# Fiber Optic Solar Energy Transfer

AThousandYoung
Posers and Puzzles 11 Jun '08 04:49
1. AThousandYoung
11 Jun '08 04:49
How efficient are fiber optics? Could solar energy collected in one place be efficiently transferred to a different climate..."pipe the sunlight" without changing it's form of energy at all?
2. uzless
The So Fist
11 Jun '08 05:00
Depends if Light travels as a wave or as a particle.

I considered lining the inside of a bottle with reflective glass, holding it up to the sun, somehow capping the bottle very fast, then taking the bottle into a dark room and taking the cap off to see if light would come out of the bottle.

Popular answer was that the light would dissipate into just heat.
3. AThousandYoung
11 Jun '08 05:261 edit
Originally posted by uzless
Depends if Light travels as a wave or as a particle.

I considered lining the inside of a bottle with reflective glass, holding it up to the sun, somehow capping the bottle very fast, then taking the bottle into a dark room and taking the cap off to see if light would come out of the bottle.

Popular answer was that the light would dissipate into just heat.
My answer is that light is so fast it would be impossible to catch it in there, but if you could do that, then maybe it could work.
4. 11 Jun '08 08:59
I like the plan, could be used for bad english summers
5. forkedknight
Defend the Universe
11 Jun '08 18:40
Originally posted by AThousandYoung
My answer is that light is so fast it would be impossible to catch it in there, but if you could do that, then maybe it could work.
You would need a completely reflective material, such that none of the light energy was absorbed.

I think nothing like that exists that we know of.
6. 11 Jun '08 21:24
Originally posted by uzless
Depends if Light travels as a wave or as a particle.

I considered lining the inside of a bottle with reflective glass, holding it up to the sun, somehow capping the bottle very fast, then taking the bottle into a dark room and taking the cap off to see if light would come out of the bottle.

Popular answer was that the light would dissipate into just heat.
Even if you did have a perfectly reflective bottle you'd only capture an instant's worth of sunlight.
7. AThousandYoung
12 Jun '08 02:23
Originally posted by forkedknight
You would need a completely reflective material, such that none of the light energy was absorbed.

I think nothing like that exists that we know of.
No, you'd need something reflective enough that it took time before all the light was absorbed.
8. forkedknight
Defend the Universe
12 Jun '08 18:101 edit
Originally posted by AThousandYoung
No, you'd need something reflective enough that it took time before all the light was absorbed.
Being that the light is moving at the speed of, well, light...anything that is 'reflective enough' to hold light in a container so you can move it elsewhere would have to be perfectly reflective.

The required quantization for "reflective enough" may be asymtotic to "perfectly reflective", but I'm an engineer -- they're equivalent in real life.
9. AThousandYoung
13 Jun '08 03:03
Originally posted by forkedknight
Being that the light is moving at the speed of, well, light...anything that is 'reflective enough' to hold light in a container so you can move it elsewhere would have to be perfectly reflective.

The required quantization for "reflective enough" may be asymtotic to "perfectly reflective", but I'm an engineer -- they're equivalent in real life.
That may be so, but I'd need to see some calculations to be convinced.
10. sven1000
Astrophysicist
13 Jun '08 06:451 edit
Say we have our reflective container, 1 meter on a side (cube shaped). The solar constant is 1366 Watts / meter^2, so our container will receive approximately S = 1366 Watts from the sun. The amount of time a photon remains inside the container (entering, then bouncing off the reflective surface) is T = 2 meters / 3x10^8 meters/sec = 6.7x10^-9 seconds.

The number of photons trapped in our container if we close it infinitely fast is N = S*T/E, where E is the energy of each photon. For simplicity, assume all the energy is in visible photons, of wavelength 550 nanometers (yellow light), which of course is not the case.

The energy of such a photon is E = h*c/wavelength, with h = planck's constant = 6.6x10^-34 Joules*seconds, c = speed of light = 3x10^8 meters/second, and wavelength = 550x10^-9 meters. So a single photon has an energy of 3.6x10^-19 Joules, and the number of photons trapped is an impressive 2.5x10^13.

Say our container, having trapped this many photons, is 99% reflective. Thus, every reflection dissipates in some way 1% of the existing photons. Because our container is 1 meter deep, we have 3x10^8 reflections every second.

This exponential decay could be represented by N = N_0 * e^(-t/tau), where N is the final number of photons, N_0 is the initial number, t is the time between capture and release of the photons, and tau is the "half-life" of the photons for getting dissipated instead of reflected. A single reflection takes 3.3x10^-9 seconds and the final number N = 0.99*N_0. Using these numbers, we find that the "half-life" tau = 3.3x10^-7 seconds.

Now, we have trapped our 2.5x10^13 photons. If we release them after one second, we'll have N = 2.5x10^13 * e^(-3x10^6) = something essentially equal to 0 (far far less than 1 photon remaining, on average).

Fiber optics are about 99.99% reflective, but even this level of reflectivity would give no remaining photons after just one second. Photons traveling through very good fiber optic wire still dissipate at a rate of 10% per kilometer, which distance the light could cover in 3.3x10-6 seconds.

http://electronics.howstuffworks.com/fiber-optic6.htm

So, funneling the light through fiber optic cable can work, because light travels so fast, but carrying it in a reflective container is a losing game.
11. 13 Jun '08 08:48
AThousandYoung didn't ask about trapping the light in a bottle. From where did the bottle came?

Is it possible to use glass fiber to move solar energy from one place to another? This was the question, wasn't it?

I say no, because sending signals through optical fibers has to be read, and re-sent in regular distances, in order to keep the signal from deteriate.
This is not practical with sending sun light through fibers. You have to amplify the sun light at regular distances, and then you lose the point of collecting it and sending it to a colder climate.
12. AThousandYoung
14 Jun '08 16:33
Originally posted by FabianFnas
AThousandYoung didn't ask about trapping the light in a bottle. From where did the bottle came?

Is it possible to use glass fiber to move solar energy from one place to another? This was the question, wasn't it?

I say no, because sending signals through optical fibers has to be read, and re-sent in regular distances, in order to keep the signal from ...[text shortened]... ar distances, and then you lose the point of collecting it and sending it to a colder climate.
Excellent answer. Thank you.
13. sonhouse
Fast and Curious
23 Jun '08 07:09
Originally posted by FabianFnas
AThousandYoung didn't ask about trapping the light in a bottle. From where did the bottle came?

Is it possible to use glass fiber to move solar energy from one place to another? This was the question, wasn't it?

I say no, because sending signals through optical fibers has to be read, and re-sent in regular distances, in order to keep the signal from ...[text shortened]... ar distances, and then you lose the point of collecting it and sending it to a colder climate.
Also, optical fibers are efficient only at one wavelength, my optical fiber wavelength is about 1.5 microns, way into the infrared band.
So it may be possible to generate a bundle of fiber each with a narrow bandwidth, the maximum the light would go is maybe 100Km and there wouldn't be much left after that distance anyway. It can still work for communications because optical sensors are very sensitive and can still extract Gigahertz of information from a weak beam but the data rate errors start to add up at the maximum distances anyway.
If you wanted to get light from point A to point B on the Earth, the best way would just to have huge mirrors in space, there would only be one reflective surface and the mirror can have a small curvature to focus the beam to a small spot. That way papparazzi's can follow a celebrity in the middle of the nightðŸ™‚