Perfect guess ! (afaik) ρ(concrete) ≈ 2.5 tons/m³
so full sphere ≈ (2.5 x 382) tons = 955 tons
they have 400 t so the cavity removes :
955 - 400 = 555 t ... so 7.51m diam. cavity
... so, yes 3/4m thick wall 😌👍 !

indeed i made a very simplified calculation not taking into account increase density of salted water nor increased density because of compressibility of water at 500 m deep. Basically i took 1m³(water) is 1 (metric) ton.

... a sphere nine metres in diameter and weighing 400 tonnes will be submerged off the coast of California at a depth of 500 to 600 metres. It will have a storage capacity of 0.4 megawatt hours (400 kWh) ...

i will try a rough calculations : suppose we can have concrete at $100 per ton, then it's a minimum investment of $40,000. Also suppose electricity is stored with a large added value of 10 cents per kilowatt hour, so, for every cycle a rough gain of $40. By these numbers, 1,000 cycles would pay for the concrete ... so, it may look good considering they plan a life of about 50 years for such devices.
On the other hand if competitive battery storage cost only one cents per kilowatt hour (temporary in and out storage) and if concrete and fabrication goes up 10 times to $1,000 per ton then it is not economically viable anymore.

A good calculation of profitability would need to take into account the less than 100% energy efficiency of batteries cycling and of hydraulic energy cycling, ... and so many more parameters which have to be studied.

... you’d need some massive ...
from the srticle :
... a sphere nine metres in diameter and weighing 400 tonnes will be submerged ...

Can you calculate the weight of a sphere of 9 m of displaced water ?
No ? Well, it is 382 tons.
So, the concrete sphere is already massive by itself. "You" don't need any complicated anchoring.
Same goes with the rest of your mechanical engineering intuitions : you did not work in this domain or study it, did you 😆 ?
Also, stress cycling is bad on most material, yes. But here it is compressive stress and the geometry is symmetric. Without further study, i want to believe this thing has good potential and my intuitions tells me it looks nice. Time will tell 😁 !

Congratulation to both sides being mature enough to agree so rapidly to this ceasefire despite (or with the help of 😋 ?) "American mediation".

you forgot to put a link to any news article

it's a basic human right to get rid of waste, including that Trump turd.

if proportional "messages" were sent by other countries, Israel would shut it's fucking mouth. For good.

Why would the robots doing all the other jobs listen to this delusional human ?

Yes ! hum ... 2 days ago I also wrote
::: spoiler this :
i think it's this, at :
56.10, 38.75

😋

was located at : 56.10, 38.75

cross-posted to (...)

very wise of you to have it cross-posted since, obviously, it will be deleted here for breaking the rules of World News 😆

Delirious electors who chose a demented president are brought back to reality

title : U.S. Chipmakers Fear They Are Ceding China’s A.I. Market to Huawei

After failing to destroy A.I. in China, Americans regret not dominating it.

This guy should be more careful with that gigantic virus in his hands ... imagine that virus reproducing in your body - - that's my own conspiracy theory 🤣

Every republican in this situation should resign, let someone brave take their place.

Genocide live streamed despite an unprecedented number of journalists being murdered to gag that ongoing atrocious suffering.

Delusion and narcissism being his basis, you can't make him see what he is.

1- make vaccination mandatory.
2- charge parents's non-compliance with immediate 10 days imprisonment.
3- make it clear that, starting next month, any children dying from parent's misbehavior will result in capital punishment for this parent - - no trial - - just execute them on public stage.

This is just a stupid rant on the internet - - i'm not taking the time to weigh exactly each of these words - - take them with a grain of salt f.f.s.