Mankind currently only harvests a minuscule fraction of the
estimated 12.2 billion kilowatt-hours of solar energy that hits the Earth every
It would seem a great folly not to pursue methods to try to harness this
power affordably. But current solar technology relies on solar cells that
are still rather expensive and often have durability issues.
That's why a new breakthrough in alternative energy at the University of Michigan is so exciting.
It promises solar power -- without the expensive cells.
No, it's not some novel photosynthesis scheme. The new
technology relies on a physics principle previously considered a trivial side
I. Magnetic Solar Energy -- a Radical Breakthrough
Light has two components -- magnetism and electricity. All solar cells
currently utilize the electric effects of light. The magnetic nature of
photons was dismissed as too weak to be of any use.
But Stephen Rand, a professor in the departments of Electrical Engineering
and Computer Science, Physics and Applied Physics at U of M, was fascinated by
this property. He wondered whether it could be somehow put to use.
During his investigations he discovered something unexpected. When light
passes through a strongly insulating material, its normally weak magnetic
output is profoundly multiplied and a relatively strong magnetic field results.
In fact, the field is 100 million times stronger than previously expected --
strong enough to produce the kind of large magnetic effect needed for power
Professor Rand admits the results will shock many physicists. He states,
"You could stare at the equations of motion all day and you will not see
this possibility. We've all been taught that this doesn't happen. It's a very
odd interaction. That's why it's been overlooked for more than 100 years."
II. How it Works
The magnetic effect comes from a unique type of "optical
rectification". Optical rectification is a general physics term that
refers to what light does when it enters certain materials.
Previously, the best-known type of optical rectification was the charge
separation that light created when passing into certain kinds of crystalline
materials (like crystalline silicon). This electric effect produces a
voltage and is the foundation of modern solar cells.
Professor Rand and his Ph.D. candidate student, William Fisher, discovered a
radical new type of optical rectification. In certain materials, they
found, the magnetic field of light was strong enough to bend electric charges
into a 'C' shape.
Describes Fisher, "It turns out that the magnetic field starts curving the
electrons into a C-shape and they move forward a little each time. That C-shape
of charge motion generates both an electric dipole and a magnetic dipole. If we
can set up many of these in a row in a long fiber, we can make a huge voltage and
by extracting that voltage, we can use it as a power source."
So what's the catch? Ah, there's always a catch with anything that seems
great, it seems.
The "catch" here is the material. In order to exhibit this
effect, light must be shown on an insulator like glass. Glass, however,
needs incredibly intense light to produce this effect -- 10 million watts
per square centimeter. Normal sunlight only produces around 0.012 watts
per square centimeter when shining.
One solution would be to create hardware to magnify the intensity of incoming
sunlight, similar to the technique used in concentrated solar cells.
Mr. Fisher states, "In our most recent paper, we show that incoherent
light like sunlight is theoretically almost as effective in producing charge
separation as laser light is. To manufacture modern solar cells, you have to do
extensive semiconductor processing. All we would need are lenses to focus the
light and a fiber to guide it. Glass works for both. It's already made in bulk,
and it doesn't require as much processing. Transparent ceramics might be even
Using novel materials, he and his professor expect that the necessary intensity
for the effect can be dropped to much lower levels. They postulate that
the sunlight conversion efficiency of cells with such new materials could
likely reach 10 percent -- on par with current generation solar cells.
They say the costs associated with such magnetic solar power devices would be
much lower, though, as they use non-rare materials like amorphous silicon
(glass) and don't rely on expensive processes like semiconductor fabrication.
IV. What's Next?
Professor Rand and his student will experiment this summer with producing
electricity from intensified sunlight and from laser light -- a directly
intensified form of light. After that wraps up, they hope to look into
novel materials to exploit the novel effect at lower intensities.
The team also states that it is in the process of patenting their discovery, as
it may one day grow into a lucrative power source.
For now you can read their paper "Optically-induced charge separation and
terahertz emission in unbiased dielectrics" [abstract] if you have a subscription to the Journal
of Applied Physics.