500x should be conceptualized as the bare minimum, not evidence of massive low-hanging fruit.

A battery that cycles daily makes revenue on its capacity about 350 times in a year. A seasonal energy store makes revenue on its capacity about once in a year.

A battery arbitrages between the most expensive and least expensive energy generators in the system. A seasonal energy store arbitrages between seasonal price averages.

A battery smoothing out solar production is operating on the difference between how much sun there is in the day, and how much sun there is at night. A seasonal energy store in the same role averages between summer and winter.

A factor 500 cheaper plus a significant quantity of solar energy production is about where you'd expect this kind of thermal storage to start making economic sense.

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Dylan16807 2 days ago | parent [-]

If we're looking at bare minimum cost then batteries are 10x cheaper than batteries.

And being capable of seasonal storage doesn't stop you from using it for daily storage. It's less efficient than batteries, but you can overcome that.

Let's say you can make a 24 hour power source with $10M in solar panels and $20M in batteries, including the other equipment and costs. $30M total. If we need twice as much solar for thermal storage, but the storage only costs $1M, then that's $21M for an equivalent system.

What stops systems like that from being built right now? I was under the impression that batteries were most of the cost if you want them to last more than a few hours.

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Imustaskforhelp 2 days ago | parent | next [-]

Yes! I created a comment here in similar aspect but the thing that was bugging me a lot was what to do about night time though

Imo, the current system of solar energy etc. might be more carbon emissions than even coal because of the way of using batteries and how they are extracted and the whole process and batteries limitations and not solar panels themselves (I think)

Like, please pardon me but I think that there might be batteries that overall are cheap/economical/less carbon emissions and they can store energy for a night cycle right? Then using those batteries in your system and I don't know the price point, but I am definitely sure that they might be orders of magnitude cheaper

So in your 21M$ example lets say that we can add such night time cheap batteries to counter solar panels not generating light at night and use this 1M$ to generate energy when its either rain or solar production is less or when winters come

I still feel like, this might be more economical than the current state of batteries + solar panels.

Okay, I just realized that the night time issue can be solved by the grid but still if that's the case, then why have batteries in the first case if lets say every community builds something like this (if this is economical) and people could just pull up energy from it 100% solar in rainy times etc.

Like maybe my mind is perfectionist or I genuinely don't know about green energy but to me I wish to know if there is a way that we can transition (almost) 100% to the green (solar) without the drawbacks that I saw in the michael's moore documentary in the sense that it produces more carbon emissions net overall theoretically (which hurts my heart :< but the logic was sound imo)

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Olreich 2 days ago | parent [-]

There aren’t grid-scale batteries that can handle hundreds of thousands of cycles at an affordable price. If we crack that problem, solar and wind for everything will immediately be the only technology worth deploying for energy in 99% of areas.

	▲	Imustaskforhelp 2 days ago \| parent [-]
		Nuclear energy sort of doesn't require batteries if they supply energy provided directly to grid man. Solar takes more space than nuclear, the batteries are a huge huge mess. Its still a huge ecological issue that we can't forgive or brush it off man

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Veedrac 2 days ago | parent | prev [-]

I meant ‘bare minimum’ in the sense of what's needed for the system to be profitable, not in the sense of ignoring costs.

The problem with using this approach for daily cycled loads is that it relies on passive heat transfer to distribute heat through substantial regions of dirt. This simply doesn't work for daily storage.

You can overbuild, but then your energy losses are going to be immense, because you never saturate or drain the bulk of the material, and are just losing energy to it.

You could build faster cycling systems instead, and active systems especially can cycle reasonably fast, but then your dominant costs no longer reduce down to a pile of dirt with a few rods stuck into it.

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Dylan16807 2 days ago | parent [-]

You would need more rods if you're cycling more of it at once... but you can add 25x as many rods and it'll still be 20x cheaper than a battery, right?

I don't think losses would be immense. You'll spend a few months warming up the neighboring dirt, but after that the amount of heat escaping per day will look about the same as the seasonal system.

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Veedrac 2 days ago | parent [-]

I'd assume the design as proposed isn't overbuilt, so we'd need to go from, say, 4 months cycle times to 8 hour cycle times, which is maybe 350x.

While that's not going to increase the cost by 350x directly, it is going to change the character of the pile from a bunch of dirt to a bunch of dirty pipes. This makes a lot of the simplifying assumptions no longer work; like you can no longer ignore the heat losses through the rods, or the lower thermal mass of the rods.

And to be clear, you can do this. There are faster-cycling thermal storage solutions out there. It's just not implied from the claim that these solutions would be so much better than batteries.

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Dylan16807 2 days ago | parent [-]

The heat right next to the rods is easier to access. With less dirt per rod, you can also get more watts per rod, so the number of rods doesn't need to scale directly with the cycle time.

	▲	Veedrac a day ago \| parent [-]
		Yes, fair.