How Tesla battery storage compares with rivals on prices

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Tesla has been credited with a step change in pricing on battery storage technology. But how does it really compare with rivals?

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(Editor’s note: This story applies to US pricing).

CleanTechnica

Since the Tesla Powerwall news came out, it seems the world has been racing to understand energy storage. It’s easy to understand the concept of storing electricity and using it at a later point in time. We’ve all been living with batteries of various sorts essentially our whole lives.

However, understanding what the purchase price means in relation to how much electricity the Tesla Powerwall will store and how much that will affect our electricity bills is a new endeavor for many. Additionally, understanding how Tesla’s utility-scale battery offering competes with top players on the market is a mystery to many.

The other day, some other curious people and I ran numbers comparing the per-kWh price of the Tesla Powerwall & what I’m going to call Powerblocks (the utility-scale battery options described on the bottom of this page) with top competitors on the market. Admittedly, that was too simplistic a comparison.

The kWh rating provided for all of these products is simply the maximum amount of electricity they can store at one point in time. So, in the case of the Powerwall, 7 kWh means that the battery can hold up to 7 kWh of electricity at one time, similar to how a 5-gallon jug of water can hold up to 5 gallons of water.

You have to multiply that capacity rating by # of cycles (# of times the battery will be filled up and then emptied), depth of discharge (whether the battery can be fully emptied during each cycle or needs to be only 80% emptied, 70% emptied, etc), and efficiency (how much electricity is actually transmitted, not lost, in each cycle), and then divide by price to determine a per-kWh price for all of the kilowatt-hours your system is expected to produce… before degrading to 80% of its rated capacity, that is (at which point it’s actually still useful, but that’s apparently the global standard for “end of product life”).

As you can see, there are a number of assumptions you have to make to perform these calculations, and even if all of your assumptions are correct, it’s not like the products are completely dead at the end of the studied time period. This also leaves out operational costs (which we’ll assume to be $0 in the calculations below).

Anyhow, this is the best method I’ve found for comparing Tesla’s Powerwall and Powerblocks to top products on the market. More importantly, on the residential side, the numbers should help a consumer to evaluate the cost-effectiveness of getting a Powerwall (should you get commercial access to one) — that’s the main aim in the next section of this article.

Note that I’ve actually left out “competing” lithium-ion and lead-acid batteries in the residential section. Basically, even at a glance, it’s clear that they don’t compete with the Powerwall, so I didn’t bother finding all of the specs and doing the calculations. If you want to do so for any particular battery, I’m happy to add the info in, but I’ll need links or company spec sheets indicating cycle life, expected DoD, efficiency, and price in order to do so.

With a ridiculous amount of help from three wonderful CleanTechnica readers, below are the assumptions and results, split into a “residential” section and a “utility-scale” section.

Residential Battery Storage — Tesla Powerwall x 4 vs Aquion Energy x 2 vs Iron Edison x 1

Subheading have you confused? I ran the numbers for 4 Powerwall purchase scenarios, 2 Aquion Energy products, and 1 Iron Edison product. Since the intro above was too long already, I’ll jump into the table first and list some of the takeaways and the assumptions underneath it:

Powerwall (cash purchase from SolarCity)Powerwall (9-year lease from SolarCity)Powerwall (wholesale cash purchase Tesla)Powerwall (retail purchase from distributor)Aquion Energy S20PAquion Energy M100-L082PIron Edison 24V Lithium Battery
Cycles5,0003,2855,0005,0003,0003,0002,000
kWh/cycle (efficiency & degradation assumptions included in calcs)5.805.805.805.801.8121.732.76
Total kWh produced over product lifetime28,98019,04028,98028,9805,43065,1785,530
Total Cost$7,140$5,000$3,000$3,600$1,155$15,795$2,761
$/kWh used$0.25$0.26$0.10$0.12$0.21$0.24$0.50

What do the “$/kWh used” figures actually mean on a practical level? Here are some examples, just using the final figure from the first Powerwall column:

  • If you buy electricity from the grid for $0.35/kWh (with no unavoidable fixed costs) and generate excess electricity from your solar panels that you can’t sell back to the grid, you can save $0.10/kWh by purchasing a Powerwall from SolarCity for $5,000.
  • If you buy electricity from the grid for $0.35/kWh (with $0.10/kWh unavoidable fixed costs) and generate excess electricity from your solar panels that you can’t sell back to the grid, you break even by purchasing a Powerwall from SolarCity for $5,000… but are using more of your own solar electricity and relying less on electricity from the grid.
  • If you buy electricity from the grid for $0.35/kWh and are not allowed to send any electricity from rooftop solar panels into the grid, and you would generate that electricity at a cost of $0.15/kWh, you would essentially pay $0.05/kWh more by purchasing a Powerwall from SolarCity for $5,000 (but you’d perhaps have to have another source of backup in winter if you don’t have much sunshine then, but you’d be protected against rising grid electricity rates).
  • If you buy electricity from the grid for $0.15/kWh (with $0.05/kWh unavoidable fixed costs) and generate excess electricity from your solar panels that you can sell back to the grid for $0.15/kWh, you pay $0.25/kWh more by purchasing a Powerwall from SolarCity for $5,000… but are using more of your own solar electricity and relying less on electricity from the grid.
  • If you buy electricity from the grid for $0.15/kWh in the middle of the day (with no unavoidable fixed costs), buy 5.8 kWh of electricity from the grid for $0.40/kWh in the evening each day, and generate excess electricity from your solar panels that you can sell back to the grid for $0.15/kWh or store for later use, you break even by purchasing a Powerwall from SolarCity for $5,000… but are using more of your own solar electricity and relying less on electricity from the grid.

As you can see, the financial benefit depends a great deal on individual circumstances related to your local utility and solar power options. If you are considering a Powerwall (or a product from Aquion Energy or Iron Edison), hopefully this helps you to make a decision.

Tesla-Powerwall-price-570x473

rsz_aquion-big-battery

 

Iron-Edison-LiFePO4-570x570

Assumptions used above:

  • Powerwall: 92% efficiency, capacity = average of 90% rated 7 kWh over product life (due to assumed degradation over time), 5,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”). Also, SolarCity prices come from statements from SolarCity, the wholesale price comes from Tesla Energy, and the retail price from a distributor includes an assumed 20% markup.
  • Aquion Energy S20P: 85% efficiency, capacity = average of 90% rated 2.366 kWh over product life (due to assumed degradation over time), 3,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”). Price from retailer linked above (and seems to be on sale).
  • Aquion Energy M100-L082P: 85% efficiency, capacity = average of 90% rated 28.4 kWh over product life (due to assumed degradation over time), 3,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”). Price from retailer linked above (and seems to be on sale). Admittedly, far larger than most homes would need — more appropriate for some businesses.
  • Iron Edison 24V Lithium Battery: 96% efficiency, capacity = average of 90% rated 4 kWh over product life (due to assumed degradation over time), 2,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”), 80% depth of discharge. Price from retailer linked above.

Utility-Scale Battery Storage — Tesla Powerblock vs Eos Aurora vs Imergy Flow Battery

Before jumping into this table, let me note that the Eos Aurora battery isn’t supposed to be available until 2016. Also, when it comes to Imergy, it has states a current price of $500/kWh (capacity) and a projected future price of $300/kWh (capacity), so I’ve run numbers for both. It’s not clear when Imergy expects to reach $300/kWh from what I’ve read.

Lastly, Imergy’s vanadium flow batteries reportedly have “unlimited” ability to cycle (no degradation like with the other batteries here), but the warranty period is just 5-10 years. So, in two examples, I give Imergy a product lifetime of 15 years (same as with Tesla, which offers a 10-year warranty but projects a 15-year lifespan) and 30 years. Whether a utility or other business customer is going to consider the cost over 30 years or bet on such a lifespan is a question to consider.

Powerblock (utility)Eos Aurora 1000 | 6000Imergy (current pricing, 15 years of life)Imergy (current pricing, 30 years of life)Imergy (projected pricing, 15 years of life)Imergy (projected pricing, 30 years of life)
Cycles5,00010,0005,47510,9505,47510,950
kWh/cycle (efficiency & degradation assumptions included in calcs)8,2804,0507,5007,5007,5007,500
Total kWh produced over product lifetime41,400,00040,500,00041,062,50082,125,00041,062,50082,125,000
Total Cost$2,070,000$648,000$3,750,000$3,750,000$2,250,000$2,250,000
$/kWh used$0.05$0.02$0.09$0.05$0.05$0.03

As you can see, the assumptions here are quite critical to determining the lowest-cost product. Will startup Eos Energy deliver as promised? Will Imergy’s battery work and be useful to you for 30 years? Will Imergy’s cost come down to $300/kWh as projected? Will Tesla’s Powerblock last 5,000 cycles and cost $250/kWh?

I imagine some utilities are going to hedge their bets a bit and buy various storage products. And I imagine other utilities will just go for the products that they most trust or prefer for their specific needs.

Of course, there are many other battery-storage companies on the market and winning contracts, as well as some reportedly coming to market in the coming year, but I couldn’t find prices or important specs for them so they were not included above. Such companies include AlevoAESBoschCODA EnergyEnerVault, and many more.

teslaenergy_utility1-570x321

Image Credit: Imergy Power Systems
Image Credit: Imergy Power Systems

ESP250-Series

Assumptions used in the table above:

  • Tesla Powerblock: 92% efficiency, capacity = average of 90% rated 10 MWh (example) over product life (due to assumed degradation over time), 5,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”), $250/kWh.
  • Eos Aurora 1000 | 6000: 75% efficiency, capacity = average of 90% rated 6 MWh (example) over product life (due to assumed degradation over time), 10,000 cycles before degrading to 80% of rated capacity (theoretical “end of product life”), $160/kWh.
  • Imergy Vanadium Flow Battery: 75% efficiency, capacity = 100% of rated 7.5 MWh, 5,475 cycles over 15-year lifespan or 10,950 cycles over 30-year lifespan (it could also cycle twice a day, in which case the 30-year examples could apply to 15 years), $500/kWh current pricing and $300/kWh projected future pricing.

Source: CleanTechnica. Reproduced with permission.

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17 Comments
  1. Miles Harding 4 years ago

    Probably some more battery options are needed:

    Home: IronEdison NiFe (100 year old technology)
    48V @ 300AH = 14.4kwh for $11,500USD
    Features:
    * Working life: 50 years+, 11,000+ cycles @ 80%DOD
    * Repeated 100%DOD will not significantly affect the life
    * 85 year old original Edison cells have been rejuvenated by electrolyte replacement
    * C/5 discharge current (60Amps for 300AH =~ 3KW)
    * Round trip efficiency is about 75% (between 65 and 85%)
    * Self-discharge is about 10% per month
    Based on the above, this Edison NiFe battery will process 121,000 kwh, or $0.09 per kwh.

    The Edison Li-ion battery looks to be a Winston-thundersky cell
    Here : http://en.winston-battery.com/index.php/products/power-battery/category/lithium-ion-power-battery in which case the cell buy price is about AUD$600 per kwh + controller

    • disqus_3PLIicDhUu 4 years ago

      No Information on the physical size, weight and triple bottom line/life cycle cost.
      How heavy and large are the non lithium batteries, in comparison, must be considered, a factor of 10X in most cases.

      • Calamity_Jean 4 years ago

        For a stationary application, size and weight are relatively minor considerations.

        • disqus_3PLIicDhUu 4 years ago

          Both size and weight are an issue.
          Besides shipping them to site, installing lithium can be done in a cabinet inside a small residence, like in an under main roof garage, venting is not so much an issue too, there’s no way you’d consider doing that with the other formats, they just physically take up much more space and weight, thousands of kilos compared to hundreds why would you bother with anything else.

          • Calamity_Jean 4 years ago

            Well, lead-acid and nickel-iron batteries need to be vented, but I think that some of the other new chemistry batteries don’t. I’m fairly sure these don’t require venting, and they are only 113 kilos each. http://www.altestore.com/store/Deep-Cycle-Batteries/Batteries-Saltwater-Technology/Aquion-Energy-S20P-Pre-wired-Battery-Stack-48V/p11629/?from=aquion-batteries_carousel121214 You’d need four of them to roughly equal the Tesla Powerwall, but that’s still only 452 kilos, a far cry from “thousands”.

            Some other type of battery other than lithium ion might be desirable because it’s #1 cheaper #2 has a wider range of operating temperatures #3 is available now instead of a year from now #4 is rated for more charge/discharge cycles or any of several other reasons.

          • disqus_3PLIicDhUu 4 years ago

            From the data sheet 1.5-2kWh =113kg.
            Dimensions 935x330x310mm
            That gives a density, at best of around 18Wh/kg

            Compared to powerwall specifications:
            Storage capacity: 7kWh or 10kWh
            Weight 100kg density 100Wh/kg
            Dimensions: 1300mm W: 860mm D:180mm.

            So yes you’re about right, you would need 4 or 5
            Still I don’t know why anyone would want to install 4 or 5 of those and they still need connecting together as a bank, with the extra cabling and protection.

          • Calamity_Jean 4 years ago

            Well, they are available sooner, for one thing. The Aquion batteries are “just” on backorder until July 2015. The Tesla Powerwall is reserved until sometime in 2016.

            Also, don’t lithium batteries burn if punctured? Someone might prefer something other than Li-ion for safety reasons.

          • disqus_3PLIicDhUu 4 years ago

            ‘There are different chemistries in the two Tesla Energy products. The backup power option, the Powerpack, is quite similar to that in the Tesla Model S and X, using a nickel-cobalt-aluminum cathode.
            The daily cycling option, the Powerwall, is made of nickel-manganese-cobalt.
            The first is meant for ~60–70 cycles per year, and the other one for 365 cycles a year.
            Tesla expects the Powerwall to last for approximately 15 years, ~5,000 cycles (but with the warranty being 10 years). The Powerpack is expected to last for, “depending on how it’s used, anywhere from 1,000 to 1,500 cycles.” And they have comparable calendar lives’.
            ‘Within the Powerwall, Tesla-designed software will provide thermal regulation, safety checks, and energy optimization’. “All of the Powerwalls and power packs are connected to the Internet,” Musk said. “We’re able to work with utilities to shift power around.

            Additional info-
            ‘Clearing up some misperceptions about the Powerwall,
            Elon noted that the product does include’
            “a DC-to-DC inverter that can interface directly with a solar panel installation. And if somebody has a solar panel installation, they’ll already have a DC-to-AC inverter for the solar panel system, and so no incremental DC-to-AC inverter is needed.”
            So it sounds like it has a built in MPPT, if it can connect directly to panels, this is then fed into the existing solar inverter dc input.
            So no additional cost of an external dc inverter/charger, that would need to marry and interface with an existing solar inverter, unless you would need to replace any existing solar inverter, to make it work.

          • Calamity_Jean 4 years ago

            I’m eager to see a bunch of them installed.

          • disqus_3PLIicDhUu 4 years ago

            Yes and be good if we see a rash of innovative similar products hitting the market as well, driving the technology price down, as the patents for these products, like the Tesla cars, are free to share.

    • Mark Roest 4 years ago

      Probably some waiting is needed — maybe 2 years, for batteries under $250 per kWh capacity. So, 14.4 kWh capacity would be about $3,600. Maybe 10,000 cycles, so 2.5 cents per kWh delivered.

  2. D. John Hunwick 4 years ago

    How about explaining breaking some of this down for the homeowner who wants to be 100% solar .I would like to live in the country town, with enough solar panels to run an average house (of two people) who will be economical, and own a tesla car and plug it in as required. I wouldn’t care if the initial price varied (by say 25%) so long as I get a package that will cut me off the grid completely and allow me to live comfortably. What do I look to buy??

  3. DarylS 4 years ago

    Hi, I’m on contract to get 44 cents per kw fed back, but am restricted in that I can’t have a bigger inverter (2kw) than originally contracted. Could I install a new separate system to charge the battery during the day, then use a timer to feed it back through my existing inverter at night?

    • Glenn Forslin 2 years ago

      why not? If you ask the power company, they might pooh pooh it, for obvious reasons. But this makes sense saving many cents….and dollars. Did you do it?

  4. Deb B 3 years ago

    I recently went to a sustainable house open day and the owner recommended the old fashioned Ni-Fe batteries as they were safe and very long lasting. It would be good to see a comparison of these, lead-acid and any other battery types with the lithium ones. It needs to be simple. Your article here shut my brain down before I got through the first paragraph (and I have a science degree with first year physics and second yr chemistry). What I want to know as a consumer is: upfront costs, longevity, ethical and environmental credentials of manufacture, ease of installation, if they need secure lockable cabinet and costs (I would be putting a battery bank in my carport which is exposed to street), ease of use (I want them just to work without me having to have an electronics degree to maintain them or outlaying on contractors to check them). I actually don;t care about the savings. I just want to get off the grid with feedback to supply others as well.

  5. Shame no one mentions Solarwatt’s MyReserve. The homebattery from German solargiant Solarwatt. They claim to have the most proffitable homebattery in the world! And the savest arround.

  6. Arpit kakkar 2 years ago

    Thanks for the solar panel information. These solar panels are very useful to convert refrigerator in solar vaccine refrigerator, which are mostly used in research lab s or hospitals to store vaccines. It is work on very low temperature.

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