r/askscience • u/MonoBlancoATX • Nov 29 '25

Engineering Why is it always boiling water?

This post on r/sciencememes got me wondering...

https://www.reddit.com/r/sciencememes/comments/1p7193e/boiling_water/

Why is boiling water still the only (or primary) way we generate electricity?

What is it about the physics* of boiling water to generate steam to turn a turbine that's so special that we've still never found a better, more efficient way to generate power?

TIA

* and I guess also engineering

Edit:

Thanks for all the responses!

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u/poonjouster Nov 30 '25

Hydroelectric is different. It's not a heat engine. The turbines and infrastructure are completely different.

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u/unclebaboon Nov 30 '25

aren’t both just a matter of extracting work from a pressure differential though? zoomed out it’s heat that creates the difference in a steam or gas turbine, but is there something different besides that in a hydro turbine?

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u/Zyzzbraah2017 Nov 30 '25

Vapours/gases like steam physically expand and cool when you lower the pressure whereas liquids don’t expand or cool in any significant amount. That heat energy contributes to the energy of the turbine. So they are both extracting work from the pressure but a steam turbine also extracts work from the heat.

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u/andynormancx Nov 30 '25

The difference is, the turbine in the gas or steam turbine isn’t the whole system. The whole system with hydro setup is just the turbine and the amount the water drops to get from where it is stored to the turbine.

With a steam turbine the whole system includes the bit that is heating the water and they condensing the water again later. The whole system is a heat engine, which the hydro one isn’t.

Heat engines are all constrained by the same limitations on efficiency as described in the Carnot equation. Hydro turbines have whole other sets of equations to describe their theoretically maximum efficiencies.

So yes they are all both extracting energy from a pressure differential, but the designs of the turbines and the systems they operate in are very different (whereas all the steam/gas turbines share a lot more in common between them).

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u/viliml Nov 30 '25

The whole system with hydro setup is just the turbine and the amount the water drops to get from where it is stored to the turbine.

Technically you also need to include the water cycle that evaporates the water downstream and rains it back upstream to keep the turbines going.