No real alternatives to fossil fuels ..

[Nozzle]

Though the energy storage solution looks interesting, what'll scupper this plan is the (unavoidable) inefficiency of the Rankine cycle.

...I've been thinking about this solution over the day. I stand by my original observation that using the Rankine cycle and a turbine to generate power from stored heat is poor utilisation. However, it would have two very useful benefits:

a) Making otherwise un-dispatchable power (wind turbines, solar) be able to perform MVar control (only performed by large rotating machines)
b) Making the same un-dispatchable power also perform grid frequency control. (Only performed by specialist hydro, coal, oil, gas, or perhaps nuclear {not currently in the UK} )

Both of the above are vital for a stable grid, and neither can be performed by solar or wind. It's why a nationwide grid can never be solely powered by either.

Nozzle

 

[IT Minion]

b) Making the same un-dispatchable power also perform grid frequency control. (Only performed by specialist hydro, coal, oil, gas, or perhaps nuclear {not currently in the UK} )

You might think that, but happily you'd be wrong.

Synthetic inertia is available from.modern wind turbines.
https://spectrum.ieee.org/can-synthetic-inertia-stabilize-power-grids
And batteries can do it too (probably, it's being tested):
https://www.pv-magazine.com/2021/10...est-with-big-battery-registered-in-australia/
I think all hydro electric features inertia too, it's a function of the spinning mass of the turbines after all.