Why 10-25 times net power?

[KitemanSA]

This whole mess started out with the following:

Article on the "Piston" fusion device states needs 10-25 times output gain to be viable.

I am a neophyte but have been following the fusion blogs avidly.

If a device had a 25% net power gain and was cheap enough to operate less energy costs, it would make enough power to sustain itself and have a surplus for the "GRID". As long as the value of net output could cover the cost of opertion and amortize the construction costs over 25 years or so, why would we need 10-25 time gain? (highlights added, ed)

If, and, as long as...; we wouldn't. But it seems that the "Piston Fusion" folk have done the Ifs and Thens and have decided they need 10-25x gain. So what does a BFR need? Who knows. Any number determined now would be a WAG.
If we had an interactive wiki connected with this sight, maybe we could turn it into a SWAG (scientific wild a$$ guess)

Oh, and folks, PLEASE preview your posts. Sometimes it is hard to follow posts that quote without

quoting; especially if one is skimming the dross.

[blaisepascal]

This whole mess started out with the following:

Article on the "Piston" fusion device states needs 10-25 times output gain to be viable.

I am a neophyte but have been following the fusion blogs avidly.

If a device had a 25% net power gain and was cheap enough to operate less energy costs, it would make enough power to sustain itself and have a surplus for the "GRID". As long as the value of net output could cover the cost of opertion and amortize the construction costs over 25 years or so, why would we need 10-25 time gain? (highlights added, ed)

I agree with that statement... I'd rephrase it:

If the value of net output power (raw power less conversion and feedback losses) is greater than the costs of fuel, maintenance, operation, and construction debt service and repayment, then why couldn't we build it?

Short form... Can we make a profit?

However, this drives a series of more questions.

1) What are the maintenance, fuel, operation, and construction costs?
2) What are the conversion losses?
3) What are the feedback losses?
4) How much profit do the investors want to make on the power?

And....

5) Are there other power generation technologies which can yield a higher profit?

These questions drive any power plant project. Fossil Fuel plants have well known answers to questions 1-3 for a variety of technologies, scales, etc. Fission plants have high construction costs, meaning that the value of net power has to be high as well to pay for the construction costs. No one is going to build a small cost-effective fission plant.

BFRs scale well for gross power, but the feedback and conversion losses are unknown. Best case scenario: Dr. Nebel is right, and drive power is 5% of pBj reactor output, and direct conversion efficiency is 95%, so net output is 90% of gross output. To get a 100MW(net) plant, you need a 111MW(gross) reactor. Worse case scenario: Dr. Carlson is right, and drive power is greater than reactor output, so there is no profitable way of doing things. Middle-case scenario, drive power is 16% of D-D reactor output, and thermal conversion efficiency is 33%, so net output is 17% of gross output. To get a 100MW plant, you need a 600MW reactor.

If it works, a pBj direct conversion plant will also win on construction and maintenance costs (and probably operation as well), so the best-case scenario is very profitable, and probably game-changing. The advantage of r^7 scaling (alright, b^4r^3 scaling) is such that, even if a direct-conversion pBr turns out to be too much of a challenge but the D-D thermal reactor can be made to work, the added construction costs of a 600MW reactor over a 100MW reactor may be small enough such that it may still be able to be profitable. Of course, you'd have to find a way to dump 500MW of waste heat somehow. If BFRs work and Dr. Carlson is right, you have a contradiction...

If it isn't profitable, no one is going to build it, unless they have other needs in mind such that the plant doesn't have to be profitable.

A D-D BFR that isn't profitable for commercial power may still end up being suitable for navy ships, or as a way for a major power consumer to lower their power costs. Some aluminum smelters have on-site multi-100MW power plants to run the smelters, for instance. It may be less expensive to use BFRs instead even if it's not profitable for utilities. Someone who needs heat, but not electricity, may find a way to use the heat directly instead of steam turbine conversion (use a molten metal coolant loops, and use them to heat the furnaces in a glass plant, maybe?)

But if you assume that the plant is profitable in the first place (as did the original quote about the piston plant), then you've assumed the engineering away.

[djmelfi]

Quote: KitemanSA

I agree with that statement... I'd rephrase it:

If the value of net output power (raw power less conversion and feedback losses) is greater than the costs of fuel, maintenance, operation, and construction debt service and repayment, then why couldn't we build it? ENDQUOTE

Thanks for considered response, my point was trying to target the gain requirements, because even on this thread they state 15-60 times as a possible requirement, whereas gain factors arn't the issue. Only dollars are an issue, so any gain that could support the project is good enough.

I agree that overall operation, if the thing worked should be competitive and mainly the initial investment is the issue.

My only objective was to remove this extraordinary sense that there needs to be this 15-60 fold gain as repeated here as some kind of montra. Obviously gain is needed, but the real factor could be very small to cross the comercial threshold, and certainly in in some cases less than a factor of 2 would work, even on small scales. On larger scales a factor of less than 1 might even be viable. I understand the 15-60 number represents pre-thermal conversion which may net 5-20 but that is a requirement that isnt even relative to the project, nice but not relative.

The real issue is what is the real cost to build the particular model. This cost must approach $100million per 100MW net to grid at pre Global Warming costs. At a Carbon Credit environment Coal is dead, Gas might only increase by 50% or so and Nuclear would remain pretty much the same. I would assume we need to compete with nuclear. My latest figure was 1400MW for $2.4 Billion. This cost is higher per megawatt but low Nuclear fuel costs recover that during operations. (Overall Costs for Nuclear MW have increased dramatically, it is now almost equal to coal plants per MW)

Assuming a similar low operational cost, following the Nuclear Model we could get away with a much higher initial investment per megawatt.

I also agree in certain environments, like moon base, for example a smaller gain and higher cost could be justified.

It is an important distinction that BFR can have a net gain, other energy plants convert energy and there is no sense of net gain and there is a continuos fuel supply rwquired. I assume the bulk of Boron needed in Fussion would be very small (Intuition I can't verify that). This distinction of semi independence is an extraordinary factor that seems to be ovwrlooked in the discussion of the BFR. This means installations can be more remote from fuel sources and more amendable to proliforation than coal or gas plants.

AND we cant ignore the clean factor (Boron) that adds a substantial incentive economically and philosophically.

How much Boron would it take to produce 100MW for one year? Anyone have a clue?

[djmelfi]

whoops! that quote was from blaisepascal

[93143]

How much Boron would it take to produce 100MW for one year? Anyone have a clue?

100 MW for a year is 3e15 J or so. At about 6 MeV (1e-12 J) net energy per fusion (with direct conversion), and a boron mass per fusion of about 1.8e-26 kg, we get about 5e13 J/kg, yielding a fuel mass estimate of about 60 kg per year.

[MSimon]

My only objective was to remove this extraordinary sense that there needs to be this 15-60 fold gain as repeated here as some kind of mantra. Obviously gain is needed, but the real factor could be very small to cross the comercial threshold, and certainly in in some cases less than a factor of 2 would work, even on small scales.

When your knowledge base is small (darn) you go by rules of thumb to decide between alternative courses.

The rule of thumb is: overall gain of 5 to 20.

It helps you decide (roughly) if it is worth it to transport coal from the East coast to California or whether a closer supply is required.

It also tells you: any gross benefit to society? Solar cells may make sense even if they operate at a net energy loss (manufacture minus energy production) if the alternative is running 20 to 30 mi of power lines for 5 customers.

Roughly: devices do not make overall sense unless the net gain is in the 5 to 20 range. This allows for unaccounted costs - both energy and dollars. Above 20 you may want to sacrifice efficiency for lower capital costs.

What the steam fusion guy is telling you when he says the fusion energy gain is 60 and overall gain is 20 is that the odds of such a set up being profitable is good.

It was one of the criteria I used when evaluating the proposal.

BTW the gain of the system tells you something about capital costs vs output. Not much. But when the knowledge base is small every little bit helps.

Note if the BFR running pBj has an ultimate gain of 20, real plants (first off the production line) will probably operate at an actual gain of 8 to 10. Which says that 10% to 13% is economically dead weight. Which is not too big a burden.

[chrismb]

Can't? Or hasn't been?

I would say 'can't' and happily wait until corrected, with the offer of eating my shorts if wrong.

The reason being that unless you have a) an electron-cooled beam and perfect mono-energetic-ness, b) zero de-collimation into the e-fields of the recovery grids, c) uniform and linear e-fields generated between electrodes of zero cross-section, then you clearly aren't going to get 100% energy conversion.

now let's see: a) p11B gives off two great lumps of a distribution, very highly NOT mono-energetic, b) by definition of the device, the particles are radiating at different angles, plus do not exclusively radiate from a singularity at the centre, plus they will have to pass the magnetic fields of the magrid when behind it (even if you thing there are no magnetic fields inside), c) an engineering compromise will have to be sought to get uniformity of e-field with minimum grid area.

let's put a few figures on this, then. So you can either slow the upper bunch of alphas down to 'zero' at which point you hope they neutralise and get evacuated, if so the slower ones will be recirculated into the reaction volume. As they will re-enter with a big MeV energy, they'll fly out the other side again, fusor style, until they collide with the magrid.

If you turn the capture potential down to catch the slower bunch then you let the other group through which, if there was one set of grids, would impact the outer surface.

Either way, within each group you'd only capture some of that modal distribution.

let's put some figures on these:

Firstly, let's say the magrid takes up 20% of the steradian surface, so we're down to 80% efficiency already.

Slowing down the lower distribution [first] means you'll 'catch' (and I give wide approximations, plenty of caveats) 2/3 of those alphas. That makes it 50% of the total by this route. maybe the grid has a transparency of 10%. Down to 45%. Now let's think about the distribution. Let's say we catch the central 1 sigma's worth of the distribution, some 63% of that. Down to 23%. The slower ones in that distribution will get reaccelerated back into the centre where they will recirculate until sputtering on the magrid.

Leaving the remainer of those fast alphas and the higher distribution to carry on. So we put in a second grid. Same process, the slower ones will get recirculated back into the centre, and receive a second acceleration by the first grid setup. So now we've lost all those higher alphas in the lower energy distribution. The higher range is a little tighter, let's say we can get 2 sigmas worth, 90%, of that 33% of fast ions. They've gone through two sets of grids, so total transparency of 20%. That gives up 24%.

Total efficiency by this calc = 45%.

Now I just want to revisit the 'captured' distribution percentage. This is presuming this is even possible. In point of fact, unless the ions match or exceed the slowing potential exactly, they will be re-accelerated back again, thereby drawing off the energy back OUT of those grids. I think I have significantly over-estimated the range of the alpha distributions that can actually be recovered, but that doesn't matter much as the numbers show that it's no better than thermal energy capture, even if everything and all else is possible.

[chrismb]

but the whole principle of p-B11 fusion is that the output is in helium ions (which I assume is what you actually meant to say) instead of neutrons and gammas and whatnot that have to be slowed down and their energy harvested as thermal energy

I very much fear, and regret to say, that you have confused a sales pitch with scientific realities.

A 'principle' is one that grows from existing known realities. There is no known demonstrated reality to this direct conversion idea, as far as I am aware. I am trying to stimulate a correction and rebuttal to this, but have not yet seen any facts presented that suggest otherwise.

[chrismb]

Dr. Bussard designed, built, and fired nuclear rocket engines. They worked. Apollo (and NERVA) got cancelled before they could be used as upper stage engines for the second-generation Saturn V. What makes you think you know better than him?

This is just a silly argument to try.

I have every respect for actual achievement, but in no way does a person's prior success mean that they cannot be questioned and pointed out to be wrong. Why do I think I know better, in regards the recovery of ion energy from fast particles? I say why not? I have never tried to do it, which is about as many times as Bussard tried, so I guess that makes us equals in this regard. He doesn't appear to have really considered the issues of such a process in regards to the actual bi-modal distributions of alphas in any detail whereas I have. I don't know if this means I know better than him or not but I am not presuming I do. I am making clear statements to try to elicit a factually based rebuttal of my rejection of the fantasy of direct energy recovery from p11B alphas.

[alexjrgreen]

I have never tried to do it, which is about as many times as Bussard tried, so I guess that makes us equals in this regard.

You have an equal opportunity to be right, but not an equal probability.

[djmelfi]

Total efficiency by this calc = 45%. ... , but that doesn't matter much as the numbers show that it's no better than thermal energy capture, even if everything and all else is possible.

But that is efficiency of capture of gross generated electron energy, not % of inputed energy, without understanding the relationship between generated electron particles and original energy requirements I cant understand these numbers.

That is, if electron energy is 3 times inputed energy a 45% recovery is a 35% gain.

Everyone seems to agree that direct capture would be a less costly process than thermal conversion.

BUT some question the viability of the concept itself. Brussard said the whole process was reduced to engineering issues not theoretical ones...?

It would be my understanding the heat is there EN MASSE whether we capture electrons or not, is this better a DO BOTH situation rather than an Either Or. Giving a greater energy capture rate? I currently understand the Boron Fussion itself will produce BOTH the heat and the electrons and reactor will need to be cooled regardless.

[chrismb]

You have an equal opportunity to be right, but not an equal probability.

Another factless, personalised comment rather than detail of a proposed mechanism I would like to understand more of, if there is a rational argument for how it could work with bi-modal distrubutions of particle energies entering an e-field at various angles.

Maybe I am less probably likely to be right, or otherwise. Still, I may be right nonetheless. Being 'probably' better, or otherwise, as a means of debate is back to the debate on qualifications. Debates here seem to be based on the background and/or intent of the postor, rather than the facts brought in to debate.

There is a reputation that a forum can gain where its postors repeatedly, repeatedly and repeatedly hark back to personalising the debate. And it is not a reputation related to the competency of science debated therein.

[chrismb]

But that is efficiency of capture of gross generated electron energy, not % of inputed energy

Yes, of course. Sorry, it has drifted off your original topic by half-a-lane; should have clarified that this would be a figure you would then compare 'direct energy conversion' with the thermal conversion efficiency, quantities which would appear to be much the same (in the most optimistic of circumstances). This wasn't a direct comment on total energy gain, as you originally asked.

[djmelfi]

But that is efficiency of capture of gross generated electron energy, not % of inputed energy

Yes, of course. Sorry, it has drifted off your original topic by half-a-lane;

Chrismb, not meant as a critisism, only an observation, I greatly appreciate yourself and the few who have tried to seriously discuss the issues with me, and thank you for your patience. What about doing BOTH?

[djmelfi]

How much Boron would it take to produce 100MW for one year? Anyone have a clue?

... yielding a fuel mass estimate of about 60 kg per year.

WIKIPEDIA: The average cost of crystalline boron is $5/g

I compute that at $300,000 a year.

One of the reoccuring themes here is transportation and remotness to fuel supply etc. I think 60,000 grams per year per 100MW basically eliminates those objections/considerations.

I would believe we are perfectly within bounds to use the operational costs of Nuclear as a guideline for operational costs.

This would actually then equate to about $175million per 100MW plant costs ala Nuclear as a viable commercial project.

This begins to approach the 200million proposed for BFR 100mw reactor.

DR. Nebel seems to think this is WORTH DOING. But when these types are negotiating for funding a 200million project the cagyness seems to abound. Now that the project is being handled in PROXY, it seems no one needs to commit in the manner that Brussard would.... that is no one's REALLY vested.

It is also not clear to me if the 200million 100MW BFR proposed includes capturing the 100MW or just in theory producing it. Obviously prototype costs arn't relative to production costs but does anyone know if the WB8-WB9 proposal includes capture? My understanding is WB9 is 100MW 1.5 meter whilst WB8 is something interim which would be continuous plasma.

Happy New Year, BTW.