Solar Breakthrough Could Provide Power Without Solar Cells 223
An anonymous reader tips a University of Michigan news release about the creation of what's being called an "optical battery" that could lead to the use of solar power without traditional solar cells (abstract). Quoting:
"Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. What Rand and his colleagues found is that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100 million times stronger than previously expected. Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect. 'This could lead to a new kind of solar cell without semiconductors and without absorption to produce charge separation,' Rand said. 'In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light and then it is ultimately capable of providing a capacitive power source.'"
Beyond the theoretical limit (Score:5, Informative)
The press office at U. Michigan has gone a long way from what they actually did to what they are speculating might be theoretically be possible. What they actually did was to predict a theoretical effect which has not yet been demonstrated. The press office then suggests that if you concentrate sunlight by a factor of a hundred million-- about seven hundred times higher than the theoretical concentration limit-- that this as-yet-unidentified material might be able to convert the light into electricity.
This is a bit speculative. They've predicted an interesting theoretical effect. Let's keep it at that, which is a nice piece of work, and leave the speculation to science fiction writers (like me).
Re:I've been reading about solar breakthroughs (Score:4, Informative)
That's because they don't pay their due externalities [skepticalscience.com].
Theoretical limit to solar concentration (Score:5, Informative)
I wasn't aware there was a theoretical concentration limit. Where did you get that from and what's the rationale for it?
The theoretical concentration limit is straightforward-- it comes from the fact that the sun has a non-zero solid angle. Basically, a concentrator works by increasing the fraction of the sky that's filled by the sun, and the best you can do is to make the light come from the whole sky. (Well, there's also a factor of n, the refractive index).
The book Solar Electricity by T. Markvart gives a calculation (page 237-- it's available on googlebooks)
Re:Wait, what? (Score:4, Informative)
Isn't a static electric charge an example of E without M?
What is a static charge? I can choose a reference frame where the charge is in motion, and thus produces a magnetic field. If you look carefully at the fundamental equations of electromagnetism, you see things like "the force on the charge is proportional to the velocity of the charge," and "the induced magnetic field is proportional to the rate of change of magnetic flux."
Both of these statements immediately imply the question in whose reference frame are we to measure the velocity of the charge or the rate of change of magnetic flux? In one frame to another the velocity is different, as is the rate of change of flux. But no matter what reference frame you pick, the particle does the same thing. This means that the electrical force and magnetic force are actually the same force, but they appear to be different when you choose some particular reference frame in which to measure them. You could have chosen a frame in which both fields took on different values, yet the net effect on the particle is the same.
It is relativity which causes the apparent splitting of the one unified force (electromagnetism) into two different forces (electricity and magnetism). You cannot have one without the other, or rather, you can have as much or as little of one as you want, depending what frame you measure in.
They are the same and can't be separated.