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Power

'Thermal Batteries' Could Efficiently Store Wind, Solar Power In a Renewable Grid (science.org) 96

sciencehabit shares a report from Science.org: How do you bottle renewable energy for when the Sun doesn't shine and the wind won't blow? That's one of the most vexing questions standing in the way of a greener electrical grid. Massive battery banks are one answer. But they're expensive and best at storing energy for a few hours, not for days long stretches of cloudy weather or calm. Another strategy is to use surplus energy to heat a large mass of material to ultrahigh temperatures, then tap the energy as needed. This week, researchers report a major improvement in a key part of that scheme: a device for turning the stored heat back into electricity.

A team at the Massachusetts Institute of Technology (MIT) and the National Renewable Energy Laboratory achieved a nearly 30% jump in the efficiency of a thermophotovoltaic (TPV), a semiconductor structure that converts photons emitted from a heat source to electricity, just as a solar cell transforms sunlight into power. "This is very exciting stuff," says Andrej Lenert, a materials engineer at the University of Michigan, Ann Arbor. "This is the first time [TPVs have] gotten into really promising efficiency ranges, which is ultimately what matters for a lot of applications." Together with related advances, he and others say, the new work gives a major boost to efforts to roll out thermal batteries on a large scale, as cheap backup for renewable power systems. The idea is to feed surplus wind or solar electricity to a heating element, which boosts the temperature of a liquid metal bath or a graphite block to several thousand degrees. The heat can be turned back into electricity by making steam that drives a turbine, but there are trade-offs. High temperatures raise the conversion efficiency, but turbine materials begin to break down at about 1500C. TPVs offer an alternative: Funnel the stored heat to a metal film or filament, setting it aglow like the tungsten wire in an incandescent light bulb, then use TPVs to absorb the emitted light and turn it to electricity.

For the new device, Asegun Henry, an MIT mechanical engineer, tinkered with both the emitter and the TPV itself. Previous TPV setups heated the emitters to about 1400C, which maximized their brightness in the wavelength range for which TPVs were optimized. Henry aimed to push the temperature 1000C higher, where tungsten emits more photons at higher energies, which could improve the energy conversion. But that meant reworking the TPVs as well. With researchers at the National Renewable Energy Laboratory, Henry's team laid down more than two dozen thin layers of different semiconductors to create two separate cells stacked one on top of another. The top cell absorbs mostly visible and ultraviolet photons, whereas the lower cell absorbs mostly infrared. A thin gold sheet under the bottom cell reflects low-energy photons the TPVs couldn't harvest. The tungsten reabsorbs that energy, preventing it from being lost. The result, the group reports today in Nature, is a TPV tandem that converts 41.1% of the energy emitted from a 2400C tungsten filament to electricity.

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'Thermal Batteries' Could Efficiently Store Wind, Solar Power In a Renewable Grid

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  • We can now convert 41% of heat radiation to electricity... that is AFTER a 30% jump in efficiency, presumably.

    At 2400 degrees celsius... how much of the energy is actually light and not thermal radiation?

    I cannot help but think this scheme overall must be less efficient than an ICE ever was...

    Compare this to the charge/decharge efficiency of a battery and I find myself yearning to ask: What would be the point?

    • by Anonymous Coward

      Slashdot had a thing about a hydrogen fuel cell recently, and in that discussion it was claimed that in/out efficiency of those was about 35% percent. Supporting materials seemed to indicate that nonetheless that was more economical than using batteries when needing to store electricity for longer than about 13 hours.

      At any rate, this is research and the point of research is finding out new things, expanding our knowledge, and so on. I don't expect this to become useful soon. At the rate it's going it migh

      • Slashdot had a thing about a hydrogen fuel cell recently, and in that discussion it was claimed that in/out efficiency of those was about 35% percent. Supporting materials seemed to indicate that nonetheless that was more economical than using batteries when needing to store electricity for longer than about 13 hours.

        It's quite funny how when calculating efficiency of electrolysis/fuel cell setup the "greens" always use numbers of fuel cells from 60s and efficiency of electrolyzer stolen from some kid's science fair display, but when talking about batteries they always assume some magical fairy dust technology breakthrough that will decrease costs tenfold, increase storage likewise, and solve the litium/cobalt/nickel shortage (and mining-related pollution) is just around the corner and can be already presumed in calcula

        • We are literally already producing lithium batteries with no cobalt. We should literally be banning cobalt from battery production.

          • by guruevi ( 827432 )

            First of all, those batteries are less dense and can't be charged as fast. Instead they are replacing cobalt with nickel, which you may not get from slave mines in Congo, but you get primarily from slave mines in Indonesia (which their government just banned nickel exports) and the next biggest producer Russia (which any Western government should have banned exports).

            Moreover nickel mines typically come with hexavalent chromium pollution, the (in)famous chemical in the Erin Brokovich stories.

            You're just tra

            • But it's even cheaper to "literally start to convert water into fuel" from renewable overgeneration than to build a nuclear reactor for it. Like, almost zero marginal cost since otherwise it would go to waste for no return on that.
              • And not only that, but if you're making fuel with the energy then you're solving the problem of intermittency by definition. It becomes wholly irrelevant as long as you have sufficient production. This is why wind is really the best source of large-scale energy. We need to solve the blade recycling problem, but I reject completely any notion that we can't do that, it's beyond ridiculous to imagine. It doesn't matter how you store the energy, so long as you have a scheme for doing so.

                The real kicker is that

              • by guruevi ( 827432 )

                But you haven't solved the problem of heavy metal requirements and pollution for the production of solar panels, wind energy etc.

        • Not even the best fuel cells on the market beat CCGTs when it comes to capital costs and conversion efficiency. So there's virtually no point to large-scale fuel cells.

          And of course the best fuel cells also require another 'magical fairy dust' called 'platinum' that *you* assume for some reason is available in unlimited quantities...

      • There was an article like 25 years ago where a new and improved thermocouple group was attached to an oil furnace allowing the system to bank energy

      • Fuel cells are a red herring. A hydrogen-burning CCGT plant will be slightly more efficient but *much* cheaper (by a factor of 10?) in capital costs than an assortment of fuel cells. Round trip efficiency around 40%, but you *need* to make green hydrogen anyway (at the very least for ammonia production, explosives etc.) so making hydrogen manufacturing facilities slightly larger and storing surpluses is a complete no-brainer since you're building them already. (And temperature control in buildings is much b
    • by Anonymous Coward
      As you may or may not know, the Kelvin scale is the same as the Celsius scale, except for an offset of -273.15K. A difference of one degree Celsius is a difference of one Kelvin. The number you find on many light bulbs, 2700K, is actually a temperature: It describes the light color by comparing it to the color of the light emitted by a black body radiator at that temperature. 2700K happens to be roughly 2400C (missing degree symbol courtesy of Slashcode, welcome to 2022). In conclusion, you know quite well
    • by AmiMoJo ( 196126 ) on Thursday April 14, 2022 @03:29AM (#62445188) Homepage Journal

      Efficiency isn't so important with renewables, because you are not paying for fuel. If the wind blows a bit stronger it doesn't cost you anything, so even if you lose 60% of the energy in the storage round trip it's not such a big deal.

      Also keep in mind that you can use thermal storage for heating and cooling directly, which increases efficiency. You can buy a home thermal storage unit to heat your hot water. You can run your AC at night when energy is cool, reducing your home's temperature by a couple of degrees, and then not need to run it during peak times.

      • Re: (Score:3, Interesting)

        Efficiency isn't so important with renewables, because you are not paying for fuel.

        But you are paying for the panels and turbines. If you waste 60% of the output, you need two and half times as many.

        A battery gives you back 95% of stored energy.

        Storing as heat using this converter gives you back 40%.

        Even a steam turbine can do better than that.

        Also, this converter is made of tungsten and ... GOLD.

        • by AmiMoJo ( 196126 )

          Sure, and you have to do a cost/benefit analysis for all of this. This is more about grid scale renewables though, where you will have a lot of over-provisioning to account for times with little wind and sun. It might come down to literally a couple of days a year, so a thermal storage solution that is extremely durable and relatively low cost might be a good option for that.

        • "Also, this converter is made of tungsten and ... GOLD."
          The gold foil (gold leaf) used in the mid-evil times was 0.001 mm thick. This means one cubic centimeter of gold per square meter of panel, or some 19g.
          We can do better with electrolysis.
          I don't think the price (or availability) of gold truly poses a problem

        • by hey! ( 33014 ) on Thursday April 14, 2022 @09:44AM (#62446110) Homepage Journal

          But you are paying for the panels and turbines.

          Yes. So you need stuff to be cheap. You put your finger on exactly the kind of efficiency that's needed: economic efficiency. A cheap, physically inefficient battery is as good for renewables as an expensive, efficiency battery. Of course what you want is a cheap, efficient battery, but an *economically* viable battery is a practical step in that direction. Once people are making money with batteries, that will attract investments in improvements.

        • Storing as heat using this converter gives you back 40%.

          Even a steam turbine can do better than that.
          A steam turbine is only marginally better.
          And: steam can not be stored. So it is completely pointless to compare this approach with heat storage to produce steam to use in a steam turbine ...

          • And: steam can not be stored.

            Steam can be generated from any source of heat.

            So if you store the heat in blocks of granite, as TFA suggests, you can either use that heat to generate steam or heat the converter.

            The differences are that the steam turbines are more efficient, less expensive, and already exist.

            • Erm, you must have a reading comprehension problem.

              Steam turbines are more or less on the exact same level of efficiency. Which part of 40% efficient escaped you?

        • Like batteries, no moving parts. So very little maintenance required, making it very durable. Heat storage and depletion do not affect the storage materials that actually store the heat too much, making it a kind of 'set-and-forget' solution.

          40% efficiency is indeed not too great of a number. But if that system lasts 25 years or more, without maintenance or repair...where do I sign?

          Also, 40% efficiency is a lot higher than practically all solar solutions. Besides, you use electricity to heat up water for co

          • Also, 40% efficiency is a lot higher than practically all solar solutions.

            The 40% is applied AFTER the solar makes the electricity.

            A typical solar panel converts 20% of incident sunlight to electricity.

            40% of 20% is 8%.

      • Efficiency isn't so important with renewables, because you are not paying for fuel. If the wind blows a bit stronger it doesn't cost you anything, so even if you lose 60% of the energy in the storage round trip it's not such a big deal.

        One of the major issues with wind and solar is the sheer volume of refined material resources that go into the production of these massive structures. Structures that don't last forever. So far solar has been mostly additive new capability comes online each year. In years from now if growth trends continue this will be stalled when you eventually get to the point where more capability is eroded by time than can be manufactured.

        It is imperative to maximize EROIs on wind and solar otherwise renewable energ

      • false like always.
        The argument that so many of the anti-nuke ppl make is that renewables are cheaper than Nukes (though it is false, unless you certain screwy conditions).
        Now, you say that efficiencies, i.e. costs, no longer matter
      • Efficiency is still important if you are a homeowner with limited lot/roof/garage space to locate your PV, wind turbines, batteries, etc.

        Utilities have the same problem on a different scale, but generally much more flexibility to relocate their generators/storage than individuals.

    • ICE needs fuel. This doesn't.

      When your 'fuel' is free, i.e. solar, you just build more infrastructure to capture more of that 'fuel'

      Efficiency case in point: enough solar energy hits the earth in 1 hour to power all forms of energy we currently use on the entire planet. 8000 hours in a year.

      8000:1 is a massive amount of overhead you can lose to efficiency losses and still be orders of magnitude higher than we'll need for centuries. and on that time scale we'll be using solar in space so even
      • When your 'fuel' is free, i.e. solar, you just build more infrastructure to capture more of that 'fuel'

        Efficiency case in point: enough solar energy hits the earth in 1 hour to power all forms of energy we currently use on the entire planet. 8000 hours in a year.

        All the direct infrastructure for material extraction, transportation, fabrication and indirect supporting infrastructure necessary to enable capturing is certainly not free and certainly does have an environmental impact.

        8000:1 is a massive amount of overhead you can lose to efficiency losses and still be orders of magnitude higher than we'll need for centuries. and on that time scale we'll be using solar in space so even higher ratio.

        What matters is the environmental cost of your collectors not what is theoretically possible if you covered the entire surface area of the world in collectors.

        • All infrastructure has cost, really nailed me there.

          My point was that renewables don't have fuel costs, like coal, oil, uranium, etc.

          As for surface coverage. You've heard of roofs right? And solar films on windows? and solar panels over parking lots? etc. Unlike your fossil fuel sources for grid power, solar can produce anywhere the sun can shine. With that 8000:1 head start, technically don't need any 'new' areas for solar.

          And fun fact: this is *just* solar. Wind can (and is) producing
    • by ceoyoyo ( 59147 )

      It's unfortunate they teach in school that infrared is "thermal radiation."

      If you heat something up to 2400 degrees the radiation that is given off is thermal, with a spectrum pretty close to what we'd call a "warm white" incandescent light bulb.

      Lithium ion batteries are 80-90% efficient, but they cost a lot. Chunks of graphite are much cheaper.

    • This concept is interesting, but 1) problematic, engineering-wise (requires a very high temperature device, strong insulation, etc.) and 2) redundant, since you can equally well generate hydrogen with greater efficiency, and you HAVE to generate hydrogen anyway (for chemical industry).
  • by Calinous ( 985536 ) on Thursday April 14, 2022 @03:05AM (#62445138)

    The conversion efficiency is very good indeed, but...
    What is the conversion efficiency of heating a tungsten mass from - lets say - 2000 to 2400 Celsius?
    What is the storage efficiency of keeping a tungsten mass at 2400 Celsius?

    This might get a very good use if we can obtain the respective temperature naturally out of some different process... Interestingly, this is just about the burning temperature of hydrogen in air...
    Also, maybe some kind of nuclear process instead of the current radio-isotopes used in deep space probes? The overall efficiency of the RTGs is a couple of percent (true, the "residual" heat is used as a heating source so we get to 100%). Yet, RTGs have relatively high mass and low electrical power.

    • Induction heating is someplace 80-90 percent efficient depending on application, so it's actually not bad in that regard, but the storage efficiency is poor. If we were doing it in space it might be a reasonable solution, but here? I'm skeptical.

    • by AmiMoJo ( 196126 ) on Thursday April 14, 2022 @05:48AM (#62445420) Homepage Journal

      Overall it's probably better to use buildings as thermal batteries. Most electrical heating is via heat pumps so it's extremely efficient, typically 300-400% for modern units. When a building is used that way the heat energy is used directly, so there is no round-trip loss.

      For example, say the energy company expects high demand in 1 hour's time. It could signal that to building owners and their AC could automatically heat or cool the building, as appropriate, by an extra 1C right now. Then in an hour when the high demand comes the AC can switch off and allow the temperature to slowly drift back to the set point. Most people won't notice a difference of 1C or less.

      It can work over longer scales too if the occupants can accept a 2-3C change, or if the building can store the energy away from occupied areas e.g. in the loft space.

      • by ffkom ( 3519199 )
        Using buildings as batteries only works during periods with certain ambient temperatures (where significant heating or cooling is needed), and for storage periods of hours. Other thermal battery systems are suitable for storing energy for days to weeks.
    • 2400 Celsius is very hot, even for tungsten. I am currently working on an upgrade to a pottery kiln design, and if I recall, you should run the kiln much beyond 1500 Celsius, and that only for a few minutes, when doing glazing. If the temperature control fails, and the power is left on, you get a kiln burnout.

    • A hot piece of tungsten isn't a thermal battery until you fill in the blanks of how to convert the heat back to electricity, which is what this story is about.

      Achieving a super-high temperature is easy with concentrated solar.

      • The molten salt solar towers work at 600+ Celsius. There's till a bit to go up to 2400C.

        • I suppose that's the optimal temperature for storing molten salts, so solar arrays designed for that purpose are tuned to that factor, but larger and/or better-focused arrays can achieve almost whatever temperature you want: "The temperature at the receiver can reach up around 3,000 C, however, we're only able to practically use temperatures of up to around 1,000 C - anything higher would basically cause the receiver to melt!"

          https://www.science.org.au/cur... [science.org.au]

    • by ffkom ( 3519199 )

      The conversion efficiency is very good indeed

      Is it really? The already existing Siemens ETES [siemensgamesa.com] thermal battery claims 45% real-world AC-to-AC efficiency, only requires existing turbines (re-using ones from former fossil fuel power plants), scales easily by adding more cheap stones to the storage, and has been demonstrated to work for real already in a 130MWh instance.

  • How do you bottle renewable energy for when the Sun doesn't shine and the wind won't blow?

    You don't, HERETIC!. The most intelligent (and orange) being in the universe has long since declared that you'll be long dead of the cancer you got from the windmills before you ever get to the battery installation phase and he is the god emperor of America so his word is holy gospel.

    • How do you bottle renewable energy for when the Sun doesn't shine and the wind won't blow?

      You don't, HERETIC!. The most intelligent (and orange) being in the universe has long since declared that you'll be long dead of the cancer you got from the windmills before you ever get to the battery installation phase and he is the god emperor of America so his word is holy gospel.

      Contrary to what leftists think, insults and smart(not really)ass remarks do not make for efficient energy storage methods.

      • How do you bottle renewable energy for when the Sun doesn't shine and the wind won't blow?

        You don't, HERETIC!. The most intelligent (and orange) being in the universe has long since declared that you'll be long dead of the cancer you got from the windmills before you ever get to the battery installation phase and he is the god emperor of America so his word is holy gospel.

        Contrary to what leftists think, insults and smart(not really)ass remarks do not make for efficient energy storage methods.

        Really? I don't have to be a 'leftist' to despise that moron, there's plenty of 'right wingers' around the planet including the USA who despise Trump with a passion. Worship of Trump is largely confined to the clown posse that makes up the cult of Trump.

    • The orange guy extended the federal tax credit for residential solar. If it wasnâ(TM)t for his actions there wouldnâ(TM)t be one right now.

  • Like we already do. We have existing solutions to this problem, but not the will.
    • Don't underestimate the value of the "no moving parts" aspect.
      • There are tradeoffs with all designs. There's no reason to avoid moving parts in this situation. Thermoelectric batteries are useful when maintenance is difficult. Since you really can't scale the temperature in this scenario, i.e. you are limited to not melting the TEG, they will have to scale by size. If you are going to do that, just use something with a higher energy density.
      • by ffkom ( 3519199 )
        "No moving parts"? What kind of material do you expect to stay at 2000C surface temperature to shine on those photovoltaic cells for long, without moving parts?
    • Like we already do. We have existing solutions to this problem, but not the will.

      Mechanical "batteries" have insanely poor energy density. If you need just a little bit of power and have an existing hole in the ground (mine shaft, tall cliff, etc) you might justify something mechanical, but trying to build some kind of crane system explicitly to use as a mechanical battery just isn't feasible. Pumped hydro, if you consider that mechanical, is passable at best and really can't scale.

      We do have chemical batteries that could be used, but they're expensive, very flammable, and have degrad

  • Storing excess electrical energy as heat is not a new idea, there is for example this facility since 2019:
    https://www.marketsgermany.com... [marketsgermany.com]
    https://www.siemensgamesa.com/... [siemensgamesa.com]

    The great thing about this facility is that, unlike the topic of the article, existing old fossil fuel fired plants can be re-used regarding their generators easily, and an insulated building with hot stone scales easily, without requiring any new rocket science or scarce materials.
  • Nuclear Power

    No if's, and's, or but's. Newer technology has made it safer and able to use spent fuel [tinyurl.com]. It should be used as a bridge to fusion.
    • “Using spent fuel is really only good for a limited number of reactors,”

      They won't be using spent fuel for the majority of their plans.
    • by ffkom ( 3519199 )
      There is a quite good overview of the pro's and con's of nuclear power from Sabine Hossenfelder: https://www.youtube.com/watch?... [youtube.com]

      The only big omission of this overview, IMHO, is not discussing the cost of waste disposal - which is an issue because that disposal costs money on a longer time scale than the companies running the power plants exist and can pay for it.
  • It was not clear from the summary why you can't just use renewable power to boil a large quantity of water, to drive a steam engine, and thus run a generator. As others have pointed out, you can tolerate some inefficiency in power conversion and storage when dealing with renewable energy sources.

    I recently worked on a small scale wind turbine project, designed to charge a battery. A major component is a power dump resistor. Once the battery is charged, you dump any excess power into the resistor. You have t

    • It was not clear from the summary why you can't just use renewable power to boil a large quantity of water, to drive a steam engine, and thus run a generator.
      Actually it was perfectly clear.

      The project is about using heat based "photovoltaics" - and the article is about the advancements they made.

      • by ffkom ( 3519199 )
        But still, if you propose a new technology to use for a certain purpose, people rightfully expect that you compare it to the best of the already existing technologies. The "Science" article claims the new technology does it "efficiently", which is weird, as they claim 40% under some ideal lab condition, while much more conventional thermal batteries [siemensgamesa.com] have claimed 45% real-world AC-to-AC efficiency. Not in a lab - you can buy that at scale.
      • The project is about using heat based "photovoltaics"

        I read that, but it was not clear to me why it is a better technology than steam power. I dare say it would work, but is it actually a good approach? The advantage of steam powered generators is that it is a tried and tested technology, and doesn't require exotic materials.

        • So: you are one of those conservatives that are against base level research?
          No wonder that we are stuck in the stone age of technology to produce electricity ...

          • So: you are one of those conservatives that are against base level research?

            I admit to a degree of conservatism, where I prefer to use a known technology, rather than an unknown techniques. The reason for mentioning the tried and tested technology of a steam turbine is as a point of comparison. What advantages and disadvantages does this new technique have, compared to a steam turbine? It is all very well to have a novel method of generating electricity from heat, but there has to be some compelling reason to develop it.

            • It is a research project.
              You have to make up your mind, if you like research, or. not.

              • You have to make up your mind, if you like research, or. not.

                I do like research, of the "that's interesting" variety, where the intent is to discover new knowledge. The James Webb telescope would be an example of looking for interesting stuff about the early universe. I can't think of any practical application for that, but it is nonetheless worthwhile doing it.

                In this particular case, I get the impression that the idea is eventually to provide a practical power source using a novel method, so I think it quite right to make comparisons with existing technology. This

Think of it! With VLSI we can pack 100 ENIACs in 1 sq. cm.!

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