# Radiometers As A Power Generator
**URL:** https://boards.straightdope.com/t/radiometers-as-a-power-generator/123473
**Category:** Factual Questions
**Created:** [August 12, 2002, 2:44am UTC](https://boards.straightdope.com/t/radiometers-as-a-power-generator/123473 "2002-08-12T02:44:34Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)
#### Post date: [August 12, 2002, 2:44am UTC](https://boards.straightdope.com/t/radiometers-as-a-power-generator/123473/1 "2002-08-12T02:44:34Z")
I know that [radiometers](http://www.scientificsonline.com/Products/DisplayProduct.cfm?productid=1484) are pretty wimpy things here on Earth. But how about in space? I’d think that it’d be fairly easy to build one large enough to do real work (after all, it’d basically be just a solar sail, but instead of pushing a ship around, it’d turn a generator). I doubt that it’d compare with solar cells as far as output would go, but I’d think that it’d be way cheaper to make than solar cells.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [August 12, 2002, 3:19am UTC](https://boards.straightdope.com/t/radiometers-as-a-power-generator/123473/2 "2002-08-12T03:19:43Z")
I thought radiometers are propelled by hot air? The black side heats up and heats the air molecules in the immediate vicinity. If that’s the case, it would only work in partial vacuum, not the high-grade vacuum of space.
I don’t see why photon pressure cannot be used for turning a generator. I doubt it’d be more cost-effective than solar panels though, since you’d need a pretty large “lightmill” to generate a meaningful amount of energy.
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### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [August 12, 2002, 3:47am UTC](https://boards.straightdope.com/t/radiometers-as-a-power-generator/123473/3 "2002-08-12T03:47:03Z")
> [@](#):
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> I thought radiometers are propelled by hot air? The black side heats up and heats the air molecules in the immediate vicinity. If that’s the case, it would only work in partial vacuum, not the high-grade vacuum of space.
That is indeed he way your typical Edmund Scientific Crooke’s Radiometer works. But th way the radiometer was _supposed_ to work (photons bounce off white side, transfr twice as much momentum as gets transferred to black side, which absorbs it, so white side goes _away_ from light source) _was_ demonstrated after they got good enough vacuums to get rid of the gas that was causing the anomalous ffect. Nowadays, you can generate a _lot_ of photon momentum oomph with lasers, so you can do all sorts of radiation-pressurde tricks.
That said, I suppose you could build yourself an orbital radiometer or something, but I think you’d get more useful energy out of solar panels.