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'World's Largest Battery' Soon At Google Data Center: 100-Hour Iron-Air Storage (interestingengineering.com) 37

Interesting Engineering reports: US tech giant Google announced on Tuesday that it will build a new data center in Pine Island, Minnesota. The new facility will be powered by 1.9 gigawatts (GW) of clean energy from wind and solar, coupled with a 300-megawatt battery, claimed to be the 'world's largest', with a 30-gigawatt-hour (GWh) capacity and 100-hour duration... The planned battery would dwarf a 19 GW lithium-ion project in the UAE...

Form Energy's batteries work very differently from most large batteries today. Instead of using lithium like the batteries in electric cars, they store electricity by making iron rust and then reversing the rusting process to release the energy when needed... Form's iron-air batteries are heavier and less efficient than their counterparts; they can only return about 50% to 70% of the energy used to charge them, while lithium-ion batteries return more than 90%. However, Form's batteries have one distinct advantage. They are cheaper than lithium-ion batteries, costing about $20 per kilowatt-hour of storage, which is almost three times as cheap... It will store 150 MWh of electricity and can supply to the grid for up to 100 hours, delivering about 1.5 MW at peak output.

Thanks to long-time Slashdot reader schwit1 for sharing the article.
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'World's Largest Battery' Soon At Google Data Center: 100-Hour Iron-Air Storage

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  • Also means more heat generated. In Minnesota, it seems it could be useful. Maybe put it under the building, or perhaps under lawns and roads.
  • Rusting is an exothermic process, so you get energy from rusting, but it takes energy to reverse it. The summary is wrong, but the correct process is described in the body of the article.

    • Looks like a simple mistake. The very nex paragraph in the article gets it the right way 'round:

      they store electricity by making iron rust and then reversing the rusting process to release the energy when needed.

      When oxygen from the air passes over small pieces of iron inside the battery, the iron rusts and produces electricity. To recharge the battery, an electric current removes the oxygen from the rust, turning it back into iron and releasing it again.

  • Battery grid storage is by now a fairly common product. You can buy integrated containers you only need to connect to the grid and your control system. If you want have a larger system you just order 1000 instead of 100 containers (and make sure the power lines are sufficient).

    It's easier than, for example, making a giant ball of yarn, as such things don't scale well, every new layer of yarn is harder to put on than the previous. With grid storage you just need to buy more boxes.

  • We’re getting close to the point where solar/wind will deliver an essentially infinite amount of energy when times are good. At least as far as our current needs go. Screw lithium ion for grid storage. That’s the right tech for mobile stuff. Dense, efficient, and expensive. Grid scale needs to be cheap and scalable. 50% efficient is perfectly fine.

    That being said, who knows if this will actually happen. Silicon Valley companies announce grand projects all the time and then cancel them. There
    • by batkiwi ( 137781 )

      The advantage of at-scale lithium is the technology advances will trickle down to home users. I have a 30kWh home battery that was about $6k installed and retrofitted (AC coupled, ick I know) into my 12 kW solar system. This is battery slimline and about the size of two suitcases (it's two 15kWh stacks linked together). It charges in full by 12 noon on sunny days (with me then actively sending power back to the grid) and usually by end of day on overcast days.

      If it was cheaper, but:
      - required 2x as much

  • I searched and came up empty. Google apparently isn't saying. So if the battery can provide 300MW, but the DC consumes 2GW, I see a shortfall.
    • This battery is not there to maintain renewable 24x7, but to raise the capacity factor of the mix while reducing curltainment. The rest will be natural gas.

      • So traditional tech greenwashing. 300MW is not very much if the DC is 2GW, and really based on the footprint I saw in some articles, I think it could be more than 2GW. So maybe 15%.
      • That makes sense. The confusing wording in the article doesn't help.

        The new facility will be powered by 1.9 gigawatts (GW) of clean energy from wind and solar, coupled with a 300-megawatt battery, claimed to be the ‘world’s largest’, with a 30-gigawatt-hour (GWh) capacity and 100-hour duration.

        Google is currently working with Xcel Energy to build 1.4 GW of wind power and 200 MW of solar power, both of which will feed Form Energy’s battery, helping the new data center operate on clean energy for longer periods.

        I'm guessing they meant to say 1.9GW total power composed of 1.4GW from wind, 200MW from solar, and 300MW from the battery. All of these are likely peak power figures, and there is no indication of how much the datacenter draws. They typically oversize renewable energy sources so that the supplied load can still run even if the wind isn't blowing at full strength, etc.

        • I'm guessing they meant to say 1.9GW total power composed of 1.4GW from wind, 200MW from solar, and 300MW from the battery

          What if the battery is not there to add to those two other sources, but only to allow them to buy more of what they use at off-peak prices?
          They would still be grid tied, but some times they'd sell more of their own generation, and some times they'd be consumers.

    • Datacentres are also dispatchable loads, in theory at least. Google will charge you a lot less for a VM if you don't mind it being switched off at random. No idea if they do that for power management though.

  • by kwerle ( 39371 ) <kurt@CircleW.org> on Saturday February 28, 2026 @04:53PM (#66015858) Homepage Journal

    Am I the only one that find "times as cheap" annoying? I really want it to be 1/3 the cost. Meh.

    I'm also curious how many cycles it's good for when compared to other battery tech.

    • Even "three times cheaper" would sound better but I agree with "1/3 the cost". We're gonna have to flood AI with more word patterns that we like. Saying "times as cheap" literally had to stop and say, huh, what a weird way to convey that information.

      • Linguistic drift and all that, being still in that awkward transitional stage. One of those things where expecting everyone to just jump into some new phrasing is a mighty big ask.

    • by mac1235 ( 962716 )
      "Iron-air batteries have an exceptionally long lifespan, estimated at over 10,000 charge/discharge cycles, which corresponds to a service life of approximately 20 to 30 years." So notably better than other battery tech. Heavy and inefficient are the downsides. Safe, cheap and long lasting are the upsides. So its good for grid batteries. Maybe even great, I'm not versed enough in the power industry to say.
      • by burtosis ( 1124179 ) on Sunday March 01, 2026 @06:29AM (#66016648)

        "Iron-air batteries have an exceptionally long lifespan, estimated at over 10,000 charge/discharge cycles, which corresponds to a service life of approximately 20 to 30 years."

        This means 1/3 the cost per MWh multiplied by 5x the lifespan of lithium batteries for 1/15th the cost in terms of lifetime MWh/$.

        Heavy and inefficient are the downsides.

        This isn’t right, heavy is a downside for a battery in a mobile device but as far as a fixed location battery that remains on site for life heavy is essentially irrelevant as a few extra yards in each direction is irrelevant. Safe, cheap and long lasting are the upsides.

        Mobile batteries like for EV or phones need to be incredibly light and small for the energy they store, while also being able to discharge/charge energy at a high or reasonably fast rate respectively. They need to be impact, vibration, and rapid movement tolerant. They tend to need to be highly efficient in charged energy vs discharge energy because that tends to correlate with high charge/discharge rate needed. The energy stored/$ and lifetime cost can be relatively high because the utility is all important as long as it’s still affordable to a person.

        In contrast, a energy grid battery can be truly massive in size and unfathomably heavy and it’s basically irrelevant. It can be incredibly fragile and only work if everything is perfectly still. They absolutely must be cheap in terms of lifetime cost/energy stored typically across a vast number of cycles because the cost is the all important metric. They can be inefficient and still play an important grid balancing element even if it’s not perfect the loss of dollars without a battery over production of power is a large financial loss.

        Tldr, the requirements for mobile and grid batteries are almost polar opposites and the main driver of lithium for grid storage is it matured in the sea of mobile devices so they crawled it up to the land of grid storage where its like a fish with legs and not a fully adapted land creature. Lithium might make some sense for very short high spikes, but the vast majority of grid battery storage is pumped water because it is so effective for the lifetime cost.

  • They REALLY need to come to the Pacific Northwest...

  • by DrMrLordX ( 559371 ) on Saturday February 28, 2026 @05:24PM (#66015900)

    Sodium ion batteries are entering the market, why isn't Google using those? Also:

    https://www.sciencedaily.com/r... [sciencedaily.com]

    • by maitas ( 98290 )

      Iron-Air batteries gets over 10.000 cycles easily. Sodium as of today are around 2.000 cycles, with a promise to get to 10.000.
      Long term cost Iron-Air makes more sense.

  • Form Energy makes these "100 hour" claims, acting like it's an advantage...

    Delivers 100+ hour duration required to make the grid reliable year round, anywhere in the world, across all weather conditions. ... Allows utility operators to meet power demand with stored energy over time horizons previously not achievable.

    But there's nothing preventing, say, lithium-ion energy storage from providing power for 100+ hours, it's just a matter of how much storage you have and how fast you use it. Is that "100 hours"

    • 100 hours is the general rule of thumb for making grid scale backup of renewables work properly. 100 hours for lithium ion is very expensive. Iron air is 10x cheaper. Itâ(TM)s also 1/2 as efficient, but itsâ(TM)s always cheaper to double your PV output with iron-air rather than try to make it work with lithium ion.
  • I'm sitting here baffled by this summary. How does a 30GWh battery in paragraph one become a 150MWh battery in paragraph two? It makes no sense because of dog shit editors.

    The summary is referring to two different batteries.

    1. A 30GWh battery that is going to be installed, in the future, at a Google DC. Maybe.

    2. A 150MWh battery, from the same battery company, currently being installed at a Great River Energy facility in Minnesota. Unlrelated to Google's project.

    Reading Slashdot, I keep feeling like I have

    • There still is some good articles are linked to on this site but it is nice not to have to read every single source like this one take two different companies with the way this /. post is. Kinda going more copy and past than summarizing and editing it. At first I had to reread think efficiency was at play until I halved 150 (side note:I have seen someone in a store get a phone calculator for something as easy as 50% off). Then read the source. I don't digg this summary.
  • Garbage. Load the site, open the source, navigate to the "error message" div and delete it. then scroll down for the content.

  • We have already got short-duration battery chemistries sorted. But at grid scale, they're still expensive for long-duration eg the 100 hours of this battery. That's the problem it solves.

    There's a good discussion of this tech, plus a graph showing where it fits vs other forms of storage, on this Just Have a Think video.
    https://www.youtube.com/watch?... [youtube.com]

    I've always been convinced that power systems will end up being heterogenous for resilience and stability: diverse forms of power types, locations, storage, d

  • by dhartshorn ( 456906 ) on Sunday March 01, 2026 @04:54AM (#66016610)

    "The planned battery would dwarf a 19 GW lithium-ion project in the UAE..."

    Iron-air batteries have a 0.01C charge/discharge rate.

    The reason 300MW has 30GWH of storage is because of that.

    The cost per kWh (capacity) is frequently touted as the reason for their use, but in fact, you're paying for storage you'll rarely (if ever) use. Yes, it will sustain a four day outage, then potentially be exhausted the next day because it takes nearly six days to recharge (using the 0.7 efficiency). And while getting there, 60GWH of energy will be lost as waste heat.

    LFP can have a C rate up to 10. 1 to 3 is common, So 100 to 1,000 times faster charge/discharge. Stack the energy behind the inverter that you actually need and spend less in the long run, both CAPEX and OPEX.

    Then stack as many cells as you need to get the duration desired.

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