Comments
istasber t1_irwisc4 wrote
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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[deleted] t1_irvvluv wrote
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dramaking37 t1_irw33pf wrote
> could be used to inject water into the artificial reservoirs
Any geologists want to help me understand if water would be a limiting factor or are these effectively closed loop systems that they are suggesting?
El_Minadero t1_irw6wxg wrote
There’s very little leakage in these systems. They mostly operate as closed loops
grambell789 t1_irwfv7m wrote
if you doing steam turbine to make electricity you have to condense the low pressure steam that came out of turbine to be able to pump it back into the boiler. its part of the carnot cycle and limits heat engine efficiency to no more than 40%.
platoprime t1_irwiyuw wrote
Pumping water up and letting it fall down to generate electricity is 80% efficient over a complete cycle. Am I crazy to think talking about storing electricity as heat in the ground is stupid?
El_Minadero t1_irx1uyb wrote
Yes. Because we can't make the entire planet a hydroelectric dam. Dams are great! but they require lots of fresh water.
Geothermal and hydroelectric power are both incredibly low carbon sources of electric power and potential energy storage mechanisms. It makes sense to use both depending local economics and logistical constraints.
FinndBors t1_irwlvy5 wrote
It's pretty stupid unless we are getting to the point where we are generating too much electricity at the wrong time and wasting it anyway.
platoprime t1_irwm0ko wrote
But it has no advantages over water storage and is half as efficient? Why not store the extra electricity as water?
FinndBors t1_irwmv5p wrote
Water storage requires favorable geography.
platoprime t1_irwo399 wrote
It doesn't require it. You can create closed loop systems and dig a hole.
FinndBors t1_irwtpan wrote
This video from Real Engineering covers a lot: https://www.youtube.com/watch?v=JSgd-QhLHRI
It touches upon a lot of these issues. There are many solutions, some are being explored.
sunsparkda t1_irx0om5 wrote
Digging a hole that has enough volume to store significant gravity based energy storage and won't collapse in on itself when the bottom reservoir is empty raises the price for it, both construction and maintenance. Presumably enough to make geothermal storage cost competitive.
Jiecut t1_irwnd8b wrote
I think it's much easier to develop storage. With water storage you need a big reservoir at a higher elevation.
With this, you're storing the energy underground.
killcat t1_irzmaxl wrote
You need somewhere to pump it up TO, not always available.
El_Minadero t1_irx1lz3 wrote
Sure. but the way newer geothermal binary cycle plants work is the hot geothermal water goes through a heat exchanger at the surface but is never allowed to change into a gas. The intermediate working fluid is typically something like butane. round trip cycle efficiency is limited by the carnot cycle but its not like closed cycle geothermal plants are just leaking water left and right into the ground.
grambell789 t1_irx2pfv wrote
i wouldn't let the well water from a geothermal system anywhere close to something like a turbine that has precise moving parts. I will look into butane as intermediate.
El_Minadero t1_irx40cb wrote
Lots of geothermal plants use a binary cycle. Look up Ormat or the FORGE project.
Psychomadeye t1_irw81km wrote
While open loop would be more efficient for say, cooling a home, heat storage would favor closed loop for obvious reasons. Closed loop would also be easier to maintain.
Lallo-the-Long t1_irwbswp wrote
I think the limiting factor here would be places to put the water. As we have learned with fracking, water injections can be quite dangerous, leading to earthquakes from faults slipping if it's not done properly.
Edit: why the downvotes?
Hyval_the_Emolga t1_irw8vb2 wrote
Maybe this is just me speaking after dropping out of a physics degree, but that sounds less efficient than simply putting that excess power into a lithium battery or H2 fuel cell somewhere.
runetrantor t1_irwgbd7 wrote
Sounds like while less efficient in terms of conversion, it wins in terms of scale, so if you are okay with some loss of energy, you can store a huge amount of power, which with batteries may be prohibitive.
Hyval_the_Emolga t1_irwhy2s wrote
That could make sense I suppose, like jet engines vs piston.
Kurigohan-Kamehameha t1_irypakl wrote
Look up flywheel batteries, it’ll change your perspective of how energy works
beatthestupidout t1_irzwp45 wrote
Look up superconducting ring storage. Same concept, but with electron momentum. Don't warm them up above the critical temperature though - that energy has to go somewhere!
bappypawedotter t1_irwhqgg wrote
Its just a balancing act. The value here is you can scale up this form of energy storage at a low cost - I am talking GWh scale. (I am assuming that this article is backed by good research. IEEE-Spectrum is a sorta the public face of the peer-reviewed technical journals from IEEE.)
Any it would have to be compared to batteries and H2 systems that are both extremely capital intensive and likely dont have the same "scales of efficiency". Batteries certainly dont- there costs are basically linear, and H2 is has its own funny equation (adding storage is cheap, but the balance of system costs are extremely high.) Also, there are pretty significant losses in both batteries and H2 storage.
The current thinking for H2 is pretty interesting. The idea is you setup the H2 system next to a NG plant. Then use renewables to power the inefficient electrolyzer when power is basically free. Store it, and then co-fire it at 10 or 20% with the natural gas. So, it does have its application, and it could become quite common. But it isn’t a stand alone system like what they are discussing here.
It also worth noting that we do have a lot of industrial heat recovery systems that may be able to take advantage of incumbent geo-thermal equipment. So, there may be some real savings here.
At the end of the day, this wont be a silver bullet. But it may have a significant role in cracking the GWH scale energy storage that we really need.
The thing you have to remember is that in many areas, there is so much excess renewable energy that its basically free. So, it doesn't really matter if its less efficient.
El_Minadero t1_irx2fif wrote
Yes. But there are logistical challenges to getting enough battery grade lithium soon enough to effectively combat climate change. Using existing geothermal reservoirs as a stopgap solution to store excess energy across years is a great way to transition the grid.
Hyval_the_Emolga t1_irx2j0u wrote
That does make sense, that was my second guess
AnimiLimina t1_irwlph6 wrote
Isn’t you storage capacity of excess electricity limited to the power requirements of the water pumps? And isn’t that only a small amount of your total energy output as your output is created by heating water to steam and not like in a pumped hydro from the work of the pumps.
So it’s not so much a battery in a sense that your output is the input minus losses, it’s a baseline power plant that is shut down intermittently to increase the output from net to gross by running your pumps with excess power at a earlier date.
If I’m not missing something here I’m very sceptical that this is a battery as much as a fast response generator with a efficiency boost by using excess renewables.
If anyone knows more please tell me, the article is not really useful.
El_Minadero t1_irx2l2n wrote
> electricity limited to the power requirements of the water pumps?
Nope. Geothermal stations don't pump up water from depth. You're limited by the ability to throttle the turbines and how much energy you can inject into the geothermal loop.
Edit: there's also only so much heat the surface heat exchanger can use. Typically geothermal plants are run as stable base power loads but its possible to add a 'peaker' capability similar to natural gas plants.
AnimiLimina t1_irx3h02 wrote
Yes not pumping up but pumping down. The described plant doesn’t use a natural reservoir but a fracked artificial one that need water injected into it. That water injection is what they want to use the excess renewable energy for and it you be equivalent to the charging of the battery.
El_Minadero t1_irx3wcs wrote
the energy in the system is limited by both how much fluid you pump down and how hot the fluid is. Even for a static flow rate you can just keep increasing the temperature of the injected fluid to increase heat transfer. Even if the steam is supercritically heated, everything should still work.
Infact, supercritical steam is preferrable! It helps catalyze the conversion from CO2 gas to stable calcite minerals, opens up pore space at depth for more efficient heat transfer to the rock reservoir, and is much more thermally conductive than plain water or steam.
minitrr t1_irvs9lk wrote
Ehh I wouldn’t bank on geothermal as a widespread solution. It’s great in active areas like Nevada and California (also some demo projects in Louisiana).
Permits for drilling are tough and can take years upon years.
wwarnout t1_irvulpc wrote
Another disadvantage is that converting electric power from wind or solar to heat, and then converting that stored heat back to electricity, is much less efficient than storing electricity in batteries.
theseldomreply t1_irw0myd wrote
Probably still more efficient & feasible than making hundreds of gigawatts worth of batteries.
El_Minadero t1_irw6td0 wrote
But you can store excess power for years underground
KevinFlantier t1_irwdgmt wrote
If you generate enough power and your batteries are big enough, efficiency barely matters. A simple, easy and non polluting way to store energy would be a lot more useful than a very efficient one that relies on rare-earth metals, that is extremely expensive to scale up and that wears down over time.
LaserAntlers t1_irwcia5 wrote
That's why we should just do solar thermal for projects like this one a large scale.
_AtLeastItsAnEthos t1_irvu50o wrote
Good thing an insane amount of our power consumption is done in those areas
minitrr t1_irvulfb wrote
I mean for the WECC, sure, but not EI, ERCOT, or the rest of the world.
Fmarulezkd t1_irw0ldc wrote
Widespread solutions are not necessary. I'd reckon that energy production and storage will be area specific.
minitrr t1_irw0xhs wrote
Absolutely I agree - different markets will require a different configuration of solutions. It’s just that geothermal will probably be particularly niche.
El_Minadero t1_irw6r4m wrote
The EGS he talks about doesn’t need a high enthalpy system to operate.
ghostcompost t1_irwmm38 wrote
Is this safe? On a global level do we understand enough about how our planet works underground to say what will happen? It sounds like a good idea, but only if it won't be trading one problem for another.
ImaCrayon t1_irwr4uw wrote
I am in agreement with you. Its a catch 22, where new technologies are implemented, that later cause problems. However, we would not know about the problems of said tech until large scale implementation. Regardless, i like the idea of cleaner methods to store excess renewable energy. I just worry because gas and oil companies are not exactly model industries for environmental issues
El_Minadero t1_irx2pra wrote
Yes. Look up the FORGE project. EGS systems are coming online with orders of magnitude less induced seismicity than conventional fracking operations
[deleted] t1_irvm6ue wrote
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[deleted] t1_irvmpmq wrote
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FuturologyBot t1_irvnkwt wrote
The following submission statement was provided by /u/filosoful:
Geothermal systems carry warmth from Earth’s interior up to the surface for heating or electricity. But geothermal power plants are expensive to build, and will get even less economically viable as wind and solar power get cheaper and more plentiful. However, even as wind and solar grow, so does the need to store electricity from those temperamental sources.
A new proposal could solve those issues and bolster all three renewable technologies. The idea is simple—use advanced geothermal reservoirs to store excess wind and solar power in the form of hot water or steam, and bring up that heat when wind and solar aren’t available, to turn turbines for electricity.
>It would allow next-generation geothermal plants to break from the traditional baseload operating paradigm and earn much greater value as suppliers of wind and solar,
says Wilson Ricks, a graduate student in mechanical and aerospace engineering at Princeton University.
Please reply to OP's comment here: https://old.reddit.com/r/Futurology/comments/y16ixm/geothermal_may_beat_batteries_for_energy_storage/irvklbm/
[deleted] t1_irvw4ca wrote
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OGCelaris t1_irwhtm2 wrote
I could be remembering incorrectly but wasn't geothermal shown to cause earthquakes in some areas? Then again, it could have just been some big oil propaganda from back in the day.
UrinalCake777 t1_irwpg5r wrote
Fracking definitely does. I'm not sure about geothermal. I believe geothermal plants are usually installed in places that already have relatively high levels of geothermal activity (ie Iceland) so it's not too much of a change.
I could be wrong on all that as I am not an expert so you may want to do some mote reading.
El_Minadero t1_irx2scn wrote
Look up the FORGE project. Its basically a non issue, especially compared to O&G
0ne_Winged_Angel t1_irwkazh wrote
I saw a similar sort of thermal energy storage system that was basically a massive brick of wax in an insulated box. The idea being that as energy is put into the brick, it is stored by melting some wax, and pulling energy causes it to freeze. In physics terms, using the latent heat of a material to store energy rather than its raw temperature.
The box I saw was more designed to be used as a source/sink for a local heat pump than as grid scale storage, but it may be possible to scale it up.
[deleted] t1_irwn0ha wrote
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Jniuzz t1_irwz1ho wrote
Why such a short article? How do those geothermal systems work?
Creloc t1_irx1q4v wrote
I remember hearing something about high efficiency chemical heating packs being developed which are able to store heat and then release it at a given signal (like those snapping hand warmers) I'd be curious to know if people have heard about something like that as a potential companion tech for this
[deleted] t1_iry9z8r wrote
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musicofspheres1 t1_irya6fx wrote
Based on Ethiopias largest mode corbetti, 460 geothermal plants can power the US. Trillions in stranded fossil fuel assets if implemented so yea..
[deleted] t1_iryho4f wrote
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GetsTrimAPlenty2 t1_iryohjw wrote
hmm injecting energy into systems with unknown stability. Seems iffy.
SalmonHeadAU t1_irzk6jw wrote
Batteries can go anywhere. Geothermal Plants cannot.
noelcowardspeaksout t1_irztu0g wrote
A new project uses an insulated silo of sand to store heat. It is a simple design that uses common and cheap materials, so might gain some traction.
filosoful OP t1_irvklbm wrote
Geothermal systems carry warmth from Earth’s interior up to the surface for heating or electricity. But geothermal power plants are expensive to build, and will get even less economically viable as wind and solar power get cheaper and more plentiful. However, even as wind and solar grow, so does the need to store electricity from those temperamental sources.
A new proposal could solve those issues and bolster all three renewable technologies. The idea is simple—use advanced geothermal reservoirs to store excess wind and solar power in the form of hot water or steam, and bring up that heat when wind and solar aren’t available, to turn turbines for electricity.
>It would allow next-generation geothermal plants to break from the traditional baseload operating paradigm and earn much greater value as suppliers of wind and solar,
says Wilson Ricks, a graduate student in mechanical and aerospace engineering at Princeton University.