inverter prize will be here Feb. 2016. The size of an Ipad, 3-5 kw, and hopefully compatible and the price of an Ipad. Perhaps no accident that Elon and Larry split this tech between Tesla and google.

          • cleantech

            The battery pack would have to have a BMS as lithium is too dangerous and is required to have BMS but DC-DC converter in the 7-10KW rage I am sure it is not included for that price. So very doubtful you could directly connect your PV panels even if they were sized properly. Then of course there would be no MMPT. As I stated above no existing solar inverters that I am aware of will operate with high voltage batteries (above 48VDC) This is code restriction. Which also is a good point safety and equipment are a big concern. Special precautions and equipment (PV Wire, DC breakers, etc) all the same issues you have with the high voltage PV panels. You would need something like the PriUPS or an Industrial UPS inverter. Then of course there is the question of safety to the home. I would never have anything larger than a laptop lithium battery anywhere near my house. Maybe in a detached garage or shed. Fire potential is just too high for my risk tolerance with lithium. I love the idea and I hope they can get it to the point of be economical but they are still just too far off.

          • GCO

            Agreed on the difficulty of connecting this battery to a PV system: it’d require some high-voltage MPPT DC/DC, likely custom-designed as I’m not aware of such a product on the market.
            Grid-tied solar inverters can take 350+V DC, but would need to be throttled to discharge the battery in some controlled fashion; the ‘radio ripple control receiver input’ may be usable for that, but nonetheless, some custom hardware required here as well. Using a grid-tied inverter also means forgoing backup power capability.

            Overall, though, I’d think that a high-voltage system would end up being safer than 48V DC (or lower), because of the much-lower currents involved.

            I also don’t share your assessment re risks with Li-ion. I’m more worried about cellphones and other consumer electronics laying around my home than the 1000x larger pack (aka EV) sitting right next to it. That one is more conservatively designed, better protected (physically and electrically) and uses a more stable chemistry.

          • vensonata

            We still don’t know the chemistry. If it is lifepo4 then there is no fire hazard. What I do not know is the Voltage of the pack ..48Volt? About the mppt, apparently if you have a decent Bms, mppt is outdated technology. Look up a site called Electrodacus. This guy is an electrical engineer who builds his own lithium BMS systems for 3kw pv arrays. It will charge a ten kwh lithium battery bank no problem. He has no charge controller or mppt, he is clear that that stuff is no longer needed or useful. The price of solar PV has outstripped the advantages of Mppt. Another curve ball for the solar industry. I am not qualified to give a reliable opinion on the details, but Electrodacus is. Type in on youtube. Nice stuff that may even be useful with the Tesla battery. Man, it is hard to keep up with the changes.

          • Will E

            find information cooperation Lichtblick Hamburg— Tesla.
            Der Spiegel, yesterday, 1 may.

          • Will E

            there is an article online in Der Spiegel, Germany.
            Tesla und Lichtblick schmieden Stromspeicher -Allianz.
            the company Lichtblick from Germany, Hamburg, will provide communication and inverter between the storage battery and the grid worldwide.
            maybe tou can find Lichtblick – Tesla on the net for more information and
            explain better than me on cleantechnica.. hehe
            its a nice article and only found it here.
            cooperation Tesla – Lichtblick. Der Spiegel.

          • Saw the press release. Article coming. But thanks. 😀

          • Mint

            Powerwall includes a DC-DC converter. I’d be shocked if it didn’t support 48V input/output.

          • vensonata

            Right. I think we all worry too much.

Back to Top ↑