Organic PV (OPV)
Rather than employ the use of semiconductors or highly-specialized synthetic materials as a base medium for creating a photovoltaic cell, another option uses organically grown polymers that can conduct electricity. A polymer is merely a long chain of other molecules strung together in a repeating pattern, making an enormous molecule. Most plastics and thick industrial greases fall under this category of material. For polymers, the larger the molecule, the harder and denser the material generally is.
OPV’s major advantage is that it’s flexible, and can be attached or embedded onto smooth curved surfaces, unlike other forms of PV technologies. However, with an overall average efficiency of less than 1% even the most whimsical and gimmicky utilization for this technology would be absurdly too expensive. As a practical means of generating power, OPV still has a long way to go.
Various forms of organic molecules that generate a photovoltaic voltage when exposed to light, courtesy of Wikipedia.
Artificial Photosynthesis (a.k.a. Solar “Cold Fusion”)
There are a plethora of different fringe-technologies that are blossoming in the “artificial and synthetic photosynthesis” fields of the solar industry, and after about a day of research, I found myself with roughly equal amounts of legitimate scientific sources to absolute crackpots. Those that seem to center around the legitimate sources seem to focus around an MIT professor named Daniel G. Nocera, who from what I can tell merely invented a chemical catalyst that uses energy from sunlight to break water (H2O) down into its elemental gasses, hydrogen (H2) and oxygen (O2).
If it sounds like I’m downplaying the man’s accomplishments, it’s because I am. From what my research has shown, the process he has established is a slight modification of standard electrolysis techniques that have been employed to convert water into H2 and O2gasses using electricity for over 100 years. Despite using his “catalyst,” Nocera’s setup still requires the use of DC electrodes, which means that even if his catalytic compound had little to no effect, the gasses would still form from the already known-to-work electrodes. It’s important to note that this process is NOT actually photosynthesis, and is NOT the chemical reaction that occurs in plant cells. This is the process of electrolysis, yet Nocera has apparently decided to re-brand this process as artificial photosynthesis…ok whatever.
In the articles that I searched for regarding how the catalyst is supposed to work, I find little to no actual science behind how the process is enhanced. Everything is neatly kept behind a curtain of “it’s a proprietary technology,” and you actually have to buy the right to read his research paper. Rather than focus on the science, from what I can tell, he goes around performing speeches and lectures on his revolutionary technology, but is not actually developing it. If I could speak to Nocera directly, from one practicing scientist to another, I’d tell him that any science that has to rely on smoke and mirrors or an air-of-mystery in order to work is simply complete bull. If your invention really works, patent it, release it to the public, and let everyone know how it works. Change the world, like you promise, quit hiding behind the “proprietary” façade.
Depicted above, Nocera lectures others about his technology.
Lastly, the articles I’ve seen are all rather heavy in terms of promises that this technology will “revolutionize the solar industry,” but I’ve seen little evidence of that. I’ve known about this technology for over four years now, since 2008, and I’ve seen the industry change directions entirely from large centralized inverters to small micro-inverters and distributed electronics in every module…I’ve never seen anything indicating to me that this artificial photosynthesis isn’t any more than a marketing promise and a free t-shirt. I wouldn’t expect anything to come out of this technology in the next 10 years.
True Artificial Photosynthesis (Added March 2012)
Where others have failed to deliver, MIT researchers Andreas Mershin and Shuguang Zhang have stepped up and taken the bar to entirely new levels. Over the past eight years, these two research scientists at MIT’s Center for Biomedical Engineering have developed a means of taking dead plant material (such as leaves fallen from a tree) and chemically convert it into a cheap coating that can be applied to any smooth surface in order to make a PV cell.
Shuguang Zhang, along with the work of his teammates, has released a paper detailing the process they created which uses dead plant material to be converted into photovoltaic cells. Whittling the process down to non-jargon terminology, dead plants are ground up and the chemical that is responsible for orchestrating the energy transfers during photosynthesis (labeled PS-I by the researchers). This PS-I chemical is extracted from the dead plant material, and then chemically stabilized in order to prevent the chemical from breaking down once it’s outside of its cellular environment.
Rather than simply spreading the PS-I chemical extract across a sheet of glass (as was done in the very first experiment), another MIT researcher, Andreas Mershin, tweaked the fabrication process and found that growing nanostructures of zinc-oxide and titanium-oxide into forest-like shapes on the surface of a semiconductor chip. Much like the coniferous (pine) trees that inspired Mershin, his nano-structured chip consists of a forest of tiny pillars, each coated with the PS-I molecule, maximizing the surface area that the incoming light strikes and boosting the power output of his experimental cell by almost 10,000 fold.
The current experimental version of Zhang and Mershin’s combined efforts has only resulted in a cell that is 0.1% efficient, not nearly enough to become commercially viable (~10% efficient at least), however the MIT researchers claim that the fact that these cells can be produced much more cheaply and from the remains of almost any dead plant material, the potential for this technology to alter the course of the solar industry in the next few years is quite vast.
Photon Enhanced Thermionic Emission (PETE)
I never thought I’d ever write these words, but this technology is the exact opposite to the way a television works (well…how old CRT TV’s used to work). Old Cathode-ray Tube (CRT) televisions worked by heating a small plate of metal to the point is was red hot, and exposing that piece of metal to a high-voltage field. This high-voltage pulled electrons off of the heated metal cathode, creating a beam of electrons that fired forward across the vacuum chamber, striking the front of the television and creating the light that illuminated the screen.
With the photonic enhanced thermionic emission, concentrated light is focused onto a surface, heating it up. This heated surface begins to eject electrons away from it, which travel across a large vacuum chamber and on the other side of the tube, landing on a metal plate that becomes the negative cathode. Unlike some of the other technologies mentioned in this article, my research into the PETE device actually yielded significant information on the how and why this device works. However, this device is so advanced and sophisticated that it takes advantage of quantum effects in order to operate. Explaining this process clearly in a few paragraphs will be a bit challenging.
A photon is a “packet” of light, as stated by Einstein himself. In this application, it’s easier to think of light as a particle, or like a tiny bullet traveling through space. A thermion is a similar “packet” however in terms of temperature. Thermions cannot travel freely through space. They act more like waves traversing a pool, where the pool in this metaphor is the “block of material” that light is being focused on. Electrons are particles with a mass that bind with nuclei of atoms to create an entire “atom” that has both a nucleus and an electron shell. When enough thermions strike an electron, energy is transferred and the electron can be energized to a higher band. Sometimes so much energy can be transferred that the electron is ripped from the atom entirely and cast out of the pool, into space. This effect of thermions colliding with electrons in an atom is a sub-process of the photoelectric effect.
So how do the thermions get so concentrated that they eject electrons? Well, sunlight from a nearby parabolic mirror focuses the slight so a very tiny point. This intensely focused light then strikes the surface of material that converts the light energy (photons) into heat and vibrational energy (thermions) within the atoms in the material. As the material is slammed with energy from the concentrated light, it naturally becomes extremely hot, eventually glowing from the heat. This glowing is actually the material becoming so stuffed with thermionic energy that it’s emitting additional photons in the form of visible and infrared light in addition to ejecting electrons.
Image courtesy of Stanford.edu.
The PETE device works by collecting and storing these stray electrons as the output terminals, while at the same time re-focusing the emitted light back onto the material, increasing its electron output. According to articles covering the process, the device has already achieved above a 50% efficiency rate, and apparently becomes more efficient when higher temperatures are involved, which matches the theory and science behind the concentration-thermal solar technologies. From what I can tell, the PETE device went from concept to working prototype in only three years, and is being designed as a retro-fit attachment to pre-existing concentrator solar-trackers. I wouldn’t be surprised if this technology took off to becoming a mainstream portion of the solar-industry within the next few years.
Thermoelectric Semiconductors
Within the last two years, yet another brand new solar technology has emerged using semiconductors as its main component, however interestingly enough, still another physical effect is being employed. Rather than the photovoltaic or photoelectric effect, this technology makes use of something called the “Thermoelectric Effect.”
The thermoelectric effect, as its name implies, works by using the energy from heat to create an electric potential. Much in the same way that hot-air expands, when a semiconductor material doped in a way to allow current to flow freely is heated, the electrons begin to move faster, and vibrate around the material more quickly. If one side of the material is heated much more than the other side, then the electrons begin to have an un-even distribution of energy. The heated electrons move much more quickly than the cooler ones, which increases the overall “pressure” of the electrons on the heated end (again, similar to hot air expanding outwards). These heated electrons expand outward, pushing the cooler electrons into a tighter bunch on the colder side of the material. This uneven distribution of electrons is actually the side-effect of the heat that creates the electric voltage. If metal terminals were attached to this heated-material, a specific and predictable voltage would be easily measured. This process is the basis behind how modern thermo-couple temperature sensors work. They are a common part of modern engineering diagnostic tools and extremely useful for many applications.
Image of thermo-couple sensor, arranged into a single grid-like pattern, courtesy of Tellurex.com, component manufacturer.
However, until recently, these devices would only generate a few micro-volts under even extreme temperatures. As a result, almost all thermocouples required an external power source to amplify their output signal to be able to even be measured. It was only as of 2009 that an effective means of combining many of these thermocouple devices together was discovered. By utilizing the same silicon-wafer layer depositing manufacturing process as common microchips, several million thermocouples can be placed in a grid in a very small area. These thermocouples are then tied together in series, very much like microscopic PV cells. These thermocouple chips are then placed in focusing lenses and placed onto solar-concentrators, in order to make optimal use of the concentrated heat and light.
Thermoelectric Solar technology is so new that it’s actually too soon to begin making speculations on its possible efficiency. Proof of concept testing has already reached 60% and there is apparently room for improvement. The technology is in its initial testing and prototype phases, however the basic scientific property that the technology is based on is sound. If the research teams working on these products can overcome the material resistivity limitations, then this technology is poised to blow the solar-industry wide open. Thermoelectric technology appears to combine the best of both the photovoltaic and concentration solar worlds together.
Counter Rotating Ring Receiver Reactor Recuperator (CR5)
Image of CR5 device and inventor, courtesy of Popular Science.
Perhaps the least creatively named of the various emerging technologies, the CR5 is actually one of the most innovative. To be clear, the CR5 does NOT produce electricity from sunlight. Instead, it produces gasoline and other hydrocarbons that can be used to create fossil fuels. The science behind this is pretty amazing, and focuses around specially engineered materials creating an environment that helps catalyze a chemical reaction.
The CR5 is actually another flavor of technology that requires a large parabolic concentrator in order to focus sunlight into a single point. However, rather than shining the sunlight onto a flat surface, the light is focused onto several spinning disks, each made of specially engineered ceramic. This ceramic is designed in such a way that its surface is porous, meaning full of microscopic holes. These holes act as “receptacles” momentarily catching and binding on to water and carbon-dioxide molecules being pulled in from the atmosphere on the hot side of the disks. The disks themselves don’t react with the air or water, they merely provide a surface for the reactants to temporarily bind to, in order to help make the reactions occur faster. This is more of a geometrical effect than a chemistry one, as it’s physically easier for molecules to bind together when one of them is held firmly in place for the other to more easily connect to. As the disks spin around, the receptacle holes cool and contract, releasing the newly formed hydrocarbon molecule.
Diagram of how the CR5 device actually works, courtesy of Greenopolis.com
Small, self-contained, and fairly simple to make, the CR5 was designed to be added as a retro-fit to already existing solar-concentrators. Although current versions are in the prototype stages, the concept has already been shown to work, and could actually stand as a legitimate answer to the looming issue of creating new sources of fossil fuels. I look forward to seeing what new developments come out of this technology in the years to come.
<< Return to Science and Explanation Articles
