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Comment by westurner

4 days ago

> all power sources rely on taking cold water and making it warm constantly so that it makes a turbine move.

PV (photovoltaic), TPV (thermopohotovoltaic), and thin film and other solid-state thermoelectric (TE) approaches do not rely upon corrosive water turning a turbine.

Turbine blades can be made of materials that are more resistant to corrosion.

On turbine efficiency:

"How the gas turbine conquered the electric power industry" https://news.ycombinator.com/context?id=38314774

It looks like the GE 7HA gas/hydrogen turbine is still the most efficient turbine? https://gasturbineworld.com/ge-7ha-03-gas-turbine/ :

> Higher efficiency: 43.3% in simple cycle and up to 64% in combined cycle,

Steam turbines aren't as efficient as gas turbines FWIU.

/? which nuclear reactors do not have a steam turbine:

"How can nuclear reactors work without steam?" [in space] https://www.reddit.com/r/askscience/comments/7ojhr8/how_can_... :

> 5% efficient; you usually get less than 5% of the thermal energy converted into electricity

(International space law prohibits putting nuclear reactors in space without specific international approval, which is considered for e.g. deep space probes like Voyager; though the sun is exempt.)

Rankine cycle (steam) https://en.wikipedia.org/wiki/Rankine_cycle

Thermoelectric effect: https://en.wikipedia.org/wiki/Thermoelectric_effect :

> The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect (temperature differences cause electromotive forces), the Peltier effect (thermocouples create temperature differences), and the Thomson effect (the Seebeck coefficient varies with temperature).

"Thermophotovoltaic efficiency of 40%" https://www.nature.com/articles/s41586-022-04473-y

Multi-junction PV cells are not limited by the Shockley–Queisser limit, but are limited by current production methods.

Multi-junction solar cells: https://en.wikipedia.org/wiki/Multi-junction_solar_cell#Mult...

Which existing thermoelectric or thermopohotovoltaic approaches work with nuclear fusion levels of heat (infrared)?

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westurner

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adrian_b  3 days ago

Gas turbines are more efficient than steam turbines simply because they can be used at higher temperatures.

However the exhaust gas of a gas turbine will still contain a great part of the input energy.

Therefore in order to reach maximum efficiency in a power plant, you must start with a gas turbine, which must be followed by a cascade of 2 or 3 steam turbines that run at lower and lower temperatures (this combination of a gas turbine with some steam turbines is what "combined cycle" means), until you obtain exhaust steam that is not much hotter than ambient temperature, and which can be used for heating, to recover even more of the input energy than what has been converted into electric energy.

Instead of gases or steam, turbines may also use supercritical fluids, e.g. carbon dioxide, which may lead to using less turbine stages and with much smaller turbines (that must work at much higher fluid pressures).

A gas turbine that is used alone, without steam turbines that recover the heat from its exhaust gas, has normally a too low efficiency. Its use can be acceptable only for mobile generators or emergency generators, where the size and complexity are more important than the efficiency.

zitterbewegung  4 days ago

Okay so I meant to say the simplest way is to heat water in this situation. But there are alternatives here https://en.wikipedia.org/wiki/Fusion_power?wprov=sfti1#Tripl...

  • westurner  4 days ago

    I wouldn't have looked this up otherwise.

    Maybe solar energy storage makes sense for storing the energy from fusion reactor stars, too.

    There's also MOST: Molecular Solar Thermal Energy Storage, which stores solar energy as chemical energy for up to 18 years with a "specially designed molecule of carbon, hydrogen and nitrogen that changes shape when it comes into contact with sunlight."

    "Chip-scale solar thermal electrical power generation" (2022) https://doi.org/10.1016/j.xcrp.2022.100789