Using electricity to create hot and cold reservoirs, then using the thermal difference to make electricity again cannot ever exceed ~40% efficiency. There are existing fully developed technologies which exceed that by far!
Where do I sign up to receive lots of money to try out a fanciful idea which goes against the basic laws of physics?
The usual efficiency calculation for a Carnot cycle tells you what fraction of heat energy that's removed from the hot reservoir can be converted to mechanical work. This is always less than 100%.
However, when running the cycle in reverse as a heat pump, it is possible to transfer more than one Joule of energy from the cold reservoir to the hot reservoir per Joule of mechanical energy used. That's why the round trip efficiency from mechanical energy back to mechanical energy can be 100%.
I have no idea what the practical efficiency of this system can be. But it's wrong to immediately reject it on theoretical grounds.
That said, due to heat capacity of pump components and conduction losses, I would be surprised if the total cycle efficiency was above 80%, putting this well below gravity and battery storage schemes. Maybe it is just incredibly cheap? Water does have a high heat capacity...
An extremely cheap solution that can store energy well might be just fine in the face of huge amounts of surplus energy.
The Federal government is subsidizing solar production to displace fossil fuel generation.
Which, unlike the headlines about 'negative prices' and being 'forced to pay other states to take their excess' sounds boring and sensible.
Does it make sense to store energy as heat differentials for long term? Insulation can only work for so long, eventually it will come back to environment temp.
One of the best ways for long-term energy storage is to take something (like water) and move it to a higher spot.
We can take advantage of the decay of an atom to generate electricity, but if we want to use that energy later, we push water up a hill.
Although, depending on your local geography, you could just dig a deep hole.
Also, you can use existing deep holes which were dug for other reasons - for instance, open-cut mine pits tend to end up flooded once they're no longer mined.
It's pretty huge, able to produce more than a gigawatt for ~8 hours.
Not sure why they use those balloons though, seems like a maintenance nightmare. A diving bell would work just as well and be much simpler.
Coal generated energy traditionally has not been very efficient, but it's cheap cheap cheap! Likewise with your home automobile: fuel is cheap enough for us to afford continuing to drive despite the "low efficiency" of an internal combustion engine.
Lithium batteries might be coming down in price, but their cost per KwH scales linearly with the battery size. You want double the capacity or halve the price? Have fun building something twice as big.
If this design can do better than linear cost scaling and bring energy storage at household electricity prices, while also using cheap materials, it's safe to say it will show up soon at a datacenter near you.
But even so, there are an awful lot of cheap energy storage schemas that are not limited by Carnot efficiency, so it's a bit baffling why anyone would try to play Maxwell's daemon with their storage facility, when they could be dumping energy into reversible chemical reactions, as one would expect inside a chemical battery. Or maybe even a flywheel system. We're getting better at materials science all the time, and we could almost certainly dump lots of energy into flywheels without exploding them.
And the article sounds a lot like they aren't just sticking a Stirling engine between a hot well and a cold well and pairing it with a motor/generator. That's about as far as I'd go in the thermal energy storage game.
You certainly deserve to receive lots of money for your scrupulous critique of this team.