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Power Science

Metal-Free 'Rhubarb' Battery Could Store Renewable Grid Energy 131

sciencehabit writes "A molecule nearly identical to one in rhubarb may hold the key to the future of renewable energy. Researchers have used the compound to create a high-performance 'flow' battery, a leading contender for storing renewable power in the electric utility grid. If the battery prototype can be scaled up, it could help utilities deliver renewable energy when the wind is calm and the sun isn't shining." Abstract.
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Metal-Free 'Rhubarb' Battery Could Store Renewable Grid Energy

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  • by Anonymous Coward

    Just had to say it. Gotta love PHC!

  • by Anonymous Coward

    That is a shame. I wish it could store non-renewable energy too...

  • by steveha ( 103154 ) on Thursday January 09, 2014 @07:22PM (#45912149) Homepage

    The summary implies that this technology could be used for large-scale power, but I wonder what the storage density is.

    Specifically I wonder how this compares to liquid metal batteries []. If everything Professor Sadoway says about the liquid metal batteries is true, those really will provide grid-level storage of power.

    • by mikael ( 484 ) on Thursday January 09, 2014 @08:16PM (#45912537)

      The research paper is here:

      There are some papers on liquid metal batteries here:

      The problem with any of these systems is that the cost of the raw materials themselves are subject to speculation by the currency markets and investment traders. So the minute, some magic energy storage chemical comes on the market, it is going to become as valuable as gold, and the manufacturing companies are going to be bought up and controlled.

      • by AmiMoJo ( 196126 ) *

        Sodium sulphur batteries have been deployed at grid scale in Japan. It's cheap and plentiful, and essay to recycle. Unlikely to be affected much by speculation.

    • by icebike ( 68054 )

      Actually neither the summary or the article state that it could be used large scale, they merely speculate.
      Their test unit is no bigger than a toaster, and they haven't run it for very long.
      They are just beginning their investigation.

      One wonders if they are allowing for the amount of energy used to pump this stuff around in
      their calculations, and the degree to which it is affected by temperature etc.

      In short, there are one of these announcements appearing on Slashdot on an average of once
      a month. There is

      • Pumping a liquid around at a constant elevation doesn't have a very high energy cost. I imagine you'd lose far more energy through the round-trip chemical reactions than you would through pumping the liquid around.

      • by smaddox ( 928261 )

        They are probably not including energy used to pump the liquids in their cycle efficiency. However, the volumetric energy density is quoted as exceeding 50Wh / L. A 5 watt water pump has a typical flow rate of ~300 L/h (maximum pumping height of 4 feet), resulting in an energy usage of ~0.017 Wh/L, which is less than 0.03% of the total energy density. So pumping should have little effect on the cycle efficiency.

    • by localroger ( 258128 ) on Thursday January 09, 2014 @08:45PM (#45912745) Homepage
      It's about storing a large amount of energy in a very large amount of electrolyte without similarly large plates and electrical connections. For power storage they are thinking in terms of batteries the size of buildings, perhaps built like current sewerage-treatment plants, to store energy in the electrolyte and move it along, bringing it back to the electrical assembly with pumps as needed. It can be considerably less energy-dense than current batteries in pounds per erg and still be far more practical for the kind of large-scale storage the tech is aimed at.
    • Storage density is only a problem for portable systems. For fixed storage installations, the important question is "what does it cost per ampere-hour of storage?" Inefficient storage that is cheap can beat highly efficient storage that is expensive.

      Of course, to correctly calculate costs one needs to include things that are the result of storage density, like land acquisition and construction of holding tanks. But if the storage medium is cheap, it could come out ahead of some higher density system that

    • by necro81 ( 917438 )
      To a certain extent, storage density isn't a particularly great concern; the real metric to look for is cost/capacity. If the energy density of this new method is only one half, or one tenth, of liquid metal batteries, but the $/kWh is likewise one half or one tenth, then who cares if you need twice or ten times as much semi-industrial space for a comparable amount of storage?
  • Wouldn't surprise me.
    That stuff is extremely sour!
    It's like eating pure H+

  • Renewable? (Score:4, Funny)

    by BradleyUffner ( 103496 ) on Thursday January 09, 2014 @07:30PM (#45912197) Homepage

    Of course any attempt to store NON-Renewable energy will invalidate the warranty,

  • I doubt the utilities would like this, but for the average home dweller with solar panels it would be useful.

    Or we could use the battery in cars, so that while we charge our car in it's garage, when the sun goes down, it can power the house back the other way.

    • Re: (Score:3, Insightful)

      by m2shariy ( 1194621 )
      Right. Buckets of liquid bromine in a gizmo at home, what could possibly gone wrong?
      • Sort of like buckets of volatile hydrocarbons in a gizmo at home?
        Sure it's also corrosive, but so is chlorine and everyone with a pool has that in their home too.

        • During WW I chlorine was used as WMD. Bromine is similar. Nobody has buckets of clorine at home, what they have is some hypochlorite salts which, when dissolved, oxidize organics in water and slo-o-owly release minimal amounts of chlorine. The flow batteries discussed here are supposed to use elemental bromine. If it leaks in your house, you have to call hazmat team. I mean, your neighbors will have to call, because you will be either dead or very busy coughing up what is left of your lungs.
    • by icebike ( 68054 )

      I doubt the utilities would like this, but for the average home dweller with solar panels it would be useful.

      Or we could use the battery in cars, so that while we charge our car in it's garage, when the sun goes down, it can power the house back the other way.

      Which makes it really difficult to get to work the next morning.

    • by mikael ( 484 )

      They don't even like the existing battery storage systems, because the energy companies are supposed to buy "surplus energy" back from home-owners. Their whole business model is based on being able to charge extra at peak times. If users are able to buy and store energy at night-rate times, they avoid the extra cost of day-time usage.

  • by Anonymous Coward
    Never rub another man's rhubarb.
  • by Animats ( 122034 ) on Thursday January 09, 2014 @07:53PM (#45912393) Homepage

    EETimes has a more useful article. [] This is more like a reversible fuel cell. The working fluid is pumped through the cell, where a chemical reaction occurs. The process is reversible. So there's a "charged" fuel tank, a "discharged" fuel tank, pumps, and plumbing. No info yet on the energy density of the "charged" fuel tank, which is the big question.

  • by Michael Woodhams ( 112247 ) on Thursday January 09, 2014 @07:55PM (#45912405) Journal

    In the galvanic direction, peak power densities were 0.246Wcm2 and 0.600W cm2 at these same SOCs, respectively (Fig. 1c). To avoid significant water splitting in the electrolytic direction, we used a cut-off voltage of 1.5V, at which point the current densities observed at 10% and 90% SOCs were 2.25 A cm2 and 0.95Acm2, respectively, with corresponding power densities of 3.342Wcm2 and 1.414Wcm2. ...

    The galvanic discharge capacity retention (that is, the number of coulombs extracted in one cycle divided by the number of coulombs extracted in the previous cycle) is above 99%, indicating the battery is capable of operating with minimal capacity fade and suggesting that current efficiencies are actually closer to 99%. ...

    AQDS has an aqueous solubility greater than 1M at pH 0, and the quinone solution can thus be stored at relatively high energy density—volumetric and gravimetric energy densities exceed 50Whl1 and 50Whkg1, respectively. ...

    As shown in Fig. 2, current efficiency starts at about 92% and climbs to about 95% over ~15 standard cycles. Note that these measurements are done near viable operating current densities for a battery of this kind. Because of this, we believe this number places an upper bound on the irreversible losses in the cell. In any case, 95% is comparable to values seen for other battery systems.

    I'm not an expert in any applicable field, but as I have institutional access to the original paper, I scanned it to find what looked to me like relevant numbers. As I interpret the above:

    It generates about 0.5W cm^-2 of membrane, so you'd need 2m^2 to get 1 kW output. (But presumably this can be in some compact folded/layered configuration.)
    It can charge much faster than it discharges: that 2m^2 of membrane would let you charge at about 4kW.
    The storage capacity of the battery fades at less than 1% per charge/discharge cycle.
    One litre of reactants lets you store 50Wh of energy (i.e. 20kg for a kilowatt hour)
    I think the last paragraph is saying that, neglecting pumping costs, it returns about 95% of the energy you put into it.

    Note that we can expect these numbers to improve with further research, but whether there are big improvements to come or only minor ones I couldn't say.

    Also: They use a two-reactant-tank set up rather than four tanks, so each tank holds a mixture of the 'charged' and 'discharged' forms of its reactants (e.g. one tank holds a mixture of Br2 and HBr.) I'd naively expected a four tank set up.

    • by c0lo ( 1497653 )

      One litre of reactants lets you store 50Wh of energy (i.e. 20kg for a kilowatt hour)

      To put in in perspective, a random pick: the 1.4L engine of the current version of Volkswagen Golf (a city car, rather) generates 59kW - to power it up using the "rhubarb flow battery" and keep its performance unchanged (also assuming 100% efficiency of the power train), one would need about in excess of 100 liters of reactant per hour.

      Me thinks:
      * lotsa room for improvement
      * even so, the more likely scenario for the next 10 years is the "renewable energy power plant buffering energy using flow batteries"

      • For grid storage your battery will be a building. It can be as large as necessary; it's the price of the infrastructure and reactant to store and re-create enough energy to get the solar farm past a rainy day which are limits.
      • even so, the more likely scenario for the next 10 years is the "renewable energy power plant buffering energy using flow batteries" one rather than an "electric car filling its reactant tanks"

        I have a 3.5 kW solar system on my roof that sells excess power back to the grid at 8c/kWh. At night, I pay 28c/kWh.

        I use about 16kWh/day, around 40% of that at night. This flow battery takes around 20kg of reactant for a kilowatt hour, so I'd need around 120kg to meet current (ha) needs.

        So, for my (probably not wildly atypical) situation, a battery like this would save me around $400/yr.

        In other words, if you could produce these right now, with the power densities as stated, at a cost of $600 or les

        • by c0lo ( 1497653 )

          I use about 16kWh/day, around 40% of that at night. This flow battery takes around 20kg of reactant for a kilowatt hour, so I'd need around 120kg to meet current (ha) needs.

          So, for my (probably not wildly atypical) situation, a battery like this would save me around $400/yr.

          My (probably not wildly atypical situation): I'm differentially charged based on the hour of consumption: 30c/kWh off-peak, 38 (or 42) c/kWh (based on the total 3-month-based consumption) for peak.
          It would make sense for me to suck power from the grid at night time and push it back in the grid during the day; it would make sense for the producers as well - can reduce their excess capacity they need to provision to deal with on-peak - this should worth something for them, even if considering only the mainte

    • As compared to your bog standard lead acid battery, which contains approximately 94 WH per L and 48 Wh per kg. This thing is slightly better than lead acid by gravimetric energy density and about half as good by volumetric energy density.

      • by Anonymous Coward

        On the other hand, you can make this as big as you like without needing absurd amounts of lead - the energy is actually stored in the liquid, not on the anode or cathode. You can have Olympic swimming pool sized reservoirs (or even bigger), which is simply not practical for conventional batteries.

  • Is this what passes for science reporting... "A molecule nearly identical".

    • I don't know why the focus is on rhubarb specifically. Anthraquinones are found all throughout nature, usually as some sort of red or yellow pigment (like the pigment carmine, for instance, made from cochineal insects). Rhubarb contains some compounds call anthraquinone glycosides, but I wouldn't characterize them as being "nearly identical" to anthraquinone disulfonic acid on account of sugar molecules not being very similar to sulfonic acid groups.

  • I'm going to start demanding a nickle in response to every press release announcing a new miracle battery technology.

    I figure that will let me retire in about 18 months.


    • Attributed to Edison when describing how many times he tried and failed to make a useful light bulb:

      “I have not failed. I've just found 10,000 ways that won't work.”

      In case you haven't noticed, you are not sitting around at night in a house illuminated by candles, kerosine, whale oil or burning gas. This is because inventing new useful technology is hard, and takes many trials over a extended period of time.

      There are at least two startups with new technology battery systems installing units

      • Edison said that, but Edison a mediocre inventor and a bad person. Inventing new useful technology isn't easy, but the best approach usually isn't to use the brute force technique.
  • by the eric conspiracy ( 20178 ) on Thursday January 09, 2014 @09:51PM (#45913265)

    Isn't anyone concerned that one of the reactants is a halogen?

  • When I was a kid I ate large amounts of rhubarb, rhubarb pie, cobbler, etc. Definitely created high performance flow issues, involving interfacing with utilities by, uh, sitting on the can.
    • FTA: "when the wind is calm and the sun isn't shining."

      Definitely where the sun wasn't shining. Can't say that the wind was calm, though. OK, I think everybody's got the picture. I'll stop now.
  • Water and hydrogen peroxide are also pretty damn close. H2O, H2O2. How much difference could an additional hydrogen atom make?
    • Well, an additional H results in H3O. The ionized version of that (H3O+) is quite common and a native element in plain water. Even distilled water, because it forms with OH- from 2 H2O molecules.
      However, an additional oxygen molecule does give H2O2. You point stands.
  • by blindseer ( 891256 ) <blindseer&earthlink,net> on Friday January 10, 2014 @12:17AM (#45913977)

    I used to be a big advocate of the idea of having big batteries to store electricity from unreliable and "green" energy like wind and solar. That was until the cost of wind and solar power really sunk in. Wind power is on about par with peak energy generation like natural gas turbines, which is somewhere between 2x and 3x the cost of typical base load power like coal and nuclear. Solar power is so expensive, and variable (based on location, weather, usage, etc.) that it boggles my mind that any utility would even consider it. Then I recall all the subsidies from tax money spent on this nonsense that it starts to make sense to me again.

    The cost of the wind and solar power is high enough that adding to the cost with storage has got to mean the total cost to the utility, and therefore the customer, would be something like 4x what coal and nuclear would cost. Then the size of these batteries would have to be astronomical.

    One thing that concerns me is the environmental impact these batteries would have. The materials for the batteries would have to come from somewhere. I assume they would have to be mined out of the ground. These batteries would have to be manufactured, transported, etc. The carbon footprint of pouring the concrete pad these would most likely have to sit upon would have to be quite large.

    Another question of environmental impact is, what if there is a leak? The stuff used in the batteries may have been derived from plant material but too much of anything can be bad. I grew up on a farm, I saw what too much water can do. I also saw what too much fertilizer can do, it burns the crops almost as if it was set on fire. What will the liquids in this battery do to crops and water supplies if there is an accidental release?

    At least with nuclear power any radioactivity will decay away, with a chemical spill that stuff will always be there. I would much rather see someone come up with a technology to make the production of ammonia cheaper and not rely on natural gas. Ammonia is a fertilizer, a naturally occurring substance, and a fuel. An ammonia leak would still be an asphyxiation hazard, a fire hazard, could burn crops, and could pollute a water supply. However, ammonia is a gas that breaks down into nitrogen and water in the air. The stuff they use in this battery contains bromine and sulfur, what would that do to the water table?

    No thanks, I'll take nuclear power instead.

    • No thanks, I'll take nuclear power instead.

      No you won't, because the banks and governments will not touch it and the energy utilities don't have enough ready cash to do it alone.
      The lesson that should have been learnt after TMI of lots of small reactors didn't happen so the price per reactor is still far too high for it to happen without vast amounts of capital.

      Also the nuclear lobby ate it's own children by lobbying against such small reactors and thorium research. Unless something comes out of India or

      • No you won't, because the banks and governments will not touch it and the energy utilities don't have enough ready cash to do it alone.

        You are absolutely correct. I'm thinking that the shift to nuclear power will not come from banks, governments, or utilities. Certainly some government involvement will be required, but only because current laws require that involvement. Government involvement is not inherent to building a nuclear power plant. I think that this infusion of cash for nuclear power will come from a private corporation that needs power for producing their product, not a corporation where power is the product.

        I think that a

        • by dbIII ( 701233 )

          but only because current laws require that involvement

          Completely wrong, as seen globally where there are plenty of places where no such laws apply. The involvement is needed because private investors will not fund it. Large reactors with large capital costs and very long lead times before any return on the investment rule out anyone that is interested in getting their money back. Governments can afford to invest in things without a financial return in the decade the investment is made.

          The reason alternat

          • Completely wrong, as seen globally where there are plenty of places where no such laws apply.

            Where would that be? Every nation has laws on the handling of radioactive material. If there are any nations that do not have laws on radioactive materials then it's likely because they don't have enough infrastructure to be concerned about nuclear power. No one is going to build a nuclear power plant if there are no customers for the power, and no electrical grid to get it there.

            I'm not advocating that there be no laws regulating nuclear material. I'm advocating sensible laws. In the USA the current r

    • by Anonymous Coward

      You know, there are remote places where it makes complete sense to install a bunch of solar panels instead of building a cable from nearest nuclear plant. There will be even more place like these if it becomes possible to store the generated power for later use, the longer the possible storing time the more sites become possible. Think between small battery packs and huge buildings. Storage sizes of small shacks.

      The rest of your post is kinda funny. "At least with nuclear power any radioactivity will decay

      • Your comment shows a common misunderstanding of radiation. You've heard the phrase, "A candle that burns twice as bright burns half as long." This phrase applies to radioactive materials. Anything that has a half life of thousands of years is not much of a radiation hazard, it's essentially inert. Anything that has a half-life of years is a massive hazard, but it's gone once it decays. A large portion of fission products have a half life of days, or even seconds, which is why being exposed to a reactor

    • Fun fact: in Houston in the 70s, an ammonia tanker crashed on a highway interchange and spilled its load. It killed everything in radius, of course, including all vegetation and a bunch of humans. Thereafter the area (in a highly visible area passed by millions of people daily) bloomed as one and all commented on how lush and green the grasses were there.
    • Sounds like you already have your mind set. You've got a very negative hypothetical here.

      Then I'd also like to know how you derive the COST of Nuclear and Coal versus Solar and Wind. Keep in mind that "what we pay" isn't the full cost and WHERE we pay it is sometimes more important than HOW MUCH. Also - the cost of putting a solar panel at my house -- huge. But if a large company is using collectors to boil some water -- it's a much different cost per kilowatt.

      For instance, a nuclear plant sucks in a lot of

      • Solar collects energy when a utility is most likely going to experience peak demand -- well, at least in the summer.

        This is false, the article in the summary even points this out. Once solar and wind reaches about 20% of total capacity it overwhelms the ability of the grid to compensate for peak load times.

        Solar power peaks at noon, power consumption peaks at about 4:00PM. Something has to fill in that gap. If we use stored electricity for that then we are paying twice for our power, once to produce it, and again to store it. Barring some great leap in solar power technology we are going to be stuck with wind, coal,

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