I recall seeing a lecture by someone at Caltech doing 'synthetic photosynthesis'. If I remember correctly, he said that one of the tricks plants use is to 'downconvert' some of the high-frequency light into lower-frequency light that was easier to capture. That way, you get (at least) 2 frequencies for the price of one. I think that someone else is trying to genetically engineer plants to absorb slightly different frequencies than normal, so that eventually, a plant could be engineered to absorb a wider spectrum. If I remember correctly, I think that the absorbing molecule was 'tunable' by adjusting some side-chains. Someone at UCSB was working on photovoltaic 'paint'; it might not be the most efficient, but it could be spread cheaply over much larger areas. The whole area of 'quantum dots' is interesting, precisely because they can be engineered to have whatever band energies (within reason) that you want. I.e., you no longer have to search the periodic table for weird/expensive elements that have a particular band gap; you engineer a quantum dot with the right properties. At 12:31 PM 7/17/2013, meekerdb wrote:
That's an interesting question. A photovoltaic only uses about 10% of the photons because they have to be in the right frequency band. The others are mostly just absorbed, since the panels look black or dark blue. But maybe the absorbtion is at the electrodes. A mesh electrode and a reflective backing might allow most of the photons that are not absorbed by the photovoltaic to be reflected to a boiler.