Horace Heffner wrote:
The vast majority of the hoped for 200 MW power then has to be from the
bouyancy due to the difference in ambient temperature (and thus column
bouyancy) between the base and the exit of the flue. This sounds like it
needs some checking. [ ... ] The use of base
solar collectors is now looking almost entirely irrelevant.
I didn't check your numbers but this conclusion _must_ be wrong.
Sanity check:
Under stable atmospheric conditions the temperature drop with increase in altitude is greater than or equal to do the drop which results from adiabatic expansion of a parcel of air as the air rises.
In other words, air that starts at the base of the tube at ambient temperature will expand as it rises in the tube (as the pressure drops) and cool as a result of the expansion. The rate at which it cools will be at least as great as the temperature drop outside the tube. If that isn't the case, then you've got cumulus clouds forming because there are spontaneous updrafts, and if the difference is at all substantial you've got thunderstorms. (I'm not talking about inversions -- an inversion is a "super-stable" state. I'm talking about ordinary conditions in which there isn't massive vertical wind shear.) In any event, you've got vertical currents working overtime to even things out and make sure the air is stable (nature's arbitrageurs). Under typical conditions, as I understand it, the atmosphere is stable (or nearly stable) _absent_ _condensation_. Once the dew point is crossed the energy gained from the condensation keeps the air warm as it rises and that's the engine that drives the thunderstorm.
In the absence of condensation, starting with ambient-temperature air, you've got nothing to drive a heat engine from. Again, you've got to push the temp up above ambient at the base; otherwise you'd have strong spontaneous updrafts taking place constantly at that spot (and I don't mean updrafts due to hot dirt heating the air just above it -- that _is_ the solar collector at the base they're talking about using, just in a less intense form). If the calculations show a different conclusion it's worth double and triple checking them because anything else doesn't seem to make sense.
