Power plants and generators

[TJP]

Most power plants do not produce electrical energy, but thermal and/or kinetic energy. Only after this heat/motion is coupled to a generator is electrical energy produced. Now, to many this has no relevance, but in a search for Greater Realism (tm) in vehicle designs, I'd like some distinction made in this. For instance, even if a gas turbine is developing power of x kilowatts, it doesn't mean you can use it as is to produce x kilowatts of electrical power - you need a generator for that. Generating electricity isn't going to be 100% effective, you're going to lose some energy in the process. Also, the generator is going to take up precious volume and add mass to your vehicle, plus it's going to cost something as well.

With this (needless complexity?) it's important to categorize power plants into two groups: those that produce electricity without a generator and those that don't - with possibly a third group for those that store electricity. I'm going to need your help on this, as I have no idea if an MHD turbine requires a generator or not, for example. I gathered a list of power plants from MT, T4 FFS and GURPS Vehicles. None of those systems make any distinction on the "type" of energy produced (BTW, the Vehicle Design System (VDS) by BTRC/Greg Porter requires generators for electricity production but unfortunately does not give details about what power plants require them, as it is a design system, not construction from lists of parts).

Produce Electrical Power
* Fuel Cells
* Solar Cells

Store Electrical Power
* Batteries (generally long storage life, low discharge rate)
* Capacitors (generally short storage life, high discharge rate)
* Superconducting loops ("power cells", long storage life, high discharge rate - ideal for energy weapons, if they exist in room-temperature versions)

Do Not Produce/Store Electrical Power Directly
* External Combustion (steam engines)
* Internal Combustion
* Gas Turbine
* Fission Reactor (but I guess, the stats assume an inherent generator)
* Fusion Reactor (as fission, inherent generator)
* Radiothermal Generators (as fission, inherent generator)

Unknowns (power production)
* MHD Turbine (GURPS describes these as having an MHD generator as well, but if they do, do they produce electricity or not?)
* Antimatter (guessing they should have an inherent generator, as with nuclear reactors)

Unknowns (power storage)
* Flywheel (so they store energy in a spinning wheel, but is that converted to electricity by default of the design and what would be their storage efficiency and life, discharge rates should/could be high)
* Homopolar Generators (from 2300AD, what are these really? Just glorified capacitors?)

What other types of power plants (or power storage) would there be? Not counting wind mills, hydroelectric dams, nor geothermal or tidal power as these would be hard to utilize in a vehicle.

P.S. As an added complication to a complication, an electric car would require an electrical motor to convert the electical power (of batteries) to motive power... Hey, I heard that, who said "damn gearhead!", who was it?

 

[Anthony]

MHD generators: works by applying a magnetic field to a moving stream of plasma, producing a current. Like a turbine, not directly dependent on a heat source, but the moving stream of plasma is normally generated by a heat source. Main advantage is no physical turbine, and can thus run very hot.

Flywheel/Homopolar generator: basically a form of battery; stores energy in spinning object. For an HPG, the spinning object is a conductor. Either will produce power directly.

Antimatter: probably a thermal generator.

 

[Uncle Bob]

Don't forget radionucleotides. Not fission, no neutrons.
RTG use bimetalic joints to turn heat into electricity
Brayton cycle- converting the heat into electricity using a steam engine
Thermionic- using the heat to boil off electrons from a gnerator at the end of a cable.

A similar concept is using atomic isomers to store energy until released as high-energy photons. It is not certain if this can be made to work.

 

[TJP]

So if I needed electrical power - flywheels, homopolar generators, RTGs and MHD turbines would not need a separate generator, but be able to produce electricity more-or-less directly (design-wise at least).

About MHD turbines: How would one harness that plasma stream for motion? Except for using it as a "plasma jet engine", would you need to use it as an electrical power source and use that electricity for motors (i.e. have it power electrical motor that turns wheels etc.) or what? In other words, they would be in the category "Produce Electrical Power" on my list above.

Uncle Bob, you lost me there, sorry. You mention "Brayton cycle" and "Thermionic." I gather these are alternate ways of producing electricity from heat. Are they more effective than "regular" generators? Or vice versa, perhaps?

Anthony, would you say that HPGs are higher TL flywheels then?

 

[TJP]

*Bump*

Sorry to repeat myself, but...

 

[DaveChase]

Organic. What about organic power sources.

I do not have my books in front of me but I know that it is possible right even though very costly and bulky. (And very, very small amounts of enegry is produced.)

In the future we might have a better understanding how organic makes 'enegry' from matter.

Dave

 

[tjoneslo]

Originally posted by TJP:
So if I needed electrical power - flywheels, homopolar generators, RTGs and MHD turbines would not need a separate generator, but be able to produce electricity more-or-less directly (design-wise at least).

Depends entirely on how much detail you are getting into. A flywheel technically requires a seperate generator. It stores power in a spinning wheel, which is then used to turn a generator. Generally the two items are tied together because the generator is also used as a motor to spin the flywheel up when storing power.

Homopolar generator works by spinning a magnet, which acts as it's own generator.

RTG's, in theory, need a seperate generator as all they provide is heat. But in your "producers" you should add a "bimetal converter" which converts a heat sources (actually a temperature differential) into electricity. The bimetal converter is extremly small and lightweight, with no moving parts (which is why it used for RTG's in spacecraft).

MagnetoHydroDynamic turbines can not use the plasma for thrust. Infact it doesn't even need to be plasma. I've seen designs using molten lead as the working fluid. They work on the principle of having something move through a strong magnetic field produces an electrical current at right angles to the magnetic field and the motion of the something. Only one moving part (the working fluid).

 

[TJP]

Originally posted by tjoneslo:
Depends entirely on how much detail you are getting into.

Yes, to clarify - I'm not aiming for detail for detail's sake. I just wanted to get the basic specs of different real-life power plants and power storage systems right. Mostly because when you're using real tech it's embarassing to make errors. IMHO, it dissolves some of that important suspension of disbelief in sci-fi RPGs when some basic tech facts aren't correct. YMMV. The generator issue is a relevant part, for me, in the pros and cons of different power plants (e.g. why some power plants are better for robots, while some are better for cars) and leads to a bit of added realism. Granted, realism is a word that needs to be used carefully in sci-fi; I used it in the context of sci-fi roleplaying not engineering science.

Thanks for the info (and for correcting my understanding of MHD turbines)!

 

[Straybow]

Cold fusion may be possible in a device similar to a fuel cell. Deuterium confined in a crystal/metallic lattice under pressure may achieve fusion at a low rate, heat from which would be absorbed by electrons in the lattice to create electricity. You couldn't get a large current, but you could produce a small current for a very long time.

10 grams of D plus 15 grams of T (created by neutrons interacting with Lithium within the lattice after initiation of fusion) could provide enough power for one individual for a lifetime of lightbulbs, kitchen appliances, hot water, recharging time for a reasonably sized electric car, etc.

This is the means by which I imagine day-to-day fusion powered devices to operate. Things like Air/Rafts would require a more intensive energy source, and ship propulsion as much as deuterium fusion can supply (see elsewhere).

This is exactly parallel to the terribly unimaginative critics of Star Wars (not me; no! harumph to those scoundrels!) who point out that exploding a whole planet with a super-duper turbo-laser would require more energy than the Sun puts out in 5000 days (one day being the recharging time for the Death Star's main weapon), or annihilation of trillions (or maybe quadrillions, who can remember) of tons of matter-antimatter.

Star Wars canon (praise be unto Lucas ) responded with hypermatter, which when annihilated with anti-hypermatter produces "a gazillion times as much." I believe that's an exact quote of a highly articulate devotee. (The less articulate response to requiring 5000 times as much power as the Sun is, "So?")

Checking under the hood of the Traveller starship may not generate a reponse of that sort. Instead people just say, "It's just a model!" while others shush loudly. Then we close the hood and pretend we never looked.

 

[Straybow]

Hmmm, did a new calc on fusion in Going Pirate. You might wanna check it out TJP.

 

[TJP]

Originally posted by Straybow:
You might wanna check it out TJP.

OK, thanks, I will! (I've been away from this forum for some time, now I've got a lot of catching up to do. One would need to come here daily to try to keep up with all this traffic. Many interesting discussions are already over before I even get to read the starting post. Bummer.)

 

[TJP]

If I understood your fusion calc right, a kilogram of deuterium would produce 570,000,000 Megajoules. Wowzie! Is that correct? (I'm no scientist and mostly slept through math in school... )

That cold fusion cell looks like a nice alternative power source to satellites and drones, a high tech RTG if you will. But if the cell uses tritium ("15 grams of T") wouldn't it make the cell become radioactive over time? Also, isn't tritium used in fusion bombs? If it is, it's not very safe to have loads of that around.

Heh, I like your comments about Star Wars' tech critics. It's very true, that in SW if someone asks how lightsabers work you just say, "because they do." It's not in the spirit of SW to ponder how something works, but in part I've always liked Traveller because it tries to keep the technology at least somewhat plausible (no blasters etc.) and offer some explanations. To most it does not matter what's under the hood, but I like to take at least a small peek and try to work out how and why something works as it does. So that I know how to represent it in the game - so that it's working consitently, isn't "off-color", etc. I'm not saying it makes the game any better if we can explain how a starship works (for example), but it does enrich the game and enforce the suspension of disbelief if at least some of it can be explained, for me at least. If too many gadgets are technobabble tech (or "black box tech" for that matter), it constantly reminds me that this is fantasy and the immersion factor drops. YMMV.

As you can see, this is one of my pet subjects and I could rave and rant about this for ages, but I'm going shut up now and hit the sack (it's 29 past midnight here).

 

[Straybow]

Yes, 5.7e14 J/kg

, about a hundred times that produced by nasty, dirty fission. That's why governments have been willing to spend billions chasing Tokomak fusion.

The idea of the fusion fuel cell is that the T isn't stored, but generated internally and used up without accumulating to any degree.

Lithium capture is the way the USA makes T for warheads. A neutron is captured by Li(7), which instantly (half-life maybe a microsecond) spits out a T. I can't remember whether it leaves behind Li(5) or something else.

You need some form of jump-start for a fusion cell, either a neutron source to spawn T or pressure spike or something. The T would not be bound in the structure but move into the intertices of the lattice with the D2, thereby increasing the confinement level and facilitating fusion. D-T fusion produces He(4) and a neutron to pop another T loose, hence a sustained reaction is possible. The presence of He(4) in the lattice will also increase the confinement of D and T.

 

[Uncle Bob]

Maybe I'm missing something. A D-T reaction gives you 17.6 MeV, fron 2 p and 3 n.
That is 2.8E-12 j/reaction. At 5 nucleon/reaction at 6E26 nucleon/kg, so a D-T reaction yields 6E26/5 * 2.8E-12= 3.36E14 J/Kg
assuming a preposterous 100% efficiency. Of course 3/4 of that energy is high energy neutrons

Traveller apparently uses the p-p reaction of simple hydrogen which creates no neutrons. It is harder to start and confine but yields 6E14 j/kg

 

[Straybow]

Yes, you did miss something. The 5.7e14 J/kg is the D-D -> He(4) reaction from the link. I didn't bother to cite power from the D-T reaction, the point is that a few grams is all you need for everyday energy consumption and portable equipment for a lifetime.

The link is to my calc showing that the 0.015% abundance of D in natural hydrogen (assuming "refined fuel" simply means eliminating heavy molecules) is sufficient to provide the energy levels cited in Traveller. A tech capable of proton fusion, or the use of concentrated D, is thousands of times greater in available energy per ton.

 

[Uncle Bob]

Refined fuel is not deuterium, or 15 kg of refined furl would be worth 1 dton of unrefined fuel.

But 1 dton of LH2 has the same number of H nuclei as 0.64 dton of water, 0.63 dtons of methane, or 0.7 dton of ammonia. Thus 1 dton of each of these could be processed into 1dton LH2 using sloppy methods.

Also D-D fusion does not follow one path, and some of the intermediate steps are dirty.
D-D=>He3 + n and 33 MeV, or D-D=> T + p + 4 MeV
Once He3 and T are in the mix you get
D-T=>He + n +17.6 Mev and D + He3 =>He4 + p + 1.3 MeV
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fusion.html

Which can be boiled down as
6 D=> 2 He +2 p +2 n + 43.2 MeV
or only 3.45e14 J/Kg. Including 5.0e25 zippy neutrons. Nearly half what you get in the dirty D-T reaction.

 

[Straybow]

But the point remains that Traveller utilizes no more than .01% of the fusion energy available. The method is so horridly inefficient that fission is actually better in terms of available energy/ton fuel. The only advantage to Traveller fusion is the low cost and safety of hydrogen compared to fissionables.

 

[Uncle Bob]

Not in CT. The preposterously low output in MW is just one of the reasons I don't use MT and later.

But my rational was always that the excess mass was fed through the power plant to add inertial confinement. That gas is expelled through MHD nozzles to extract electic power and dumped overboard with the excess heat.

Thus, at one stroke I explain both the lack of radiator and the glowing "rocket nozzles" in CT.

 

[Straybow]

No, I don't think the output is preposterously low; just the opposite. I think the power range for maneuver (roughly 1MW/G/dT) is quite reasonable. It is only the amount of fuel required to achieve it that needs some explanation.

Confinement criteria and MHD generators help but still leave the door open for dramatic increases in efficiency (eg, heat sinks, multistage MHD generators, impeller turbines) to allow lower fuel requirements.