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Funneling sunlight...


Externet
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What contraptions can re-direct sunlight during dawn to dusk hours towards a single direction ?  Is there some prisms, lenses, mirrors, combination of them ?

The solar tubes product seems does it well to a certain degree; may have been designed as best as the manufacturer could.  

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The point of entrance/collection of solar light...  What other passive methods exist ?  -No heliostats, no moving parts-

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2 hours ago, Externet said:

What contraptions can re-direct sunlight during dawn to dusk hours towards a single direction ?  Is there some prisms, lenses, mirrors, combination of them ?

The solar tubes product seems does it well to a certain degree; may have been designed as best as the manufacturer could.  

Find Solatube Dealer Near You - Solatube | Geodesic dome homes, Tubular  skylights, Energy efficient homes

The point of entrance/collection of solar light...  What other passive methods exist ?  -No heliostats, no moving parts-

What’s wrong with a window, or skylight? 

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9 hours ago, Externet said:

  Is there some prisms, lenses, mirrors, combination of them ?

Deck prisms are used on ships/boats.

A cheap option is a clear plastic bottle filled with water, fitted into the roof. (aka a liter of light)

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Do not assume dwelling illumination.  Am after gathering a ~2 square metres of sunlight opening into a duct with a flat fresnel lens at its exit to get focalized ~2KW of heat.  Works good around noon but not at lower sun elevations.

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  • 3 weeks later...

I don't see any simple, cheap, low-tech object that orients light from a variable direction without moving itself. If really nothing moves nor changes, my strong intuition tells that efficient funnelling and concentration to a fixed direction goes against the second law of thermodynamics.

Provided the application is not cooking in the Andes, some high-tech is more or less conceivable.

A fixed lens or mirror can alternate black and reflective or transmitting zones (aka gratings, zoned lens etc). You can adapt these zones without "movement" by using liquid crystals. They wear in sunlight, so maybe my old patent is better, if it survives the number of cycles:
https://patents.google.com/patent/EP0564012A1/en

A laser accepts pumping light from variable direction, and sunlight does pump Yag lasers, but the pumping light must be concentrated. A set of lenses might do the trick.

Have a limited set of useful directions, build one setup for each?

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On 7/14/2021 at 12:16 PM, Externet said:

Do not assume dwelling illumination.  Am after gathering a ~2 square metres of sunlight opening into a duct with a flat fresnel lens at its exit to get focalized ~2KW of heat.  Works good around noon but not at lower sun elevations.

Power is going to be a function of the area of your collector and the efficiency of coupling.  

Your stated requirement means you need 1 kW/m^2 of sunlight. You start with ~1380 W/m^2 at the top of the atmosphere, and you lose some from absorption and scattering in the atmosphere, and you have to modify for the angle from latitude and time of day, so your goal is only possible near the equator and around noon, unless your system is tracking the sun, which would buy you some more time. It also assumes you are coupling all of the light, and it's never cloudy.

(None of the above violates the second law of thermodynamics. The 2nd law limits you to not being able to heat the target to a temperature higher than the source)

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Thanks.

No need for temperatures higher than the source.  Just capability to gather sun radiation into a hole on a roof by optically redirecting at also lower sun elevations.  Seems moving parts/mirrors for tracking are mandatory. 

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  • 4 weeks later...

Either moving parts in a mechanical sense, or something more costly that redirects light, but that doesn't "move" depending on what one wants to call "move".

One more device type to redirect light uses surface acoustic waves. Called "acousto-optic modulator" approximately. An acoustic wave at many MHz creates ripples in a piezo material, these ripples diffract light like gratings do. I expect very low light efficiency.

The original query was to redirect light from any direction. That prompted my comment about thermo's second law.

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14 minutes ago, Enthalpy said:

Either moving parts in a mechanical sense, or something more costly that redirects light, but that doesn't "move" depending on what one wants to call "move".

One more device type to redirect light uses surface acoustic waves. Called "acousto-optic modulator" approximately. An acoustic wave at many MHz creates ripples in a piezo material, these ripples diffract light like gratings do. I expect very low light efficiency.

AOM elements are small and can’t handle high power. Efficient free-space coupling (80%) requires good beam quality, and they only handle a limited wavelength range.

14 minutes ago, Enthalpy said:

The original query was to redirect light from any direction. That prompted my comment about thermo's second law.

I don’t see the connection to the 2nd law.

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