istasber t1_irwisc4 wrote
Reply to comment by filosoful in Geothermal May Beat Batteries for Energy Storage: Enhanced geothermal systems are well suited to store excess renewable power as heat. by filosoful
Three's been talk about using molten salt storage as a way to smooth over the fluctuations from renewables, particularly solar.
The idea is that you'd use the energy from the renewable to heat salt from ~250C to ~500C, and then you'd use the hot salt to heat water to spin turbines. Supposedly the storage would keep for around a week, which is enough to smooth over daily and weekly energy demand fluctuations. It seems like it'd be an easier system to work with than trying to store superheated water, since the salt is a liquid at standard pressure both in the "cold" state and the hot state, but I haven't really heard or seen anything about it since I read about it in like a scientific american or something some 20 years ago.
FinndBors t1_irwlpsd wrote
Not an expert but one drawback to molten salt is that it is really corrosive.
I've read about that issue when reading about next gen nuclear reactors, but I assume it would apply here too.
pastor-raised t1_irwps92 wrote
What about using excess energy to pump water up a mountain and releasing the water through turbines down the mountain as power in needed. Too inefficient?
sunsparkda t1_irwzd7i wrote
That's pumped hydro storage, and it's already implemented in most of the places that have the geography for it. It's the most widely deployed power storage system at the moment.
Squirmin t1_irwr5is wrote
It looks like the biggest disadvantage to molten salt is the drop in generation efficiency. While the long term storage is fairly efficient, it loses a lot when they try to convert back to electricity. Hydro storage can lose efficiency due to evaporation, but they can still maintain 70-80% efficiency.
There's also geography that has to be taken into account for hydro, as you can't put it just anywhere.
>In a complete PHES cycle, water is pumped from a lower to an upper reservoir and at a later time returns to the lower reservoir, with a round-trip efficiency of about 80%. In other words, about 20% of the electricity is lost in a complete pumping/generation cycle.
>The topic is crucial because, at the present stage of power industry development, molten salt power plants are pioneering solutions promoted mainly in Spain and the US. Molten salt reservoirs have high storage efficiency (above 90%), but the efficiency of the energy transformation from heat to electricity is much lower at about 50%, which is a significant disadvantage.
VladVV t1_iry6tby wrote
It’s been proposed to simply use groundwater reservoirs as the lower reservoir and enable pumped hydro (almost) independently of geography. It’s only been implemented as small-scale tests, however, and the long-term consequences (if any) of repeatedly pumping water out of and back into deep underground wells are not known.
oppositetoup t1_is07k30 wrote
It's very dependent on the geography of the area. You can't just use a mountain as there's no space at the top to actually store enough water to make it worthwhile.
It also takes up A lot of space
killcat t1_irzm7ww wrote
Depends on the salt mix, and alloys used.
pspahn t1_irwn9qz wrote
> but I haven't really heard or seen anything about it since I read about it in like a scientific american or something some 20 years ago.
There are plans to convert a retiring coal plant in Colorado to salt storage:
The coal plant has two units that will retire in 2027 and 2028.
El_Minadero t1_irx27u6 wrote
Solar thermal plants do use molten salt as thermal storage. However, they aren't able to store heat energy seasonally.
The Earth is such an excellent thermal insulator that volcanic areas that received their last pulse of power 150,000 years ago are still hot! Geothermal energy storage could locally solve the solar "duck" curve where the subsurface conditions and economic factors are optimal with no need for tons of battery metals and virtually no greenhouse emissions.
[deleted] t1_irwlm59 wrote
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