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4X10N t1_j023iu1 wrote

"Best" is not a the best choice of words in this case, very much depends of what are your "wishes". (try googling "thermoelectric generators for deep space exploration" for a fun different application of what's best in nuclear fission energy recovery) This said as pointed out previously , steam turbines have an efficiency going from 60% for small systems all the way ip over 90% for big turbines, the kind you might expect from a huge reactor. So, up to date, steam engines are the most efficient for domestic energy production

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-Metacelsus- t1_j02iewx wrote

> steam turbines have an efficiency going from 60% for small systems all the way ip over 90% for big turbines, the kind you might expect from a huge reactor.

To clarify, this is expressed as a percentage of the Carnot efficiency, it's not 90% overall.

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KingoPants t1_j0azou2 wrote

To explain this just a bit further for people who have never taken thermodynamics.

You can't take heat and turn it into useful work. You always need to raise entropy in any spontaneous process (second law of thermodynamics).

Cutting out the motivations, basically taking a (infinitely small) amount of heat energy out of a system reduces it's entropy by Q/T where Q is heat in joules and T is absolute temperature in kelvin. Adding that much heat energy also adds that much entropy.

If you have a hot and a cold reservoir with temperatures T_h and T_c then and you are taking heat Q_h out of T_h and putting heat Q_c into T_c then because the entropy change must be positive you get that Q_c/T_c > Q_h/T_h.

By energy conservation the work you get out of this process is W = Q_h - Q_c. If you do some basic algebra you can figure out that W/Q_h < (T_h - T_c) / T_h

The cool thing is the algebraic derivations for this efficiency are very easy although the verbal explaining for why entropy works like this is much more complex.

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Reviewingremy t1_j020ks6 wrote

Yes.

The radiation gives off energy in the form of thermal energy and the most efficient way to convert that into electricity on a large scale is to create kinetic energy. Ie turn a turbine.

And the best way to make heat, turn a turbine is to create steam.

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Holden_place OP t1_j021pok wrote

Thanks for reply. Do you know how much energy is lost? For example, ‘Only about 12%–30% of the energy from the [gasoline] you put in a conventional vehicle is used to move it down the road’.

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mfb- t1_j026zve wrote

Around 1/3 of the heat gets converted to electricity in fission power plants, fusion power plants would be similar.

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Reviewingremy t1_j0228d9 wrote

I don't. But don't forget in both those examples the processes are very different.

A lot of the "waste energy" from gasoline will be in the form of thermal energy. Whereas in a nuclear reactor it's the thermal energy you want.

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Holden_place OP t1_j0249lq wrote

Understood. I was just using that as example as I learn about the fusion breakthrough.

I read that 300 megajoules power 2 megajoules of lasers. I am wondering how much more is lost on the back end.

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PerspectivePure2169 t1_j052cmi wrote

It's not just that it's the best way, it's that it's the only way to practically extract a sizable portion of the energy produced.

The other capture options are generally effective on only a portion of the energy types released, and are often hindered by high heat.

Steam generation captures all the direct heat as well as any other energy forms such as light that resolve as heat. And convert that to electricity through one of mankind's most efficient machines, the turbine.

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GenericUsername2056 t1_j07pmhq wrote

It's not so much extracting energy as it is transforming heat into useful electricity through performing work. If your goal was to heat homes and businesses directly, you'd use a heat exchanger and a fluid with a high heat capacity to distribute the heat. But because you want energy in a different form, you're pretty much left to the Rankine cycle if you want high efficiencies between your conversion from heat to electricity. The reason water is typically used as the working fluid in most Rankine cycles is because it is non-toxic, cheap/abundant and has a high heat of vaporisation amongst other thermodynamically favourable properties. There are other working fluids, for instance for an Organic Rankine Cycle (ORC), such as toluene, but an ORC is better suited for lower-temperature waste heat and the like, and toluene for instance is nasty stuff you'd prefer not to use.

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