Jones Beene
Thu, 10 Jul 2008 06:56:02 -0700
--- R C Macaulay wrote: > Question? How do you reconcile the heat trapped in the parabolic collector with the thin film materials mechanical properties that portend fast degradation due to heat? OK - I didn't make it clear that as envisioned, the photovoltaic surface is not placed around the collector tube. Instead, this film replaces the mirrors. Since the mirrored reflective surfaces would not be enclosed, heat build-up would not be the problem to overcome, and would actually be less than in the normal usage of these cells. As Michel pointed-out - the problem with this concept would be: can you efficiently reflect only the photonic energy (mostly IR) which you are NOT going to use in the cells? I think that you could reflect most of it, based on the analogy below, but that critical point is far from proved. As envisioned, the solar cells would replace what was formerly mirrors. Imagine the trough shown here: http://www.rise.org.au/info/Tech/hightemp/image003.jpg ... except that the reflective surface, not the collector tube (which is unchanged), is covered with the flexible printed solar cells, *except* that the protective coating on the surface of these photovoltaic cells is designed somewhat like a two-way mirror. IOW the coating allows that (mostly) the spectra of solar photons which can be collected by the "ink" which is used pass through, but the rest of the photons are reflected, which is mostly the infrared spectrum... and "mostly" is the operative word here. I could cloud the issue by throwing-in "nano" i.e. the possibility of adding a nano particle to the coating (which is usually a thin Teflon film) and suggest that the nano-particles would do this efficiently, but I do not know that such a particle of the correct specifications actually exists now (to be honest). I am *hoping* that (and this idea is really dependent on the possibility) a photo-luminescent nanoparticle like titania or zirconia, when added to the teflon coating, would not only reflect longer frequencies to the heat pipe collector (for raising steam) but also would "semi-cohere" the most active solar wavelengths and slightly improve the efficiency of the direct conversion. That is part and parcel of Dicke "superradiance" and it has actually been demonstrated to some extent, so it is not all "pie-in-the-sky" so to speak. If you can imagine a tall glass office building, which uses the highly tinted glass, the glass may look to be shiny black from a distance, but yet it is highly reflective. By analogy (revers analogy), only the photons which pass through the solar film would be collected for direct conversion and the others are reflected to the tubular collector which heats up a molten salt, which is then piped over to a steam plant. This is of course a very 'green' idea (in more ways than one), and ultimately it depends on the economics of trying to hybridize two dissimilar methods and at the same time to apply superradiance techniques to solar radiation. Jones
