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As a newbie in nuclear fusion, this explanation is the most interesting part: > Lee Margetts at the University of Manchester, UK, says that the physics of fusi
by j15e 4y ago
As a newbie in nuclear fusion, this explanation is the most interesting part:
> Lee Margetts at the University of Manchester, UK, says that the physics of fusion reactors is becoming well understood, but that there are technical hurdles to overcome before a working power plant can be built. Part of that will be developing methods to withdraw heat from the reactor and use it to generate electrical current.
> “It’s not physics, it’s engineering,” he says. “If you just think about this from the point of view of a gas-fired or a coal-fired power station, if you didn’t have anything to take the heat away, then the people operating it would say ‘we have to switch it off because it gets too hot and it will melt the power station’, and that’s exactly the situation here.”
- bumblebritches5 4y ago
- baby 4y agoSimilar to how energy is extracted from fission reactors currently: the heat is used to boil water which makes large turbines spin and produce energy. It's dumb engineering. (I don't mean that in a bad way.)
- z3rgl1ng 4y ago
- bryanlarsen 4y agoIt's also very expensive engineering. That's how a coal plant works, and the last coal plant that the US built cost $2B for a 600MW plant. Given how much cheaper solar & wind are, fusion will be dead in the water if it doesn't come up with a cheaper way of extracting energy from the reaction.
- nemo44x 4y agoSolar and wind are not serious solutions to the energy needs of the planet today or in the future. As billions more people become part of a global middle class our energy requirements will expand dramatically from today.
- ceejayoz 4y ago> As billions more people become part of a global middle class our energy requirements will expand dramatically from today. https://www.nrel.gov/docs/fy04osti/35097.pdf https://www.nrel.gov/docs/fy04osti/35097.pdf "In the United States, cities and residences cover about 140 million acres of land. We could supply every kilowatt-hour of our nation’s current electricity requirements simply by applying PV to 7% of this area—on roofs, on parking lots, along highway walls, on the sides of buildings, and in other dual-use scenarios." "We would need only 10 million acres of land—or only 0.4% of the area of the United States—to supply all of our nation’s electricity using PV."
- robertlagrant 4y agoI really wish this sort of thing would either be better thought through or better articulated. 10 million acres is enormous. And is it continuous supply (if so, how?) Or just supply when it's sunny?
- ncmncm 4y agoIsn't it amazing that no one has ever thought about these things before you dropped in?
- robertlagrant 4y agoYou've missed my point.
- ncmncm 4y agoEverybody has known all along that renewables generation is intermittent. Mentioning it adds no light. And renewables happily coexist with other uses of the same land, so none is used up.
- robertlagrant 4y ago> Everybody has known all along that renewables generation is intermittent That doesn't mean it's made clear in statistics. I've read plenty of people say "X generates as much as Y", where X is intermittent and Y is suitable for base load. Certainly enough to disagree that everyone knows it and is able to discern that from context-free statistics.
- flavius29663 4y agosolar and wind can be free, if the sun does not shine and wind is not blowing 100% of the time...
- ncmncm 4y agoThis trivial observation, always trotted out, is always meant just to distract. Trolling, really.
- flavius29663 4y agoIt's not trolling, look at what Germany and California are struggling with... Also Texas, another state where they pushed green energy (wind) and slowed the investment in fossil fuels. We all want cleaner energy, but we must acknowledge that it is not easy.
- bryanlarsen 4y agoOn the contrary, California is struggling with with electricity generation during times of high A/C loads due to a heat wave. Those times correspond with high solar power generation, without solar they'd be doing a lot worse. On the contrary, Germany has met their goal of 80% full natgas storage several weeks early despite the French nuclear reactors being offline due to higher than expected renewable energy supplies.
- flavius29663 4y agoYou're saying that Germany and California are not struggling with the electric grid...now I believe you're trolling They invested a lot in solar power, which is expensive, so they couldn't afford to invest enough in transmission and backup generators, and now they have expensive electricity and unreliable grids. Ignoring current year, I think Germany is second in the world in regards to expensive electricity (after Denmark) and California is one of the most expensive states in the US.
- 4y ago
- sdenton4 4y agoIt's easy enough to solve... point an energy-collecting device at the giant pre-built fusion reactor in the sky.
- gridspy 4y agoYes, but most of the time that fusion reactor is behind a giant hunk of iron covered in various other matter. Even when in the sky, the sky itself is an effective insulator that only allows 1/4 of the energy through. That's why we are considering placing a converter above the sky to more efficiently pierce the sky with energy.
- markdown 4y agoTowing the converter outside the environment is something I can get behind.
- u320 4y agoYou cannot build a grid out of solar and wind alone.
- zardo 4y agoYou also need transformers and batteries and power lines.
- ncmncm 4y agoMost storage won't be batteries.
- salty_biscuits 4y agoThen don't do it. Grids are expensive. Microgrids and storage seem like a winning plan.
- u320 4y agoMicrogrids and storage cost way more than any method of generating power we are currently using. Please stop using buzzwords and look at the actual numbers.
- ben_w 4y agoAt grid scale, batteries were about the same cost as a functionally equivalent fission reactor last time I looked (a few years ago). Despite which, batteries are one of the more expensive ways to store energy at scale.
- u320 4y agoI don't know where you looked then because batteries are not anywhere near low cost enough to be deployed at grid scale at the amounts required to run a grid of wind and solar. Even in a sunny climate with reliable solar output, if you assume that there is a 10% chance that in any year you will have a 10 day period of cloud cover and 50% lower solar output and your entire grid cost goes up by 5x! The math for storage is BRUTAL.
- tomatotomato37 4y agoSpeaking of solar it would be nice if we could just plate the inside of a reactor with photoelectrics instead of blowing all the budget on a clusterfuck of a steam system. Too bad silicon doesn't like 100M degrees... Actually thinking about it figuring that out would make fission a lot more tenable too
- u320 4y agoFusion produces neutrons, not photons.
- DFHippie 4y agoI'm pretty sure it produces both.
- fy20 4y agoIs there an equivalent of the photoelectric effect for neutrons?
- ncmncm 4y agoNone. Hot neutrons are the lowest-grade sort of energy.
- blincoln 4y agoMaybe a dumb question, but could one use bricks of depleted fission fuel as the neutron shield in a fusion reactor, and swap them back into a fission reactor every time they become fuel-grade again?
- ncmncm 4y agoIt would be an overwhelmingly smarter and better use of money to burn uranium in an ordinary fission plant, and maybe breed up extra fuel there. But we already know that fission, too, is uncompetitive, moreso each day as costs for renewables and storage continue relentlessly downward. Fusion has no chance of ever catching up.
- compumike 4y agoI'm not sure where your numbers are from, but just because $2B sounds like a big number, it isn't inherently a dealbreaker. If that's 600 MWe, running at 80% capacity factor, amortized over 30 years, then the $2B becomes: 2e9/(600 * 1000 * 0.8 * 24 * 365 * 30) = $0.0158 / kWh -- the $2B capital cost amortizes to 1.6 cents per kWh of electricity sold. Not zero, but 1.6 cents is far less than the current market price of a kWh. If you're going to compare to utility-scale solar or wind, be sure to include their much lower capacity factor: https://en.wikipedia.org/wiki/Capacity_factor#/media/File:US_EIA_monthly_capacity_factors_2011-2013.png https://en.wikipedia.org/wiki/Capacity_factor#/media/File:US... (Admittedly: we don't yet know the capital cost of a working fusion heat source, or its capacity factor. Both will determine whether this is economically competitive.)
- dtgriscom 4y agoYou aren't including fuel costs; any guesses?
- compumike 4y agoYou might be interested in Lazard's "Levelized Cost Of Energy" PDF (https://www.lazard.com/media/451905/lazards-levelized-cost-of-energy-version-150-vf.pdf https://www.lazard.com/media/451905/lazards-levelized-cost-o... , from https://www.lazard.com/perspective/levelized-cost-of-energy-levelized-cost-of-storage-and-levelized-cost-of-hydrogen/ https://www.lazard.com/perspective/levelized-cost-of-energy-...). On page 15 note "This analysis does not take into account potential social and environmental externalities or reliability-related considerations", and that solar and wind do not get the checkmark for "baseload" -- only "intermittent". Pages 13 and 14 show Fuel Costs as: Wind: 0 Solar: 0 Coal: $13-$18/MWh ($0.013 - $0.018 per kWh) Fission: $9/MWh ($0.009 per kWh) Natural Gas: $21-34/MWh ($0.021 - $0.034 per kWh) As a retail consumer, I'm paying about $0.15 per kWh, though I know that includes transmission and distribution and retail markup. Fusion has the potential to be very low on fuel costs. But the capital costs are an unknown. In my original comment, I tried to show that when amortized over enough kWh for sale, even $Billions in capital costs could make sense, if they give us a machine that produces zero-carbon baseload electrical generation at scale.
- lake_vincent 4y agoYes, exactly! There are two problems here: 1. What's the most efficient way to boil water? 2. How do we generate electricity on a population scale without having to boil water? Question 1 is, apparently, much more tractable. We are still pretty much building the world's most sophisticated tea kettle.
- mrec 4y agoAs a Brit, I wholeheartedly approve.
- Mvandenbergh 4y agoIronically all but one of our UK reactors are carbon dioxide cooled although to be fair that carbon dioxide is then used to boil water.
- cameronh90 4y agoThe power grid is just a way to remotely boil a kettle.
- throwaway0a5e 4y ago>1. What's the most efficient way to boil water? Doesn't need to be the most efficient. Just more efficient per energy transferred to the water than all the other options.
- robbomacrae 4y agoI don't follow. What you said seems to me the definition of the most efficient. Or at least.. it is what I assumed they meant.
- heavyset_go 4y agoMost efficient can mean theoretically optimal efficiency or more efficient than other options. I think the OP was using the first definition.
- ok_dad 4y agoIt's a fusion reactor, so how do you get the water into the part with the hot stuff? That's all inside a magnetic field, I think. Also, you have to consider the neutron radiation's effect on the pipes that carry the water into the core, it's going to activate several metals in there, and cause weakening of the pipe wall, which will necessitate inspections and replacements. It's a way harder engineering problem than you're letting on. Your comment is like a software user saying "How hard could it be just to add feature X?".
- johnbcoughlin 4y agoThe heat transfer is not (will not be) directly from the plasma to the water. The fusion neutrons will impact a "blanket", which is water-cooled, and kept at a temperature of around 600-800 C. Weakening of the pipes and all other structural components will primarily be from neutron irradiation. Not to say that any of it's easy, just not for the reasons you suppose. :)
- ok_dad 4y agoAh, cool! I wasn't sure how it would work, but it seems the hard part is the stuff leading to and including the "blanket? Thanks for clarification.
- ncmncm 4y agoIt won't happen at all, because it would be astronomically expensive, way more than fission, and fission is already not competitive. So it is all castles in the sky.
- pfdietz 4y agoExactly! Unlike in a fission reactor, where you can flow the coolant through the core, in a fusion reactor the energy has to be radiated through the surface of the reactor. The square/cube law comes into play: the surface area you can radiate through goes as r^2, while volume (and cost) of the reactor goes as r^3. This problem has been known for decades. http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trouble-With-Fusion_MIT_Tech_Review_1983.pdf http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trou... https://pure.mpg.de/rest/items/item_2131865_1/component/file_2131864/content https://pure.mpg.de/rest/items/item_2131865_1/component/file... (see section 4.1.1)
- tremon 4y agoIt's not my area, but I suspect that the heat extraction rate for a fusion reactor must be several orders higher than current fission reactors if we are to run them continuously. Fission reactions can be actively controlled by using reaction moderating material (control rods), which means we can tune the reactor activity to match the amount of heat extraction available. Fusion plasma must be sustained at a few million Kelvin or it shuts down again, and I'm not sure how finely we can control the operating temperature without either overheating the reactor or shutting down the plasma. I think it will take a lot more than dumb engineering to accomplish this.
- johnbcoughlin 4y agoThe heat flux management from the plasma is certainly not dumb engineering, true. However, the actual heat transfer technology is, I think it's fair to say, "dumb" compared to all of the plasma physics that has to enable the reactor in the first place. It's more or less just running cold water through the lithium blanket, which they hope to keep under around 1000 Celsius or so.
- ncmncm 4y agoIt is moot: it would cost far, far more than other power generation methods, so will never be built.
- Gwypaas 4y agoCould be interesting if they couple it with a Closed Cycle Gas Turbine [1] and a tiny steam plant, like the gas CCGT plants of today. Then the heat engine part should see similar, or even higher, efficiencies compared to gas based CCGT plants. Boiling water using the Rankine cycle [2] and it will be as dead in the water as nuclear and coal is today. A thing to keep in mind though is that it is very hard to compete with the engineering of an axle straight into a generator like wind turbines or a solid state system like solar PV. Working fluids, cooling loops and what not are awful to build and maintain. [1]: https://en.wikipedia.org/wiki/Closed-cycle_gas_turbine https://en.wikipedia.org/wiki/Closed-cycle_gas_turbine [2]: https://en.wikipedia.org/wiki/Rankine_cycle https://en.wikipedia.org/wiki/Rankine_cycle
- spoils19 4y agoCoal is very much alive in prospering countries, and I stand with other conservatives in that we don't need new fancy energy production.
- mlazos 4y agoI suppose I’ll bite here. We don’t need “fancy” energy production as Southern California and the Midwest becomes uninhabitable, you serious? Coal power should be dead in the water if it isn’t. It’s bad for workers, bad for the air we breathe, water we drink, bad for the people who live around plants. That has been well established. It actually kills more people than nuclear, solar and wind combined. There’s no redeeming quality to it other than being plentiful and cheap. It shouldn’t be cheap based on the externality of the destruction it causes here and around the world.
- Twirrim 4y agoI was talking about this with the my kids (10, 7) the other day. Blew their minds a little that pretty much every power source comes back to the same central thing: moving magnets. Then I pointed out that our electric car does it in both directions too.
- gridspy 4y agoWell, it's just another of our favorite converters - kinetic <-> electric energy. electric <-> kinetic - spinning magnets kinetic <-> pressure - turbine / pump pressure <- heat - boiler heat <- chemical potential - furnace
- pdpi 4y agoI always find it slightly amusing how there's remarkably few forms of power generation that don't eventually boil down to "use water/air/steam to make a turbine spin".
- gridspy 4y agoIt is amusing. But it's just because that is the most efficient way we know to turn heat into electricity at scale.
- deleted 4y ago[deleted]
- amelius 4y agoAnd also because it is easy to turn most types of energy into heat.
- JadeNB 4y ago> It is amusing. But it's just because that is the most efficient way we know to turn heat into electricity at scale. Despite the 'but', I don't think you are disagreeing with your parent (who I took to be saying that they found it slightly amusing that we haven't discovered any more efficient ways to turn heat into electricity). If you meant that steam turning a turbine is the most efficient way that we know to turn heat into electricity, then it seems that you're saying the same thing as your parent, and it's not clear what 'just' adds. If you meant that it's the most efficient way that exists, then, first, I wonder how you know; and, second, I think that far from this being 'just' anything, it's pretty remarkable that we stumbled on the literally most efficient possible way so early in our history of working with electricity!
- ncmncm 4y agoIf you read what he wrote, your question is answered already. Saying the best way we know is the best way we know is vacuous. Nothing about steam is especially good except that water is cheap. It was cheap before, and still is. Its problems are problems we have learned to live with. But it costs more than wind or solar, even with free heat. So it is a dead end.
- mandeepj 4y ago> the heat is used to boil water which makes large turbines spin and produce energy I believe the containers would have to be really large. Also, if we have to continue boiling water at scale, we might reach water crisis some day. Although, it'd take very long time.
- mandeepj 4y agoYou can downvote with passion, but also let me know - what you find wrong. This is the single most thing that annoys me about HN.
- stevenhuang 4y agoLook into the water cycle. Water doesn't just disappear. With sufficient means of energy generation the lack of _fresh_ water can be solved.
- Dylan16807 4y agoTo put that into perspective, we need about a thousand gallons of water to produce a megawatt-hour of power. We can desalinate a thousand gallons of water out of the ocean by spending about ten kilowatt-hours. So that's a 1% energy overhead.
- legohead 4y agoAssuming we can run an actual fusion reactor consistently, how is the power taken out? I've seen lots of comments about water/steam, but we're talking 100M°C degrees here, that's insane! Do we bury this thing in the ocean? I'm being silly, but I'm genuinely curious if there are any plans, even speculative ones, on how to do this.
- DFHippie 4y agoI haven't actually read the announcement, but I assume the tremendous temperature is in a tremendously small quantity of plasma. Basically, it's a few extremely fast nuclei.
- ncmncm 4y agoIt is moot: none will be built, because it would cost far, far more than other clean power sources already being built out. By the time this could be made to work, nobody will want it at any price.
- madelyn 4y agoYou warm up a piece of metal and pour water on it. The water keeps it cool and makes steam.
- vintermann 4y agoWell, when it's that much heat, you're going to need a lot of water. Also, when dealing with that much high energy radiation, your metal has a tendency to wondrously become another metal, with all the problems that comes with.
- xani_ 4y ago> Well, when it's that much heat, you're going to need a lot of water. we want a lot of water! That's a lot of energy! > Also, when dealing with that much high energy radiation, your metal has a tendency to wondrously become another metal, with all the problems that comes with. That's kinda problem with anything fusion or fission, wherever neutrons hit things get weird. Probably much worse for fusion tho.
- kadoban 4y agoThe question is more how you get the heat to the water in a sensible way. It's _probably_ just engineering, but it's still something that needs to be worked out.
- deleted 4y ago[deleted]
- NovaVeles 4y ago> “It’s not physics, it’s engineering,” When it comes to fusion I am always in too minds about statements like this. On one hand, yeah, it is something that we may be able to wrangle into something useful. On the other, fusion can be seen as a perpetual motion machine that doesn't defy the laws of physics. It can kind of inhabit that same mind space.
- YZF 4y agoRight. It's not physics (though arguably plasma isn't that well understood but let's ignore that) it's just incredibly difficult engineering and needing to solve multiple extremely difficult engineering problems. In that same sense reversing climate change is just an engineering problem, populating Mars is just an engineering problem, a space elevator to orbit is just an engineering problem, quantum computers etc. etc. ;)
- pfdietz 4y agoEngineering issues are perfectly capable of ruining the prospects for a technology, even if they are "lower class" than physics issues.
- Schroedingersat 4y agoCase in point. Hydrogen energy storage. It's so very nearly amazing in several different formats and applications. Net result is it's kinda okayish in a couple of niches.
- pfdietz 4y agoThose niches look very important, though, especially for reaching a 100% renewable energy system.
- Schroedingersat 4y agoThere are other competitors in those niches. Some of which are just indirect ways of storing hydrogen depending how you use it. Ammonia, methane, dimethyl ether, methanol, and longer chain hydrocarbons. All have positive and negative tradeoffs Similarly there are other competitors for fusion. The difference here is they are orders of magnitude better in most ways. Fission and chemical reactions have much higher power density and vastly lower cost (and fission is already cost prohibitive), renewables are vastly cheaper even with battery or chemical fuel storage. There's not really a good niche for D-T fusion even if we had it today rather than in 50 years.
- pfdietz 4y agoAnd the engineering here is very problematic. Indeed, the issue mentioned may be a showstopper for DT fusion. The problem is limits on power/area through the wall of the reactor. Because all the produced energy has to go through the wall, and because the area of the wall grows as r^2, the volumetric power density of a DT reactor (that doesn't exceed the power/area limit on the wall) must decline with increasing size. This leads to DT fusion reactors having horrible volumetric power density. ITER, for example, has a volumetric gross fusion power density of 0.05 MW/m^3. The 2014 ARC design, 0.5 MW/m^3. A PWR's reactor vessel? 20 MW/m^3. (If you look at the power density of the plasma alone, or the fission reactor core alone, you get similar wildly discrepant numbers: https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/39/files/2022/06/Final-FINAL-CIMTEC-2022-copy-Perugia-Italy-6-29-2022.pdf https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/... see slide 26) If you want to make heat to make steam to drive a turbine, a fission reactor will be much smaller, and much cheaper, than a DT fusion reactor.
- IX-103 4y agoWhat's wrong with pulling the energy from the magnetic containment system? We already are using the magnetic containment system to redirect charged particles in the plasma back into the plasma. If we do so less forcefully than they were heading out, but still enough to stop them from leaving, we can convert particle velocity directly into electricity (AC with a relatively linearly decreasing frequency distribution, I think). This also has the effect of cooling the plasma (since temperature is related to average particle velocity). The challenges I see here are: 1) The faster the control system, the more efficient it is at extracting energy -- it can extract the energy of higher frequency components. 2) You may need a very large magnetic field (larger than needed for containment) to make this practical 3) Coil geometry and efficiency becomes critical.
- pfdietz 4y ago80% of the fusion energy from DT fusion comes out in fast neutrons, which ignore magnetic fields. The other 20% has to come out somewhere. If it could be converted to electrical energy maybe it could avoid surfaces (Helion plans to do this, with DD + D3He) but when it's just 20% of the output that doesn't buy you much.
- ngcc_hk 4y agoBomb vs power plant … explosion is quick heat in a sense.
- Schroedingersat 4y agoSo we think about the engineering problem and reject the entire concept on that basis. Even if I give you a magic box full of near vacuum 100 million degree plasma that emits 1MW/m^3 in the form of neutrons whenever you want as long as you stop it from touching the sides with supercooled magnets. How do you turn that into a remotely viable power station? Just the heat exchanger and steam turbine portion is going to be uneconomical against renewables+storage.
- ncmncm 4y agoYes. Just just keeping a steam turbine up and running, completely ignoring where the heat comes from, costs more than both building out and operating wind and solar.
- Schroedingersat 4y agoTEGs are pretty neat, but the temperature and energy flux is very hard on the materials. If only there was some way to get energy from a fusion reaction via a semiconductor junction by running them in parallel at low temperature rather than in series at extremely high temperature, and a long way away so the neutrons could thermalize and you could absorb much easier to handle photons. Oh well.
- ncmncm 4y agoWhere do the photons come from?
- Schroedingersat 4y agoThe usual place. Surround your fusion reactor in a very thick blanket of opaque hydrogen plasma so the neutrons can bump into something. Contain the whole thing in some kind of force field (if only there was some alternative to the EM force for this purpose), then when the photons hit your photon electric generators you get electricity. If you arrange things such that the outside of the opaque hydrogen blanket is about 5800 Kelvin and your photon-electric generator panels are spread out in parallel to...let's say about a kilowatt of energy per square metre they should last a couple of decades and your efficiency will be okay, maybe around 20-30% There. Fusion power plant invented. Sadly it's just a pipe dream though because we couldn't roll it out without first waiting for a stable fusing plasma source on earth.
- pyinstallwoes 4y agoThermoelectric generator. Take the differential and output a voltage? Why hasn't this been done? Why do we go to the steam stage when we could just exploit the termoelectric properties of temperature and current? 1. Thermoelectric generator: https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator 2. Thermocouple https://en.wikipedia.org/wiki/Thermocouple https://en.wikipedia.org/wiki/Thermocouple 3. https://en.wikipedia.org/wiki/Thermoelectric_effect https://en.wikipedia.org/wiki/Thermoelectric_effect
- snaily 4y ago> The typical efficiency of TEGs is around 5–8% A steam turbine is many times more efficient.
- pyinstallwoes 4y agoBut it has way more parts... And it moves. This other path has no moving parts.
- lambdatronics 4y agoIt's been considered, for a variety of heat sources. I'm long-term bullish on a related technology (thermophotovoltaics), although presently the efficiencies are not great & the compatibility with nuclear radiation is probably poor.
- pyinstallwoes 4y agoIt seems relatively accessible too, at least as a technology and conceptual model it shows a simplicity that allows the majority to get their hands on it and thus a potential for more growth and innovation. It’s interesting that it also allows refrigeration. If we could combine heating, refrigeration, with a configurable output of either end on top of it being a generator of voltage… is quite amazing.
- lambdatronics 4y ago
- fsniper 4y agoI still don't understand why we don't really have a reliable and good way to convert chemical bond/radioactive energy into electrical energy directly? Why do we still require 2 conversions of Chemical -> Heat -> Electrical ? Is that something that is impossible or not cracked yet?
- tullianus 4y agoSome examples exist for directly converting alpha, beta, and gamma particles into electricity, but I didn't find anything for neutrons in my brief search. https://en.wikipedia.org/wiki/Atomic_battery#Radiovoltaic_conversion https://en.wikipedia.org/wiki/Atomic_battery#Radiovoltaic_co... https://en.wikipedia.org/wiki/Betavoltaic_device https://en.wikipedia.org/wiki/Betavoltaic_device
- lambdatronics 4y agoFuel cells convert chemical -> electrical directly, batteries go both ways. For nuclear fusion, the only practical reaction releases 80% of the energy as uncharged particles (neutrons), for which the only way to harness their energy is to convert it to heat. The 20% of the energy that is emitted as charged particles could in principle be converted with high efficiency, but the other 80% dominates. For fission, more of the energy is emitted as charged particles, but it's not clear how one would harvest it directly in bulk. (It can be done on small scales, but not efficiently.)