Everyone knows that solar power is great. No fuel, easy to install, scalable, etc.
The problem is that it is not very efficient. The absolute best production photovoltaic panel is less than 20% efficient. That means that only about 20% of the energy hitting the panel is converted into a useful form.
Well, there are a couple of reasons, but one of them is that only a little bit of the energy can be captured. The light, in this case, in the form of particles called photons. The photons from the sun have to hit an electron inside an atom in the photovoltaic cell. That’s roughly akin to firing a .22 bullet and hitting a bowling ball in orbit about the black hole in the center of the Milky Way galaxy. Fortunately the sun is sending out lots of photons and there are a lot of electrons to hit.
The other aspect (and someone correct me if I screw this up), is that the electrons in photovoltaic cells have to be given the right amount of energy from the photon. It’s an all or nothing thing at the sub atomic level. Either you knock the electron loose entirely or you don’t do anything to it and have to wait for the next photon to come along and hope it has enough energy. The effects of multiple photon strikes are not cumulative. Don’t ask me why… it’s quantum mechanics and anyone who says they understand quantum mechanics… doesn’t understand quantum mechanics.
Photons have slightly different energies. A photon for red light has less energy than a photon for blue light. Because of the energy requirements of the electrons involved, some photons won’t have enough energy (thereby not being used and being wasted). Some photons will have leftover energy (thereby the leftovers are not used and wasted). Which is why photovoltaic panels are very limited in their ability to convert sunlight directly into electricity.
Which is why I like solar thermal.
We’ve been talking so far about photons being a particle. But we can also think of photons as a wave… specifically an electromagnetic wave. Now this gets into some really odd stuff about quantum mechanics, but just go with me here. This is a well understood phenomenon, even if we don’t really know how or why it happens (of course, the same can be said for gravity too).
So, if we think of photons as waves with a specific frequency (which they are), then what could we use to harvest that energy?
Well, radio waves are electromagnetic waves… just like light. In fact, exactly like visible light, just with a longer wavelength and a lower frequency. Antennas are good at capturing radio waves… why not light too?
You see, that’s why radio stations are measured in watts of power. That’s what they do. The transmitter is literally sending out waves of energy. The antenna on your car is picking up a small bit of that energy in a very specific frequency and converting it into (through a few steps) the motion of speakers.
Here’s the deal though, the antenna has to be a very, very specific size in relation to the wavelength of the wave. For radio, this isn’t a big deal. The wavelength of radio is commonly in the centimeter to meter range (though it can go all the way to kilometers in length).
Light however, has a wavelength in the nanometer range. That’s billionths of a meter. Until very recently it was impossible to make antennas that size.
The researchers at Tel Aviv University have done so however. And they are looking at 95% efficiency of their system. Now, it’s not a completely functional power generation system, so it probably won’t get to 95% in actual use, but even it’s just 50%, it will be better than any other photovoltaic system in existence.
Part of the idea is to have antennas that are sized to capture all the frequencies of light, not just visible, but UV and infrared too. Allowing for many more photons to be involved.
Sounds good to me. I’m looking forward to more information about this one.