# Solar updraft turbine towers: Why so tall? **URL:** \ **Category:** Factual Questions\ **Created:** [May 23, 2010, 3:50pm UTC](https://boards.straightdope.com/t/solar-updraft-turbine-towers-why-so-tall/540464 "2010-05-23T15:50:33Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [May 23, 2010, 3:50pm UTC](https://boards.straightdope.com/t/solar-updraft-turbine-towers-why-so-tall/540464/1 "2010-05-23T15:50:33Z")
The “solar tower” idea is new to me but very fascinating. Note: this is not the solar tower that uses concentrated heat aimed at a tower, but uses heated air to turn turnbines. See video. My question: why does the tower need to be so high? Is the area under the plastic sheets tha power the tower what determines it’s height? If so, how big would you have to build a tower and how much land to generate just a couple thousand watts? Could a half acre of land on a farm be used to power much? [![](https://img.youtube.com/vi/C-EvV90MeDY/hqdefault.jpg "EnviroMission's Solar Tower Pilot Plant - Solar and Wind Renewable Energy") ](https://www.youtube.com/watch?v=C-EvV90MeDY) ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [May 23, 2010, 4:36pm UTC](https://boards.straightdope.com/t/solar-updraft-turbine-towers-why-so-tall/540464/2 "2010-05-23T16:36:34Z")
If there’s only one set of blades, at the bottom, why does the height of the tower matter? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [May 23, 2010, 5:10pm UTC](https://boards.straightdope.com/t/solar-updraft-turbine-towers-why-so-tall/540464/3 "2010-05-23T17:10:59Z")
For chimneys, [taller ones](http://en.wikipedia.org/wiki/Chimney#Chimney_draught_or_draft) have more draft. I’d imagine the same basic principle applies. Making them tall and large in diameter increases the flow rate, Q, as given in that section. Of course, T[sub]i[/sub] is increased with a larger surface collection area. Presumably, the sizes of all three are optimized together to get the most energy per dollar. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [May 23, 2010, 5:41pm UTC](https://boards.straightdope.com/t/solar-updraft-turbine-towers-why-so-tall/540464/4 "2010-05-23T17:41:58Z")
The taller the stack the lower the pressure at the top of the stack. It is called stack effect.