A solar updraft tower is gloriously simple: a vast glass greenhouse heats desert air, the air rushes up a tall central chimney via the stack effect, and turbines at the base harvest the wind. The 1982 Manzanares prototype in Spain (195 m tall) produced 50 kW for seven years. EnviroMission later proposed a 1-km tower delivering 200 MW. So what happens when we crank the height to 10 km — taller than Everest?

The thermodynamic prize. Stack pressure scales linearly with height. For a temperature lift of ΔT = 30 K over ambient T = 300 K:

Δp = ρ · g · H · (ΔT/T)
   = 1.2 · 9.81 · 10,000 · (30/300)
   ≈ 11,800 Pa

That's 10× the pressure of a 1-km tower. Chimney updraft velocity (from v = √(2Δp/ρ)) caps near 140 m/s ideally, but wall friction and turbine backpressure keep it around 15 m/s in a 200-m-diameter shaft. Volume flow ≈ 470,000 m³/s, thermal power ≈ Δp · Q ≈ 5.5 GW. With turbine and Carnot losses (~30% overall), you net about 1.6 GW electrical — a respectable nuclear plant, all from sunshine and hot air.

To feed it, the collector greenhouse must be roughly 40 km across (~1,200 km² of glass) — about the area of metro Berlin, paved in greenhouse glazing.

The structural nightmare. A self-supporting hollow tower's max height before crushing under its own weight is roughly σ/(ρg). For ultra-high-performance concrete (σ = 150 MPa, ρ = 2400 kg/m³), that's 6.4 km — not enough. You need a CFRP composite shell (σ ≈ 1500 MPa, ρ ≈ 1600 kg/m³, theoretical limit ~95 km), but buckling is the actual killer. A thin-walled tube buckles when:

σ_cr ≈ 0.6 · E · (t/r)

For r = 100 m and the carbon shell to resist its own compression, you need wall thickness t ≥ ~1.5 m of layered composite, stiffened by helical ribs every 50 m vertical. Total structural mass: about 5 million tonnes — five Burj Khalifas stacked.

And then there's the jet stream. The summit pokes into the subtropical jet, where winds hit 60 m/s and density drops to ~0.4 kg/m³. Drag per meter of altitude near the top:

F/H = ½ · 0.4 · 60² · 200 · 0.7 ≈ 100 kN/m

Integrated lateral force ≈ 1 GN; overturning moment at the base ≈ 5 × 10¹² N·m. You'd need a foundation ring 2 km across, tensioned by guy cables anchored across 20 km of desert — essentially a planetary-scale tent. Vortex shedding at the upper third would oscillate the structure at its natural frequency unless you add Stockbridge-style tuned mass dampers totaling ~50,000 tonnes.

Bonus weirdness: the air exiting at 10 km is below freezing. Moisture in the desert updraft (humidity from the collector floor) would form an artificial cirrus plume — a permanent 200-km contrail. You've built a rain machine and a weather modification system as a side effect.

The cost? Glass and CFRP run ~$200/m² and ~$30/kg respectively. Just the materials clear $400 billion. At 1.6 GW × $0.05/kWh × 8760 h = $700 M/year revenue, the payback is 600 years before maintenance — and the tower's design life is maybe 80. Two orders of magnitude underwater.

But split it into ten 1-km towers across the Sahara and the economics flip: same total power, square-cube scaling on your side, and no one tower picks a fight with the jet stream.