[HN Gopher] A new heat engine with no moving parts is as efficie... ___________________________________________________________________ A new heat engine with no moving parts is as efficient as a steam turbine Author : WithinReason Score : 394 points Date : 2022-04-13 15:48 UTC (7 hours ago) (HTM) web link (news.mit.edu) (TXT) w3m dump (news.mit.edu) | danans wrote: | > The researchers plan to incorporate the TPV cell into a grid- | scale thermal battery. The system would absorb excess energy from | renewable sources such as the sun and store that energy in | heavily insulated banks of hot graphite. | | The article doesn't provide the efficiency of this insulated hot | graphite battery. Given that this device is meant to be paired | pretty exclusively with such a battery, it seems like a narrowly | applicable solution. Or are there other renewable sources of heat | between 1900C and 2400C that could be used for this purpose? | kragen wrote: | The efficiency of heating things up is pretty much 100%. The | efficiency of insulation can be arbitrarily high (up to 100%) | or arbitrarily low; heat loss is proportional to surface area | and storage time and inversely proportional to insulation | thickness. If your heat engine is only 40% efficient you might | as well design your insulation to be 80% efficient or so over | the expected time span, which would be a few hours for grid | storage systems. | danans wrote: | I was thinking more about the efficiency of the mechanism | that transfers the heat from battery to the TPV engine. The | article said that the device has to be exposed to photons | coming off a white-hot source. | | I suppose that if the TPV devices are closely coupled with | the white-hot source this should be minimal but it's not | clear from the article whether there is an intermediary step, | or how they plan to control the TPV's exposure to the heat | source to discharge the battery. | | Given that this works via radiation (vs convection like a | traditional heat engine), the path between the heat source | and the TPV would have to be fairly direct, and not lose much | heat to any adjacent non-TPV material. | | Maybe they have some kind of massively insulated | opening/closing heat shield that they can use in a manner | similar to the gates used to control water in hydroelectric | plants. | inetknght wrote: | So does this mean I can attach one of these things to my CPU and | get back some of the power used? | lazyier wrote: | Only if your CPU is producing around 1,900 to 2,400 degrees | Celsius | ziffusion wrote: | My soup then. | disqard wrote: | It requires "a heat source of between 1,900 to 2,400 degrees | Celsius, or up to about 4,300 degrees Fahrenheit" -- so your | Nvidia gpu should work great for this purpose :) | sfink wrote: | Sure, if you're running your CPU at 1900degC. | zionic wrote: | Sure, you get ~40% back once you hit 1,900 to 2,400C | jotm wrote: | No, but you could realistically make a small Stirling engine | that would act as a heatsink for your processor while | generating electricity. | | Would be noisy as hell, but quite a cool project haha | HPsquared wrote: | It's not really fair to compare this, which takes heat at | 2000degC, to a steam turbine that takes heat at say 550degC. | | A turbine system would have much better efficiency than 40% if | its heat was available at that temperature. For example a closed | Brayton cycle gas turbine + steam turbine system. Certainly | complex and expensive, but could get much better than 40% | efficiency. | lovemenot wrote: | If a steam turbine _could_ operate at those higher temperatures | it would be more efficient. But it cannot do so under any | reasonable condition. If you want the higher efficiency from | storing high grade heat energy, it 's not feasible to use a | steam turbine. | | Think of the steam turbine as a baseline. Like rating a vehicle | in horse power. | cormacrelf wrote: | Also I wonder if, using similar principles to a heat pump's | operation, you could still get juice out of stored heat at | lower temperatures. Surely you can have this hot graphite | sitting at under 2000degC, heat some fluid/gas to say | 1000degC, and then compress the gas to increase its | temperature? Surely that would be the ideal solution anyway, | since you don't want your hot graphite to become a chunk of | useless heat simply for dropping below temp briefly. | | On the topic of heat pumps, you could also use a TPV for | geothermal power. Since there are no moving parts and | presumably no huge steam engine installation, it would be | more feasible to have one of these in your back yard. The | grid powers a heat pump, you compress the fluid till it hits | 2000degC, and your TPV extracts power. The heat pump itself | is >100% efficient, so overall you can steal a fair bit of | electricity from the ground. Right? | bigcat123 wrote: | omgJustTest wrote: | The Carnot efficiency of a heat engine favors large delta T! This | is the theoretical limit of efficiency. For steam turbines this | efficiency should be around 60-70%, theoretically. | | While cool (1,900 to 2,400 degrees C cool) the Carnot effiencies | should be closer to 86%. | | The idea that heat engines get more efficient as you increase | delta T has been around for a while. The problem is constructing | a delta work extraction loop that doesn't have more losses as a | result of the delta T increase, ie the practicalities of | extracting work energy. | | Warning: I am assuming they are working with an approximately | room temperature cold side, as article doesn't say. The | practicalities of allowing for the delta-t is usually where the | efficiency losses are made. | | source: I am an electrical / chemical engineer. | driverdan wrote: | While this is far away from being a production device it's pretty | exciting to see 40% efficiency. | | How would you go about converting the energy stored in a thermal | battery to a high enough temp for this to work? Some kind of heat | pump? It has never been clear to me how to concentrate heat like | that. | jandrese wrote: | I think they're planning to heat up big chunks of graphite to | thousands of degrees C with electric heaters powered by the | grid and then attach these thermocouples when the renewable | sources start to flag (windless nights) to cover the gap. | diarrhea wrote: | Heat radiation losses (scaling with the fourth power of the | temperatures) would obliterate such a storage solution. I | could only imagine it as very short-term, at which point | heating using electricity and converting back shortly after | quickly becomes pointless. | danans wrote: | I don't know how they mitigate the radiation losses (huge | amounts of insulation?), but it appears that graphite has | some interesting properties when heated, like it gets | stronger 1000-2500C and doesn't expand much when heated | [1]. Perhaps those properties help it to store heat | effectively at those extreme temps. | | 1. https://nucleus.iaea.org/sites/graphiteknowledgebase/wik | i/Gu.... | lazyier wrote: | > I don't know how they mitigate the radiation losses | (huge amounts of insulation?) | | My guess is a vacuum flask made of tungsten. Tungsten | sheet metal is a thing and it has the second highest | melting point of currently known elements, which is | 3,422C. | | Then for the 'battery' you will want to find a material | that has a phase change around the temperature required | for this heat engine to operate. The energy required for | water to go from 100c water to 100c steam is considerably | more significant than the energy required to go from 0c | water to 100c water. | | Graphite will likely come into play because you need to | have electrodes to heat the material up to storage | temperature. Graphite is a good for this sort of thing. | Although gradual erosion will likely limit the life of | the battery. | danans wrote: | If that's the case, would the tungsten flask heat up to | 2000C and give off the photons that are absorbed by the | TPV? I still don't understand how they will control | transmission of the heat at those temperatures. | jandrese wrote: | Maybe insulate with reinforced carbon-carbon? I'm not an | expert on this, but it doesn't seem outright impossible | on the surface, but the details are always what get you. | namibj wrote: | You need vacuum super insulation. Basically take a | thermos, and fill the vacuum with (mostly) non-touching | reflective foil. It's the golden stuff satellites are | wrapped in. | danans wrote: | The insulation I sort of understand. It's how they | temporarily breach the insulation to let out the photons | to strike the TPV that I don't understand. With normal | heat->electricity conversion, you transfer heat to a | turbine via a fluid (i.e. water) that is allowed to | contact the exterior of a heated vessel, but in this case | you need to somehow open a slot to let the photons | radiate out. | z3c0 wrote: | I'm curious what the implications would be for solar panels, or | for any device that outputs excess thermal energy (like our | computers). Would a solid device like this allow recapturing | some of the energy that would otherwise be lost? | visarga wrote: | I don't think it's hot enough. | diarrhea wrote: | Only at tremendously low efficiencies it seems. | waynecochran wrote: | How long/well can "insulated banks of hot graphite" hold heat? | lacrosse_tannin wrote: | What is it made of? | arc-in-space wrote: | 0 comments after 20 minutes on an energy post? How am I supposed | to know why this won't work, won't be useful, won't be cost | effective, won't scale, and that it's just a fad? | | Jokes aside, this seems impressive, I have no idea what the best | applications would be but wikipedia claims that current similar | devices have fairly bad efficiency(https://en.wikipedia.org/wiki/ | Thermoelectric_generator). | willhinsa wrote: | Thanks for the laugh! So true. | javajosh wrote: | _> why this won't work, won't be useful, won't be cost | effective, won't scale_ | | Not an expert, but reading this a few negatives popped out. | Basically they are heating a black body to 2400C and then | making electricity from gathering the emitted light in a cell. | They get to pick a temperature to match the bandgap of the | cell. | | The key problem is getting something that hot without using | another (lossy) form of power. The Sun's surface is ~5600C so | that's enough headroom to get there from solar. That's cool. | But are there any fission reactors that get (or could get) that | ridiculously hot? | Animats wrote: | _" The team's design can generate electricity from a heat | source of between 1,900 to 2,400 degrees Celsius"_ | | That's way up there. That's well above the melting point of | steel. That's above the highest temperature jet engines made | for experimental aircraft.[1] Most jet engines try for | exhaust gas temperatures around 600C or so, for a long useful | life. Typical nuclear reactors, around 300C. | | It's not impossible to operate up at those temperatures. | Every steel plant does it. There are ceramic and brick | materials that can deal with such temperatures.[2] The | storage medium would probably be some molten metal. | | This seems way too much trouble just to store energy. | | Now if this thing worked at 600C or so, there would be more | uses. | | [1] | https://www.nasa.gov/centers/dryden/pdf/88068main_H-1375.pdf | | [2] https://www.ceramicsrefractories.saint- | gobain.com/refractory... | thehappypm wrote: | I think they're envisioning a no-moving-parts kind of | system, which makes dealing with difficult environments | easier. | walnutclosefarm wrote: | No, they claim no moving parts for the generator, but | refer to engineering designs that use pumped liquid tin | to move the heat within the system. Clearly the challenge | there is building a pump that can handle liquid tin at | 2400C. | Animats wrote: | Liquid metals can be pumped with a linear motor type | magnetic field, with the liquid metal being the moving | part.[1] | | But all this just to replace a battery? | | [1] https://www.comsol.com/model/inductive-liquid-metal- | pump-590... | hetspookjee wrote: | I think the sheer size would make it interesting. The | heat energy potential of acres full of graphite is | enormous and presumably much cheaper to construct than an | energy equivalent battery. Now I wonder how it holds up | to other methods of storing energy. | [deleted] | robotresearcher wrote: | The article mentions the planned storage medium is | insulated banks of graphite. | giantg2 wrote: | Chernobyl did. | | I think most try to keep temperatures under 1000C. I think | many FAST reactor designs are looking at 600C operating temps | with peak temp reaching maybe 1200C during emergency testing. | But my memory might be wrong. | sandworm101 wrote: | Biggest key problem imho is how they expect to store this | heat energy. It looks like this cell will, like a PV cell, | constantly be absorbing photons. If those photons aren't | creating electricity/voltage across a gap then they are being | converted into heat. So to keep the medium at temperature you | would need to insulate it, to wrap it in a mirror, only | exposing the flux to the energy-collecting cell as needed. | That means moving parts. | | As for available temperatures from fission reactors: | https://en.wikipedia.org/wiki/NERVA | | "When the reactor was operating at full power, about 1,140 | MW, the chamber temperature was 2,272 K (2,000 degC)" | thehappypm wrote: | This is a bummer, but probably a reality. Perhaps some kind | of LCD type tech could make for it to be more digital/less | big metal moving around. | DontGiveTwoFlux wrote: | Not mentioned in the article is power density. How quickly can | the energy be released? Consider solar panels, you need a table | sized cell to get 100W. That can make for a big battery to get | grid scale power output if these cells are only as power dense | as solar panels. The energy density of a heat based solution | can be very high- metals can get very hot and they are dense | enough to store a lot of energy. But if you can't get the | energy out of the battery fast enough that limits the | applications. By comparison lithium ion batteries can dump | power out extremely quickly, which is what makes them great for | cars. Hydro is even better. | walnutclosefarm wrote: | The article in Nature quotes an energy density of 2.38 | w/cm^2. Which means a Gw battery would require 10e5 m^2 of | absorber surface, exposed directly and at close range to the | radiation from molten metal (which is the heat transfer fluid | they propose). It has to be direct, and at close range, | because the efficiency they quote relies on the absorber | reflecting non-absorbed photons directly back into the | emitter, where they are re-absorbed as heat and potentially | re-emitted. | | That's about 25 acres of absorber, and an implied 25 acre | surface area of the liquid metal emitter pool. | | There is a basic challenge here to the design - the energy | storage density for the thermal battery they envision scales | as the cube of the characteristic dimension of the plant, but | the power density that can be delivered scales only as the | square of dimension. Not saying that can't be dealt with in | engineering, but it ain't going to make this easier or | cheaper. | matthewfcarlson wrote: | I think their application is grid scale and you can scale | across hundreds of batteries to provide the throughput you | need. I don't know how I feel about having a small molten | ball of metal inside the hood of my car. Turns my car into | the most dangerous gusher in the case of an accident (for | those who aren't familiar, gushers are a gummy like candy | with juice inside). | Retric wrote: | Surface area is relevant for solar because the sun is so far | away. A local heat source allows you to surround it with 3D | shapes not just a flat plain. | | As to temperature this thing is for very high temperatures: | _can generate electricity from a heat source of between 1,900 | to 2,400 degrees Celsius_. At 40% efficient you need a wide | temperature difference which would suggest a high energy | density. | walnutclosefarm wrote: | This design is photovoltaics, just like solar, but | optimized for infrared photons. There is no avoiding the | reality that energy storage density will scale as the cube | of the facility size, but power density only as the square. | And at 2.38 w/cm^2, the scale coefficient is not all that | great. | ethbr0 wrote: | For long term energy banking and if we can get them | working, flow batteries seem vastly superior to all | alternatives, by scaling storage with regards to tank | volume. Instead of some difficult-to-manufacture structure. | smrtinsert wrote: | Exactly why I clicked in, but man this technology sounds like a | serious gamechanger. | GoodJokes wrote: | Manuel_D wrote: | This device doesn't really change the energy landscape. Let's | rephrase the title: "A new heat engine is as efficient as a | steam engine but needs a thermal source 1,800 degrees celsius | hotter to work". The device described in the article is | interesting in that it has no moving parts and might have an | application one something like a nuclear powered spacecraft. | Actually trying to harvest energy from TEGs is exceptionally | difficult, since renewable energy sources aren't nearly as | energy dense as thermal fuels like hydrocarbons or fission. The | thermal gradients produced through renewable sources like solar | are tiny [1]. It could be used for something like geothermal | power, but again it needs temperatures way hotter than | conventional steam engines which already work fine for | geothermal energy production. | | 1. https://www.youtube.com/watch?v=Tdge8vEODeY | samatman wrote: | > _" A new heat engine is as efficient as a steam engine but | needs a thermal source 1,800 degrees celsius hotter to work"_ | | But this title would not be correct. | | Methane combusts at 1,957 degC, right in the band for this | thermal cell, and is a normal heat source for steam power. | | The steam doesn't reach this temperature, of course, but nor | does it need to. | zdkl wrote: | Re. thermal gradients, have you considered plain old mirrors? | https://en.wikipedia.org/wiki/Odeillo_solar_furnace | | > 54 metres (177 ft) high and 48 metres (157 ft) wide > more | than 2,500 h/year [sunlight] > peak power of 3200 kW > | Temperatures above 2,500 degC (4,530 degF) | | Sounds like it could be useful as a "default load" inside an | otherwise inactive solar furnace at least. | Manuel_D wrote: | You're describing solar thermal energy [1]. Use solar | collectors to turn light into heat, then use a heat engine | to turn that heat into electricity. This TEG could be used | as a heat engine for this task. But again, our heat engines | are already capable of this task and don't need such high | temperatures. A solar collector array even getting to this | TEG's operating temperature might not be feasible. | | Photovoltaics just turn solar energy into electricity, and | don't need the heat engine. This has made them way cheaper | to deploy than solar thermal energy. So unless there's | something very important about this new TEG, the solar | thermal vs photovoltaic calculus doesn't really change. | | 1. https://en.wikipedia.org/wiki/Solar_thermal_energy | guelo wrote: | The point is to store the thermal energy for later use to | smoothen out photovoltaic's intermittency issues. | Manuel_D wrote: | Right. But we already have that technology with | conventional heat engines which have the advantage of | much, much, lower operating temperature requirements. If | you have a 3,000 degree vat of thermal storage material | this new engine stops working after draining 1000 | degrees. Existing heat engines can usually work down to | several hundred Celsius - though superheated steam | engines need around 700 Celsius. But that's still an | extra 1000 degrees you can bring it down, even in the | conservative case. | gibolt wrote: | This is the first of its kind to reach this efficiency, | correct? | | I assume that means there could be room to significantly | improve its efficiency or operating requirements with | more investment and research. | | Having one example, even if 'useless' or elementary, is | key to developing new technology. | Manuel_D wrote: | Compared to other TEGs. Not compared to steam turbines. | The article is actually being very generous in saying | it's "as efficient" as steam turbines. Steam turbines are | more efficient with scale, and industrial ones for power | generation are over 90% efficient [1]. This new TEG's | efficiency is "around 40 percent". Higher than the | previous TEGs in the 25-35% range. But not compared to | steam engines, that also benefit from much lower | operating temperatures. | | 1. _Multistage (moderate to high pressure ratio) steam | turbines have thermodynamic efficiencies that vary from | 65 percent for very small (under 1,000 kW) units to over | 90 percent for large industrial and utility sized units._ | | https://www.epa.gov/sites/default/files/2015-07/documents | /ca... | jvanderbot wrote: | This is an absolute game changer for planetary exploration, | where RTGs are common. | xyzzyz wrote: | RTGs do not get anywhere close to 1800 degrees Celsius. | Even if they did, it wouldn't be a game changer, because | you can make up for loss of efficiency with a bigger RTG. | jvanderbot wrote: | OK, perhaps I stand corrected (or just tempered). | pvarangot wrote: | No news is good news, this one probably will work I guess. | yetihehe wrote: | > won't be useful, won't be cost effective | | > The team's design can generate electricity from a heat source | of between 1,900 to 2,400 degrees Celsius | | Pretty high temperature for me, copper melts at 1800C. | giantg2 wrote: | That might be when copper _liquifies_. It will lose its | structural integrity and deform easily at much lower | temperatures. | wishawa wrote: | High temperature is the point. The efficiency of heat engines | depend on the temperature difference (relative to ambient). | The hotter you can go, the better. (granted this thing isn't | really an "engine", but the trend still applies) | dv_dt wrote: | But for practical applications, the availability and cost | of materials to survive the operating temperature is also | relevant. | diarrhea wrote: | A Carnot heat engine operating between, say, 2600K and 400K | can reach almost 85% efficiency. | | The higher the temperature, the higher the share of exergy in | the heat flux. At high enough temperatures, it's no longer a | feat to convert to electricity at high efficiencies. | rowanG077 wrote: | It would be pretty hard to create a carnot heat engine that | can withstand 2600k. I'm not even sure if for example | Tungsten has structurally integrity at that point. | marcosdumay wrote: | This is not similar to anything on that page, as it operates on | temperatures of thousands of degrees. The comparison with steam | engines is also quite bad, as the Carnot efficiency on that | kind of temperature difference is way above 90%. | | So, it's just an overrating research PR piece, like the ones | people like to complain. This thing probably scales just fine, | and may be quite useful. The entire problem is that science | gets divulged on those insane PR pieces where it's compared to | completely different things, or promise completely impossible | results. | diarrhea wrote: | At those temperatures, Carnot efficiency is between 80 and 90 | percent. | | The comparison to steam engines is misleading, but there's an | important distinction. Steam or gas turbines _would_ reach | very high efficiencies at these temperatures too, but won't | because of material properties and limitations thereof. | | These limitations don't seem to exist for this new | technology. Hence, reaching very high efficiencies becomes | possible. In theory... In practice, I don't see how heat | sources with temperatures that high are feasible or could | stem from renewable sources. (something with the thermal | battery? Wasn't explained much in the article) | | In any case, _in comparison to steam turbines_ , the | technology presented here does absolutely nothing in terms of | decarbonising the grid, as claimed. It's just potentially | more efficient. But what's the source for the primary energy? | sroussey wrote: | Heliogen for solar, and Quaise for geothermal. Both have | high temperatures to deal with. | whimsicalism wrote: | Not to beat a dead horse, but nuclear? | fsloth wrote: | "in comparison to steam turbines, the technology presented | here does absolutely nothing in terms of decarbonising the | grid, as claimed" | | I understood the claim to be that this would have close to | no moving parts. That sounds it's cheaper to mass | manufacure and operate? | walnutclosefarm wrote: | The actual generator has no moving parts. The "tanks" for | storing the heat can be made from graphite, but the | thermal battery made by combining the storage tank with | the generator that they propose has to pump heat around | using liquid tin (or perhaps liquid silicon) as the | working fluid, at temperatures up to 2400C. That requires | not just moving parts, but some pretty far out | engineering. All of the metals we commonly build things | like pumps out of are liquid at those temperatures, after | all. And of course, you want pumps that run reliably for | years in that hostile environment. | diarrhea wrote: | Of all things keeping the energy transition back, steam | turbine manufacturing is probably very low on the list. | I'm not aware it's an issue. It's an old and proven | technology. | intrepidhero wrote: | I think the (unstated) idea is to use an arc furnace, | during peak solar/wind output to heat graphite and recover | the energy later using their fancy new TPV cell. That's | going to require some really good insulation, since your | heat source is intermittent and your temperature difference | is huge. | | My first thought was let's use it in fission (and later | fusion) reactors. | marcosdumay wrote: | It's too hot for a fission reactor. Probably for fusion | too, but that's not clear. | | I got the impression they would heat the graphite with | concentrated solar power. | MisterTea wrote: | The problem is it only generates electricity when the | input temperature is 1900-2400 C whereas uranium melts at | 1132.2 C. | the8472 wrote: | Most civilian reactors use uranium dioxide, which has a | melting point of 2865degC. Or uranium carbide, which | melts at 2350degC | klyrs wrote: | Passively slurping the heat off a critical puddle of | molten uranium is the disruptive startup pitch I'd make | to secretly record audience reactions. | marcosdumay wrote: | With unmoderated fast neutrons, and critical geometry | your startup will be always exceptionally close to | booming and taking over a huge flank of the market. | MisterTea wrote: | You can use this as an inspirational soundtrack for the | presentation: | https://sentientruin.bandcamp.com/album/wormboiler | 13of40 wrote: | I think they're talking about something like this: | | https://www.theverge.com/2022/2/22/22945975/rondo-energy- | dec... | | Basically, in their words, "a large insulated shoebox | full of brick". And I could be wrong, but I think you | should be able to scale the amount of "brick" up to | whatever size and keep the insulation the same thickness, | so the storage capacity would increase by the cube of the | scale and the amount of insulation would only increase by | the square of the scale. | | That would allow you to minimize the fluctuation in | temperature - i.e. if it takes 10 days to get up to | temperature, because it's big, you don't have to cool it | all the way back to room temperature when you take an | afternoon worth of energy back out. | biomcgary wrote: | For non-mobile storage, it seem that the waste heat (from | cooling the TPV) would still be at such a high temperature | that it can be used for co-generation to improve total | system efficiency. Do existing technologies exists to make | optimal use of this "temperature bandgap"? Would direct to | steam work efficiently? | abeppu wrote: | > the Carnot efficiency on that kind of temperature | difference is way above 90%. | | This is definitely not my area, but is Carnot efficiency | directly comparable to the efficiency numbers cited in the | article? Or is the "work" in Carnot efficiency the mechanical | work, prior to being converted to electricity? | kragen wrote: | Yes, it's directly comparable. You can interconvert | mechanical work and electricity freely; electricity isn't | like heat. Everyday machinery does it with 95% efficiency, | but there's no fundamental limit. | frankus wrote: | The university where I did a post-bacc had a research project | back in the late 1990s to build a TPV-powered hybrid electric car | that used compressed natural gas to heat an emitter surrounded by | water-cooled PV cells. | | With the technology at the time they weren't able to get the | efficiency to be competitive with an internal combustion engine, | but something like this probably could've made it competitive. | I'm not sure if there's any need for it with today's battery | performance/price, but maybe as a range extender or something. | | https://vri.wwu.edu/viking-series-cars-history/ (scroll down to | Viking 29) | | https://www.sae.org/publications/technical-papers/content/97... | (technical paper) | KennyBlanken wrote: | Toyota has had a 41% efficient engine in production for five | years. If it were set up as a range extender it would likely be | even more efficient (fixed RPM range and load can be optimized | for.) | | https://en.wikipedia.org/wiki/Toyota_Dynamic_Force_engine | jacquesm wrote: | Those are all amazing vehicles. I played a bit with water | cooled solar cells, I found that the hard part wasn't the | cooling but to be able to draw that much current from a single | cell, the attachment points for the wiring typically really | weren't up to the job and having multiple attachment points | became a necessity. You also need a pretty beefy pump and | radiator to get rid of the excess heat, though I guess in a | vehicle you would use an active system with a fan. | | What I don't understand about the Viking 29 article is how an 8 | KW generator is going to power a 75 KW motor, is there | something I'm missing? | opwieurposiu wrote: | There was a battery used for peak acceleration power. 8KW is | enough to cruise at highway speeds if you have an aerodynamic | enough body. | | More details: http://fennetic.net/pub/viking_29_thermophotovo | ltaic_electri... | jacquesm wrote: | Thank you! Very interesting design this. | tinco wrote: | If you point concentrated solar at a vantablack object, | heatsinked to this 40% efficient TPV, do you get an easy 39.94% | efficiency, easily outpacing mass produced photovoltaic or am I | missing a loss? | wishawa wrote: | What you suggested is more similar to what Solar Thermal | systems do | (https://en.wikipedia.org/wiki/Solar_thermal_energy). They are | known to be more efficient than solar photovoltaics. They have | their own downsides of course. | diarrhea wrote: | They are more efficient because converting anything to heat | is trivial. Heat is just losses basically. A process | consisting of 100% losses is great for heat generation. | | However, extracting exergy (electricity is pure exergy) from | a flow of energy is the tricky part and will always be | associated with efficiencies way below unity, based on | fundamental principles. | kragen wrote: | Yes, but labs have also produced 40% efficient multijunction | solar cells that work directly from sunlight without the | intermediate heat absorber. Off-the-shelf multijunction PV for | space applications is I think 36% efficient. | | Also, you don't need Vantablack, a regular cavity absorber | would be fine.) | jayd16 wrote: | Does vantablack have some kind of clear coat that makes it | suitable for industrial use and cleaning? | JaimeThompson wrote: | I don't think such a coating has been developed, but I could | be wrong but I do know that by default just touching it can | really damage vantablack. | tinco wrote: | You could encase it in glass under a vacuum or in some inert | gas. | prewett wrote: | It sounded like it wasn't the heat that got converted to | electricity, but rather the photons emitted by the hot object | glowing, and since your vantablack object is not glowing you | would expect to get nothing. | | But maybe not, the glowing comes from black body radiation, so | the vantablack material would presumably glow as well | (ironically). As long as the heatsink coupling did not block | the visible "white" light produced, or glowed itself, then at | least the photons from the back would get used. I expect that | getting a heatsink paste rated for 2200 C is ... challenging, | but, conveniently, you'd do better if you just skipped the | paste. | wongarsu wrote: | > I expect that getting a heatsink paste rated for 2200 C is | ... challenging, but, conveniently, you'd do better if you | just skipped the paste | | Liquid metal is some of the best performing thermal paste | around. In computer applications that's normally an alloy | made from Gallium, Indium and Tin, but at 2200C the majority | of metals should work. Maybe Gold to reduce oxidation. | multiplegeorges wrote: | The vantablack material would indeed "glow", as everything in | the universe glows. It just does so outside the visible | spectrum. The difference between this thermo-voltaic cell and | a photo-voltaic cell is that photo is visible spectrum and | thermo is IR. It's all just photons! | rosetremiere wrote: | The article says, if I'm not mistaken, that the heat source | must be between 1900 and 2400 degrees (Celcius), and I would | bet that Vantablack loses its blackness at such temperatures? | chucksta wrote: | Wikipedia indicates the melting point of vantablack being | 3000C. I would think a black coloring is pretty heat | resistant. It looks like it needs to be 500-750C to create it | as well | sbierwagen wrote: | In vacuum, maybe. Vantablack is made of carbon nanotubes, | and those oxidize away in atmosphere above 750C. | VBprogrammer wrote: | One minor issue is diffusion due to clouds, similar to all | concentrated solar power systems it needs direct sunlight. | Normal solar panels can produce some power even under a thin | cloud layer. | voakbasda wrote: | I'm guessing the vantablack would be destroyed by the | concentrated heat or UV. Or is there an industrial formulation | that could withstand the high temperatures? | dioxide wrote: | You'd need the solar to heat something white hot. | adrian_b wrote: | This is just a multi-junction photovoltaic cell optimized for | temperatures of the radiant body between 1900 and 2400 Celsius | degreees. | | Such multi-junction photovoltaic cells, but optimized for the | higher temperature of the Sun, have existed for many years and | efficiencies over 45% are well known. | | So there is no point in heating anything, the concentrated | solar light must be directed to an appropriate multi-junction | photovoltaic cell, for the best efficiency. | | Despite their very high efficiency, the multi-junction | photovoltaic cells are seldom used for solar energy, because | they are expensive, so they can only be used together with | light-concentrating mirrors, to achieve a reasonable cost. | | Even with mirrors, the price is still much higher than for | normal solar panels, so they might be chosen only when space | constraints would prohibit the use of a larger area with solar | panels. | moffkalast wrote: | Might be useful for electric planes or cars where you have | very limited area? How high of a price multiplier are we | talking about? 2x, 10x, 100x? | | I can't seem to find any place that sells these with a brief | search, so I'm thinking 1000x. | tinco wrote: | Electric cars don't have enough area for solar power, and | planes have even less. | djrogers wrote: | No - you'd get nothing - concentrated solar gets you in the | 800-1000* range, and per TFA the TV cells work at 1900-2400*. | | [0] | https://www.sciencedirect.com/topics/engineering/concentrate... | jandrese wrote: | Isn't that because the current designs use liquid sodium as | the working fluid at the boiling point is near 900C? | WJW wrote: | Apart from the vantablack heating issues sibling comments have | already mentioned, you'd also need to take into account the | energy used by the cooling system for the cold end of the TPV. | In practice you'd need to pump either water or air past some | form of heatsink and the energy consumption of the pumps would | reduce the efficiency below that of the 40% of just the TPV. | jandrese wrote: | This would be a heck of a lot of waste heat to deal with. You | could probably boil water with the leftover energy to turn a | steam turbine to power the cooling apparatus. A dual stage | solar plant. | rowanG077 wrote: | If water is viable this would indeed seem almost too good | to be true. | tshaddox wrote: | It would be less waste heat than a system that captured the | same amount of sunlight but converted it to electricity | less efficiently, right? | jandrese wrote: | The reason for the high level of waste heat is that the | system has to operate at thousands of degrees C. There is | still a huge potential above room temperature. Most | systems work closer to room temperature so there is space | to squeeze them in after this system has extracted all of | the energy it can. | kragen wrote: | Yes, but the pumping power is about 0.2% of the total power, | so this is not a significant consideration in practice. If it | was, people would use solar chimneys instead of mechanical | fans and pumps. | nicoburns wrote: | > The researchers plan to incorporate the TPV cell into a grid- | scale thermal battery. The system would absorb excess energy from | renewable sources such as the sun and store that energy in | heavily insulated banks of hot graphite. | | It's clearly not ready for production yet, but storing energy as | concentrated heat seems like one of the plausible proposed grid- | scale storage solutions to me. I'm interested to see where this | goes. | diarrhea wrote: | Concentrated energy is not a technical term. But high- | temperature internal energy storage (aka heat storage) is | terrible because of the losses. | | For example, low temperature floor heating is very efficient. | | You don't want high temperature deltas because of the | associated exergy losses. | CSSer wrote: | Does anyone know if we already use things like this to increase | the efficiency of existing energy usage in applications which | require high degrees of heat output by recycling energy that is | otherwise lost as excess thermal output? | | The example that springs to mind for me is a steel mill. The | temperatures required there easily meet and exceed what is | required to generate and store energy with this device. | 323 wrote: | Probably not in a steel mill, because otherwise you could have | just heat water to steam and use it to run a generator. Since | this is not done, there is a catch. | | An example where this idea works is a condensing boiler where | the burned gases heat is used to increase efficiency by 10-30%. | tomxor wrote: | > can generate electricity from a heat source of between 1,900 to | 2,400 degrees Celsius [...] plan to incorporate the TPV cell into | a grid-scale thermal battery. The system would absorb excess | energy from renewable sources such as the sun and store that | energy in heavily insulated banks of hot graphite. When the | energy is needed, such as on overcast days, TPV cells would | convert the heat into electricity, and dispatch the energy to a | power grid. | | Heating graphite based thermal batteries to >1900C using the Sun | for long term storage? I'm not sure why the article is refraining | from being explicit, but i'm guessing the intended application | here is to replace the steam turbine usually found at the centre | of high temperature solar thermal collectors. | | I wonder how feasible and cost effective it is to insulate a | battery well enough to maintain over 2000C for multi day periods | without substantial loss? The heat storage strategies used for | steam turbines doesn't require such high temperatures. | lapinot wrote: | relevant lowtechmag article: | https://solar.lowtechmagazine.com/2020/05/thermoelectric-sto... | | tldr: thermoelectric generators don't have great efficiencies, | but by cogenerating heat and electricity they can get viable (if | you need heat and electricity, make a bit more heat than you need | and put a thermoelectric generator, the non-converted heat will | just end up as useful heat). This would be adapted to households, | which typically need a lot of heating. | Simon_O_Rourke wrote: | This is great, but all of this feels like it's coming 15 to 20 | years too late. I worked with a guy in Berlin who had previously | worked in PV energy. He predicted that unless the costs were | reduced by a factor of half the price point of fossil fuels that | it would go nowhere. We're addicted to cheap, no hassle sources | of energy right now, and it's depressing. | GoodJokes wrote: | andrepd wrote: | Millions of people already die yearly from pollution. It's | definitely not hassle free. | Maursault wrote: | You have to wonder what PV would cost if even a tenth of the | resources invested in developing nuclear energy were instead | invested in solar energy development. I expect by 1980, solar | energy would have been the cheapest way to generate | electricity, President Carter would have been reelected, no | Iran-Contra affair, and no deregulation of banks leading to the | 2008 recession, and likely would have avoided 911, both Iraq | wars and the one in Afghanistan. We could have saved all kinds | of money, had cheap energy, still had plenty of nuclear power, | and it wouldn't be so damn hot all the time. | TSiege wrote: | This is a great timeline to imagine :) | outworlder wrote: | > You have to wonder what PV would cost if even a tenth of | the resources invested in developing nuclear energy were | instead invested in solar energy development. | | Not enough was invested in nuclear. Fossil fuels received | massive funding (and subsidies). Had we deployed more nuclear | power for baseline and industry, we would have been in a far | better place. The Cold War also messed up things, and caused | the reactors that were deployed to be the ones better suited | for weapons first, energy second. | | Note that our solar panels are similar to computer chips. | Investing more money would have sped up the development but | not in time for it to be viable in the 80s. | Maursault wrote: | > Not enough was invested in nuclear. | | The Manhattan Project cost, adjusted for inflation, $22B. | That was just to blow something up. Had the United States | and Great Britain not subsequently developed nuclear | energy, it is likely it never would have been developed | because it would have been impossible due to cost. Only a | nation can develop nuclear energy, it is not something that | could have been developed privately, again, due to cost. | | When factoring the cost of the energy produced by nuclear | fission, the cost of that electricity, the cost of the | development of nuclear energy is never factored in. If it | were, it would be clear there has never been a more | expensive way to generate electricity than nuclear fission. | Nuclear energy development was a freebee, and the biggest | freebee in the history of civilization: nuclear energy | development, paid for by tax payers, was _given away_ and | the tax payers ' investment _never had one penny of | return_. "Electricity too cheap to meter," never | materialized, and not even close. The tax payers were | bamboozled. | | When all is said and done, the treehuggers have the weaker | argument. Sure, nuclear energy has some environmental | concerns, but these kinds of arguments pale in comparison | to the economic argument: nuclear energy has never been and | will never be economically viable. There are reasons, but | they can be ignored, because we can see the result, no | investor will touch nuclear. And complaining about the type | of nuclear plants serves no purpose because the fission | plants we built are the cheapest designs there are. Seeder | reactors would be cool, but, you see, they're even less | economically viable than the fission steam turbine plants. | | We could invest everything, every dollar earned, every | possible value society could produce, into nuclear energy | development, but even if we did, nuclear energy would | remain economically unviable. | | Again, if we could just invest a small portion of what we | wasted on nuclear energy development into solar energy | development... well jusT look at how cheap solar has gotten | in 20 years with _private_ development. Imagine if it was | 80 years instead of 20 and included massive, mind-boggling, | government subsidies. Forget any government investment in | solar, if solar subsidies could merely match nuclear | subsidies, dollar for dollar, no one would be talking about | nuclear power anymore. | soperj wrote: | >The Manhattan Project cost, adjusted for inflation, | $22B. | | China spends 4 times more than that yearly on solar. | Maursault wrote: | And well they should, as they can expect a 20% ROI, | meanwhile, nuclear fission, since inception, has yet to | be profitable. Not even once. | 8bitsrule wrote: | Agreed ... but I'll posit the existence of technical | 'treehuggers' who knew it early on (and kept quiet after | what happened to Oppenheimer.) | | Further posit: they were aware that nukes were more about | making Pu than heat. No insurance company back in the day | would accept the risk either (thus the 1957 'Price- | Anderson Nuclear Industries Indemnity Act'). | | Anyway, I'll quote a 1951 expert: "t is safe to say ... | that atomic power is not the means by which man will for | the first time emancipate himself economically.... At | present, atomic power presents an exceptionally costly | and inconvenient means of obtaining energy which can be | extracted much more economically from conventional | fuels.... This is expensive power, not cheap power as the | public has been led to believe." -- C. G. Suits, Director | of Research, General Electric, who who was operating the | Hanford reactors. | [https://www.ieer.org/pubs/atomicmyths.html] | nynx wrote: | Thankfully, the price of PV has dropped by far more than a half | over the past ten years. | k__ wrote: | Can it also absorb excess heat from me? | outworlder wrote: | Unless you are a member of the Fantastic Four, no. | mfrieswyk wrote: | Could something like this directly harvest the heat from a | traditional nuclear plant? Or would it degrade from the | radiation? | philipkglass wrote: | This thermophotovoltaic cell is tuned to operate with radiant | energy from a body heated to between 1900 and 2400 degrees | Celsius. That is much hotter than any current reactor core. It | wouldn't work with a traditional nuclear plant; it would | require (at a minimum) developing reactors that operate at a | much higher temperature. The most common power reactor design, | the pressurized light water reactor, heats water to around 315 | degrees Celsius: | | https://en.wikipedia.org/wiki/Pressurized_water_reactor#Cool... | worldsayshi wrote: | Could this maybe be used as part of a fusion reactor? | short_sells_poo wrote: | I think the problem isn't that we can't achieve 2000 | degrees with fission, but the entire design would need to | be re-thought to handle such temperatures. | | You need a completely different sort of materials and need | to consider new types of risks for a reactor that's | supposed to operate at such temperatures. | aidenn0 wrote: | Most semiconductors don't like ionizing radiation. In addition, | the bottom-end of the operating range for this (1900C) is well | above what google suggests is the typical coolant temperature | (300C). | aidenn0 wrote: | TFA says turbines can't operate for heat sources around 2000C. | I'd believe they can't operate with _steam_ at 2000C, but can 't | you decrease the temperature of the steam relative to the heat | source by increasing the flow rate? | wayfarer1291 wrote: | There's a silicon-valley based company that's building a combined | thermal storage and TPV system: https://www.antoraenergy.com So | these ideas may be get to market sooner than a typical university | press release. | | https://www.nrel.gov/news/features/2021/new-projects-move-th... | | (some of the same people involved in this paper at NREL seem to | also be collaborating with Antra, which is great to see) | pooloo wrote: | Dyson sphere, maybe? | mwattsun wrote: | Sometimes I like to take a step back and imagine a world with | nearly free energy. Converting sea water to fresh water to | irrigate the deserts is always the first thing that comes to | mind, but that's mundane compared to the changes nearly free | energy will bring, which is the direction we seem to be heading. | civilized wrote: | It will be unimaginable. I truly hope it is closer than I think | it is. | kibwen wrote: | As long as proof-of-work cryptocurrencies exist, free energy is | impossible. Any time the price of energy falls below a certain | point, the energy consumption of the network will increase to | compensate. PoW is a floor on the price of energy. | synalx wrote: | I love that the article talks about realizing a "decarbonized | grid" by storing energy in literal chunks of carbon. | after_care wrote: | That's funny wordplay, but atmospheric carbo is clearly the | intended implication. | falcolas wrote: | I'm not well enough versed in these kinds of devices - how does | this differ from a traditional thermocouple device? | djrogers wrote: | Thermocouples are far less efficient - 5% or less, vs 40% for | these. | jandrese wrote: | Traditional thermocouples have abysmal efficiency. 5% is about | the best you can hope for. This device claims to be 8x as | efficient. | lisper wrote: | More efficient by an order of magnitude or so. | XorNot wrote: | I'm struggling to figure out what this is. If you can capture | heat from a "white hot" object, why is it not just a good solar | cell? The sun is easily in this range. | icodestuff wrote: | If I'm reading this right, this actually has a larger usable band | gap range than traditional photovoltaics -- the article talks | about capturing the high-energy photons -- in the first pass. | This means that the cell can actually capture the electrons | knocked out by those high-energy photons, which is something we | haven't been able to do. | | Silicon's band gap (1.11 eV) corresponds to 1110 nm (NIR), and | any photons with more than 3 eV energy (413 nm) are lost (and all | the excess energy in photons in between is lost as heat). Newer | cells are around 0.6-0.7 eV, but I don't know their maximum | capture energy. That's all the violet light and UV. There's a | startup that makes a polymer film that can create two lower | energy photons in the band gap from a high-energy photon to | capture some of that wasted light. This would seem to be a cell | that could capture it directly. Very very cool; that's a lot more | energy captured per photon. | | What I'm unclear on is why you need to heat it up so much to get | to those efficiency levels, and it wouldn't just work as an | ordinary solar cell. | MatteoFrigo wrote: | The article is confusing, but I read it the same way as you: | these guys have figured out a way to capture a larger part of | the blackbody spectrum than a normal photovoltaic cell. I don't | think they are saying that the cell needs to be heated up. I | think they are saying that they capture 40% of the power of a | blackbody at 2000K. I am not sure why they don't mention what | happens for a blackbody at 5600K such as the Sun. | SnowHill9902 wrote: | To everyone in this thread commenting about the Carnot | efficiency: yes, the Carnot efficiency grows with T, but you must | use a Carnot engine for that! The Carnot theorem is an upper | bound not a property of a given engine. It's trivial to build a | heat engine whose real efficiency (measured efficiency / Carnot | efficiency) approaches 0. | gene-h wrote: | This would be interesting for powering spacecraft because it | doesn't have any moving parts. For the most part, spacecraft are | not serviced ever, so it's best to minimize things that can | break. | | Nuclear powered spacecraft have been hard to develop because of | the need for moving parts. NASA's cancelled Advanced Stirling | Radioisotope Generator, which was supposed to be a more efficient | radioisotope powered generator than the thermoelectric generators | previously used, had trouble because the moving part based | generator wasn't very reliable.[0] | | In addition to eliminating moving parts this is also interesting | for nuclear powered spacecraft because it may be possible to pass | light through a radiation shield to prevent damage to the | converter. The problem is that the reactor would need operate at | extremely high temperatures. While this probably isn't high | enough to melt the fuel, the fuel might not be structurally | stable. Although liquid uranium nuclear rockets are being | considered[1]. | | [0]https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope.. | . | | [1]https://www.uah.edu/news/items/bubble-through-nuclear- | engine... | beambot wrote: | I was under the impression that NASA RTGs relied on solid-state | Peltier / Seebeck thermocouples that had no moving parts: | | https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge... | blamazon wrote: | Those thermocouples are less than 10% efficient, usually less | than 5%. | | This means you have to dissipate more than 10 times more | energy as heat than the energy you actually want to use as | electricity. | | Dissipating heat in space is not easy because unlike earth | there is no surrounding fluid to dissipate heat into through | convection. This means you have to spend precious mass budget | on huge (compared to your energy budget) direct heat | radiation systems that cannot leverage convection | efficiencies. | | Thus, a significant energy efficiency increase would be a big | deal for RTG powered spacecraft design. It is curious that | the article above does not consider this. | | Bonus thought: consider what this lack of convection problem | means for "Hyperloop" type vehicle systems that operate in a | vacuum tunnel, as most conventional trains dissipate excess | braking energy through convection from resistive heating | elements atop the roof. | caf wrote: | Conventional trains that run under wires can also dump | excess braking energy into the overhead. That seems | feasible even if you had to have your resistive heating | elements somewhere outside the tunnel system. | foxyv wrote: | That is correct, I think the RPG design was to improve the | efficiency of the RTG. | tomxor wrote: | Yup, Voyager 1 and 2 are still running off RTGs right now | since 1977. | | However the thermoelectric converter used in those RTGs | exploit a different effect, and appear to have quite | different properties as a result... What I can tell from a | quick dig: | | - Thermocouples ("Seebeck effect") operate on a temperature | difference, and are more commonly used as temperature | sensors. They have the advantage of working at a larger range | of temperatures, but the disadvantage of needing to maintain | a temperature gradient for power production... Any inherent | efficiency is likely negated by the requirement for constant | cooling. [0] | | - Themal Diodes ("Thermophotovoltaic") is more like a solar | panel for a different wavelength (infrared). The principle | they operate on suggests no temperature gradient is required, | not sure about cooling for other reasons though, but the | clear disadvantage is the requirement for a high operating | temperature for effective use in power production. [1] | | Historically thermal diodes don't appear to have been | particularly efficient compared to thermocouples either, | obviously this particular one changes that. | | [0] | https://en.wikipedia.org/wiki/Thermocouple#Power_production | | [1] https://en.wikipedia.org/wiki/Thermophotovoltaic | the8472 wrote: | > The principle they operate on suggests no temperature | gradient is required | | A temperature gradient is absolutely required. Ignoring | materials problems (such as melting) a photovoltaic cell | ultimately does work off a temperature differential because | it has to absorb photons. It cannot do that if its | temperature is the same as the black body temperature of | the lightsource illuminating it, otherwise they would be at | an emission/absorption equilibrium. | | This is also why PV cells could theoretically work in | reverse mode at night, emitting IR into space. They'd just | do that paltry power ratings because _DT(earth, cosmic | background)_ is much smaller than _DT(photosphere, earth)_. | And they 'd have to be made of a material with a much | smaller bandgap. | tomxor wrote: | You're right, I kinda knew it needed cooling, but I guess | your point is even though the effect being exploited | doesn't require a temperature gradient, in practice the | heat dissipation requirements are the same if the TVP is | to survive - or are they different... surely for the | purposes of satisfying the first law the temperature | dissipation requirements are dependent on the efficiency | of conversion? | | Which would make the cooling requirements of this TVP | lower (relative to input) due to it's higher efficiency? | but still substantial. | [deleted] | jvanderbot wrote: | OK, so perhaps it's not the de-carbonization future we all | wanted, but this could be an absolute game changer for planetary | exploration, where RTG (nuclear-decay-driven thermal engines) are | common. The existing efficiency for those is abysmal, which is | actually OK since heat is such a useful product in itself. | | I'm looking at Dragonfly, specifically, where an RTG provides the | electricity and heat to keep everything alive. Imagine what 10x | longer flights would do for that mission. | tomxor wrote: | The advantage does appear to be higher efficiency compared to | themocouples, and the TVP should in theory require less cooling | _relative_ to the input due to the higher efficiency - However | the disadvantage is that TVPs generally require a far higher | operating temperature for effective power production, which may | actually require more sophisticated cooling. | | This particular one requires around 2000C, which appears to be | above the critical temperature of most RTGs (though not all!): | | https://www.researchgate.net/figure/Critical-temperatures-to... | | I wonder if those RTGs also have any disadvantages or are | simply more substantial. | | [edit] | | Corrected cooling requirements as pointed out by the8472 in | another comment. | nautilius wrote: | Do RTG reach the >2170K necessary for this? | jvanderbot wrote: | Apparently not, as someone below pointed out. | | Oh well, I was briefly excited but there's a big enough gap | that it probably won't work as is | perihelions wrote: | Apparently not. This 1991 document [0] says the GPHS heat | source [1] has (?) an upper operating limit of 1,300 degC | (1,573 K), at the iridium cladding that contains the Pu-238 | fuel. There's a suggestion this could be raised to 1,500 | degC. | | [0, pdf] https://ntrs.nasa.gov/api/citations/19910015359/down | loads/19... (2.2 "Temperature Constraints") | | [1] https://en.wikipedia.org/wiki/GPHS-RTG | WheelsAtLarge wrote: | "OK, so perhaps it's not the de-carbonization future we all | wanted, but this could be an absolute game changer" | | I hate to throw water on the situation but we constantly read | articles about tech that will be a game changer only to never | be seen again mainly because it can't be scaled to the size | needed and provide the advantages we need. | | Yes, it sounds good. But what we need now is a proof of concept | rather than theories on how much of a miracle the tech is. My | question is, "How can we help to move it forward to a point | where we can see actual advantages?" | petermcneeley wrote: | Keep in mind that Carnot efficiency at this temperature is nearly | 90% https://en.wikipedia.org/wiki/Carnot_cycle | | 1 - Tc/Th = 1 - 295k/2000k | SnowHill9902 wrote: | Yeah but heat losses grow with the 4th power (!). | mrfusion wrote: | We could drastically shrink coal, and nuclear power plants if we | can do away with the steam turbine portion. | tenthirtyam wrote: | Well now. We can have a heat pump with a COP of 3.5 or so. Let's | say we put in 1kW of electricity, and take out 3.5kW of heat | energy. Now let's take 2.5kW of that heat energy, push it through | this gadget at 40% efficiency to get 1kW electricity out. Push | that back into the heat pump and, viola, 1kW of free heat left | over! | | What am I missing? | danans wrote: | > We can have a heat pump with a COP of 3.5 or so. Let's say we | put in 1kW of electricity, and take out 3.5kW of heat energy. | | A heat pump COP of 3.5 or higher or happens only at relatively | low delta-T between the source and destination temps of the | heat pump [1] - like the delta-T typical for space or water | heating. The COP degrades exponentially with increasing delta T | as it has to work ever harder to pump heat against an ever | higher temperature/pressure (assuming thermal storage with a | fixed volume with few losses). | | The refrigeration cycle can't raise temperatures even hundreds | (much less thousands) of degrees C - otherwise we'd already | have heat pump stoves and ovens. | | This is coincidentally also one reason why all else equal, heat | pump clothes dryers (which are great) take a bit longer than | conventional technologies to dry clothes: they only reach about | 50C (vs 70C-75C for standard gas or electric resistance | dryers). | | > Push that back into the heat pump and, viola, 1kW of free | heat left over! | | Because the COP degrades with the delta-T, it bottoms out at 1 | (an electrical resistance heater), and in your scenario, you | end up with 1kWH in, and 400Wh out, so a theoretically 40% | efficient battery. | | Minus the electrical generation, and at much lower | temperatures, your scenario with a heat pump + thermal storage | does however describe how the new domestic thermal heat | batteries can work with heat pumps [2]. | | 1. https://www.engineeringtoolbox.com/heat-pump-efficiency- | rati... | | 2. https://sunamp.com/ | syntaxing wrote: | Entropy. You cannot look at a system purely from an energy | conservation stand point. Take Carnot efficiency for instance. | That's the extreme case where it teeters on the fully | recoverable entropy. For your example, the entropy price has to | be paid somewhere in the system (usually in the heat to work | ratio). | audunw wrote: | > What am I missing? | | Just guessing, but a heat pump that can actually output at | least 1900degC of heat? | | If we had those kinds of heat pumps I guess we'd use them in | all kinds of industrial processes | usrusr wrote: | If the stored heat is on the level of getting the emitter into | the white-hot, how is the "battery" turned off, to hold the | "charge"? | | The article mentions a mirror layer as part of the cell, for | retaining the energy of out of band photons. Would that be the | "off" solution, just bounce them back when they are not needed? | Cell moved out of the path? Somehow that triggers "too simple to | be true" heuristics in me, but on the other hand... yeah, mirrors | (or just very white surfaces, precise direction is not needed) | can be quite capable of not getting heated by incoming photons, | and that must mean bouncing them back. | karamazov wrote: | You have a heat reservoir, i.e. a well-insulated and very hot | object, that stores energy as heat. If you insulate it with | mirrors, that can look like bouncing photons back into the | reservoir. | | When you want to generate energy, you open the insulation and | let heat out to hit this chip. | | It's like opening an oven door to let some hot air out. | megaman821 wrote: | Is there some sort of physical property when you are that hot | (2400C) that you begin glowing? Then just open a slot in the | insulation so the photons cell whenever you need electricity. | robotresearcher wrote: | That's what the article says. | | "The heat engine is a thermophotovoltaic (TPV) cell, similar to | a solar panel's photovoltaic cells, that passively captures | high-energy photons from a white-hot heat source and converts | them into electricity." | | One detail is that objects radiate at all temperatures. The | trick is to choose the temperature so that you get a lot of | emission in the band that matches the best performance of the | PV component. | scythe wrote: | https://en.wikipedia.org/wiki/Black-body_radiation | tialaramex wrote: | If your question is "wait, do all hot things glow?" then the | answer is Yes. | jacquesm wrote: | Everything above absolute zero emits infrared photons, as | something gets hotter it will also start to emit in the visible | range because some of the photons are more energetic resulting | in a shorter wavelength. That's why you see the progression | from barely visible red to red to orange, yellow and eventually | white when you make something hot enough. But it will always | continue to output photons at lower energy levels as well, | though not in equal proportion (and that's why a hot _object_ | is white and not blue, and why a hot _gas_ flame can be blue). ___________________________________________________________________ (page generated 2022-04-13 23:00 UTC)