Solar power without solar cells

[Tom Ligon]

Antenna. Diode. Turn ambient RF into electrical energy. They can actually be pretty efficient.

Is this all that different? Just the scale, I think.

I'd like to get into this a little deeper. Most descriptions of photosynthesis use existing QM pumping theoretical explanations (but with mechanisms far more intricate than common photovoltaics). I believe parts of photosynthesis are still not well understood. Possibly nature already uses this?

Worth a look, anyway.

[chrismb]

Antenna. Diode. Turn ambient RF into electrical energy. They can actually be pretty efficient.

It says rectified [static] dipoles. How do you get resonant coupling out of a static field (screened by a dielectric, to boot!)?

[Giorgio]

How do you extract useful work from the static electric fields within a dielectric?

Is the electric dipole moment presence that stores the work. In other words, in a capacitor you apply an electric field to a dielectric where its molecules act like dipoles that are free to rotate and line up to the applied electric field.
In this system the dipole moment to the molecules is supplied by the magnetic component of the light.

I didn't ask where the work done by the mag fields goes - I think you should anticipate I know how a dielectric can store electric energy - I'm asking how you take work from dipoles in a dielectric. It's not like you can just plug in wires or something! And if there is no current flowing, then there is no coupled current. If you were to set up some sort of charge-discharge arrangement with a plate that generates work as it moves up to the thing, discharges and returns to starting point, then you'd only be able to extract work from the surface charges of the material, which'd be not very much at all.

As asked - why don't we have electret batteries, if this is possible?

Maybe I am the one being thick now, but I do not get what you do not get. It looks pretty straightforward to me. It's a polarized capacitor that is charged by light interaction with the dielectric.
How do you take work from a capacitor?

[chrismb]

How do you take work from a capacitor?

By doing work on the capacitor first. You have conductive plates, to which you attach wires.

[kurt9]

After reading the PhysOrg article, I got the impression that this discovery is like 'giant magneto-resistance' a few years ago: When we knew it was possible, it needed optimised materials to be commercially viable...

And now they're the read-heads in a zillion hard-drives...

Now, where would we find high-density sunlight that could be concentrated to drive a high-efficiency, non-plumbing, non-mechanical, non-PV collector ? Outer-space ? Arizona ? The Sahara ?

Also, if it rectifies broad-band light, a variant should be able to rectify broad-band RF-- Don't Polywells emit such ??

When the GMR effect was discovered, it was already understood that it would be adopted to R/W heads. The only difference between GMR and the previously used MR effect is the number and structure of layers in the head structure. Since R/W heads are very small in area (essentially a MEMS device) where hundreds or thousands of them can be made on a single substrate, that the materials may be specialized or expensive is not an issue. Compared to the size of the head, the value added is sufficient to cover the cost of expensive exotic thin film materials.

Solar is completely different. Solar requires large area panels, which means that the per area cost must be orders of magnitude lower than that of semiconductor or MEMS devices and about a order of magnitude smaller than that of flat panel displays. This is the fundamental hurtle of developing low-cost solar.

This effect will probably show up in value added photonics/optics applications such as optical computing rather than solar PV.

[Giorgio]

How do you take work from a capacitor?

By doing work on the capacitor first. You have conductive plates, to which you attach wires.

Here you pump the work into it by light interaction with the dielectric, switch light off and collect it in a standard fashion.

It's just the way of charging it that changes.

[D Tibbets]

And the speed of light is constant in a material

Are you completely sure about that?

Pretty sure. Note I did not say the speed of light was a constant. I qualified it by designating that it was dependent on the medium it was passing through. The speed of light in a vacuum is certainly a constant. And I do not believe the speed varies within a homogenous material, like a perfect transparent glass. Interesting things happens at the interface between materials.

Dan Tibbets

[D Tibbets]

I don't know what effects may occur, and it may be interesting, but like very high temperature superconductors at millions of atmospheres of pressure, any practical application is , um... remote.
They mention the lower threshold for the effect is ~ 7 MW per square cm. That would be ~ 70 GW per square Meter. I don't think you need to worry about any Polywell or anything else generating such radiant flux, with the possible exception of hydrogen bombs.
Solar radiation provides ~ 2,000 W/ M^2 at the Earths surface, or ~ 0.2 W/ cm^2. To utilize this effect you would need to concentrate the light by at least a factor of 35 million.That is a large magnifying glass. I don't know how brief their tests were. But, practically, unless the conversion and extraction efficiency is ~99.99 % or more, the device will quickly disappear in a puff of gas (slight exaggeration)..

Dan Tibbets

[chrismb]

And the speed of light is constant in a material

Are you completely sure about that?

Pretty sure. Note I did not say the speed of light was a constant. I qualified it by designating that it was dependent on the medium it was passing through. The speed of light in a vacuum is certainly a constant. And I do not believe the speed varies within a homogenous material, like a perfect transparent glass. Interesting things happens at the interface between materials.

It is quite incorrect, I believe.

The dielectric tensor is complex - meaning a material can be anisotropic both spatially (in different axes) and temporally (in phase, leading to polarisation rotations) and, together, in magnitude you can have non-linear effects (high electric fields may cause changes in refractive index).

[D Tibbets]

So, the speed could still be constant in the material. You are just changing the material, and it is given that the speed is dependant on the material it is passing through. There are interesting effects that can occur with the wave distribution, that can seem impossible, but the critical information carrying speed test is unchanged. If not, then I think special relativity would be violated. Polarization has nothing to do with speed. The wave shape may be changed, or there may be less transparency to certain oriented waves, but that does not change the overall speed as the light passes through the homogenous material. The speed may only be 1 cm per second, but it is constant (the information carrying aspect) throughout the length of the homogenous material.

And remember I said a homogenous material. Applying an electrostatic field or some other energy or structural change applied to a portion of a material means that it is not homogenous, but effectively two different materials sandwiched together.
Such manipulations could even be applied to a vacuum. A nearby black hole could seem to change light speed, but only if you ignore special, or is it general relativity. And, again, space near a black hole has different characteristics than flat space, so if you ignore relativity, you would have to consider these two regions of space as different materials.

Dan Tibbets