Kevin has been tearing up Facebook, arguing against the meme that you could put photovoltaic cells in an array in the Sahara and solve the world's energy woes. It's patently false, by the way, just from a technological standpoint.
Photovoltaic cells (or Solar Cells) rely on a pretty simple principle and pretty exotic materials. The concept is this- If you bang a photon against a chunk of difficult-to-obtainium, you bang an electron loose. If you bang enough electrons loose- you have current! It's dreadfully inefficient... the current record effeciency of a photovoltaic array is 44.7%...and that was using concentrated sunlight and multiple junction cells.
Dismal. You can't even really pay for the energy used in manufacturing a photovoltaic cell over it's operational lifespan.
There is a better way. Rather than thinking of photons like billiard balls bouncing off a doped silicon substrate, let's think of them as waves... like radio waves. And instead of building photonic trampolines, why don't we build antennas?
Well, back in the early '70's a patent was awarded for an "electromagnetic wave converter". About ten years later, Alvin Marks got a patent for a device using sub micron antennas for the use of directly converting light power to electrical power. The research is ongoing, but in the latest attempts, a key issue was identified.
Instead of banging around photons, the 'nantenna' works like this: The lightwaves cause corresponding movement in the electrons in the nano scaled antennas. Unlike photovoltaic cells, nantennas produce alternating current....
... and this is the problem. In order to make that current so it's usable, you have to rectify it. This is done (in general) by running the current through some diodes, and ta-da! AC becomes DC.
Well... one problem with this is the frequencies that visible light produces in nantennas run in the terahertz band. We don't have diodes that can rectify current in the terahertz range.
But NASA (Not a Space Agency) has developed something that may (accidently) help.
Completely unrelated (in fact, this may be the first posting that makes this connection between Nantennas and this discovery), NASA has been trying to develop chips that will allow Moore's Really Strong Suggestion (It used to be called "Moore's Law"...) to continue. We are reaching the limits as to how fast we can make computer chips operate- we are reaching the limits of purity and scale; we're about to run into a wall with regards to processing power and speed.
So NASA researchers dust off (literally) an old concept- Vacuum Tubes.
As it turns out, the things that make vacuum tubes unworkable in anything but my old Fender amp don't matter at chip scales. They don't require heat to shed electrons, they don't have to be bulky, they don't require as much of a vacuum... and they are screaming fast. In fact, when integrated on a computer chip and run, they are capable of hitting clock frequencies in the terahertz range....
This new vacuum tube on a chip could be used to rectify nantennas.
The other challenge is regarding finding materials that can operate as antennas at nano scales, and actually MAKING them that small... the solution to that one is fairly straightforward. You print them. We can now print nantenna structures out of gold onto a substrate at a cost per square foot of slightly less than a dollar. (A square foot of photovoltaic cells is around $40)- and the concept of the rectifying antenna has already been proven to be 85-90% efficient.
So, we have Solar produced electricity at 2.5% of the manufacturing cost and more than twice as efficient as best-case Photovoltaics...
What's not to love?
Oh, I'm making sure this synthesis is mildly protected. Vacuum Channel Transitors as rectifiers for Nantennas, copyright 1 Jul 2014, Robert Ian Sutherland. All rights reserved.