Solar thermal isn't used because solar panels are much cheaper and simpler. In world without cheap solar panels, solar thermal would be preferred form of solar energy, and could be done with advanced technology.
If you’ve read Project Hail Mary, the sci-fi part isn’t collecting energy, its the lossless transport.
Hopefully that’s not a spoiler.
In the end it seems like it should be cheap but nobody got it anywhere lose to PV pricing.
“You can’t win, you can’t break even, and you can’t quit the game.” - C.P. Snow [1] (No idea if that’s the correct attribution, I heard it from a professor 20 years ago)
My personal shorthand for this is to focus on the efficiencies of energy transformation and transport. Converting or moving energy means we lose some fraction of the total energy. All we can do is minimize that fraction.
The main point being that with that mental framework, I can easily assume that your posited approach won’t be more efficient than a solar panel or some other process with fewer transformation steps because each step magnifies energy loss inefficiencies.
Basically, the entirety of the energy debate is two things: How can we harvest energy cheaply and move it with minimal waste.
This is the basis for the whole room temp superconductor story that captured a bunch of our nerd imaginations, what happens if you get super close to zero energy loss while moving electrons?
Also, one more thing to keep in mind is constraints. Your proposed solution may be way more efficient by some metric if we change the constraints. For instance, my brain mostly goes to transportation which is transport and storage with immediate demand requirements. However, if our requirements were different along the lines of “lets store as much energy as possible over months, to slowly release it over months”, inefficiencies of scale change things. Then maybe slowly moving water uphill during summer while releasing slowly during winter is a valid thing to consider [2].
[1] https://gohighbrow.com/laws-of-thermodynamics/
[2] https://medium.com/drax/how-to-turn-a-mountain-into-a-giant-...
However, what you have described is similar to the basic design of closed-loop industrial solar thermal systems: they concentrate solar power to heat a liquid or other medium and use the heat (or heat differential) conventionally (see, for example the Ivanpah Solar Power Facility near Las Vegas).
Condensing the steam down and trying to extract energy from the condensation flowing downhill is orders of magnitude away from being worth it. The sun is boiling a few gallons of water per minute at best, while hydroelectric systems are measured millions of gallons per minute.
Steam turbines work not because of steam alone, you can fill a room with steam insert a turbine and nothing happens. To get them to spin you need higher pressure on the input side of the turbine than the output. If you want to have steam go up a shaft that’s going to increase the pressure on output side and thus reduce the amount of energy generated by the turbine.
Concentrated solar thermal (CST) is a solar energy technology that uses sunlight to generate heat.
Spain is the world leader in the use of CST to produce electricity, with around 2.3 GW in operation, followed by the United States with around 1.7 GW in operation.
The Australian Renewable Energy Agency (ARENA) has announced it has approved $65 million in funding to Vast Solar to construct VS1, a first-of-a-kind 30 MW / 288 MWh concentrated solar power (CSP) plant in Port Augusta, South Australia.
ARENA’s funding for VS1 is conditional upon the project reaching financial close, which is targeted to occur in late 2023. VS1 is expected to take two years to build with commercial operations commencing late 2025.
CSP uses mirrors to concentrate and capture heat from the sun in solar receivers, with high temperature heat transferred via sodium and stored in molten salt. The stored heat can then be used to heat water to create steam to power a turbine and produce electricity, or the heat can also be used directly to decarbonise some industrial processes.
One of the benefits of CSP is that the captured heat can be stored cost-effectively for long periods with little loss of energy. This means that CSP can be used to generate electricity or provide heat on demand, including overnight.
Vast's modular CSP v3.0 technology has been proven at its 1.1 MW, grid-synchronised demonstration project in Australia and will be used in a growing pipeline of zero-carbon power projects globally.