This scheme, if it works, makes PV work great in Alaska.
This scheme is probably superior though, with lower capex and working at smaller scale, especially if one doesn't have deep salt formations to solution mine for hydrogen storage caverns.
> There is an efficiency penalty converting back to electricity; round-trip efficiency is 40%-45%, but sometimes the steady supply of electricity is worth it.
The power to gas is also carbon neutral, even negative depending on what you decide to do with the natural gas (if you don't burn it for power but use it for industrial chemistry, you get some sequestration out of it).
Direct air capture is out, so it'll have to be recovered from the combustion of the synfuel. Using the Allam cycle has been explored to do this (you also have to store the oxygen from electrolysis for later use in this oxyfuel combustion cycle) but it ends up being more expensive than just burning hydrogen, if there's reasonable geology for hydrogen storage.
So, if this thermal storage scheme is cheaper than hydrogen, as it appears it will be, then these alternative synfuel schemes are ruled out.
But, if you read the wikipedia article, you can see there are prototype plants using ambient air capture. It's probably a bit less efficient, but since it's actually reducing carbon levels, it's even better than just a battery.
Meanwhile multiple grids are now paying renewable to curtail, because guess what, the variability is correlated (it's the exact same damn mathematics we used to fuck up the entire global economy in 2008, which is why I'm so surprised people are handwaving that too, but whatever). If you want to minimise cost without relying on gas to save you on dark still days, you want a cheap use for the surplus, round-trip be damned.
Batteries are already economical in most grids where they can arbitrage daily prices of 0-10c during the day to 10-30c during the night, with the occasional outlier event contributing dollars per kwh.
They will never load-shift across seasons, agreed, but for daily loadshifting they are already economical, and being 90%+ efficient (and very simple/easy to deploy and scale) is part of why they're popular. It opens up power shifting opportunities that aren't just daytime solar too.
This is systematic fraud by the renewables industry and should be called out.
Sand batteries don't need sharp sand.
I wonder if it has to be the same kind of sand, or could be some that we neither have another use for, nor would damage any ecosystem (too much).
In a situation where you have a lot of energy generation that would go to waste, storing it in a system with low round trip efficiency could be better than losing it.
For planned installations where the generation cost is nontrivial (like a solar install) then increasing the generation to compensate for poor battery efficiency isn’t as easy of a decision.
And when electricity is in essence too cheap like with solar and wind it can be, losing half in efficiency actually doesn't matter too much.
Practically speaking, you're probably not going to get 1000s of years out of any storage method. There's just too much stuff that breaks down.
Heck - a lot of historic dams are in the low hundreds of years old and are experiencing serious problems.
IMO, the shorter lifespan of batteries isn't that big of a downside as long as the "bad" batteries can be mined for raw materials eventually.