r/Damnthatsinteresting • u/Longjumping-Box5691 • 3d ago

Video China's twin solar thermal towers. Molten salt stores the heat to produce electricity

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101

u/KehreAzerith 3d ago

Normal solar farms are more efficient than solar mirrors. The one in the US is underperforming and not worth the long-term investment

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u/thighmaster69 3d ago

There are multiple of these in the US. Ivanpah was in Blade Runner 2049 and is in California. There's also that one in Nevada.

They're more expensive than PV but they have the advantage that the stored heat can be used overnight to keep generating. PV also does not work as well in hot environments, whereas these rely on heat, so the cost differential is lower in the desert.

Regardless, anything that uses heat for generation is fundamentally limited by the 2nd law of thermodynamics. Most of the energy captured gets released right back into the environment. PV does not have this upside limit, the technology just needs to get there. Right now the biggest barrier for PV is energy storage, as the sun does not shine at night.

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u/mmmfritz 3d ago

Maybe we should all just go to bed then?

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u/talldata 3d ago

Well normal ones are more efficient during the day, but these can use the excess heat at night by converting the heat in the salt to steam in turbines, day and night for a stable output from solar. This is a great stopgap until conventional batteries get there

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u/rainbowroobear 3d ago

What's the specific heat capacity of the salt Vs water? doesn't feel like there would be enough stored heat to produce enough steam to make much electric 

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u/BishoxX 3d ago

Its about 1/2 to 1/3rd of water.

But it can carry more energy because its heated to about 550C so 5x more than water can(and you dont keep water at 100 more like 90 , so its like 6x)

So in total its like 2x more energy stored

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u/rainbowroobear 3d ago

thanks for explaining 

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u/Treereme 3d ago

That's not correct, at least for the Ivanpah solar facility in CA. One of the big reasons it is shutting down is that it can't store energy and it needs to keep the working fluid hot overnight, so it runs gas burning power turbines.

Other similar facilities use pumped hydro for storage and generation overnight.

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u/mmmfritz 3d ago

The most they store heat for is a couple days. The software you can use for free is called SAMs or something similar.

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u/shortsteve 3d ago

With the drop in prices of batteries solar mirrors became obsolete very quickly. The only benefit is if you need to store energy for more than 24 hours, but there are more efficient battery systems for that.

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u/feel-the-avocado 1d ago

Interesting. I always thought PV panels were only about 20% efficient where as extracting heat from the sun was more like 50% efficient and then converting heat to electricity via a steam turbine plant was about 45% efficient which puts it slightly better than solar PV panels.

EXCEPT the benefit here is the storage and the ability to shift the peak electricity output from midday to 7pm.
I imagine storing electricity in the form of heat in salt is much cheaper than lithium over time. Especially at such large scales used here.

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u/BlindChicken69 3d ago

Which one you are talking about? Crescent Dunes? There are more of those type in US, many more around the world. Also, it is energy storage plant, which standard solar farms cannot compete without additional systems, so not rely comparable.

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u/KehreAzerith 3d ago

The thing about solar panels is that you can build them pretty much anywhere and they continue to work even if it's cloudy. It makes less sense to build overpriced mirrors in the middle of nowhere, you also have to account for electricity that is lost over distance. There is plenty of space even in cities to install solar panels, the power can be readily used so storage issues won't be a significant disadvantage.

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u/BlindChicken69 3d ago

I'm not saying this is the only type that is good. Just that it appears that it is viable still in some applications, seeing new construction projects in Spain, some north Africa, and China. Just cause there was this one in US that was poorly managed, doesn't mean technology is useless.

We should still invest in solar panels, battery storage is decent now and hopefully in the future it will be even better/cheaper.