In a recent exchange with my former high school physics professor and now good friend Dan Heim, we discussed the current and forthcoming technologies applied to solar photovoltaic power generation, as follows:
> > The latest and greatest innovation are the bifacial panels by Sanyo.
> > I intend to use them on our (yet to be built) east deck area, mounted
> > horizontally to provide both shade and electricity. They’ll tie into our
> > existing system, which has a 4 KW inverter, and bring us very close
> > to electrical self-sufficiency.
> > They claim up to 30% more power generation than single-sided PV
> > panels, depending on ground reflectivity. So with a nice light
> > color of flagstone for the decking, we’ll get the reflected light
> > needed to make them do just that.
> Have you found a website which showcases the % of visible vs infrared
> vs higher frequencies of light utilized by silicon based PV panels?
> If you were to place a mirror beneath the double-sided panels, would
> that work well?
I couldn’t find an actual spectral diagram, but if you go to The Physics of Photovoltaic Cells and scroll down to Silicon Photovoltaic Cells you get some idea. I happen to know that standard silicon PVs get most of their energy in the 500-700 nm range (blue-green to red). Not unlike plants that photosynthesize, curiously.
Outside that range, efficiency drops, and more of the incident solar energy is transformed into heat. It all comes down to the band-gap the electrons need to jump in order to become “available” for conduction. That’s why even the best silicon PVs are only slightly more than 20% efficient.
But there’s a lot of work being done to increase that wavelength range and improve efficiency using different dopants to get different band-gaps. The available solar energy ranges from infrared to ultraviolet, which normally just becomes heat in a PV cell. The prospect of a “full range” PV cell is something many researchers are working on.
I’ve also read about some work exploring the use of organic compounds, as well as nanotechnology, to boost performance, but they don’t provide many details.
Regarding mirrors under the bifacial PVs, most definitely that would boost output. How much more you’d get with an actual mirror, compared to say shiny metal or white flagstone is hard to estimate. There’s also the problem that mirrors are more fragile, susceptible to hail damage, and would need to be kept clean. A layer of fine dust would decrease their performance to the point where a mirror might not be much better than shiny metal –Dan