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# Coaxial Updraft/Downdraft Solar Tower

What goes up, must come down!
 (+4) [vote for, against]

A solar updraft tower <link> is essentially a large chimney with a turbine in it. The turbine is powered by hot air rushing up the chimney. The hot air is made by constructing a large greenhouse around the base of the tower and using solar energy to heat the air under it.

A downdraft energy tower <link> is sort of the opposite. You have a large tower, and water is sprayed into the top of it. The water evaporates and cools the air inside the tower. This increases density and the air falls, through turbines in the base of the tower to generate power.

Why not do both? The net result of the first tower is a lot of hot air at the top of the tower. Why not build a second tower around* the first. Solar heating pushes air up the inner tower, then water is sprayed around the periphery causing the air between the first and second tower to fall, where it will rush down and out over the top of the solar collector, which thermally & physically isolates the two countercurrent air streams.

Now you can drive turbines on the way up, and the way down. A clever addition would be to have the updraft air entrance facing into the prevailing wind, and the downdraft away.

*or inside, I don't really mind

 — bs0u0155, Jun 18 2021

Solar Updraft Tower https://en.wikipedi...Solar_updraft_tower
[bs0u0155, Jun 18 2021]

Downdraft Energy Tower https://en.wikipedi...g%20at%20the%20top.
[bs0u0155, Jun 18 2021]

Can you generate more power than it takes to pump the water to the top?
And you probably wouldn't want the "down" inside the up, as it will get warmed by the "up".
Might even need a cavity for insulation between the two (so 3 concentric tubes; warm - cavity - cool)