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Batteries tesla-storage-unit

Published on November 3rd, 2014 | by Zachary Shahan

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What Does A SolarCity/Tesla Storage System Cost?

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November 3rd, 2014 by Zachary Shahan 

tesla-storage-unitWe’ve written about SolarCity’s residential and commercial storage systems a couple of times before. But I don’t think I’ve ever seen a price tag on these. If you go to SolarCity’s home energy storage page, you can see that it asks you to “Get a free quote.” Not having a home in the US (and my legal home base in Florida not being in SolarCity territory), I couldn’t really do so even if I had thought to, but one of our readers (Kyle Field) actually went and got a quote.

The first thing Kyle found out is that SolarCity is only offering the residential storage solution to SolarCity customers at this moment (“due to limited supply of batteries”).

Even so, he did get some figures that would apply to his case if he was an existing SolarCity customer (he has solar but got it elsewhere, btw). He could (hypothetically) get a 10-kWh Tesla battery (to power the refrigerator, lights, etc. in a power outage) under a 10-year lease for a $1500 upfront cost + $15/month. That amounts to $3300 over 10 years. Not super cheap, but is actually less than I would have guessed off the top of my head. I’m curious to see how much the price for this comes down by the time the Tesla & Panasonic Gigafactory is pumping out batteries. I imagine it will come down a lot, as SolarCity has said that it plans to sell battery storage with every solar system within 5-10 years.

Image Credit: SolarCity

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About the Author

spends most of his time here on CleanTechnica as the director/chief editor. Otherwise, he's probably enthusiastically fulfilling his duties as the director/editor of Solar Love, EV Obsession, Planetsave, or Bikocity. Zach is recognized globally as a solar energy, electric car, and wind energy expert. If you would like him to speak at a related conference or event, connect with him via social media. You can connect with Zach on any popular social networking site you like. Links to all of his main social media profiles are on ZacharyShahan.com.


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  • Garn

    People, please be weary of Ray Bogus (AKA Boggs). He comments on any and all articles written about Solarcity and tries to discredit them because they are his competition. It’s sad but VERY true. Don’t take my word, search “Solarcity Ray Boggs” and let those results speak for themselves. You will mainly see him posting very negative comments towards Solarcity.

    Sorry for posting this, because otherwise it was/is a very good discussion on the issues. I was very happy to see/read all of the comments until I seen that old Ray was at it AGAIN! Makes me sad actually… It’s holding up progress of some very valuable and important discussions when you have to wade through FUD like his.

  • TedKidd

    Cheaper than a generator, and if you have tou rates and can draw upon it during peak, it might even pay for itself.

  • Patrick James Bayham

    easy answer” $120 per month frozen for 20 years

  • Ray Boggs

    My company has been selling both grid tie battery back up systems and off grid systems throughout the U.S. since the late 1990s and I have a pretty good idea why this 10kW Li-ion battery pack appears to be so cost effective.

    I clicked on the link that you provided for Kyle and was directed to a page that made several references to California. If Kyle is located in California then that would explain things.

    California currently offers an Advanced Energy Storage rebate of $1.62 per watt. Systems sized at less than 30 kWh are paid up front so a 10 kWh Li-ion battery pack would qualify for a cash rebate of $16,200.

    That rebate would go to the owner of the system which in the case of a lease would be SolarCity.

    There is also the 30% federal tax credit that would also go to SolarCity for the solar system and may even apply to the batteries in this leased system. So as you can see the total amount of this 10 kW that is going to SolarCity is far greater than the $3,300 that is mentioned in the article.

    I would be interested in seeing a quote for a home that is located in a state that does not offer such an incredibly high cash rebate.

    • Kyle Field

      I am in california – thanks for the added context. I’m curious – what would the price of a 10kwh li-on pack be? I’ve heard pricing in the range of $500/kwh so roughly $5k was what I was thinking (though this might be wholesale/scale pricing vs retail). You’re comment about a $16.2k rebate has me scared :/

      • Ray Boggs

        Current pricing for Li-ion technology for use in automobiles is approximately $500 per kilowatt hour depending on the source. But for a residential application, you will also need to consider the added switch gear, BMS (Battery Management System) cooling, cabling, battery housing etc.

        Another issue that hasn’t been addressed is the probability of increased insurance costs due to the increased potential for fire.

        Do keep in mind that although a 10 kWh battery pack might make sense in limited run time power outage situations, 10 kWh is far too small for most residential “off grid” scenarios.

        • Kyle Field

          Good point about pack sizing. I dont know why that didnt connect for me earlier but it does only come with a very slim benefit. I don’t have good context in this area but would be curious to see what a typical off-grid battery size would be (actuals), what ideal would look like for a peak shaving system (theoretical), etc. Seems like a dynamic area with lots of solutions based on the specific use case. Do you have any detail on these specs (at a high level)?

          • Ray Boggs

            A typical off grid application where the homeowner is not willing to give up common comforts like air conditioning, conventional lighting, blow dryers, microwave oven, refrigerators, TVs, etc where heating is provided by natural gas, will require a battery pack sized roughly between 35 kWh to as high as 80 kwh depending on their usage habits, but that’s considering a 100% DOD (Depth of Discharge) which would dramatically shorten the life of most battery technologies including Li-ion.

            In order to get a reasonable life expectancy out of any battery, the battery should be sized so that is not discharged consistently below 50% at most. So in reality, the battery pack’s size in the above example should be doubled which would mean a 70 to 160 kWh battery back respectively for full time off grid use.

          • GCO

            In addition to what @RayBoggs wrote re batteries: unlike a grid-tied system, an off-grid setup will also need enough generation to cover even the worst months, ie maybe December/January for solar.

            This implies much larger PV array(s) [in my situation in Northern California, I'd need 12~15 kW DC instead of the 6 kW sufficient for grid-tied, net metered], and/or complementing solar with wind and/or a backup diesel generator, all of which will significantly increase the price of the system.

          • Bob_Wallace

            If you’re off grid it makes more sense to put your money into panels and batteries rather than an expensive diesel generator. (At least where I live.)

            Use a <$500 gasoline generator. With a bit of shopping you can get one with an electric starter for that price. What you would save on diesel would never pay for the cost of a diesel. (And diesel fumes are not fun to live with.)

            Plus, if my experience is typical, when the genhead goes a new one will cost more than a "use for a few years and toss out" gas generator. And if you don't do your own repairs it's (unfortunately) cheaper to buy new than to repair in the case of anything more than a battery replacement or spark plug change.

        • eveee

          Ray – The Balqon units are offered at 36kwhr for $12,650, all included. Thats a solar compatible system with charge controller, BMS, inverter, housing, batteries. All for the same price as quoted in the article on a per khwr (storage) basis. Based on the rebates you quoted, the Balqon system would be quite competitive.

          http://www.balqon.com/store-2/#!/Energy-Storage-System-36kWhr-3-week-Lead-Time/p/12477202/category=2860254

          • Ray Boggs

            Thanks for the link. My only concern would be the quality and safety of the cells. The individual cells that are depicted in the photos on their website bear a resemblance to the Chinese cells that were offered under the brand name of Thundersky that have been used by DIYers in the EV industry.

            I own a 2014 Chevy Spark EV which recently experienced a failure of it’s Li-ion battery pack with only 2,700 miles on the odometer, requiring a replacement of the entire propulsion battery pack. And Chevy’s battery obviously included very high quality cells.

            So I hope that Balqon is successful. It would be nice to have a reliable as well as safe Li-ion storage solution available at a competitive price.

          • eveee

            Hi Ray. Sorry to hear of your troubles. I have some experience with Thundersky, which is now called Winston. They are pretty robust and reliable, one of the better LiFe vendors out there and I installed them in some Prius plug in conversions and EVs. A lot of the difference is in the BMS and the quality of the construction. EV pack fires are famous. You can’t mess up the contacts or there is heating.

          • Ray Boggs

            Thanks for the tip eveee. I will contact Balqon so that I can learn more about their product. Always interested in offering new, quality products to our customers.

          • eveee

            Ray – My bad. The brochure shows the charge controller and inverter, but I don’t think they are included. Just the BMS, fuse, and disconnect.

      • GCO

        Balqon sells a bare 9 kW⋅h pack with BMS for 3.4k$: http://www.balqon.com/energy-storage/
        Their online store lists other sizes from 2.6 to 18 kW⋅h for a similar 350-ish$/kW⋅h, and I’m sure they do custom designs as well. They also apparently offer matching enclosures etc, although the pricing for those isn’t on their website.

    • Offgridman

      Thanks for this additional info/perspective.

      • Ray Boggs

        You’re very welcome.

  • EVcine

    They should be using PANASONIC NiMH for solar.

    • Kyle Field

      Why do you say that? Are there benefits to NiMH vs Lithium based batteries?

      • EVcine

        NiMH when PANASONIC/Ovonics quality has a far broader temperature tolerance range than lithium and is far less volatile and thus more suited for home use.

        • Bob_Wallace

          Home temperatures generally don’t move in a huge range.

          • EVcine

            Exactly. I stlll say NiMH has great rebirth potential.

    • Larmion

      NiMH shines in high-discharge scenarios. For a domestic application, you’d have to deal with significant self-discharge and the associated wasted energy (and heat that shortens your battery’s lifespan).

      More importantly, however, NiMH is notoriously picking when it comes to charging. It prefers a well regulated trickle charge, not the highly variable input from solar panels.

      In practice, storage via NiMH is only done in environments where temperatures are variable and often high because other battery types suffer in those environments. For energy storage in a mild environment, lithium wins on lifespan, efficiency and quite possibly cost if the cost of replacement and the lost energy are factored in.

      • EVcine

        You could store energy first in a water tank then drip charge to the NiMH batteries.

        • Kyle Field

          If that were built into a home energy storage solution product, it might be worth considering but feels like a bit of a stretch, talking it in theory. I understand the chemistry but doesnt seem like something I would want to hack together on my own.

          • EVcine

            Maybe for a farm or a larger villa type house.

      • GCO

        Large Ni-MH self-discharges 0.5~2%/day, not enough to produce any significant heat. Lower charging efficiency at high SoC would be a more important issue.
        Nickel chemistries also handle high charge/discharge rates very well, as long as you don’t need to get to 100% SoC, as the Prius has demonstrated. With proper charge termination, Ni-MH actually prefers nominal charging current (1C+) to slow charging ( http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

        • EVcine

          The Prius batteries are not up to date. Consider the Sanyo Panasonic rechargeable ENELOOP batteries as a test case
          they have improved a lot over the past few years. Plus the Prius battery is not the quality of the original EV95 I know people with the original RAV4-EV and they have done 150,000 miles on their original 1990s chemistry NiMH pack and the cars are still going.

  • David Morton

    Why do you imagine it used for a power outage???
    The plan is for it to be used at night over and over and over again. You need to investigate the charge and recharge cycles and life of the battery. You need to figure out if this storage means you can dump the power company.
    You might start with Tesla as that is the same battery likely used. What is the life of a Tesla battery?
    Do you actually think that the plan for this energy storage is for power outages?

    • http://zacharyshahan.com/ Zachary Shahan

      That’s what has been communicated. Which makes me think that it’s not yet ready/built for daily peak shaving.

      • Offgridman

        I agree that the price seems reasonable for the amount of storage with the caveat that the lease can be renewed for the next ten years after without another big down payment. It seems this might be possible as what is supposed to happen when the solar leases come up for renewal. The consumer is not going to get a lot of value from this system if their grid connection is fairly reliable other than as a security blanket for just in case situations. Which for some people it might seem worthwhile.
        If they are still someplace where net metering is applicable and you don’t have peak rating to worry about (like here in Tennessee where new systems can lock in net metering for twenty years right now) it would probably pay off better to use the extra money that would have been spent for storage to instead be sure you have enough panels to cover all of your usage year round. Then setup your own storage or backup for the fridge and lights in case of power outage.
        If you live somewhere that does have peak usage rates I was wondering while it is only setup for use during power outage if you used a timer and disconnect switch in the feed line to the storage if you could see some additional savings on your utility bill by cutting peak usage with the storage? But if these storage units have internet connections you might get in trouble with Solar City for doing so.
        It is good to see some information on the pricing for storage from Solar City, but as to its actual usefulness for the cost it still raises some questions.

        • Kyle Field

          About the renewal – I fully expect this size of batteries to look completely different (in terms of price, storage density, weight, chemistry, etc). Having said that, it might be nice to have the option to renew, assuming no second “down payment” as they would likely have to replace the existing pack but It would still imply that batteries are in the $180/kwh range ($15/mo*10yrs) for those terms to make sense…which I hope would not be the case.

          • Offgridman

            I agree that in ten years system sizes, capabilities, and prices will be very different (or we all hope so anyways).
            But if someone is just concerned about the emergency backup and gets one now the financials would make a lot more sense spread over twenty years of the 15$/month payments.
            As for the lifetime of the batteries, if they are only used a few times a year when the power goes out (average around here is 2-4) and are kept charged by the panels to prevent excessive discharge couldn’t they last for the full twenty years? It would seem that with the experience that Tesla has and if they are monitoring the systems that these are probably over sized to allow the 10 Kwh of use and only charged to the 80% capacity to allow for the longest use. In a worst case scenario (fire, extreme storm damage) how many days a year would these cycle ten or fifteen? Even at thirty days a year it would be at least fifty or sixty years that these should last.

        • Bob_Wallace

          (I’m late to this one and have read comments only this far, maybe this has been covered further down…)

          This summer I paid $2050 for a dozen deep cycle lead acid batteries which should last ten years before they lose capacity.

          12 1.35 kW batteries for a pack size of 16.2 kW. But I need to hold my discharge level to 20% or less for these batteries to last 10 years, so what I have is 3.24 kW of usable storage.

          The SolarCity pack would give me 10 kW of storage? (I assume they’ve set the system so that its batteries aren’t over/under charged. For $3,300?

          I’d have gone that route if available. The extra storage would have meant the ability to go a few days without sunshine. Boosting my array would mean that I could quickly get charged back up when the Sun was in play.

          Actually, I think I’m going to allow myself to abuse the lead acid batteries I have and not worry if they last only five years. In five years I should be able to get new storage for a song.

          • Offgridman

            I know what you mean, because when I got the cell tower backup set a few years ago now I was counting on at least ten years and hoping for twenty because our average over night draw barely takes 10% if that when the turbine is feeding in too.
            With all of the improvements in quality and price over the past couple years it seems that when replacement time comes in the next 5-10 years there are going to be a lot of options that just weren’t there 5-10 years ago, and not even dreamed about being possible.
            What I would prefer to be possible when that time comes is for the liquid metal to be available on a residential scale. With the addition of some more panels and if everything pans out for them I will be able to leave the boys a home that will be energy secure for the next 50-100 years. Even if they only ever come back up here for vacations.

    • Patrick James Bayham

      storage batteries are already built…just DWP getting in the way with red tape..

    • Kyle Field

      I didn’t push for detail on this but would expect that they are only trying to meet the base need / desire of solar system owners – to have the ability to store and use energy from that storage. What’s funny is that we had a power outage later in the night on the same day I requested the quote which was ironic.

      Having said that, as it’s a Tesla product and this is really only a pricing change, I would expect that the functionality to build “smart usage / storage based on pricing” would definitely be added to future models with a web front end. It could even be added to the current models depending on the OTA / web connected functionality built in (think Tesla firmware updates).

      • http://MyRenaultZoe.com/ TrevorJL

        Kyle, that wasn’t ironic – that was SolarCity trying to close the deal!

  • Jim W

    Interesting. How do these costs compare with the costs for lead acid batteries? What is the expected lifetime?

    • David Morton

      Lifetime would be the same as a Tesla Battery, IMO.

      • Kyle Field

        I read an article a few days back (on Reddit I think) about Lithiums. My take aways were basically that if the charging logic dictates that the battery is charged up fully all the time, you’ll get a 2-3 year life. If the battery is only charged up to 75%, the life can be as great as 8-10 years.

        Heat was the other major factor with Tesla having an edge here – which is why they use the rounded cells in their batteries to allow for cooling (dont have any facts to back this up). Batteries that are allowed to get warmer have shorter lifetimes.

        So yes – I agree that the lifetime should be 8-10 years, similar to Tesla car batteries.

    • Larmion

      Assuming a deep cycle lead acid battery (one optimised for lifetime rather than peak output, so the sort you find in a golf cart rather than in a car), you can get about 1000 to 1300 cycles. However, that’s an estimate based on a 50-60% depth of discharge. If you go any deeper, lifespan drops very quickly. This compares with 2000 and more cycles at 80% discharge for lithium.

      A lead-acid battery could compete if you typically draw less than half your battery’s capacity before recharging. Achieving that requires significantly oversizing your battery pack, so whatever cost advantage lead acid has is likely to vanish – and that’s before mentioning the sheer bulk of such an array.

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