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"extracting the excess heat" is nice. Unless there is some other path to conversion of the fusion energy to "useful" energy, this heat is the primary mechanism: you drive a heat exchanger, to drive a turbine, to make electricity. This is what we want: excess heat, to drive a turbine.
Clearly, _this_ tokomak isn't going to make net positive contribution to energy delivery. Some future (30 years?) tokomak is meant to do it.
I do get that for an experiment, "extracting" the heat is what its all about.
(Happy to be put right by wiser heads, if there is some other path to useful energy out from fusion)
I read up, the two other choices are fusion-fission driving: use the neutrons to activate fissionable materials and then put them into a classic fission reactor as food (not what we want really) and direct electic extraction of surplus charge, which is at 48% efficiency according to the wiki.
So yes: surplus heat is likely to be one of the useful products but not the only one, and if 48% efficiency is acceptable, it might be better to do direct charge take-off and process the heat as a problem as a much as the solution to a problem.
Once the heat isn't a problem, its useful. You can have a hot bath. Or feed tomato roots in a greenhouse. Or I guess, run a turbine...
Achieving fusion would be a god-send, but aneutronic fusion - which is generally considered 'the next step' - would be utterly spectacular.
First, it would save you having to build very expense and complex steam turbines. Like Chernobyl had 4 nuclear reactors powering 1 steam turbine, because the engineering required to build a high quality high capacity one is super expensive. With aneutronic fusion you could just use the energy from the generated charged particles and directly turn that into juice.
The huge, huge, huge thing though would be no more neutron radiation. It would vastly simplify reactor construction, reactor cleanup, biological shielding, etc. etc.
Aneutronic fusion would also us to just _spam_ power plants, safely and cheaply, in a way that's difficult for modern society to even understand. Assuming the aneutronic reactor itself isn't mega expense of course.
I'm pretty sure the Chernobyl plant had 4 separate "blocks" each with one reactor and two turbo generators? No.4 was the one that exploded but the other three kept on producing power for years after.
https://en.wikipedia.org/wiki/Chernobyl_Nuclear_Power_Plant
You're totally correct. It was 4 reactor buildings feeding one turbine _house_, but the house contained two turbo generators. Thanks for the correction!
Aneurotnic fusion sounds like exciting stuff. Are there any pilots in development? Is it realistically achievable at the moment (well, as realistic as _any_ fusion efforts), or still in the realm of room-temperature superconductors?
Why do you need to put those neutrons in a fission reactor?
Neutrons would still be absorbed and produce heat.
Is it because those neutrons damage the reactor structure?
yes. aneutreonic, a reaction with "less" neutrons would be cleaner. either you have less/no neutrons, or you absorb the neutrons you have. they make the structure radioactive and/or change it chemically (embrittlement) or, you absorb them into other things to make them radioactive, and useful.
https://en.wikipedia.org/wiki/Neutron_embrittlement
The Royal Society has held a couple of talks on Fusion, there’s audio from the talks, but no YouTube video alas:
[0]
https://royalsociety.org/science-events-and-lectures/2020/03...
[1]
https://royalsociety.org/science-events-and-lectures/2018/03...
I attended the second day of the 2018 talk [0], the talks are free and it was extremely interesting.
Awesome to see that this project has achieved first plasma on their MAST Upgrade tokamak, see a video of this at the end the article.
Meanwhile the consortium running ITER [1] is spending €22 billion but the UK is no longer a member because we left the EU. For engineering at this scale, cooperation is going to get results - not small projects like this.
Those are very different projects with very different goals. ITER is designed conservatively to produce 10x fusion energy output vs electrical energy input. As in you out 1 MW of electricity in and get 1 + 10 = 11MW of heat output. While not designed to be an economic fusion system it would unequivocally demonstrate a working design and a provide a test bed for experiments relating to reactor materials and full scale operations.
This however is aimed to explore novel geometries which may aid in future designs. However, the net efficiency at this scale would be vastly lower. It’s still a useful project, but it’s just one of many possible designs.
It's not 10-11MW heat out for 1MW electricity in. It's "500 MW plasma from 50 MW of injected thermal power" which would need 300 MW electrical input. After conversion back to electricity, it might give as much electricity out as is put in!
See these links for more: Question asked in the EU parliament:
https://www.europarl.europa.eu/doceo/document/E-8-2018-00081...
https://news.newenergytimes.net/2020/11/03/open-letter-to-it...
Useful clarification, but I think ITER’s website makes it unambiguous.
_For 50 MW of injected heating power it will produce 500 MW of fusion power for long pulses of 400 to 600 seconds._
https://www.iter.org/sci/Goals
. To be more clear, injected heating power excludes the energy required to get to a steady state, as otherwise pulse length needs to be factored in.
That said ITER is running a lot of equipment unnecessary for a commercial power plant making engendering Q factors misleading. For example a power plant would not need to collect, process, and store the vast amount of scientific data that’s the point of the experiment. It’s really better if their not turning the rooms lights off trying to hit some arbitrary target.
PS: It was posted ~3AM and I am still out of it. So, I am kind of surprised how coherent that was even though I mess up conveying some heat was from electricity where the other heat was from fusion.
Why would it not be economic?
After the first reactor, do we expect building a replica, without all the R&D costs would be significantly more expensive than a standard nuclear reactor?
To me, 10x the energy sounds really good.
10x energy doesnt mean 10x electricity. How one captures that energy and converts it effectively remains an open question. Can all those particles be turned into heat? Will those particles degrade the reactor so fast that it is no longer economically viable?
ITER seems to be addressing the "capture the energy" part?
https://www.iter.org/sci/MakingitWork
_"The neutrons will be absorbed by the surrounding walls of the tokamak, where their kinetic energy will be transferred to the walls as heat. In ITER, this heat will be captured by cooling water circulating in the vessel walls and eventually dispersed through cooling towers. In the type of fusion power plant envisaged for the second half of this century, the heat will be used to produce steam and—by way of turbines and alternators—electricity."_
And without breeding blankets, yes you can capture the heat, but you rapidly run out of tritium. ITER will only be operate on DT for a few weeks, total over its lifetime, before the available tritium supply is exhausted (and its materials reach their neutron limits).
A "real" reactor will need to have tritium breeding blankets to regenerate the tritium. Otherwise, the cost of tritium alone, if made in fission reactors, for a 1 GW(e) DT fusion reactor would be $15B/year.
Isn't testing that approach of breeding tritium explicitly part of what ITER is trying to do with its TBM programme?
ITER has a few places where test blanket modules can be installed. ITER will not be able to simulate the neutronic environment of a full reactor (and so will not be able to confirm adequate breeding), nor subject the modules to the cumulative neutron loading they will have to withstand.
For this reason, a Fusion Nuclear Science Facility has long been proposed as something that will be needed before DEMO is built. This could be a small, Q < 1 DT fusion device, as the goal would not be plasma physics related. It itself will need to breed its own tritium to operate long enough, so there's a circular dependency in the development.
There are many such technology advances needed for fusion power to work. This is why spending $22 billion on ITER is a very inefficient use of money for research. Maybe as a diplomatic effort of having all the world's major powers [] (China, the European Union, India, Japan, Korea, Russia and the United States) work together it is worth it. Sort of like the space station. Big symbol and cost but little scientific value per dollar.
Unfortunately the budget for ITER comes out of the US science budget instead of the State Department. Most US fusion funding only goes to ITER at this point.
Fusion blankets are not just needed for fusion to work, they are needed for the next fusion reactor experiment (the one that has a burning plasma) to run. This is not a technology that we'll need some day for commercialization; it's a requirement for DT fusion to progress at all.
That's not capturing in a utility sense, it's merely preventing system failure from overheat (edit: autocorrect was turning this into "merrily preventing" which was kind of fitting as well). The result is a high volume, low delta-T coolant cycle and those are notoriously difficult (read: impossible) to capture meaningful amounts of electricity from, it will actually consume a lot. That quote is just a slightly more elaborate way of saying: no, we'll definitely not do any utilizeable capture.
How is what they just said any different than a standard nuclear reactor that just heats up water to produce steam into electricity?
Because ITER is not designed to be running for more than a few minutes at a time. Its successor, DEMO, will be designed for continuous power output.
https://en.wikipedia.org/wiki/DEMOnstration_Power_Station
I’m not sure if you can quite say the UK has left.
The UK is part of ITER via Euratom, which requires EU membership. It seems the UK is in a grace period for the time being, but hasnt quite left:
https://www.iter.org/newsline/-/3394
The UK left Euratom on 31st January 2020.
I thought the UK has left, giving notice for Euratom explicitly at the same time as for the EU because the UK government wasn’t sure leaving Euratom would be automatic? And that Switzerland was a participating associated state?
From the ITER link, the UK has left Euratom, but not fully left ITER due to a grace period, with the hope that the UK will in some way join ITER.
As I understand it from the links I’ve found the UK has not explicitly left ITER yet.
Ah, looks like I misunderstood your initial post, I incorrectly thought you were saying the UK was still in Euratom. My bad. :)
UK leaving EURATOM was widely criticised, I struggle to see how it makes any sence to leave an purely technical institution that has nothing to do with brexit.
If the UK wanted to I'm sure that they could stay in ITER considering that "third countries" (ie. non EU) like China are major participants.
You make it sound like Brexit is some sort of rational process based on what's best for the UK. That seems pretty far from the truth.
I've checked ITER's details and it's a truly international project, just that the EU is a member rather than member states individually.
All major powers are members (EU, US, Russia, India, Japan) and it would be disturbing (at least to me) if the UK walked away...
Counterpoint: is there an obligation to share in ITER such that walking away could produce competitive advantage, or are there no such restrictions on non-ITER national projects?
Doing what you promised based a referendum is "what's best for the UK". What constitutes rationality in a democratic process is a matter of opinion - and the point is no one is allowed a privileged opinion over consensus.
Funny you should say that because the Tory election promise for the referendum was that they would give a referendum on the deal they arranged ... so, not "what [they] promised" in a pretty key way.
Also I'm pretty sure they promised not to break the Good Friday Agreement; and it seems clear they don't care.
That aside, the whole point of having a representative democracy was supposed to be that expert politicians could act on the public's behalf in complex arrangements. The vast majority of MPs (including ex-PM May, for example) supported UK staying in the EU ...
Then there's things like how almost all countries have rules requiring a supermajority in any vote leading to major constitutional change ... but the advisory vote of the referendum was passed on the slimmest of margins. If the vote has been "leave with no deal" then the Leave, camp (funded heavily by a Russian oligarch as we now know) would have lost the vote.
The whole point of our UK democracy was supposed to be to allow complex decisions to be made without simplistic populism.
The economic experts, the scientific experts, the political experts, the legal experts ... amongst these groups the consensus was very clearly for remaining in the EU. It was an act of subversion to arrange a referendum with no clear aim (contrary to the election manifesto) in which the population could be swayed with simple lies.
It hasn't even brought the much maligned sovereignty, instead we had an unlawful prorogation of parliament and because of the removal of oversight the current Covid19 crisis has been used to route 100s of ÂŁmillions to Tory owned corporations under the guise of buying PPE which simply hasn't been delivered (or has and had been deficient ... but that's no surprise, none of these companies were previously PPE suppliers).
What constitutes rationality in a democracy surely is open, fair, and democratic as a first step. It's truthful and forthright. These words do not fit this process at all.
Convincing people through lies to vote against their own interests isn't democracy.
Convince me.
[_These views are my own and do not relate to my employment._]
So, allow the GFA to hold the rest of the country hostage? Maybe such considerations should have been made when britain joined the EU - I voted for brexit, but I had no choice on whether to join. It's been argued that the current generation has no right to make such an impactful action as brexit, but why is it such that a single generation can sign up to such an alliance without an exit plan in the first place?
> expert politicians could act on the public's behalf in complex arrangements
And yet do they? How much does the public trust the motivations of their politicians? It seems to me that the public inherits an old and cludgy system, and you'd have to spend multiple lifetimes fighting it to have a chance of change. That the majority needed to accept the leadership of a clown like Boris shows how little the political class represents its public.
> funded heavily by a Russian
As opposed to public funds? Or English oligarchs?
There are many factors that could affect the vote; having a goverment that represents, rather than manipulates, the public for instance.
> without simplistic populism
What about simplistic dismissals of brexit as racist/xenophobic. So many characterisations of the EU as the spirit of cooperation; where is the scepticism towards large political unions, democratic divide and conquer, and the forgotten fact that the EU is _still_ an elitist institution despite whatever diversity you might think it has.
> economic experts, the scientific experts, the political experts, the legal experts
There are winners and losers in brexit. The biggest losers tend to be lower paid, lower class demographics who where fed promises (lies) about how joining the EU would help them somehow. The biggest winners are businesses who can squeeze those lower classes, and middle class professionals (who started off with greater mobility in the first place). Guess which camp economists, scientists, politicians and lawyers fall into...
> Convincing people through lies to vote against their own interests isn't democracy
Who convinced people through lies? And since when is that acted on? I dont recall anyone suggesting we be able to kick out Thatcher when she turned on the miners. The issue is, the public don't seem to get to decide when to hold a referendum, nor control the narrative of whether it is appropriate to do so; hence thd suggestion yhe Brexit is based on lied, when in fact any/all referendums are.
In any case, how does brexit relate specidically to that. For whatever democracy is worth the EU will fix nothing of the rot in britain or its politics, but joining the EU is likely to make it worse. Reforming the electoral system might be a start, hopefully both Tories and neo-tories aka labour will die, but that's a scope beyond.
But ITER is not EU only, having the US and other countries, so they might still participate
(Regardless of the merits of ITER of course)
ITER isn't all it's cracked up to be. Certainly some senior fusion scientists don't believe so:
https://thebulletin.org/2018/02/iter-is-a-showcase-for-the-d...
Only half way through the article, but the issue does not appear to be that ITER project in praticular has a glaring flaw.
Rather, the scientist appears to be sceptical of fusion as a near term practical energy source on the whole.
I feel that humanity will never amount to anything without fusion.
Energy requirements of space travel assure of that.
DT fusion is bad for space travel. The reactors are simply too large, and burn only a small fraction of their mass in fuel before they are too damaged to continue. ITER, for example, if it could be operated continuously forever (it cannot) would take 300,000 years to fuse its own mass in fuel.
"would take 300,000 years to fuse its own mass in fuel."
Most of ITER's mass is concrete in the building, are you including that?
I was using the described ITER mass of 23,000 tonnes. The concrete structure around ITER contains 30,000 tonnes of rebar and 150,000 cubic meters of concrete.
I see DT fusion as a stepping stone to evolution. It doesn't have to be the answer for space travel or even Earth's clean energy.
If within a few thousand years we managed to go from illiteracy to studying fusion, I'm hopeful of what can be achieved within the next few thousand years.
Evolution explores huge numbers of dead ends. So if we go with that metaphor, the most likely fate of fusion is failure and extinction.
Tokamaks are good for science and understanding the physics of plasmas, but seem to be particularly unfriendly to utilising the energy produced by fusion. The materials in the reactor become radioactive and need replacing frequently, diverting the heat out is tricky, but not impossible, as it is essentially a sealed ring.
I certainly agree that fusion would be the biggest thing to happen to civilization. It would help us to clean this planet, and get to others.
i am not sure but in the promo video they say that the data coming out of this project is fed into ITER, which is the whole purpose of this project supposedly to collect data
The video in the link clearly states (2:37) that data from this experiment will feed directly into ITER.
Advances in high temperature superconductors have made ITER obsolete before it will be finished. They won't ever be able to produce electricity, whereas the current generation of fusion reactor designs have a decent shot at it. Though it would be politically difficult, it likely would be pragmatic to scrap the current design and start over.
I think this is more comparable in goals to the
Wendelstein 7-X project.
Sure, but the article does mention that results from MAST Upgrade feedback into preparations for ITER.
It's not either-or.
DISAGREE on this. Real innovation happens bottoms up. co-operation at national level is all a spectacle.
I am used to hearing this from software engineers who are secure in the knowledge that when they want to try out a concept, hardware time to do so will be cheap and readily available. At some point, you are going to have to take all of your shiny materials science and turbulence simulations, and actually build a piece of apparatus to test it out on the scale that your chosen application (in this case, power generation) will require. The universe is under no obligation to make sure that it will cost less than billions to do so; hence ITER.
Having said that, there's been a lot of extremely promising recent progress in high field superconductors and fusion designs based on them (MIT ARC, Tokamak Energy, etc) that could shrink the necessary scale for a working reactor, so perhaps it will turn out we're lucky with the physics on this one after all.
you have answered your own question. cool.
You might be right on this one. I'm a bit curious if any other HN-reader is aware of the private fusion project (aka the SAFIRE project) which is now run by the company Aureon Energy (
). I do highly recommend watching the video (also available on the legacy page
) for the video recording of the experiments. It's not yet quite mainstream physics but we have to remember that once upon the time the mainstream physics people didn't think that heavier-than-air flying machines are possible while nowadays they have wasted countless billions on their fusion experiments and achieved close to nothing.
> we have to remember that once upon the time the mainstream physics people didn't think that heavier-than-air flying machines are possible while nowadays they have wasted countless billions on their fusion experiments and achieved close to nothing
Challenging authority gets you cool-guy points, but does nothing for actual understanding. “The experts don’t know what they’re talking about and are blinded by tribalism” is rhetoric of the 20th century. Physics has moved on.
“The experts don’t know what they’re talking about and are blinded by tribalism” is rhetoric of the 20th century.
How would you describe the medical abuses of the last century? e.g. lobotomies to cure mental conditions, refusal of surgeons to wash hands etc.
Have scientists moved on from tribalism?
I said physics has moved on.
Also, if experimental surgeries were never attempted in the 20th century the quality and length of our lives, and potentially trillions of future human lives, would be nasty, brutish, and short. Not all attempts had a sound basis and I don’t defend them. I do say the good of the total if 20th century experimental surgeries far outweighs the bad. Importantly, we are able to learn from our mistakes quickly. It took centuries to stop using the breaking wheel. It took less than a lifetime to stop lobotomies.
I’m struggling to understand your point though. Do doctors still practice lobotomies and refuse to wash hands, or have they cast aside their tribalism and make decisions based on science?
So you say. Though I don't see any evidence humanity as a whole has moved past groupthink. But yeah, I might be wrong about SAFIRE, as I haven't done any fusion experiments myself, just read a bit of research.
I work with fusion researchers. We regularly talk about non-mainstream designs and unexplored areas of physics. It’s a lot of fun. The mainstream is mainstream because it’s what works, not because that’s what our fathers built. The theoretical physicists are actively working on a dozen empirical models. They throw out what they need to. No one’s saying “don’t fund alternatives”. Fund alternatives. Show that they work. They haven’t in the past, but if one did the most excited people will be the mainstream fusion researchers.
Hey, I'd really appreciate it if you were to bring up my design next time you're chatting about new and different designs.
This one is completely new, very simple, and in great need of more eyes
I have a website at
Kind of ironic to post this on the web, given it's history.
> Kind of ironic to post this on the web, given it's history.
it's funny because you think it happened because tim berners lee and CERN. I think, it happened because arpanet and universities connecting with each other.
Internet wasn't an organised effort. it was a bottoms up manifestation. Do i need to remind you what CERN was actually supposed to do?
Hopefully this doesn’t work
There will be no earthbound, commercial Tokamak fusion power in the lifetime of anyone reading this. For reasons.
The energy density of the plasma is necessarily so low that a useful power plant would be absolutely monstrous. Then, it would destroy itself with neutron flux in short order, leaving thousands of tons of radioactive scrap. There is no possibility of such a plant being competitive with solar and wind at current prices, and they are still on their way down.
The prospect of commercial power generation is not the driver of fusion research. Rather, it is a jobs program for high neutron flux physicists, to maintain a population available to draw upon for weapons work. So, expect it to continue burning $billions indefinitely, with no deliverable.
The numbers I've seen thrown around for the flux expected out of ITER are containable with existing material science, and it's a very conservative design which is modeled to generate 10x the input power. I'd call that a deliverable.
ITER's volumetric thermal power density (volume of reactor + plasma) will be 50 kW/m^3, some 400x worse than the volumetric power density of a commercial PWR (reactor vessel + core).
ITER also use a CuZr alloy backing up its first wall materials. This material is unsuitable for long neutron exposure. DEMO would have to use RAFM steel instead there, with an order of magnitude lower thermal conductivity. As a result, the power/area at the surface of the first wall in DEMO may be even lower than in ITER.
The first wall has an 8 mm layer of Be facing the plasma.
Yes, and it is backed up by CuZr. Replacing that CuZr with steel will significantly impede cooling.
Note that ITER's output is heat, rather than electricity. Maybe the heat will be useful, but it's an important distinction.
Only replying to this low-effort response because it is currently the top response.
> The energy density of the plasma is necessarily so low that a useful power plant would be absolutely monstrous.
The size of e.g. the SPARC proposal is so low that you could fit on the order of 10 units of 50 MW within the tower of one 10 MW wind turbine [0].
> ... Rather, it is a jobs program for high neutron flux physicists ...
You do realize that many current effort in fusion power are privately funded, right?
[0]:
https://www.cambridge.org/core/journals/journal-of-plasma-ph...
your link has 404 status
The power density of the ARC proposal (volume of the magnets and everything inboard of that) is some 40x worse than the volumetric power density of a commercial PWR (volume of the primary reactor vessel + core). This is much better than ITER, but still much worse than existing fission reactors.
I'd characterize as "low effort" the shallow dismissal of very real issues facing fusion.
PWRs are some of the highest power-density energy sources that exist, though (which is why they're so popular on submarines). 40x less than a PWR is not low.
I agree that ITER is an overwrought boondoggle, however.
Fusion and fission plants will be similar outside the nuclear island. So if you take a small fission reactor, and replace it with a much larger, much more complex, fusion reactor, you're going to increase the cost of your power plant.
How’s it fare against a gas turbine power plant? Because that’s what it would actually replace, not a PWR.
Since a fusion or fission reactor is a source of thermal energy, and the power density there does not include the volume of external heat exchangers or turbines, the proper comparison is to the COMBUSTOR of a gas turbine. Gas turbine combustors have thermal power densities of 100 MW/m^3 or higher, some five times the power density of a PWR primary reactor vessel and 2000x the power density of ITER.
Gas turbines also have large advantages in the rest of the plant, though. Fusion plants or PWRs will require at least two sets of heat exchangers (one for transfering heat to the external cooling water, and one for isolating the nuclear coolant from the fluid going through the turbines). Simple cycle gas turbines (without regeneration) don't require any heat exchangers, and combined cycle plants get most of their power from the topping cycle, so the heat exchangers on the bottoming cycle are smaller.
The cost of a simple cycle turbine power plant is around $400/W, maybe 5% of the capital cost of a fission power plant.
$400/kW, I meant
Not an expert at all but this contradicts everything else I've seen on the subject, could you support your claims? I thought there recently were advances in superconductors that would enable way smaller reactor designs?[0]
[0]: Dr. Dennis Whyte. - Small, modular & economically attractive fusion enabled by high-field superconductors -
https://www.youtube.com/watch?v=rY6U4wB-oYM
Better superconductors allow reactors to be made smaller, up to a point. But they still would have lousy power density. ARC's power density (total reactor volume, not just plasma volume) is 40x worse than a commercial PWR.
Fusion reactor power is ultimately limited by the need to radiate energy through the wall of the reactor, and the limit from that would apply even if plasma confinement were a nonissue.
Turns out we just needed stronger magnetic fields:
Materials science delivered an order of magnitude more powerful magnetic field in the form of better superconducting ribbons. Add in molten salt blanket for neutron recovery and heat working fluid, design for maintenance: and voìla!
You have a garage sized fusion reactor which outputs net energy.
Imagine you have installed one of these things in your garage, or maybe better 10 or 20 ft below, to keep from sterilizing your offspring. You got it for a _fire-sale bargain_ at only $50M, even including the turbine and cooling tower. It produces, what, 100kW? (Plus 100kW of waste heat you might be able find a use for.) Or is that too optimistic?
How many MW of solar panels can you buy for that $50M? Let's even figure in plenty of battery backup. (Hint: lots.) How many MW of wind turbines? (Hint: lots.)
Where would such a garage-sized fusion reactor be useful? And how long before it is a radioactive slag heap? (It was good planning to bury it up-front.) How many GW-years does the fleet need to produce before it pays off the tens of $billions already sunk, to date?
The only guaranteed product of all nuclear power schemes is monstrous exaggeration of cost effectiveness.
"Outputs net energy" is very, very far short of useful.
You seem to be comparing construction costs of an experimental project to the LCOE (basically, utility rates) for a massively scaled and mature industry. Let's ignore the R&D costs it took us to get solar to its current state. According to
https://www.eia.gov/todayinenergy/detail.php?id=36813
, the construction costs in 2016 for utility-scale solar plants were ~$2.5k per kilowatt, or ~$2.5M per megawatt.
> How many MW of solar panels can you buy for that $50M?
About 20MW. Definitely not 1000GW, which is what you would get by dividing $50, today's approx. solar power MWh LCOE, into $50M. From the tone of your reply it seems like you were assuming the latter.
Ignoring large jumps in the price of land, and ignoring potential taxes for their environmental impact (deserts and plains have ecosystems, too), solar and wind will likely be cheaper than fusion far into the future, even by optimistic fusion predictions. But it's still debatable whether it'll be _so_ expensive that we shouldn't even bother making the investment. The LCOE of natural gas is 3x that of solar power today, and yet we're still building natural gas plants like crazy.
(FWIW, the LCOE for _new_ fission plants as expensive as Vogtle Units 3 & 4, the former coming online next year, is comparable to natural gas.
https://www.lazard.com/media/450784/lazards-levelized-cost-o...
In China the LCOE seems to be closer to that of contemporary solar LCOEs.
https://www.mdpi.com/2071-1050/10/6/2086/pdf
Which explains why China has many more reactors under construction.)
I will only note that 20 megawatts is always "lots" more than 100 kilowatts. Even 10MW is. And if you think you will be able to buy a garage-sized fusion reactor for $50M in our grandchildrens' lifetime... good luck.
One might be useful onboard a spacecraft, at the end of a long, long tether. But a pB reactor would still be a better choice.
China is also building new coal plants. The actions of a command economy are not a sound indicator of relative cost and value.