It's nice to see a technical and cost conversation developing!
Yeah, apples to apples is difficult, and every cake wants a different fruit.
The current 1414 turbine tech is *gas* turbine, not *steam* turbine. Gas here doesn't mean "fossil" gas but any gas theoretically. "Gas" powered electrical generators burn "fossil" gas (or anything really - a lot are dual-fuel with diesel, or even triple-fuel), and the hot exhaust gas runs the "gas" turbine. Same tech here, except the gas used in the TESS is "hot air". Steam and gas turbines are different tech, different cost. You also gotta compare "system cost" vs just "turbine cost" - steam system has a lot more components.
However, when 1414 talks about the proposed large-scale TESS-GRID "approaching the electrical efficiency of modern power plants" at 60+%, that would require a more complicated system with multiple turbines (gas and or steam) in series/parallel, heat recovery systems etc etc. The cost per MW would definitely be higher and the cost per MWh perhaps also - it depends where in the system you draw the line as the energy recovery system actually starts inside the storage device. I'm not sure if 1414 would do a re-design that runs steam through the TESS instead of air - I haven't seen such details in any of the patent stuff. I think it would be challenging given the high pressures. It would also become less flexible, slower to ramp, less tolerant of cycling, generally more baseloady. But then, you also can think about the possibility of ripping out the coal/gas station burners, replacing them with TESS, and keeping the rest of the system intact.
I wasn't suggesting anyone would want to build a TESS with a 0.0056 C-rating. That's over a week's storage. At grid level you're likely to only need that kind of storage maybe 2-3 times a year at 90+% RE penetration with high interconnection. The rest of the time it's just leaking through the walls. We're a long way away from there. Snowy2 style PHES is much better for that scenario as apart from minor evaporation losses, the water can just sit there until you need it. Hydrogen (as ammonia) might also be a good option although ammonia is nasty nasty stuff so you better make real sure your storage is really secure against accidental or deliberate damage. No-one's talking about what happens when your ammonia tanker pulls an Exxon Valdez - oil spills are a tickle compared to ammonia. And it's worse on land.
But a higher discharge rate would be nice to have - industries also can save money by "peak shaving" if they stay grid-connected, and can have processes which need energy in high/short spurts rather than continuously.
Fossil fuels are also a really good option for those infrequent week-long lulls, even into the future, as long as there's enough time-shifting storage around. To think of it another way, you can only make money (value) on the stuff you're pulling in and then sending out, not on the stuff you're storing.
If you need a month's storage, you're in nuclear/asteroid/volcanic winter and screwed anyway.
Yeah, Snowy already has the "Storage" built in a sense, so the 5.1B is for "Generation". Tunnels, turbines, wires etc.
You can save something on batteries by designing for lower C rates, but not much, and it makes little sense to do it - it's the high Cs that make (grid) batteries the big money.
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