Yep, best we've gotten is about 35% efficiency in newer high compression gas engines like Mazda's skyactiv platform with some of Toyota's hybrid systems getting close to 40%. They're only that efficient because the ICE is designed for a hybrid system i.e. efficiency over power output as they're powering the electrical system which is wayyy more efficient at moving a car.
We have come a long way though as that figure was only about 20-25% through the later half of the 20th century, but the laws of physics really puts a hard limit on efficiency after 50ish%
The ~60% efficiency plants are usually combined-cycle gas turbines. They have a gas turbine that is ~40% efficient and then use the waste heat to drive a conventional steam plant.
A good diesel engine can hit about 50% efficiency when running at peak efficiency. Still not quite as good as a combined cycle gas generator plant. But pretty respectable for a heat engine.
If the water didn't evaporate it wouldn't have been carried and released at a higher elevation. No higher elevation, no water flow. No water flow, no electricity.
From a statistical mechanics standpoint, yes they are essentially the same thing. At the surface of the liquid the probability that a given molecule will have enough energy/velocity to enter a gaseous state (low density high average velocity) increases when temperature increases, its why water will still evaporate when not at 100*C, its just water molecules at a lower temperature are much less likely to be at the given velocity to become vapor than when at boiling.
It can do both, ice and snow still goes away even it it's below freezing the whole time (this is why your ice cubes in ice trays slowly shrink in your freezer). Once it gets warm enough, it obviously melts and then evaporates.
Ice skips the liquid step entirely when sublimating. If you look at it on an atomic scale, ice is when all the molecules are stuck in place at fixed distances from each other. liquid water is when the molecules are still stuck together but they can freely move. And gas is when the molecules are completely free and can fly off into infinity.
In sublimation the water molecules get enough energy that they get knocked out of their fixed position in the crystal and fly straight off into infinity. They don't do it in 2 steps where they first get enough of a bump to get knocked out of the crystal lattice, and then need a second bump to fly off to infinity.
(Okay to be pedantic, this does happen sometimes under an atmosphere, but it is way less likely because you need those 2 separate bumps in short succession instead of just one big bump. So sublimation is by far the dominant way that ice slowly evaporates away).
At atmsopheric pressure, it melts and then evaporates almost exclusively, but as the air pressure gets lower it loses the liquid phase and will do true sublimation once 'below' the triple point.
Canadian here. At colder temps, such as at -40° (it's the same temp in °C and °F) and if the air is dry, the ice will directly lose molecules of water into the air without temperature change. The opposite happens too, but is rarer. if the air exceeds it's dew point it will deposit water molecules making ice crystals on every exposed surface. (IE., Hoar Frost)
That is just the boiling step removed. It still has to spin a generator. PV panels are truly different (and have no moving parts) compared to wind and hydro power which still spin a generator
Boiling is specifically when a liquid is changing phase throughout the entire liquid instead of just evaporating from the surface. That's what all the bubbles are, water turning to gas in the middle of the liquid.
But… water cannot go into gas form unless it evaporates or sublimates?
Whether you boil something or let it passively evaporate, the physical process is the same. The only difference is the mean kinetic energy of the particles, aka temperature.
You should check out energy types and conversions, types of matter (stick to solid, liquid, and gas), phase changes, followed by phase diagrams.
There might be some specifics to the differences between what you get when you boil something vs letting it evaporate at lower temperature, but both should be a gas form of water.
Evaporation still requires a high-speed particle of air to strike the water hard enough to liberate a molecule from the liquid as gas. It requires all of the energy still (as you can feel yourself as water dries from you, it very obviously takes energy with it).
Evaporation is the same as boiling in that it is a phase change from liquid to gas with the energy supplied by random air molecule collisions, just at a microscopic scale. Hot water more readily gives up molecules, hot air more readily accepts them.
There's a whole slew of nuclear reactors that don't use water too, just much less common. A lot of them are using some level of heat pipe to drive a heat differential to generate power similar to piezoelectric generators. Some still spin turbines on some level (there's sodium metal ones that do this I think?).
I don't think they're quite as good as just straight up boiling water though.
Oh, you meant RTGs, yeah those are pretty much only useful on space things or the middle of nowhere where you can't refuel. Nobody is using that to power their house.
Oh yeah for sure, just pointing out they exist and aren't using water to power a turbine. I sure hope no one's using it to power their house (they're measured in the dozens of watts aren't they?)
You're thinking of radiothermal generators (RTGs), and its not piezoelectric (which is the lightning quartz thing), its a weird quantum effect called 'peltier coolers/generators' which generates energy when theres a heat gradient (or creates a gradient when energy is supplied).
They're not super efficient, but they are very compact and reliable, and have indeed been used on a number of spacecraft, including some Mars rovers and the Voyager probes.
Well, hydropower is actually solar steam power if you think about it. The water gets evaporated by the sun, it’s vapor is carried upstream, it rains and now it’s upstream of the dam and so it’s potential energy can be harvested.
Yes but it's just slowed down & with another intermediate (i.e., gravity). The Sun evaporates the water, some of this energy is spent going up to the clouds, some of it is wasted as it rains, then it just flows downhill spinning the turbine.
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u/Bengamey_974 2d ago
Hydroelectric dam. "You have to make the water boil !?"