As we watch First Solar
The leading (and bankable) Chinese crystalline silicon manufacturers will continue to price their product exactly where it needs to be to win commercial and utility business. And folks like SunPower
So, why aren't there solar panels everywhere?
What if utility electricity prices were really high? Installing solar panels would be a no-brainer, and everybody would do it. There would be solar panels on every roof.
Well, not really.
It's not a perfect example -- but Kauai has ample sun and expensive electricity prices. It's a situation where one could declare "grid parity" -- and yet Kauai is not seeing a rush on installing solar power. Why? Because the up-front price is too high. At, say, $6.50 per watt installed, a 4-kilowatt system is still a $26,000 investment and, absent a financing or leasing tool, it's just not going to be found on the rooftops of regular folk. Subsidies help, but they don't change the game.
But what if a technology firm were to emerge and turn those cost numbers on their collective ears? What if a new technology drove costs down to fifty cents per watt -- or even twenty cents per watt? That could translate to a reduction in the retail installed price of one to two dollars. Factor in some reductions in balance-of-system and installation cost, and we would start to see installed solar costs at the residential level looking more like buying an expensive refrigerator instead of a new car.
Here are some technologies that might lead to that kind of profound market disruption:
- High efficiency III-V
- Intermediate band
- Quantum dots
- Thermophotovoltaics and Thermovoltaics
- Nanotubes and Nanowires
- Photonic Crystals
High Efficiency III-V Materials
The best compound semiconductor triple-junction solar cells from incumbents Emcore
Start-up Alta Devices is working on a thin-film compound semiconductor material with high efficiencies and low costs. This patent identifies the use of GaAs, AlGaAs, InGaP and alloys thereof in the Alta Devices tool kit. The firm appears to be using an epitaxial lift-off technique pioneered by Eli Yablonovich, which has yielded 26.1 percent thin-film GaAs solar cells in this research by Bauhuis, et al.
Thermovoltaics and Thermophotovoltaics
In most cases, the heat accumulated by rooftop solar panels is viewed as a nuisance rather than an ally. What if that heat could be converted to energy in tandem with the photonic energy harvest?
Stanford researchers are working on ways to combine "quantum and thermal mechanisms into a single physical process" to generate electricity and make solar power production twice as efficient as existing technologies. It's called PETE -- photon-enhanced thermionic emission. This process does require some exotic materials (cesium-coated gallium nitride) and works best at high temperatures -- more likely with concentrators or parabolic dishes than flat solar panels.
Nanostructures, Nanotubes and Nanowires
Bandgap Engineering has developed tunable methods for nano-structuring silicon. Unlike bulk silicon, nano-silicon's optical properties can be tuned to reduce reflection and increase absorption, critical characteristics for any solar cell.
The firm claims that the absorption of nano-silicon is enhanced by up to several orders of magnitude over bare silicon over a wide range of wavelengths. This enables nano-silicon to absorb the light in the first four microns versus the top 50 to 100 microns that bulk silicon needs to absorb most of the light. This could impact cell efficiency and direct manufacturing cost -- and make for much thinner wafers.
Bandgap claims that solar photovoltaic cells based on nano-silicon have less reflection than bulk silicon or a traditional PV cell. Specifically, while bulk silicon reflects over 30 percent of light across the spectrum (at normal incidence) and PV manufacturers are able to reduce this to 5 to 8 percent with anti-reflective (AR) coatings and surface texturing, nano-silicon can reflect less than one percent of incoming light.
Researchers at The Netherlands' University of Eindhoven are aiming for nanowire-enabled solar cells with 65 percent efficiency. The research is being conducted at Philips MiPlaza with funding from the Dutch Ministry of Economic Affairs. The researchers believe that nanowires, in combination with concentrators, have the potential for the world's most efficient solar cells, with a cost lower than 50 cents per watt.
Nanowires allow a number of subcells (junctions) to be stacked, with each subcell converting one wavelength-band of sunlight to electricity. Researchers have commented that a protective shell around the nanowires can boost efficiency, and that stacking five to ten junctions will yield efficiencies of 65 percent.
(See also: Scitech Solar.)
RoseStreet Labs Energy (RSLE) is developing an intermediate band nitride thin film semiconductor material. It's an alternative to the multijunction designs for improving power conversion efficiency of solar cells. From the RoseStreet website: "Theoretical calculations (performed at 46,000x concentration) indicate that with the proper location of a narrow band of gap states a single junction cell can achieve an ideal power conversion efficiency of 63.2 percent, much larger than the 55-percent ultimate limit for two-junction tandem cells."
The intermediate band solar cell developed by RSLE, is a thin-film technology based on highly mismatched alloys. The three-bandgap, one-junction device has the potential of improved solar light absorption and higher power output than III-V triple-junction compound semiconductor devices.
Also working on intermediate band technology is SiOnyx.
Physicists, I throw myself on your mercy. Plasmonic technology uses engineered metal structures to guide light at distances less than the scale of the wavelength of light in free space. Plasmonics can improve absorption in photovoltaics and broaden the range of usable absorber materials to include more earth-abundant, non-toxic substances, as well as to reduce the amount of material necessary.
Lightwave Power, funded by the Quercus Trust is working on plasmon-enabled solar.
Photonic crystals are nanostructured materials in which repeated variations in the refractive index on the length scale of visible light produces a photonic band gap. This gap affects how photons travel through the material and is akin to the way in which a periodic potential in semiconductors influences electron flow. In the case of photonic crystals, light of certain wavelength ranges passes through the photonic band gap while other wavelength ranges are reflected. The photonic crystal layer could be attached to the back of a solar cell.
Lightwave Power, funded by the Quercus Trust, is working on photonic crystal-enabled solar.
Solar cell efficiency could theoretically be raised to more than 60 percent using quantum dots -- electrons can be transferred from photo-excited crystals to an adjacent electronic conductor. Researchers have demonstrated the effects in quantum dots made of PbSe, but the technique could work for quantum dots made from other materials.
As always, there is an enormous temporal and financial chasm between the demonstration of these enticing phenomena in the lab and building this technology at gigawatt scale and at competitive prices. But, with enough innovators and entrepreneurs working on this in the coming decade -- things could get really interesting.
The "new black swan improbable pyro-nano-quantum-thingamajig technology" term is borrowed from Vinod Khosla's recent thin-film solar piece in Greentech Media.
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